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Sample records for mediated charge exchange

  1. Charge exchange system

    DOEpatents

    Anderson, Oscar A.

    1978-01-01

    An improved charge exchange system for substantially reducing pumping requirements of excess gas in a controlled thermonuclear reactor high energy neutral beam injector. The charge exchange system utilizes a jet-type blanket which acts simultaneously as the charge exchange medium and as a shield for reflecting excess gas.

  2. Charge exchange molecular ion source

    DOEpatents

    Vella, Michael C.

    2003-06-03

    Ions, particularly molecular ions with multiple dopant nucleons per ion, are produced by charge exchange. An ion source contains a minimum of two regions separated by a physical barrier and utilizes charge exchange to enhance production of a desired ion species. The essential elements are a plasma chamber for production of ions of a first species, a physical separator, and a charge transfer chamber where ions of the first species from the plasma chamber undergo charge exchange or transfer with the reactant atom or molecules to produce ions of a second species. Molecular ions may be produced which are useful for ion implantation.

  3. Charge Exchange with Highly Charged Ions

    NASA Astrophysics Data System (ADS)

    Glick, Jeremy; Ferri, Kevin; Schmitt, Jaclyn; Hanson, Joshua; Marler, Joan

    2016-05-01

    A detailed study of the physics of highly charged ions (HCIs) is critical for a deep understanding of observed phenomena resulting from interactions of HCIs with neutral atoms in astrophysical and fusion environments. Specifically the charge transfer rates and spectroscopy of the subsequent decay fluorescence are of great interest to these communities. Results from a laboratory based investigation of these rates will be presented. The experiment takes advantage of an energy and charge state selected beam of HCIs from the recently on-line Clemson University EBIT (CUEBIT). Progress towards an experimental apparatus for retrapping HCIs towards precision spectroscopy of HCIs will also be presented.

  4. Charge exchange in zinc-neon

    NASA Technical Reports Server (NTRS)

    Chubb, D. L.

    1975-01-01

    Excitation of the 4d and 5p levels of Zn+ by charge exchange bewteen Ne+ and Zn was investigated. From measured electron temperature and line intensity ratios it was concluded that charge exchange is the dominate mechanism for populating the 4d2D5/2 level of Zn+. Comparison of Zn-Ne and Zn-Ar results imply the same conclusion. No evidence for charge exchange as the dominant pumping mechanism for the 5p2Pl/2, 5p2P3/2, or 4d2D3/2 levels was obtained.

  5. Pion double charge exchange and hadron dynamics

    SciTech Connect

    Johnson, M.B.

    1991-01-01

    This paper will review theoretical results to show how pion double charge exchange is contributing to our understanding of hadron dynamics in nuclei. The exploitation of the nucleus as a filter is shown to be essential in facilitating the comparison between theory and experiment. 23 refs., 3 figs., 2 tabs.

  6. Charge exchange avalanche at the cometopause

    NASA Technical Reports Server (NTRS)

    Gombosi, Tamas I.

    1987-01-01

    A sharp transition from a solar wind proton dominated flow to a plasma population primarily consisting of relatively cold cometary heavy ions has been observed at a cometocentric distance of about 160,000 km by the VEGA and GIOTTO missions. This boundary (the cometopause) was thought to be related to charge transfer processes, but its location and thickness are inconsistent with conventionally estimated ion - neutral coupling boundaries. In this paper a two-fluid model is used to investigate the major physical processes at the cometopause. By adopting observed comet Halley parameters the model is able to reproduce the location and the thickness of this charge exchange boundary.

  7. Solar wind charge exchange during geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Robertson, I. P.; Cravens, T. E.; Sibeck, D. G.; Collier, M. R.; Kuntz, K. D.

    2012-04-01

    On 2001 March 31 a coronal mass ejection pushed the subsolar magnetopause to the vicinity of geosynchronous orbit at 6.6 R_E. The NASA/GSFC Community Coordinated Modeling Center (CCMC) employed a global magnetohydrodynamic (MHD) model to simulate the solar wind-magnetosphere interaction during the peak of this geomagnetic storm. Robertson et al. then modeled the expected soft X-ray emission due to solar wind charge exchange with geocoronal neutrals in the dayside cusp and magnetosheath. The locations of the bow shock, magnetopause and cusps were clearly evident in their simulations. Another geomagnetic storm took place on 2000 July 14 (Bastille Day). We again modeled X-ray emission due to solar wind charge exchange, but this time as observed from a moving spacecraft. This paper discusses the impact of spacecraft location on observed X-ray emission and the degree to which the locations of the bow shock and magnetopause can be detected in images.

  8. Ring current proton decay by charge exchange

    NASA Technical Reports Server (NTRS)

    Smith, P. H.; Hoffman, R. A.; Fritz, T.

    1975-01-01

    Explorer 45 measurements during the recovery phase of a moderate magnetic storm have confirmed that the charge exchange decay mechanism can account for the decay of the storm-time proton ring current. Data from the moderate magnetic storm of 24 February 1972 was selected for study since a symmetrical ring current had developed and effects due to asymmetric ring current losses could be eliminated. It was found that after the initial rapid decay of the proton flux, the equatorially mirroring protons in the energy range 5 to 30 keV decayed throughout the L-value range of 3.5 to 5.0 at the charge exchange decay rate calculated by Liemohn. After several days of decay, the proton fluxes reached a lower limit where an apparent equilibrium was maintained, between weak particle source mechanisms and the loss mechanisms, until fresh protons were injected into the ring current region during substorms. While other proton loss mechanisms may also be operating, the results indicate that charge exchange can entirely account for the storm-time proton ring current decay, and that this mechanism must be considered in all studies involving the loss of proton ring current particles.

  9. New Charge Exchange Calculations for Lowly-Charged Ions

    NASA Astrophysics Data System (ADS)

    Stancil, P. C.

    2005-05-01

    The process of charge exchange, which occurs during the collision of an ion with a neutral species, is important in a variety of astrophysical and atmospheric environments. It can have an influence on the ionization and thermal balances of the plasma and may also contribute to the emission spectrum. The charge exchange of multiply-charged ions (q>2) usually proceeds at a fast rate with rate coefficients typically of 10-10 to 10-9 cm3s-1. Therefore, highly-charged ions, which are created in UV or x-ray ionized gas, quickly recombine to smaller charges. However, the rate coefficients for singly- and doubly-charged ions can vary over five orders of magnitude depending on the ion species, the neutral target, and the temperature. In particular, the rate coefficients depend sensitively on the dominant mechanism which may be due to radial, rotational, radiative, or spin-orbit coupling and the corresponding quasi-molecular curves can be very complicated. Measurements of such processes are complicated by metastable contamination and uncertainties in target purity and estimates of empirical values inferred from astrophysical modeling are typically suspect. Therefore, the state of knowledge of lowly-charged electron transfer processes is generally poor, but these reactions can be critical in determining the state of the plasma. If, for example, the rate coefficient for a q=2 ion is very small, the process would result in a bottle-neck in the recombination cascade from higer charges. In an effort to address these problems, quantum-mechanical calculations have been carried out for a number of singly- and doubly-charged ions and benchmarked to measurements when available. I will present a summary of these results which reveal significant differences from values adopted in rate coefficient compilations used by various modeling packages. This work was performed in collaboration with L. B. Zhao, C. Y. Lin, J. P. Gu, H. P. Liebermann, R. J. Buenker, and M. Kimura. Support from NASA

  10. Charge-exchange plasma environment for an ion drive spacecraft

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.; Carruth, M. R., Jr.

    1981-01-01

    A model was reviewed which describes the propagation of the mercury charge-exchange plasma and extended to describe the flow of the molybdenum component of the charge-exchange plasma. The uncertainties in the models for various conditions are discussed. Such topics as current drain to the solar array, charge-exchange plasma material deposition, and the effects of space plasma on the charge-exchange plasma propagation are addressed.

  11. Charge symmetry breaking two-pion exchange

    SciTech Connect

    Niskanen, J.A. )

    1992-06-01

    Two-pion exchange (TPE) contribution to the charge symmetry breaking class IV neutron-proton interaction is examined in a potential and coupled channels approach. Based on nonrelativistic {pi}{ital NN} and {pi}{ital N}{Delta} vertices, a TPE interaction is treated in two ways, as a potential or as a part calculable by the coupled channels method plus a residual potential interaction. A practical parametrization of the TPE potentials is given, which can also be used in the case of class III charge symmetry breaking (CSB) forces as well as for charge symmetric interactions. The results show that below 300 MeV the TPE contribution to CSB in elastic {ital np} scattering is insignificant, whereas at higher energies it should not be neglected.

  12. Charge exchange lifetimes for ions in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Smith, P. H.; Bewtra, N. K.

    1977-01-01

    Latest and best measurements of physical quantities involved in complete calculation of the charge exchange lifetime of mirroring magnetospheric ions are coalesced and summarized. It is critical that the charge exchange lifetimes for ions be known as accurately as possible in order to apply the charge exchange mechanism to ion phenomena within the earth's magnetosphere.

  13. Solar Wind Charge Exchange During Geomagnetic Storms

    NASA Technical Reports Server (NTRS)

    Robertson, Ina P.; Cravens, Thomas E.; Sibeck, David G.; Collier, Michael R.; Kuntz, K. D.

    2012-01-01

    On March 31st. 2001, a coronal mass ejection pushed the subsolar magnetopause to the vicinity of geosynchronous orbit at 6.6 RE. The NASA/GSFC Community Coordinated Modeling Center (CCMe) employed a global magnetohydrodynamic (MHD) model to simulate the solar wind-magnetosphere interaction during the peak of this geomagnetic storm. Robertson et aL then modeled the expected 50ft X-ray emission due to solar wind charge exchange with geocoronal neutrals in the dayside cusp and magnetosheath. The locations of the bow shock, magnetopause and cusps were clearly evident in their simulations. Another geomagnetic storm took place on July 14, 2000 (Bastille Day). We again modeled X-ray emission due to solar wind charge exchange, but this time as observed from a moving spacecraft. This paper discusses the impact of spacecraft location on observed X-ray emission and the degree to which the locations of the bow shock and magnetopause can be detected in images.

  14. Ring current proton decay by charge exchange

    NASA Technical Reports Server (NTRS)

    Smith, P. H.; Hoffman, R. A.; Fritz, T. A.

    1976-01-01

    Explorer 45 (S3-A) measurements were made during the recovery phase of the moderate magnetic storm of February 24, 1972, in which a symmetric ring current had developed and effects due to asymmetric ring current losses could be eliminated. It was found that after the initial rapid decay of the proton flux, which is a consequence of the dissipation of the asymmetric ring current, the equatorially mirroring protons in the energy range 5-30 keV decayed throughout the L value range of 3.5-5.0 at the charge exchange decay rate calculated by Liemohn (1961). After several days of decay, the proton fluxes reached a lower limit where an apparent equilibrium was maintained, between weak particle source mechanisms and the loss mechanisms, until fresh protons were injected into the ring current region during substorms. While other proton loss mechanisms may also be operating, the results indicate that charge exchange is more than sufficient as a particle loss mechanism for the storm time proton ring current decay.

  15. Charge exchange in the Io torus and exosphere

    NASA Technical Reports Server (NTRS)

    Johnson, R. E.; Strobel, D. F.

    1982-01-01

    Charge-exchange cross sections and their velocity dependence have been estimated for the most important reactions in the Io torus and exosphere. The methods used for calculating the cross sections are given and discussed in some detail. For symmetric-resonant single and double charge exchange, the cross sections are slowly varying functions of velocity. For inelastic charge-exchange collisions, the transition probabilities into a given final state can depend critically on velocity. Models are described which can be used to estimate both the most rapid charge-exchange processes and those states which play an important role. Calculated cross sections are used to obtain reaction rates as a function of radial position, demonstrating the importance of charge exchange in the inner torus. Charge-exchange reactions of torus ions with molecular species in Io's exosphere may yield a net supply of neutrals and plasma to the torus.

  16. Visible charge exchange recombination spectroscopy on TFTR

    SciTech Connect

    Stratton, B.C.; Fonck, R.J.; Jaehnig, K.P.; Schechtman, N.; Synakowski, E.J.

    1991-03-01

    Visible charge exchange recombination spectroscopy is routinely used to measure the time evolution of the ion temperature (T{sub i}) and toroidal rotation velocity (v{sub {phi}}) profiles on TFTR. These measurements are made with the CHERS diagnostic, a fiber-optically coupled spectrometer equipped with a two-dimensional photodiode array detector which provides both spectral and spatial resolution. The instrumentation, data analysis techniques, and examples of T{sub i} and v{sub {phi}} measurements are described. Recently, CHERS has been used to perform impurity transport experiments: radial profiles of diffusivities and convective velocities for helium and iron have been deduced from measurements of the time evolutions of He{sup 2+} and Fe{sup 24+} profiles following impurity injection. Examples of these measurements are given. 12 refs., 8 figs.

  17. Dependence of the charge exchange lifetimes on mirror latitude

    NASA Technical Reports Server (NTRS)

    Smith, P. H.; Bewtra, N. K.

    1976-01-01

    The dependence of the charge exchange lifetimes on the mirror latitude for ions mirroring off the geomagnetic equator was re-computed using the improved hydrogen distribution models. The Chamberlain model was used to define the spatial distribution of the neutral hydrogen environment through which the ring current ions traverse. The resultant dependence of the charge exchange lifetime on mirror latitude is best fitted by the approximation that contains the charge exchange lifetime for equatorial particles.

  18. Suzaku Observations of Charge Exchange Emission from Solar System Objects

    NASA Technical Reports Server (NTRS)

    Ezoe, Y.; Fujimoto, R.; Yamasaki, N. Y.; Mitsuda, K.; Ohashi, T.; Ishikawa, K.; Oishi, S.; Miyoshi, Y; Terada, N.; Futaana, Y.; Porter, F. S.; Brown, G. V.

    2012-01-01

    Recent results of charge exchange emission from solar system objects observed with the Japanese Suzaku satellite are reviewed. Suzaku is of great importance to investigate diffuse X-ray emission like the charge exchange from planetary exospheres and comets. The Suzaku studies of Earth's exosphere, Martian exosphere, Jupiter's aurorae, and comets are overviewed.

  19. 76 FR 10498 - Exchange Visitor Program-Fees and Charges

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-25

    ... Part 62 RIN 1400-AC67 Exchange Visitor Program--Fees and Charges AGENCY: Department of State. ACTION: Final rule. SUMMARY: The Department of State is amending its regulations regarding fees and charges for Exchange Visitor Program services. The fees permit the Department to recoup the cost of providing...

  20. X-ray emission from charge exchange of highly-charged ions in atoms and molecules

    NASA Technical Reports Server (NTRS)

    Greenwood, J. B.; Williams, I. D.; Smith, S. J.; Chutjian, A.

    2000-01-01

    Charge exchange followed by radiative stabilization are the main processes responsible for the recent observations of X-ray emission from comets in their approach to the Sun. A new apparatus was constructed to measure, in collisions of HCIs with atoms and molecules, (a) absolute cross sections for single and multiple charge exchange, and (b) normalized X-ray emission cross sections.

  1. Charge-exchange plasma generated by an ion thruster

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.

    1977-01-01

    The charge exchange plasma generated by an ion thruster was investigated experimentally using both 5 cm and 15 cm thrusters. Results are shown for wide ranges of radial distance from the thruster and angle from the beam direction. Considerations of test environment, as well as distance from the thruster, indicate that a valid simulation of a thruster on a spacecraft was obtained. A calculation procedure and a sample calculation of charge exchange plasma density and saturation electron current density are included.

  2. Charge-exchange collisions of C 60z+ : a probe of the ion charge distribution

    NASA Astrophysics Data System (ADS)

    Cameron, Douglas B.; Parks, Joel H.

    1997-06-01

    We present Paul trap measurements of charge-exchange collisions of Li, Cs and C 60 with C 60z+ ions ( z = 1-3) at thermal energies. Surprisingly, the measured charge-exchange rates for each neutral species are not proportional to the ion charge z as would be expected for Langevin collisions involving a uniformly charged ion. The relative rates can be reproduced by a model based on a symmetric distribution of point charges that are free to move on the ion surface during the neutral trajectory. Such behavior can be attributed to static and possibly dynamic Jahn-Teller effects in C 60z+ ions.

  3. 78 FR 28137 - Exchange Visitor Program-Fees and Charges

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-14

    ... Part 62 RIN 1400-AD28 Exchange Visitor Program--Fees and Charges AGENCY: Department of State. ACTION... Application Fee for Sponsor Designation or Redesignation and the Administrative Fee for Exchange Visitor (J-1..., 2013 (RIN 1400-AD28; 78 FR 6263), with a request for comments, to amend 22 CFR 62.17 (``Fees...

  4. Ion momentum and energy transfer rates for charge exchange collisions

    NASA Technical Reports Server (NTRS)

    Horwitz, J.; Banks, P. M.

    1973-01-01

    The rates of momentum and energy transfer have been obtained for charge exchange collisions between ion and neutral gases having arbitrary Maxwellian temperatures and bulk transport velocities. The results are directly applicable to the F-region of the ionosphere where 0+ - 0 charge is the dominant mechanism affecting ion momentum and energy transfer.

  5. Impurity charge-exchange processes processes in Tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Puiatti, M. E.; Breton, C.; Michelis, C.; Mattioll, M.

    1981-02-01

    Charge exchange reactions between multiply charged impurity ions and neutral hydrogen isotopes were considered. Ionization equilibrium and radiative losses were evaluated for oxygen and iron in the presence of either thermal or beam neutrals. The influence of thermal neutrals on recently reported results from chemically heated TFR discharges is also discussed.

  6. Charge exchange cooling in the tandem mirror plasma confinement apparatus

    DOEpatents

    Logan, B. Grant

    1978-01-01

    Method and apparatus for cooling a plasma of warm charged species confined in the center mirror cell of the tandem mirror apparatus by injecting cold neutral species of the plasma into at least one mirroring region of the center mirror cell, the cooling due to the loss of warm charged species through charge exchange with the cold neutral species with resulting diffusion of the warm neutral species out of the plasma.

  7. Characterization of an atomic hydrogen source for charge exchange experiments

    NASA Astrophysics Data System (ADS)

    Leutenegger, M. A.; Beiersdorfer, P.; Betancourt-Martinez, G. L.; Brown, G. V.; Hell, N.; Kelley, R. L.; Kilbourne, C. A.; Magee, E. W.; Porter, F. S.

    2016-11-01

    We characterized the dissociation fraction of a thermal dissociation atomic hydrogen source by injecting the mixed atomic and molecular output of the source into an electron beam ion trap containing highly charged ions and recording the x-ray spectrum generated by charge exchange using a high-resolution x-ray calorimeter spectrometer. We exploit the fact that the charge exchange state-selective capture cross sections are very different for atomic and molecular hydrogen incident on the same ions, enabling a clear spectroscopic diagnostic of the neutral species.

  8. Charge Exchange Spectra of Hydrogenic and He-like Iron

    SciTech Connect

    Wargelin, B J; Beiersdorfer, P; Neill, P A; Olson, R E; Scofield, J H

    2005-04-27

    We present H-like Fe XXVI and He-like Fe XXV charge-exchange spectra resulting from collisions of highly charged iron with N{sub 2} gas at an energy of {approx}10 eV amu{sup -1} in an electron beam ion trap. Although high-n emission lines are not resolved in our measurements, we observe that the most likely level for Fe{sup 25+} {yields} Fe{sup 24+} electron capture is n{sub max} {approx} 9, in line with expectations, while the most likely value for Fe{sup 26+} {yields} Fe{sup 25+} charge exchange is significantly higher. In the Fe XXV spectrum, the K{alpha} emission feature dominates, whether produced via charge exchange or collisional excitation. The K{alpha} energy centroid is lower in the former case than the latter (6666 versus 6685 eV, respectively), as expected because of the strong enhancement of emission from the forbidden and intercombination lines, relative to the resonance line, in charge-exchange spectra. In contrast, the Fe XXVI high-n Lyman lines have a summed intensity greater than that of Ly{alpha}, and are substantially stronger than predicted from theoretical calculations of charge exchange with atomic H. A discussion is presented of the relevance of our results to studies of diffuse Fe emission in the Galactic Center and Galactic Ridge, particularly with ASTRO-E2.

  9. Exchange bias mediated by interfacial nanoparticles (invited)

    SciTech Connect

    Berkowitz, A. E.; Sinha, S. K.; Fullerton, E. E.; Smith, D. J.

    2015-05-07

    The objective of this study on the iconic exchange-bias bilayer Permalloy/CoO has been to identify those elements of the interfacial microstructure and accompanying magnetic properties that are responsible for the exchange-bias and hysteretic properties of this bilayer. Both epitaxial and polycrystalline samples were examined. X-ray and neutron reflectometry established that there existed an interfacial region, of width ∼1 nm, whose magnetic properties differed from those of Py or CoO. A model was developed for the interfacial microstructure that predicts all the relevant properties of this system; namely; the temperature and Permalloy thickness dependence of the exchange-bias, H{sub EX}, and coercivity, H{sub C}; the much smaller measured values of H{sub EX} from what was nominally expected; the different behavior of H{sub EX} and H{sub C} in epitaxial and polycrystalline bilayers. A surprising result is that the exchange-bias does not involve direct exchange-coupling between Permalloy and CoO, but rather is mediated by CoFe{sub 2}O{sub 4} nanoparticles in the interfacial region.

  10. Charge exchange and energy loss of slow highly charged ions in 1 nm thick carbon nanomembranes.

    PubMed

    Wilhelm, Richard A; Gruber, Elisabeth; Ritter, Robert; Heller, René; Facsko, Stefan; Aumayr, Friedrich

    2014-04-18

    Experimental charge exchange and energy loss data for the transmission of slow highly charged Xe ions through ultrathin polymeric carbon membranes are presented. Surprisingly, two distinct exit charge state distributions accompanied by charge exchange dependent energy losses are observed. The energy loss for ions exhibiting large charge loss shows a quadratic dependency on the incident charge state indicating that equilibrium stopping force values do not apply in this case. Additional angle resolved transmission measurements point on a significant contribution of elastic energy loss. The observations show that regimes of different impact parameters can be separated and thus a particle's energy deposition in an ultrathin solid target may not be described in terms of an averaged energy loss per unit length.

  11. X-ray Line Formation by Charge Exchange

    NASA Astrophysics Data System (ADS)

    Beiersdorfer, Peter

    Existing X-ray telescopes have revealed charge exchange to be a key astrophysical process leading to X-ray emission when highly charged ions from such diverse sources as stellar winds, supernova remnants, or galactic super-winds interact with comets, planetary atmospheres, or the interstellar neutral gas. Charge exchange with bare sulfur ions, for example, was proposed as an alternative explanation of the 3.5 keV X-ray feature in the emission of galactic clusters that had been associated with the possible decay of sterile neutrinos. Fe XVII dominates the spectral emission of a large number of astrophysical X-ray sources and, thus, is of prime diagnostic importance, as illustrated in numerous measurements by Chandra and XMM-Newton. Although immense progress has been made in laboratory measurements and spectral calculations of collisional plasmas since the launch of these X-ray observatories, model calculations of the Fe XVII X-ray spectrum still do not yield agreement with astrophysical observations that is completely satisfactory. As a result, charge exchange has been invoked as an alternative explanation for the poor agreement between models and observations. Theoretically, line formation by charge exchange, however, is still only poorly understood both in the case of the rather 'simple'K-shell spectra of hydrogenlike or heliumlike ions, such as Fe XXV and Fe XXVI, and the more complex L-shell spectra of neonlike ions such as Fe XVII. Experimentally, there is only a small set of laboratory measurements involving X-rays from K-shell ions, and almost no measurements of the charge exchange produced X-ray emission involving L-shell ions. Moreover, the existing laboratory measurements have focused mostly on charge exchange processes pertaining to the solar wind interacting with complex (molecular) gases in cometary and planetary atmospheres. By contrast, we propose here to perform X-ray measurements pertaining to astrophysical exchange processes dominated by atomic

  12. Pion Charge Exchange Cross Section on Liquid Argon

    NASA Astrophysics Data System (ADS)

    Nelson, Kevin; LArIAT (FNAL T-1034) Collaboration

    2017-01-01

    The observation of neutrino oscillations allows charge parity violation to be probed in the neutrino sector. Detectors with high calorimetric energy resolution and high spatial resolution will provide precise measurements of neutrino oscillations. By measuring small π+/- cross sections for individual interaction channels, specifically charge exchange, we will make a measurement in the first of its kind on liquid Argon and demonstrate the physics capabilities of a relatively new detector technology: the Liquid Argon Time Projection Chamber (LAr TPC). This analysis will report on the thin slab cross section measurement technique and the Monte Carlo cross section measurements in the energy range of 0.2 - 1.0 GeV. This analysis is the first iteration in classifying charge exchange events from a sample of incident pions, and it aims to identify events in which a π0 was produced without any charged pions leaving the interaction vertex. We will also report on the methodology and efficiency of this algorithm in identifying particles and their interactions in liquid argon. This analysis will inform a future measurement of the π+/- charge exchange cross section on liquid argon. This work was supported in part by the National Science Foundation under Grant No. PHY-1359364.

  13. Krypton charge exchange cross sections for Hall effect thruster models

    SciTech Connect

    Hause, Michael L.; Prince, Benjamin D.; Bemish, Raymond J.

    2013-04-28

    Following discharge from a Hall effect thruster, charge exchange occurs between ions and un-ionized propellant atoms. The low-energy cations produced can disturb operation of onboard instrumentation or the thruster itself. Charge-exchange cross sections for both singly and doubly charged propellant atoms are required to model these interactions. While xenon is the most common propellant currently used in Hall effect thrusters, other propellants are being considered, in particular, krypton. We present here guided-ion beam measurements and comparisons to semiclassical calculations for Kr{sup +} + Kr and Kr{sup 2+} + Kr cross sections. The measurements of symmetric Kr{sup +} + Kr charge exchange are in good agreement with both the calculations including spin-orbit effects and previous measurements. For the symmetric Kr{sup 2+} + Kr reaction, we present cross section measurements for center-of-mass energies between 1 eV and 300 eV, which spans energies not previously examined experimentally. These cross section measurements compare well with a simple one-electron transfer model. Finally, cross sections for the asymmetric Kr{sup 2+} + Kr {yields} Kr{sup +} + Kr{sup +} reaction show an onset near 12 eV, reaching cross sections near constant value of 1.6 A{sup 2} with an exception near 70-80 eV.

  14. A time-resolved study on the interaction of oppositely charged bicelles--implications on the charged lipid exchange kinetics.

    PubMed

    Yang, Po-Wei; Lin, Tsang-Lang; Hu, Yuan; Jeng, U-Ser

    2015-03-21

    Time-resolved small-angle X-ray scattering was applied to study charged lipid exchange between oppositely charged disc-shaped bicelles. The exchange of charged lipids gradually reduces the surface charge density and weakens the electrostatic attraction between the oppositely charged bicelles which form alternately stacked aggregates upon mixing. Initially, at a high surface charge density with almost no free water layer between the stacked bicelles, fast exchange kinetics dominate the exchange process. At a later stage with a lower surface charge density and a larger water gap between the stacked bicelles, slow exchange kinetics take over. The fast exchange kinetics are correlated with the close contact of the bicelles when there is almost no free water layer between the tightly bound bicelles with a charged lipid exchange time constant as short as 20-40 min. When the water gap becomes large enough to have a free water layer between the stacked bicelles, the fast lipid exchange kinetics are taken over by slow lipid exchange kinetics with time constants around 200-300 min, which are comparable to the typical time constant of lipid exchange between vesicles in aqueous solution. These two kinds of exchange mode fit well with the lipid exchange models of transient hemifusion for the fast mode and monomer exchange for the slow mode.

  15. Pion double charge exchange scattering above the delta resonance

    SciTech Connect

    Burleson, G.R.

    1989-01-01

    Data are presented on pion-nucleus double-charge-exchange scattering at energies between 300 and 500 MeV, the highest energies measured so far, together with a review of results at lower energies. The small-angle excitation functions disagree with predictions based on a sex-quark cluster model and on an optical model consistent with single-charge-exchange scattering at these energies, but they are consistent with a distorted-wave calculation. Data on f{sub 7/2}-shell nuclei are in partial agreement with a two-amplitude model which is successful at lower energies. In order to achieve good understanding of this process at these energies, more work; both experimental and theoretical, is needed. 16 refs., 6 figs.

  16. Significant enhancement of the charging efficiency in the cavities of ferroelectrets through gas exchange during charging

    NASA Astrophysics Data System (ADS)

    Qiu, Xunlin

    2016-11-01

    Ferroelectrets are non-polar polymer foams or polymer systems with internally charged cavities. They are charged through a series of dielectric barrier discharges (DBDs) that are caused by the electrical breakdown of the gas inside the cavities. Thus, the breakdown strength of the gas strongly influences the charging process of ferroelectrets. A gas with a lower breakdown strength has a lower threshold voltage, thus decreasing the onset voltage for DBD charging. However, a lower threshold voltage also leads to a lower value for the remanent polarization, as back discharges that are caused by the electric field of the internally deposited charges can take place already at lower charge levels. On this basis, a charging strategy is proposed where the DBDs start in a gas with a lower breakdown strength (in the present example, helium) and are completed at a higher breakdown strength (e.g., nitrogen or atmospheric air). Thus, the exchange of the gas in the cavities during charging can significantly enhance the charging efficiency, i.e., yield much higher piezoelectric coefficients in ferroelectrets at significantly lower charging voltages.

  17. PLASIM: A computer code for simulating charge exchange plasma propagation

    NASA Technical Reports Server (NTRS)

    Robinson, R. S.; Deininger, W. D.; Winder, D. R.; Kaufman, H. R.

    1982-01-01

    The propagation of the charge exchange plasma for an electrostatic ion thruster is crucial in determining the interaction of that plasma with the associated spacecraft. A model that describes this plasma and its propagation is described, together with a computer code based on this model. The structure and calling sequence of the code, named PLASIM, is described. An explanation of the program's input and output is included, together with samples of both. The code is written in ANSI Standard FORTRAN.

  18. Momentum transfer in relativistic heavy ion charge-exchange reactions

    NASA Technical Reports Server (NTRS)

    Townsend, L. W.; Wilson, J. W.; Khan, F.; Khandelwal, G. S.

    1991-01-01

    Relativistic heavy ion charge-exchange reactions yield fragments (Delta-Z = + 1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (Delta-Z = 1, -2,...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.

  19. Systematics of heavy-ion charge-exchange straggling

    NASA Astrophysics Data System (ADS)

    Sigmund, P.; Schinner, A.

    2016-10-01

    The dependence of heavy-ion charge-exchange straggling on the beam energy has been studied theoretically for several ion-target combinations. Our previous work addressed ions up to krypton, while the present study focuses on heavier ions, especially uranium. Particular attention has been paid to a multiple-peak structure which has been predicted theoretically in our previous work. For high-Z1 and high-Z2 systems, exemplified by U in Au, we identify three maxima in the energy dependence of charge-exchange straggling, while the overall magnitude is comparable with that of collisional straggling. Conversely, for U in C, charge-exchange straggling dominates, but only two peaks lie in the energy range where we presently are able to produce credible predictions. For U-Al we find good agreement with experiment in the energy range around the high-energy maximum. The position of the high-energy peak - which is related to processes in the projectile K shell - is found to scale as Z12 , in contrast to the semi-empirical Z13/2 dependence proposed by Yang et al. Measurements for heavy ions in heavy targets are suggested in order to reconcile a major discrepancy between the present calculations and the frequently-used formula by Yang et al.

  20. Charge-exchange plasma generated by an ion thruster

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.

    1975-01-01

    The use of high voltage solar arrays greatly reduces or eliminates power processing requirements in space electric propulsion systems. This use also requires substantial areas of solar array to be at high positive potential relative to space and most of the spacecraft. The charge exchange plasma conducts electrons from the ion beam to such positive surfaces, and thereby electrically load the high voltage solar array. To evaluate this problem, the charge-exchange plasma generated by an ion beam was investigated experimentally. Based upon the experimental data, a simple model was derived for the charge-exchange plasma. This model is conservative in the sense that both the electron/ion density and the electron current density should be equal to, or less than, the preducted value for all directions in the hemisphere upstream of the ion beam direction. Increasing the distance between a positive potential surface (such as a high voltage solar array) and the thruster is the simplest way to control interactions. Both densities and currents vary as the inverse square of this distance.

  1. Charge-Exchange Processes of Titanium-Doped Aluminate Crystals

    NASA Astrophysics Data System (ADS)

    Wong, Wing Cheong

    1995-01-01

    Titanium exists in more than one charge state in the aluminate crystals: it is stable as Ti^ {3+} and Ti^{4+}. Other than the intense Ti^{4+ } absorption, a ubiquitous absorption/luminescence excitation band in the UV region is identified as a titanium -bound exciton in Al_2rm O_3, Y_3Al_5rm O_{12}, {rm YAlO}_3, MgAl_2O _4, and LaMgAl_{11} {rm O}_{19}. One -step and two-step photoconductivities of Ti^ {3+} are measured and compared. While the selectivity of the two-step process is demonstrated, its use in locating the energy threshold is hampered by the small Franck-Condon factor for the transition between the Ti^{3+} ^2{ rm E} excited state and Ti^ {4+}. The titanium-bound exciton band, together with the one-step photocurrent signal, makes it possible to determine the photoionization energy threshold accurately. The charge-transfer transition energy thresholds of Ti^{4+} are obtained from the emission and the luminescence excitation spectra. Locally and non-locally charge compensated Ti^{4+ } are found in Al_2{rm O}_3. The luminescence kinetics for the two kinds of Ti^{4+} are well explained by a three-level system with a lower triplet excited state and a higher singlet excited state. These charge-exchange threshold energies can be deduced from the Born-Haber thermodynamical cycle. The electrostatic site potentials are calculated and from it, the calculated photoionization and charge-transfer energy thresholds are found to be consistent with the experimental results. The deficiency of this model is pointed out and possible improvement is discussed. Quantitatively, the sum of the two charge-exchange energy thresholds is close to the band-gap energy of the host crystal. This offers a convenient way for material characterization. Provided that any two of the three quantities (band-gap energy, photoionization energy threshold, and charge-transfer transition energy threshold) have been found, the third quantity can be calculated. In addition, the trapping of charge

  2. Modeling the Hydrogen-Proton Charge-Exchange Process in Global Heliospheric Simulations

    NASA Astrophysics Data System (ADS)

    DeStefano, A.; Heerikhuisen, J.

    2015-12-01

    The environment surrounding our Solar System has a vast and dynamic structure. As the Sun rounds the Milky Way galaxy, interstellar dust and gas interact with the Sun's outflow of solar wind. A bubble of hot plasma forms around the Sun due to this interaction, called the heliosphere. In order to understand the structure of the heliosphere, observations and simulations must work in tandem. Within the past decade or so, 3D models of the heliosphere have been developed exhibiting non- symmmetric as well as predicting structures such as the hydrogen wall and the IBEX ribbon. In this poster we explore new ways to compute charge-exchange source terms. The charge-exchange process is the coupling mechanism between the MHD and kinetic theories. The understanding of this process is crucial in order to make valuable predictions. Energy dependant cross section terms will aid in settling non-linear affects coupling the intestellar and solar particles. Through these new ways of computing source terms, resolving fine structures in the plasma in the heliopause may be possible. In addition, other non-trivial situations, such as charge-exchange mediated shocks, may be addressed.

  3. Anion exchangers with negatively charged functionalities in hyperbranched ion-exchange layers for ion chromatography.

    PubMed

    Uzhel, Anna S; Zatirakha, Alexandra V; Smirnov, Konstantin N; Smolenkov, Alexandr D; Shpigun, Oleg A

    2017-01-27

    Novel pellicular poly(styrene-divinylbenzene)-based (PS-DVB) anion exchangers with covalently-bonded hyperbranched functional ion-exchange layers containing negatively charged functionalities are obtained and examined. The hyperbranched coating is created on the surface of aminated PS-DVB substrate by repeating the modification cycles including alkylation with 1,4-butanediol diglycidyl ether (1,4-BDDGE), and amination of the terminal epoxide rings with methylamine (MA) or glycine (Gly). The influence of the position and the number of the layers with glycine, as well as of the total number of the layers of amine in the coating on the chromatographic properties of the obtained stationary phases is investigated. Chromatographic performance of the obtained stationary phases is evaluated using the model mixtures of inorganic and organic anions with hydroxide eluent. It is shown that the best selectivity toward weakly retained organic acids and oxyhalides is possessed by the anion exchanger obtained after 5 modification cycles, with glycine being used in the first one. Such anion exchanger packed in 25-cm long column is capable of separating 22 anions in 58min including 7 standard anions, mono-, di- and trivalent organic acids, oxyhalides, and some other double- and triple-charged anions.

  4. Charge exchange in slow collisions of Si3+ with H

    NASA Astrophysics Data System (ADS)

    Joseph, D. C.; Saha, B. C.

    2010-10-01

    Low energy electron capture from atomic hydrogen by multi-charged ions continues to be of interest and has wide applications including both magnetically confined^ fusion and astrophysical plasmas. The charge exchange process reported here, Si^3+ + H -- Si^2+ + H^+ is an important destruction mechanism of Si^3+ in photo-ionized gas. The soft X-ray emission from comets has been explained by charge transfer of solar wind ions, among them Si^3+, with neutrals in the cometary gas vapor. The state selective cross sections are evaluated using the semi-classical molecular orbital close coupling (MOCC) [1] methods. Adiabatic potentials and wave functions for a number of low-lying singlet and triplet states are calculated using the MRD-CI package [2]. Details will be presented at the conference. [1] M. Kimura and N. F. Lane, At. Mol. Opt. Phys 26, 79 (1990). [3] R. J. Buenker, ``Current Aspects of Quantum Chemistry'' 1981, Vol 21, edited by R. Carbo (Elsevier, Amsterdam) p 17.

  5. Electrolyte-Mediated Assembly of Charged Nanoparticles

    PubMed Central

    2016-01-01

    Solutions at high salt concentrations are used to crystallize or segregate charged colloids, including proteins and polyelectrolytes via a complex mechanism referred to as “salting-out”. Here, we combine small-angle X-ray scattering (SAXS), molecular dynamics (MD) simulations, and liquid-state theory to show that salting-out is a long-range interaction, which is controlled by electrolyte concentration and colloid charge density. As a model system, we analyze Au nanoparticles coated with noncomplementary DNA designed to prevent interparticle assembly via Watson–Crick hybridization. SAXS shows that these highly charged nanoparticles undergo “gas” to face-centered cubic (FCC) to “glass-like” transitions with increasing NaCl or CaCl2 concentration. MD simulations reveal that the crystallization is concomitant with interparticle interactions changing from purely repulsive to a “long-range potential well” condition. Liquid-state theory explains this attraction as a sum of cohesive and depletion forces that originate from the interelectrolyte ion and electrolyte–ion–nanoparticle positional correlations. Our work provides fundamental insights into the effect of ionic correlations in the salting-out mechanism and suggests new routes for the crystallization of colloids and proteins using concentrated salts. PMID:27163052

  6. Charge-exchange reactions with a radioactive triton beam

    SciTech Connect

    Jaenecke, J.

    1998-12-21

    A high-resolution (t, {sup 3}He) test experiment has been performed recently by making use of a secondary triton beam produced by fragmentation of {alpha}-particles. The purpose of this charge-exchange experiment was to achieve good energy resolution in an (n,p)-type reaction at intermediate bombarding energies. The experiment was carried out with the K1200 cyclotron at the National Superconducting Cyclotron Laboratory using the A1200 beam-analysis system and the S800 magnetic spectrometer. The beam-analysis system was used to transport the energy-dispersed radioactive triton beam from the production target to the target position, and the magnetic spectrometer was used to focus the dispersion-matched {sup 3}He particles from the (t, {sup 3}He) reaction at 0 degree sign onto the focal plane of the spectrometer. An energy resolution of 200-250 keV was achieved.

  7. Improved edge charge exchange recombination spectroscopy in DIII-D

    DOE PAGES

    Chrystal, Colin; Burrell, K. H.; Grierson, Brian A.; ...

    2016-08-02

    The charge exchange recombination spectroscopy diagnostic on the DIII-D tokamak has been upgraded with the addition of more high radial resolution view chords near the edge of the plasma (r/a > 0.8). The additional views are diagnosed with the same number of spectrometers by placing fiber optics side-by-side at the spectrometer entrance with a precise separation that avoids wavelength shifted crosstalk without the use of bandpass filters. The new views improve measurement of edge impurity parameters in steep gradient, H-mode plasmas with many different shapes. The number of edge view chords with 8 mm radial separation has increased from 16more » to 38.As a result, new fused silica fibers have improved light throughput and clarify the observation of non-Gaussian spectra that suggest the ion distribution function can be non-Maxwellian in low collisionality plasmas.« less

  8. Improved edge charge exchange recombination spectroscopy in DIII-D

    SciTech Connect

    Chrystal, Colin; Burrell, K. H.; Grierson, Brian A.; Haskey, Shaun R.; Groebner, R. J.; Kaplan, David H.; Briesemeister, Alexis R.

    2016-08-02

    The charge exchange recombination spectroscopy diagnostic on the DIII-D tokamak has been upgraded with the addition of more high radial resolution view chords near the edge of the plasma (r/a > 0.8). The additional views are diagnosed with the same number of spectrometers by placing fiber optics side-by-side at the spectrometer entrance with a precise separation that avoids wavelength shifted crosstalk without the use of bandpass filters. The new views improve measurement of edge impurity parameters in steep gradient, H-mode plasmas with many different shapes. The number of edge view chords with 8 mm radial separation has increased from 16 to 38.As a result, new fused silica fibers have improved light throughput and clarify the observation of non-Gaussian spectra that suggest the ion distribution function can be non-Maxwellian in low collisionality plasmas.

  9. Improved edge charge exchange recombination spectroscopy in DIII-D

    NASA Astrophysics Data System (ADS)

    Chrystal, C.; Burrell, K. H.; Grierson, B. A.; Haskey, S. R.; Groebner, R. J.; Kaplan, D. H.; Briesemeister, A.

    2016-11-01

    The charge exchange recombination spectroscopy diagnostic on the DIII-D tokamak has been upgraded with the addition of more high radial resolution view chords near the edge of the plasma (r/a > 0.8). The additional views are diagnosed with the same number of spectrometers by placing fiber optics side-by-side at the spectrometer entrance with a precise separation that avoids wavelength shifted crosstalk without the use of bandpass filters. The new views improve measurement of edge impurity parameters in steep gradient, H-mode plasmas with many different shapes. The number of edge view chords with 8 mm radial separation has increased from 16 to 38. New fused silica fibers have improved light throughput and clarify the observation of non-Gaussian spectra that suggest the ion distribution function can be non-Maxwellian in low collisionality plasmas.

  10. Cometary X-Rays: Line Emission Cross Sections for Multiply Charged Solar Wind Ion Charge Exchange

    SciTech Connect

    Otranto, S; Olson, R E; Beiersdorfer, P

    2006-12-22

    Absolute line emission cross sections are presented for 1 keV/amu charge exchange collisions of multiply charged solar wind ions with H{sub 2}O, H, O, CO{sub 2}, and CO cometary targets. The present calculations are contrasted with available laboratory data. A parameter-free model is used to successfully predict the recently observed x-ray spectra of comet C/LINEAR 1999 S4. We show that the resulting spectrum is extremely sensitive to the time variations of the solar wind composition. Our results suggest that orbiting x-ray satellites may be a viable way to predict the solar wind intensities and composition on the Earth many hours before the ions reach the earth.

  11. Two-pion exchange contributions to nuclear charge asymmetry

    SciTech Connect

    Coon, S.A.; Niskanen, J.A.

    1995-04-01

    An explicit 2{pi} exchange (TPE) potential based on non-relativistic {pi}NN and {pi}{Delta}N vertices with the baryon mass differences taken into account in the vertices is extended to the study of mirror nuclear systems. For the latter study, one must also include baryon mass differences in the intermediate state energy denominators. The TPE potential includes box and crossed box diagrams with two nucleons and those with one nucleon and one {Delta}. Nuclear charge asymmetry is characterized, in part, by a positive value for the difference {Delta}a = {vert_bar}a{sub nn}{vert_bar} {minus} {vert_bar}a{sub pp}{vert_bar} {approx} O(1 fm) and a positive value for the {sup 3}H - {sup 3}He binding energy difference {Delta}E {approx} O(100 keV). The charge asymmetry from baryon mass differences in the vertices is small on this scale and in the wrong direction compared to the empirical values. The contribution from baryon mass differences in the intermediate state energy denominators is positive and is of the order of the empirical scales, in contrast to the previous estimate of {Delta}a {approx} +0.3 fm obtained from an SU(2) symmetric covariant field theoretical potential. This discrepancy between models of TPE is being investigated.

  12. Numerical calculation of charge exchange cross sections for plasma diagnostics

    NASA Astrophysics Data System (ADS)

    Mendez, Luis

    2016-09-01

    The diagnostics of impurity density and temperature in the plasma core in tokamak plasmas is carried out by applying the charge exchange recombination spectroscopy (CXRS) technique, where a fast beam of H atoms collides with the plasma particles leading to electron capture reactions with the impurity ions. The diagnostics is based on the emission of the excited ions formed in the electron capture. The application of the CXRS requires the knowledge of accurate state-selective cross sections, which in general are not accessible experimentally, and the calculation of cross sections for the high n capture levels, required for the diagnostics in the intermediate energy domain of the probe beam, is particularly difficult. In this work, we present a lattice numerical method to solve the time dependent Schrödinger equation. The method is based on the GridTDSE package, it is applicable in the wide energy range 1 - 500 keV/u and can be used to assess the accuracy of previous calculations. The application of the method will be illustrated with calculations for collisions of multiply charged ions with H. Work partially supported by project ENE2014-52432-R (Secretaria de Estado de I+D+i, Spain).

  13. High-throughput charge exchange recombination spectroscopy system on MAST

    SciTech Connect

    Conway, N. J.; Carolan, P. G.; McCone, J.; Walsh, M. J.; Wisse, M.

    2006-10-15

    A major upgrade to the charge exchange recombination spectroscopy system on MAST has recently been implemented. The new system consists of a high-throughput spectrometer coupled to a total of 224 spatial channels, including toroidal and poloidal views of both neutral heating beams on MAST. Radial resolution is {approx}1 cm, comparable to the ion Larmor radius. The toroidal views are configured with 64 channels per beam, while the poloidal views have 32 channels per beam. Background channels for both poloidal and toroidal views are also provided. A large transmission grating is at the heart of the new spectrometer, with high quality single lens reflex lenses providing excellent imaging performance and permitting the full exploitation of the available etendue of the camera sensor. The charge-coupled device camera chosen has four-tap readout at a maximum aggregate speed of 8.8 MHz, and it is capable of reading out the full set of 224 channels in less than 4 ms. The system normally operates at 529 nm, viewing the C{sup 5+} emission line, but can operate at any wavelength in the range of 400-700 nm. Results from operating the system on MAST are shown, including impurity ion temperature and velocity profiles. The system's excellent spatial resolution is ideal for the study of transport barrier phenomena on MAST, an activity which has already been advanced significantly by data from the new diagnostic.

  14. Heat exchange mediated by a quantum system

    NASA Astrophysics Data System (ADS)

    Panasyuk, George Y.; Levin, George A.; Yerkes, Kirk L.

    2012-08-01

    We consider heat transfer between two thermal reservoirs mediated by a quantum system using the generalized quantum Langevin equation. The thermal reservoirs are treated as ensembles of oscillators within the framework of the Drude-Ullersma model. General expressions for the heat current and thermal conductance are obtained for arbitrary coupling strength between the reservoirs and the mediator and for different temperature regimes. As an application of these results we discuss the origin of Fourier's law in a chain of large but finite subsystems coupled to each other by the quantum mediators. We also address a question of anomalously large heat current between the scanning tunneling microscope (STM) tip and substrate found in a recent experiment. The question of minimum thermal conductivity is revisited in the framework of scaling theory as a potential application of the developed approach.

  15. Heat exchange mediated by a quantum system.

    PubMed

    Panasyuk, George Y; Levin, George A; Yerkes, Kirk L

    2012-08-01

    We consider heat transfer between two thermal reservoirs mediated by a quantum system using the generalized quantum Langevin equation. The thermal reservoirs are treated as ensembles of oscillators within the framework of the Drude-Ullersma model. General expressions for the heat current and thermal conductance are obtained for arbitrary coupling strength between the reservoirs and the mediator and for different temperature regimes. As an application of these results we discuss the origin of Fourier's law in a chain of large but finite subsystems coupled to each other by the quantum mediators. We also address a question of anomalously large heat current between the scanning tunneling microscope (STM) tip and substrate found in a recent experiment. The question of minimum thermal conductivity is revisited in the framework of scaling theory as a potential application of the developed approach.

  16. Electrolyte-Mediated Assembly of Charged Nanoparticles

    NASA Astrophysics Data System (ADS)

    Kewalramani, Sumit; Bedzyk, Michael; Guerrero-García, Guillermo; Moreau, Liane; Zwanikken, Jos; Mirkin, Chad; Olvera de La Cruz, Monica

    Solutions at high salt concentrations are used to crystallize or segregate colloids, proteins and polyelectrolytes via an unknown mechanism referred to as ``salting-out''. Here, we show salting-out is a long-range interaction controlled by electrolyte concentration and nanoparticle charge density. Small-angle X-ray scattering (SAXS) shows that DNA-coated Au nanoparticles designed to prevent inter-particle assembly via Watson-Crick hybridization undergo ``gas'' to FCC to ``glass-like'' transitions with increasing NaCl or CaCl2 concentration. Simulations reveal that the crystallization is concomitant with inter-particle interactions changing from purely repulsive to a long-range potential well condition. Liquid-state theory explains this attraction as a sum of cohesive and depletion forces. Our work reveals the mechanism behind salting-out and suggests new routes for the successful crystallization of colloids and proteins using concentrated salts.

  17. Charge-exchange reaction by Reggeon exchange and W{sup +}W{sup −}-fusion

    SciTech Connect

    Schicker, R.

    2015-04-10

    Charge-exchange reactions at high energies are examined. The existing cross section data on the Reggeon induced reaction pp → n + Δ{sup ++} taken at the ZGS and ISR accelerators are extrapolated to the energies of the RHIC and LHC colliders. The interest in the charge-exchange reaction induced by W{sup ±}-fusion is presented, and the corresponding QCD-background is examined.

  18. XMM-Newton Observations of Solar Wind Charge Exchange Emission

    NASA Technical Reports Server (NTRS)

    Snowden, S. L.; Collier, M. R.; Kuntz, K. D.

    2004-01-01

    We present an XMM-Newton spectrum of diffuse X-ray emission from within the solar system. The spectrum is dominated by O VII and O VIII lines at 0.57 keV and 0.65 keV, O VIII (and possibly Fe XVII) lines at approximately 0.8 keV, Ne IX lines at approximately 0.92 keV, and Mg XI lines at approximately 1.35 keV. This spectrum is consistent with what is expected from charge exchange emission between the highly ionized solar wind and either interstellar neutrals in the heliosphere or material from Earth's exosphere. The emission is clearly seen as a low-energy ( E less than 1.5 keV) spectral enhancement in one of a series of observations of the Hubble Deep Field North. The X-ray enhancement is concurrent with an enhancement in the solar wind measured by the ACE satellite. The solar wind enhancement reaches a flux level an order of magnitude more intense than typical fluxes at 1 AU, and has ion ratios with significantly enhanced higher ionization states. Whereas observations of the solar wind plasma made at a single point reflect only local conditions which may only be representative of solar wind properties with spatial scales ranging from less than half of an Earth radii (approximately 10 s) to 100 Earth radii, X-ray observations of solar wind charge exchange are remote sensing measurements which may provide observations which are significantly more global in character. Besides being of interest in its own right for studies of the solar system, this emission can have significant consequences for observations of more cosmological objects. It can provide emission lines at zero redshift which are of particular interest (e.g., O VII and O VIII) in studies of diffuse thermal emission, and which can therefore act as contamination in objects which cover the entire detector field of view. We propose the use of solar wind monitoring data, such as from the ACE and Wind spacecraft, as a diagnostic to screen for such possibilities.

  19. Localized, positive charge mediates adhesion of rhodosporidium toruloides to barley leaves and polystyrene

    PubMed

    Buck; Andrews

    1999-05-01

    The physicochemical forces that mediate attachment of yeasts to the phylloplane are unknown. Cell surface charge and hydrophobicity and adhesion to polystyrene, glass, and barley were assessed for wild-type Rhodosporidium toruloides and attachment-minus (Att-) mutants. Cells were grown under conditions promoting (excess carbon) or not promoting (excess nitrogen) capsule production. Hydrophobicity was measured by adhesion to xylenes, and surface charge characteristics were assessed by attachment to either DEAE (positive)- or carboxymethyl (CM) (negative)-Sephadex ion-exchange beads. Hydrophobicity and adhesiveness of nonencapsulated, wild-type R. toruloides decreased from mid-log to late stationary phase. Encapsulated wild-type R. toruloides cells were more hydrophobic and more adhesive than nonencapsulated cells. However, two encapsulated Att- mutants were more hydrophobic than the wild type and levels of adhesion of R. toruloides were similar on polystyrene and less hydrophobic glass surfaces. Adhesion of wild-type yeast to barley and polystyrene was correlated with attachment to CM-Sephadex beads, indicating a positive cell surface charge. Sixteen Att- mutants did not exhibit a positive cell surface charge, and wild-type yeast cells that did not attach to CM-Sephadex did not adhere to either polystyrene or barley. Wild-type R. toruloides attached to CM-Sephadex beads by the poles of the cells, indicating a localization of positive charge which was also visualized with India ink. We conclude that localized, positive charge, and not hydrophobic interactions, mediates attachment of R. toruloides to barley leaves.

  20. Spin-Isospin responses via charge exchange reactions of RI beams at SHARAQ

    SciTech Connect

    Shimoura, Susumu

    2012-11-12

    Nuclear spectroscopy via direct reactions of RI beams is discussed focusing on characteristics of charge-exchange reactions of RI beams. Recent experiments using the SHARAQ spectrometer at the RIBF are presented, where isovector spin monopole and spin-non-flip monopole responses are studied by charge exchange reaction of RI beams. Some experimental plans and perspectives are also presented.

  1. Double charge exchange on Te isotopes in the generalized seniority scheme

    SciTech Connect

    Wu, H.C. |; Ginocchio, J.N.; Dieperink, A.E.; Scholten, O.

    1996-09-01

    The pion double-charge-exchange reactions on the Te isotopes are discussed in the generalized seniority scheme. The elementary process of charge exchange is described in a double scattering process within the plane wave limit. The transition rates are calculated for double-isobaric-analog state as well as for ground-state reactions. {copyright} {ital 1996 The American Physical Society.}

  2. Charge Exchange, from the Laboratory to Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Betancourt-Martinez, Gabriele; Beiersdorfer, Peter; Brown, Gregory; Hell, Natalie; Leutenegger, Maurice A.; Porter, Frederick S.; Reynolds, Christopher S.

    2016-04-01

    X-ray emission due to charge exchange (CX) between solar wind ions and neutrals in comets and planetary atmospheres is ubiquitous in the solar system, and is also a significant foreground in all observations from low-Earth orbit. It is also possible that CX is common astrophysically, in any environment where hot plasma and cold gas interact. A current challenge is that theoretical models of CX spectra do not always accurately describe observations, and require further experimental verification. This is especially important to focus on now, as the recent launch of Astro-H is providing us with the first high-resolution spectra of extended x-ray sources. In order to improve our understanding and modeling of CX spectra, we take advantage of the laboratory astrophysics program at the Lawrence Livermore National Laboratory and use an Electron Beam Ion Trap (EBIT) to perform CX experiments, using the EBIT Calorimeter Spectrometer. We present experimental benchmarks that can be used to develop a more comprehensive and accurate CX theory. On the observational side, we also investigate the possibility of CX occurring in the filaments around the central galaxy of the Perseus cluster, NGC 1275. We use Chandra ACIS data, combined with what we know about laboratory CX spectra, to investigate the possibility of CX being a significant contributor to the x-ray emission.

  3. Charge exchange recombination spectroscopy on the T-10 tokamak.

    PubMed

    Klyuchnikov, L A; Krupin, V A; Nurgaliev, M R; Korobov, K V; Nemets, A R; Dnestrovskij, A Yu; Tugarinov, S N; Serov, S V; Naumenko, N N

    2016-05-01

    The charge exchange recombination spectroscopy (CXRS) diagnostics on the T-10 tokamak is described. The system is based on a diagnostic neutral beam and includes three high etendue spectrometers designed for the ITER edge CXRS system. A combined two-channel spectrometer is developed for simultaneous measurements of two beam-induced spectral lines using the same lines of sight. A basic element of the combined spectrometer is a transmitting holographic grating designed for the narrow spectral region 5291 ± 100 Å. The whole CXRS system provides simultaneous measurements of two CXRS impurity spectra and Hα beam line. Ion temperature measurements are routinely provided using the C(6+) CXRS spectral line 5291 Å. Simultaneous measurements of carbon densities and one more impurity (oxygen, helium, lithium etc.) are carried out. Two light collecting systems with 9 lines of sight in each system are used in the diagnostics. Spatial resolution is up to 2.5 cm and temporal resolution of 1 ms is defined by the diagnostic neutral beam diameter and pulse duration, respectively. Experimental results are shown to demonstrate a wide range of the CXRS diagnostic capabilities on T-10 for investigation of impurity transport processes in tokamak plasma. Developed diagnostics provides necessary experimental data for studying of plasma electric fields, heat and particle transport processes, and for investigation of geodesic acoustic modes.

  4. STUDIES OF X-RAY PRODUCTION FOLLOWING CHARGE EXCHANGE RECOMBINATION BETWEEN HIGHLY CHARGED IONS AND NEUTRAL ATOMS AND MOLECULES

    SciTech Connect

    Brown, G V; Beiersdorfer, P; Chen, H; Clementson, J; Frankel, M; Gu, M F; Kelley, R L; Kilbourne, C A; Porter, F S; Thorn, D B; Wargelin, B J

    2008-08-28

    We have used microcalorimeters built by the NASA/Goddard Space Flight Center and the Lawrence Livermore National Laboratory Electron Beam Ion Trap to measure X-ray emission produced by charge exchange reactions between highly charged ions colliding with neutral helium, hydrogen, and nitrogen gas. Our measurements show the spectral dependence on neutral species and also show the distinct differences between spectra produced by charge exchange reactions and those produced by direct impact excitation. These results are part of an ongoing experimental investigation at the LLNL EBIT facility of charge exchange spectral signatures and can be used to interpret X-ray spectra produced by a variety of laboratory and celestial sources including cometary and planetary atmospheres, the Earth's magnetosheath, the heliosphere, and tokamaks.

  5. Metal Complexes for DNA-Mediated Charge Transport

    PubMed Central

    Barton, Jacqueline K.; Olmon, Eric D.; Sontz, Pamela A.

    2010-01-01

    In all organisms, oxidation threatens the integrity of the genome. DNA-mediated charge transport (CT) may play an important role in the generation and repair of this oxidative damage. In studies involving long-range CT from intercalating Ru and Rh complexes to 5′-GG-3′ sites, we have examined the efficiency of CT as a function of distance, temperature, and the electronic coupling of metal oxidants bound to the base stack. Most striking is the shallow distance dependence and the sensitivity of DNA CT to how the metal complexes are stacked in the helix. Experiments with cyclopropylamine-modified bases have revealed that charge occupation occurs at all sites along the bridge. Using Ir complexes, we have seen that the process of DNA-mediated reduction is very similar to that of DNA-mediated oxidation. Studies involving metalloproteins have, furthermore, shown that their redox activity is DNA-dependent and can be DNA-mediated. Long range DNA-mediated CT can facilitate the oxidation of DNA-bound base excision repair proteins to initiate a redox-active search for DNA lesions. DNA CT can also activate the transcription factor SoxR, triggering a cellular response to oxidative stress. Indeed, these studies show that within the cell, redox-active proteins may utilize the same chemistry as that of synthetic metal complexes in vitro, and these proteins may harness DNA-mediated CT to reduce damage to the genome and regulate cellular processes. PMID:21643528

  6. Excitation and Charge Exchange Phenomena in Astronomical Objects: Measurement of Cross Sections and Lifetimes

    NASA Technical Reports Server (NTRS)

    Chutjian, Ara; Smith, S.; Lozano, J.; Cadez, I.; Greewnood, J.; Mawhovter, R.; Williams, I.; Niimura, M.

    2003-01-01

    This document addresses extreme ultraviolet radiation and X-ray emissions from comets, planets and heliospheric gases focusing on the measurement of charge-exchange cross sections and radiative lifetimes. Highly-charged heavy ions present in the solar wind, and their abundance relative to the total oxygen-ion abundance are detailed. The plan for the Jet Propulsion Laboratory high-charge ion facility is outlined detailing its ability to measure absolute collisional excitation cross sections, absolute charge-exchange cross sections, lifetimes of metastable ion levels, and X-ray emission spectra following charge changes.

  7. Neutral Collisions and Charge Exchange in Titan's Exosphere

    NASA Astrophysics Data System (ADS)

    Sillanpää, I.; Johnson, R. E.

    2012-12-01

    Results from new hybrid simulations for Titan are presented. These simulations take into account the elastic collisions between ions and neutral gas as well as the charge exchange reactions for protons and oxygen ions. We used SRIM [1] cross sections for hydrogen and oxygen ions in nitrogen gas to calculate cross sections for the five ions species used in the HYB-Titan hybrid model [2, see also 3] (H+, H2+, O+, CH4+, and N2+). The N2 density profile used was from INMS measurements over a dozen flybys. In addition, we are studying the effect the charge transfer (CT) reactions for H+ and O+ leading to simple CT, dissociative CT and CT with ionization. All reaction cross sections are energy dependent. Neutral particles are not created, but the total ENA energy is recorded as well as the resulting reaction rates. The results show that both of neutral collisions and CT processes have a significant role in the development and shape of Titan's ionotail and wake structure. Results will be described in detail as well as the implications of the ion-neutral collisions for the heating of Titan's neutral corona and atmospheric escape [4]. References [1] Stopping and Range of Ions in Matter (SRIM), Monte Carlo software by James F. Ziegler (online at http://www.srim.org/ ) [2] Sillanpää, I., Hybrid Modelling of Titan's Interaction with the Magnetosphere of Saturn, Ph.D. dissertation, Finnish Meteorological Contributions, 68, Yliopistopaino, Helsinki, 2008. (online at http://urn.fi/URN:ISBN:978-951-697-660-3) [3] Sillanpää, I., D. Young, F. Crary, M. Thomsen, D. Reisenfeld, J-E.Wahlund, C. Bertucci, E. Kallio, R. Jarvinen, and P. Janhunen, Cassini Plasma Spectro:meter and Hybrid Model Study on Titan's Interaction: Effect of Oxygen Ions, J. Geophys. Res., doi:10.1029/2011JA016443, 2011. [4] Johnson, R.E., O.J. Tucker, M. Michael, E.C. Sittler, H.T. Smith, D.T. Young, and J.H. Waite, Mass Loss Processes in Titan's Upper Atmosphere, Chap. 15 in "Titan from Cassini-Huygens" (eds

  8. Highly charged swelling mica-type clays for selective Cu exchange.

    PubMed

    Ravella, Ramesh; Komarneni, Sridhar; Martinez, Carmen Enid

    2008-01-01

    There is a need to develop highly CU2+ selective materials which can potentially remediate copper contaminated soils and water. Here we show that several highly charged synthetic swelling mica-type clays are highly selective for copper exchange. The synthetic micas have cation exchange capacities (CECs), which are close to their theoretical values. Both Na-saturated and Mg-saturated micas were investigated for Cu ion exchange selectivity. Ion exchange isotherms and Kielland plots were constructed using the equilibrated solution analyses. From these studies it was found that Na-4-mica and Na-3-mica could selectively exchange copper at lower concentrations from solution, whereas Na-2-mica sample performed better by showing Cu ion exchange selectively to almost its capacity. The EPR spectra of Cu-exchanged micas coincide with the mica's charge characteristics that predict increased binding strength of exchangeable Cu in Na-4-mica and Na-3-mica than in Na-2-mica.

  9. First Demonstration of Laser-Assisted Charge Exchange for Microsecond Duration H- Beams

    NASA Astrophysics Data System (ADS)

    Cousineau, Sarah; Rakhman, Abdurahim; Kay, Martin; Aleksandrov, Alexander; Danilov, Viatcheslav; Gorlov, Timofey; Liu, Yun; Plum, Michael; Shishlo, Andrei; Johnson, David

    2017-02-01

    This Letter reports on the first demonstration of laser-assisted H- charge exchange for microsecond duration H- beam pulses. Laser-assisted charge exchange injection is a breakthrough technology that overcomes long-standing limitations associated with the traditional method of producing high intensity, time structured beams of protons in accelerators via the use of carbon foils for charge exchange injection. The central theme of this experiment is the demonstration of novel techniques that reduce the laser power requirement to allow high efficiency stripping of microsecond duration beams with commercial laser technology.

  10. The bacterial chemical repertoire mediates metabolic exchange within gut microbiomes.

    PubMed

    Rath, Christopher M; Dorrestein, Pieter C

    2012-04-01

    Microbial communities in the gut have been hypothesized to play key roles in the health of the host organism. Exploring the relationship between these populations and disease states has been a focus of the human microbiome project. However, the biological roles of the compounds produced by the gut bacteria are largely unknown. We hypothesize that these compounds act as metabolic exchange factors-mediating inter-species and intra-species interactions in the microbiome. This view is supported through this review of known bacterial metabolic exchange factors and evidence for uncharacterized metabolic exchange factors in the gut. The impact of model systems and technological developments in exploring this hypothesis are also discussed. Together, these investigations are revolutionizing our understanding of the gut microbiome-presenting the possibility of identifying new strategies for treating disease in the host.

  11. X-ray emission cross sections following charge exchange by multiply charged ions of astrophysical interest

    SciTech Connect

    Otranto, S.; Olson, R. E.; Beiersdorfer, P.

    2006-02-15

    State selective nl-electron capture cross sections are presented for highly charged ions with Z=6-10 colliding with atoms and molecules. The energy range investigated was from 1 eV/amu(v=0.006 a.u.)to 100 keV/amu(v=2.0 a.u.). The energy dependence of the l-level populations is investigated. The K shell x-ray emission cross sections are determined by using the calculated state-selective electron capture results as input and then applying hydrogenic branching and cascading values for the photon emission. A major shift in the line emission from being almost solely Lyman-{alpha} transitions at the highest collisions energies to strong high-n to 1s transitions at the lowest energies is observed. The calculated cross sections are in reasonable accord with measurements made by Greenwood et al. [Phys. Rev. A 63, 062707 (2001)], using O{sup 8+} and Ne{sup 10+} on various targets at 3 keV/amu. The calculations are also in accord with x-ray emission cross section data obtained on the EBIT machine at Lawrence Livermore National Laboratory (LLNL) where O{sup 8+} and Ne{sup 10+} high resolution measurements were made at a temperature of 10 eV/amu for a series of targets with varying ionization potentials. The Ne{sup 10+} data clearly shows the contribution from multiple capture followed by Auger autoionization in the line emission spectra. Our calculated line emission cross sections are used to provide an ab initio determination of the soft x-ray spectrum of comet C/Linear 1999 S4 that was observed on the Chandra X-ray Observatory. The calculations show that the spectrum is due to the charge exchange of the neutral gases in the comet's coma with the ions of the slow solar wind.

  12. Recent Excitation, Charge Exchange, and Lifetime Results in Highly Charged Ions Relevant to Stellar, Interstellar, Solar and Comet Phenomena

    NASA Technical Reports Server (NTRS)

    Chutjian, A.; Hossain, S.; Mawhorter, R. J.; Smith, S. J.

    2006-01-01

    Recent JPL absolute excitation and charge exchange cross sections, and measurements of lifetimes of metastable levels in highly-charged ions (HCIs) are reported. These data provide benchmark comparisons to results of theoretical calculations. Theoretical approaches can then be used to calculate the vast array of data which cannot be measured due to experimental constraints. Applications to the X-ray emission from comets are given.

  13. Pion single- and double-charge-exchange reactions at low energies

    SciTech Connect

    Baer, H.W.

    1987-01-01

    The general features of pion charge-exchange reactions at energies of 20 to 80 MeV leading to nuclear isobaric-analog states (IAS) and double-isobaric-analog states (DIAS) are reviewed. The recent progress achieved in understanding the role of short-range N-N correlations in the double-charge-exchange reactions is presented. 36 refs., 21 figs., 2 tabs.

  14. Neutral atomic oxygen beam produced by ion charge exchange for Low Earth Orbital (LEO) simulation

    NASA Technical Reports Server (NTRS)

    Banks, Bruce; Rutledge, Sharon; Brdar, Marko; Olen, Carl; Stidham, Curt

    1987-01-01

    A low energy neutral atomic oxygen beam system was designed and is currently being assembled at the Lewis Research Center. The system utilizes a 15 cm diameter Kaufman ion source to produce positive oxygen ions which are charge exchange neutralized to produce low energy (variable from 5 to 150 eV) oxygen atoms at a flux simulating real time low Earth orbital conditions. An electromagnet is used to direct only the singly charged oxygen ions from the ion source into the charge exchange cell. A retarding potential grid is used to slow down the oxygen ions to desired energies prior to their charge exchange. Cryogenically cooled diatomic oxygen gas in the charge exchange cell is then used to transfer charge to the oxygen ions to produce a neutral atomic oxygen beam. Remaining non-charge exchanged oxygen ions are then swept from the beam by electromagnetic or electrostatic deflection depending upon the desired experiment configuration. The resulting neutral oxygen beam of 5 to 10 cm in diameter impinges upon target materials within a sample holder fixture that can also provide for simultaneous heating and UV exposure during the atomic oxygen bombardment.

  15. Lipid exchange between membranes: effects of membrane surface charge, composition, and curvature.

    PubMed

    Zhu, Tao; Jiang, Zhongying; Ma, Yuqiang

    2012-09-01

    Intermembrane lipid exchange is critical to membrane functions and pharmaceutical applications. The exchange process is not fully understood and it is explored by quartz crystal microbalance with dissipation monitor method in this research. It is found that intermembrane lipid exchange is accelerated with the decrease of vesicle size and the increase of charge and liquid crystalline lipid composition ratio. Vesicle adsorption rate, membrane lateral pressure gradient, and lipid lateral diffusion coefficient are inferred to be critical in deciding the lipid exchange kinetics between membranes. Besides that, the membrane contact situation during lipid exchange is also studied. The maximum total membrane contact area is found to increase with the decrease of vesicle size, charged and liquid crystalline lipid composition ratio. A competition mechanism between the vesicle adsorption rate and the intermembrane lipid exchange rate was proposed to control the maximum total membrane contact area.

  16. X-ray Signature of Charge Exchange in the Spectra of L-shell Iron Ions

    SciTech Connect

    Beiersdorfer, P; Schweikhard, L; Liebisch, P; Brown, G V

    2007-01-05

    The X-ray signature of charge exchange between highly charged L-shell iron ions and neutral gas atoms was studied in the laboratory in order to assess its diagnostic utility. Significant differences with spectra formed by electron-impact excitation were observed. In particular, a strong enhancement was found of the emission corresponding to n {le} 4 {yields} n = 2 transitions relative to the n = 3 {yields} n = 2 emission. This enhancement was detectable even with relatively low-resolution X-ray instrumentation (E/{Delta}E {approx} 10) and may enable future identification of charge exchange as a line-formation mechanism in astrophysical spectra.

  17. Laboratory simulation of charge exchange-produced X-ray emission from comets.

    PubMed

    Beiersdorfer, P; Boyce, K R; Brown, G V; Chen, H; Kahn, S M; Kelley, R L; May, M; Olson, R E; Porter, F S; Stahle, C K; Tillotson, W A

    2003-06-06

    In laboratory experiments using the engineering spare microcalorimeter detector from the ASTRO-E satellite mission, we recorded the x-ray emission of highly charged ions of carbon, nitrogen, and oxygen, which simulates charge exchange reactions between heavy ions in the solar wind and neutral gases in cometary comae. The spectra are complex and do not readily match predictions. We developed a charge exchange emission model that successfully reproduces the soft x-ray spectrum of comet Linear C/1999 S4, observed with the Chandra X-ray Observatory.

  18. Local charge exchange of He+ ions at Aluminum surfaces

    NASA Astrophysics Data System (ADS)

    Riccardi, P.; Sindona, A.; Dukes, C. A.

    2017-04-01

    We report on experiments designed to observe the correlation between the autoionization of doubly excited helium atoms and the Auger decay of 2p vacancies in Al. The autoionizing states are formed when incident He+* and He++ are neutralized by resonant electron capture at the surface. 2p excitation in Al occurs in dielectronic charge transfer during the close encounter of an excited helium ion and an Al atom. These results clarify the mechanism for Al-2p excitation in the case of singly charged ground state He+(1s) ion impact, where the dielectronic transition occurs after promotion of the 1s electron of incoming ions.

  19. Charge-Transfer Effects in Ligand Exchange Reactions of Au25 Monolayer-Protected Clusters.

    PubMed

    Carducci, Tessa M; Blackwell, Raymond E; Murray, Royce W

    2015-04-16

    Reported here are second-order rate constants of associative ligand exchanges of Au25L18 nanoparticles (L = phenylethanethiolate) of various charge states, measured by proton nuclear magnetic resonance at room temperature and below. Differences in second-order rate constants (M(-1) s(-1)) of ligand exchange (positive clusters ∼1.9 × 10(-5) versus negative ones ∼1.2 × 10(-4)) show that electron depletion retards ligand exchange. The ordering of rate constants between the ligands benzeneselenol > 4-bromobenzene thiol > benzenethiol reveals that exchange is accelerated by higher acidity and/or electron donation capability of the incoming ligand. Together, these observations indicate that partial charge transfer occurs between the nanoparticle and ligand during the exchange and that this is a rate-determining effect in the process.

  20. 78 FR 6263 - Exchange Visitor Program-Fees and Charges

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-30

    .... This analysis was grounded on the guiding principle that fees should be fair and reflect the full cost... ``activity-based costing'' (ABC) approach to develop a sustainable model to align the associated costs of the.... According to legislative and regulatory guidance, user charges should be based on the full cost to...

  1. Consumer-mediated health information exchanges: the 2012 ACMI debate.

    PubMed

    Cimino, James J; Frisse, Mark E; Halamka, John; Sweeney, Latanya; Yasnoff, William

    2014-04-01

    The American College of Medical Informatics (ACMI) sponsors periodic debates during the American Medical Informatics Fall Symposium to highlight important informatics issues of broad interest. In 2012, a panel debated the following topic: "Resolved: Health Information Exchange Organizations Should Shift Their Principal Focus to Consumer-Mediated Exchange in Order to Facilitate the Rapid Development of Effective, Scalable, and Sustainable Health Information Infrastructure." Those supporting the proposition emphasized the need for consumer-controlled community repositories of electronic health records (health record banks) to address privacy, stakeholder cooperation, scalability, and sustainability. Those opposing the proposition emphasized that the current healthcare environment is so complex that development of consumer control will take time and that even then, consumers may not be able to mediate their information effectively. While privately each discussant recognizes that there are many sides to this complex issue, each followed the debater's tradition of taking an extreme position in order emphasize some of the polarizing aspects in the short time allotted them. In preparing this summary, we sought to convey the substance and spirit of the debate in printed form. Transcripts of the actual debate were edited for clarity, and appropriate supporting citations were added for the further edification of the reader.

  2. Time-dependence ion charge state distributions of vacuum arcs: An interpretation involving atoms and charge exchange collisions

    SciTech Connect

    Anders, Andre

    2004-08-27

    Experimentally observed charge state distributions are known to be higher at the beginning of each arc discharge. Up to know, this has been attributed to cathode surface effects in terms of changes of temperature, chemical composition and spot mode. Here it is shown that the initial decay of charge states of cathodic arc plasmas may at least in part due to charge exchange collisions of ions with neutrals that gradually fill the discharge volume. Sources of neutrals may include evaporated atoms from macroparticles and still-hot craters of previously active arc spots. More importantly, atoms are also produced by energetic condensation of the cathodic arc plasma. Self-sputtering is significant when ions impact with near-normal angle of incidence, and ions have low sticking probability when impacting at oblique angle of incidence. Estimates show that the characteristic time for filling the near-cathode discharge volume agrees well with the charge state decay time, and the likelihood of charge exchange is reasonably large to be taken into account.

  3. X-Ray Emission Cross Sections following Charge Exchange by Multiply-Charged Ions of Astrophysical Interest

    SciTech Connect

    Otranto, S; Olson, R E; Beiersdorfer, P

    2007-03-12

    The CTMC method is used to calculate emission cross sections following charge exchange processes involving highly charged ions of astrophysical interest and typical cometary targets. Comparison is made to experimental data obtained on the EBIT-I machine at Lawrence Livermore National Laboratory LLNL for O{sup 8+} projectiles impinging on different targets at a collision energy of 10 eV/amu. The theoretical cross sections are used together with ion abundances measured by the Advanced Composition Explorer to reproduce cometary spectra. Discrepancies due to different estimated delays of solar wind events between the comet and the Earth-orbiting satellite are discussed.

  4. Removal of charged micropollutants from water by ion-exchange polymers -- effects of competing electrolytes.

    PubMed

    Bäuerlein, Patrick S; Ter Laak, Thomas L; Hofman-Caris, Roberta C H M; de Voogt, Pim; Droge, Steven T J

    2012-10-15

    A wide variety of environmental compounds of concern, e.g. pharmaceuticals or illicit drugs, are acids or bases that may predominantly be present as charged species in drinking water sources. These charged micropollutants may prove difficult to remove by currently used water treatment steps (e.g. UV/H(2)O(2), activated carbon (AC) or membranes). We studied the sorption affinity of some ionic organic compounds to both AC and different charged polymeric materials. Ion-exchange polymers may be effective as additional extraction phases in water treatment, because sorption of all charged compounds to oppositely charged polymers was stronger than to AC, especially for the double-charged cation metformin. Tested below 1% of the polymer ion-exchange capacity, the sorption affinity of charged micropollutants is nonlinear and depends on the composition of the aqueous medium. Whereas oppositely charged electrolytes do not impact sorption of organic ions, equally charged electrolytes do influence sorption indicating ion-exchange (IE) to be the main sorption mechanism. For the tested polymers, a tenfold increased salt concentration lowered the IE-sorption affinity by a factor two. Different electrolytes affect IE with organic ions in a similar way as inorganic ions on IE-resins, and no clear differences in this trend were observed between the sulphonated and the carboxylated cation-exchanger. Sorption of organic cations is five fold less in Ca(2+) solutions compared to similar concentrations of Na(+), while that of anionic compounds is three fold weaker in SO(4)(2-) solutions compared to equal concentrations of Cl(-).

  5. Atomic hydrogen escape rate due to charge exchange with hot plasmaspheric ions

    NASA Technical Reports Server (NTRS)

    Maher, L. J.; Tinsley, B. A.

    1977-01-01

    Data on ion and electron temperatures and concentrations to several thousand kilometers of altitude were obtained from the Atmosphere Explorer C satellite for 1974 and to 850 km from Arecibo incoherent scatter radar measurements. These data were used to normalize diffusive equilibrium profiles. From these profiles and by using the neutral atmospheric model of Jacchia (1971) and a new hydrogen model, the charge-exchange-induced neutral hydrogen escape fluxes for equatorial and middle latitudes were calculated. The data confirm earlier estimates that the charge exchange loss is more important than Jeans escape for the earth. It is also found that inside the plasmapause this charge exchange process with hot plasmapheric ions is the major production and loss process for the satellite population in the hydrogen geocorona.

  6. The influence of charge exchange on the velocity distribution of hydrogen in the Venus exosphere

    NASA Technical Reports Server (NTRS)

    Hodges, Richard R., Jr.; Tinsley, Brian A.

    1986-01-01

    The simulation of the exosphere of Venus by a Monte Carlo technique has been extended to provide velocity distribution profiles that can be used with radiative transfer simulation to model the Lyman-alpha emission seen by spacecraft. The line profiles show a narrow core due to the exobase thermal source of hydrogen superimposed on the broad profile of hot hydrogen from charge exchange with hot ions in the nighttime ionosphere. Nightside radial profiles show long tails of upward flowing, escaping atoms. There are some downward and lateral superescape signatures, because the charge exchange source extends well above the exobase. At higher altitudes, flattening and even shallow central valleys appear in the transverse profiles. The planetary average escape rate due to charge exchange was found to be 2.8 x 10 to the 7th/sq cm per s, which is several times larger than escape rates for other candidate mechanisms.

  7. Ion temperatures in HIP-1 and SUMMA from charge-exchange neutral optical emission spectra

    NASA Technical Reports Server (NTRS)

    Patch, R. W.; Lauver, M. R.

    1976-01-01

    Ion temperatures were obtained from observations of the H sub alpha, D sub alpha, and He 587.6 nm lines emitted from hydrogen, deuterium, and helium plasmas in the SUMMA and HIP-1 mirror devices at Lewis Research Center. Steady state discharges were formed by applying a radially inward dc electric field between cylindrical or annular anodes and hollow cathodes located at the peaks of the mirrors. The ion temperatures were found from the Doppler broadening of the charge-exchange components of spectral lines. A statistical method was developed for obtaining scaling relations of ion temperature as a function of current, voltage, and magnetic flux density. Derivations are given that take into account triangular monochromator slit functions, loss cones, and superimposed charge-exchange processes. In addition, the Doppler broadening was found to be sensitive to the influence of drift on charge-exchange cross section. The effects of finite ion-cyclotron radius, cascading, and delayed emission are reviewed.

  8. Pion single charge exchange in three body nuclei at intermediate energies

    SciTech Connect

    Dowell, Marla L.

    1994-01-01

    The purpose of this thesis is to present new experimental information about modifications to the pion-nucleon single charge exchange interaction, π+n → π0 p or π- p → π0n, due to the presence of other nucleons. The results of two experimental studies of pion single charge exchange in the three nucleon system near the Δ-resonance are presented. Both of these experiments were performed at the Clinton P. Anderson Meson Physics Facility (LAMPF), a division of the Los Alamos National Laboratory. Each explored different aspects of pion single charge exchange in three body nuclei--3He and 3H. Since the nuclear wavefunctions of the three nucleon systems are believed to be well understood, it should be possible to perform theoretical calculations of pion interactions with this system and compare their predictions with the experimental results.

  9. Coherent spin-exchange via a quantum mediator

    NASA Astrophysics Data System (ADS)

    Baart, Timothy Alexander; Fujita, Takafumi; Reichl, Christian; Wegscheider, Werner; Vandersypen, Lieven Mark Koenraad

    2017-01-01

    Coherent interactions at a distance provide a powerful tool for quantum simulation and computation. The most common approach to realize an effective long-distance coupling 'on-chip' is to use a quantum mediator, as has been demonstrated for superconducting qubits and trapped ions. For quantum dot arrays, which combine a high degree of tunability with extremely long coherence times, the experimental demonstration of the time evolution of coherent spin-spin coupling via an intermediary system remains an important outstanding goal. Here, we use a linear triple-quantum-dot array to demonstrate a coherent time evolution of two interacting distant spins via a quantum mediator. The two outer dots are occupied with a single electron spin each, and the spins experience a superexchange interaction through the empty middle dot, which acts as mediator. Using single-shot spin readout, we measure the coherent time evolution of the spin states on the outer dots and observe a characteristic dependence of the exchange frequency as a function of the detuning between the middle and outer dots. This approach may provide a new route for scaling up spin qubit circuits using quantum dots, and aid in the simulation of materials and molecules with non-nearest-neighbour couplings such as MnO (ref. 27), high-temperature superconductors and DNA. The same superexchange concept can also be applied in cold atom experiments.

  10. Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization.

    PubMed

    Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

    2016-08-01

    The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M(+.) decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques. Graphical Abstract ᅟ.

  11. Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

    NASA Astrophysics Data System (ADS)

    Vaikkinen, Anu; Kauppila, Tiina J.; Kostiainen, Risto

    2016-08-01

    The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M+. decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques.

  12. Selective Cu{sup 2+} and Pb{sup 2+} exchange with highly charged cation exchanger of Na-4-mica

    SciTech Connect

    Kodama, Tatsuya; Komarneni, Sridhar

    1999-09-01

    Selective cation exchange for Cu and Pb has been demonstrated with the high-charge-density sodium fluorophlogopite mica, Na-4-mica. The 2Na{sup +} {yields} M{sup 2+} exchange reaction (M = Cu or Pb) was investigated with Na-4-micas prepared by two different synthetic processes. One was easily and economically prepared by crystallization from a mixture of NaF, MgO, and metakaolin, the latter serves as an inexpensive aluminosilicate source. Another was prepared by solution-sol-gel processing. Ion-exchange isotherms for Cu{sup 2+} and Pb{sup 2+} were obtained at room temperature. The thermodynamic functions for the initial ion-exchange reactions were calculated because the isotherms were not completed., High selectivities for both copper and lead exchange were found on the highly crystallized Na-4-mica prepared from metakaolin. Their ion-exchange capacities were 225 and 257 milliequivalents per 100 g of dry clay for Cu{sup 2+} and Pb{sup 2+}, respectively. This high level decontamination of copper and lead with the highly crystallized Na-4-mica from metakaolin will be a very important separation required for purification of drinking water as well as for wastewater treatment and disposal.

  13. Aggregate-mediated charge transport in ionomeric electrolytes

    NASA Astrophysics Data System (ADS)

    Lu, Keran; Maranas, Janna; Milner, Scott

    Polymers such PEO can conduct ions, and have been studied as possible replacements for organic liquid electrolytes in rechargeable metal-ion batteries. More generally, fast room-temperature ionic conduction has been reported for a variety of materials, from liquids to crystalline solids. Unfortunately, polymer electrolytes generally have limited conductivity; these polymers are too viscous to have fast ion diffusion like liquids, and too unstructured to promote cooperative transport like crystalline solids. Ionomers are polymer electrolytes in which ionic groups are covalently bound to the polymer backbone, neutralized by free counterions. These materials also conduct ions, and can exhibit strong ionic aggregation. Using coarse-grained molecular dynamics, we explore the forces driving ionic aggregation, and describe the role ion aggregates have in mediating charge transport. The aggregates are string-like such that ions typically have two neighbors. We find ion aggregates self-assemble like worm-like micelles. Excess charge, or free ions, occasionally coordinate with aggregates and are transported along the chain in a Grotthuss-like mechanism. We propose that controlling ionomer aggregate structure through materials design can enhance cooperative ion transport.

  14. DNA-mediated charge transport for DNA repair

    PubMed Central

    Boon, Elizabeth M.; Livingston, Alison L.; Chmiel, Nikolas H.; David, Sheila S.; Barton, Jacqueline K.

    2003-01-01

    MutY, like many DNA base excision repair enzymes, contains a [4Fe4S]2+ cluster of undetermined function. Electrochemical studies of MutY bound to a DNA-modified gold electrode demonstrate that the [4Fe4S] cluster of MutY can be accessed in a DNA-mediated redox reaction. Although not detectable without DNA, the redox potential of DNA-bound MutY is ≈275 mV versus NHE, which is characteristic of HiPiP iron proteins. Binding to DNA is thus associated with a change in [4Fe4S]3+/2+ potential, activating the cluster toward oxidation. Given that DNA charge transport chemistry is exquisitely sensitive to perturbations in base pair structure, such as mismatches, we propose that this redox process of MutY bound to DNA exploits DNA charge transport and provides a DNA signaling mechanism to scan for mismatches and lesions in vivo. PMID:14559969

  15. Charge exchange and ionization in hydrogen atom-fully stripped ion collisions in Debye plasmas

    SciTech Connect

    Zhang, H.; Wang, J. G.; He, B.; Qiu, Y. B.; Janev, R. K.

    2007-05-15

    The processes of charge exchange and ionization in collisions of ground state hydrogen atom with fully stripped ions in a weakly coupled plasma are studied by the classical trajectory Monte Carlo method in the collision energy range 10-900 keV/amu. The interparticle interactions are described by the Debye-Hueckel model with inclusion of dynamical effects associated with the projectile velocity. The microcanonical distribution of initial state electronic coordinates and momenta has been determined by inclusion of plasma screening effects. The cross section dependencies on plasma parameters and ion charge and velocity are investigated. It is shown that plasma effects on charge exchange and ionization cross sections are significant and particularly pronounced at low collision velocities. The results of systematic cross section calculations for different values of Debye screening length (in the range 1-50a{sub 0}) and ion charges (in the range 1-14) are presented.

  16. Interaction of a solar array with an ion thruster due to the charge-exchange plasma

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.

    1976-01-01

    The generation of a charge exchange plasma by a thruster, the transport of this plasma to the solar array, and the interaction of the solar array with the plasma after it arrives are all described. The generation of this plasma is described accurately from thruster geometry and operating conditions. The transport of the charge exchange plasma was studied experimentally with a 15 cm thruster. A model was developed for simple thruster array configurations. A variety of experiments were surveyed for the interaction of the plasma at the solar array.

  17. Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination

    NASA Technical Reports Server (NTRS)

    Wargelin, B.

    2003-01-01

    The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory to study the X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in the existing experimental and theoretical data and are needed to explain all or part of the observed X-ray emission from the Galactic Ridge, solar and stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae.

  18. The roles of charge exchange and dissociation in spreading Saturn's neutral clouds

    NASA Astrophysics Data System (ADS)

    Fleshman, B. L.; Delamere, P. A.; Bagenal, F.; Cassidy, T.

    2012-05-01

    Neutrals sourced directly from Enceladus's plumes are initially confined to a dense neutral torus in Enceladus's orbit around Saturn. This neutral torus is redistributed by charge exchange, impact/photodissociation, and neutral-neutral collisions to produce Saturn's neutral clouds. Here we consider the former processes in greater detail than in previous studies. In the case of dissociation, models have assumed that OH is produced with a single speed of 1 km s-1, whereas laboratory measurements suggest a range of speeds between 1 and 1.6 km s-1. We show that the high-speed case increases dissociation's range of influence from 9 to 15 RS. For charge exchange, we present a new modeling approach, where the ions are followed within a neutral background, whereas neutral cloud models are conventionally constructed from the neutrals' point of view. This approach allows us to comment on the significance of the ions' gyrophase at the moment charge exchange occurs. Accounting for gyrophase (1) has no consequence on the H2O cloud, (2) doubles the local density of OH at the orbit of Enceladus, and (3) decreases the oxygen densities at Enceladus's orbit by less than 10%. Finally, we consider velocity-dependent, as well as species-dependent cross sections and find that the oxygen cloud produced from charge exchange is spread out more than H2O, whereas the OH cloud is the most confined.

  19. Effect of the disruptive instability on the flux of charge-exchange atoms in a tokamak

    SciTech Connect

    Alabyad, A.M.; Ivanov, N.V.; Khudoleev, A.V.

    1984-01-01

    Experiments have been carried out on the spatial distribution of the flux of neutral charge-exchange atoms from a tokamak plasma and on the time evolution of this distribution during a disruptive instability. The experimental results are analyzed on the basis of the model of the tearing-mode instability.

  20. Population inversion calculations using near resonant charge exchange as a pumping mechanism

    NASA Technical Reports Server (NTRS)

    Chubb, D. L.; Rose, J. R.

    1972-01-01

    Near resonance charge exchange between ions of a large ionization potential gas such as helium or neon and vapors of metals such as zinc, cadmium, selenium, or tellurium has produced laser action in the metal ion gas. The possibility of obtaining population inversions in near resonant charge exchange systems (Xe-Ca, Xe-Mg, Xe-Sr, Xe-Ba, Ar-Mg, N-Ca) was investigated. The analysis is an initial value problem that utilizes rate equations for the densities of relevant levels of the laser gas (Ca, Ba, Mg, or Sr) and an electron energy equation. Electron excitation rates are calculated using the Bohr-Thomson approximation for the cross section. Approximations to experimental values of the electron ionization cross section and the ion-atom charge exchange cross section are used. Preliminary results have been obtained for the Ca-Xe system and show that it is possible to obtain gains greater than 10 to the 14th power/m with inversion times up to 8x10 to the minus 7th power second. A possible charge exchange laser system using a MPD arc plasma accelerator is also described.

  1. Short-range NN and N. Delta. correlations in pion double charge exchange (DCX)

    SciTech Connect

    Johnson, M.B.

    1990-01-01

    I will review several important results related to the short-range nucleon-nucleon and delta-nucleon interaction that have been obtained from recent studies of pion double charge exchange in selected nuclei. 32 refs., 5 figs., 3 tabs.

  2. Charge-dependent many-body exchange and dispersion interactions in combined QM/MM simulations

    NASA Astrophysics Data System (ADS)

    Kuechler, Erich R.; Giese, Timothy J.; York, Darrin M.

    2015-12-01

    Accurate modeling of the molecular environment is critical in condensed phase simulations of chemical reactions. Conventional quantum mechanical/molecular mechanical (QM/MM) simulations traditionally model non-electrostatic non-bonded interactions through an empirical Lennard-Jones (LJ) potential which, in violation of intuitive chemical principles, is bereft of any explicit coupling to an atom's local electronic structure. This oversight results in a model whereby short-ranged exchange-repulsion and long-ranged dispersion interactions are invariant to changes in the local atomic charge, leading to accuracy limitations for chemical reactions where significant atomic charge transfer can occur along the reaction coordinate. The present work presents a variational, charge-dependent exchange-repulsion and dispersion model, referred to as the charge-dependent exchange and dispersion (QXD) model, for hybrid QM/MM simulations. Analytic expressions for the energy and gradients are provided, as well as a description of the integration of the model into existing QM/MM frameworks, allowing QXD to replace traditional LJ interactions in simulations of reactive condensed phase systems. After initial validation against QM data, the method is demonstrated by capturing the solvation free energies of a series of small, chlorine-containing compounds that have varying charge on the chlorine atom. The model is further tested on the SN2 attack of a chloride anion on methylchloride. Results suggest that the QXD model, unlike the traditional LJ model, is able to simultaneously obtain accurate solvation free energies for a range of compounds while at the same time closely reproducing the experimental reaction free energy barrier. The QXD interaction model allows explicit coupling of atomic charge with many-body exchange and dispersion interactions that are related to atomic size and provides a more accurate and robust representation of non-electrostatic non-bonded QM/MM interactions.

  3. Charge-dependent many-body exchange and dispersion interactions in combined QM/MM simulations

    SciTech Connect

    Kuechler, Erich R.; Giese, Timothy J.; York, Darrin M.

    2015-12-21

    Accurate modeling of the molecular environment is critical in condensed phase simulations of chemical reactions. Conventional quantum mechanical/molecular mechanical (QM/MM) simulations traditionally model non-electrostatic non-bonded interactions through an empirical Lennard-Jones (LJ) potential which, in violation of intuitive chemical principles, is bereft of any explicit coupling to an atom’s local electronic structure. This oversight results in a model whereby short-ranged exchange-repulsion and long-ranged dispersion interactions are invariant to changes in the local atomic charge, leading to accuracy limitations for chemical reactions where significant atomic charge transfer can occur along the reaction coordinate. The present work presents a variational, charge-dependent exchange-repulsion and dispersion model, referred to as the charge-dependent exchange and dispersion (QXD) model, for hybrid QM/MM simulations. Analytic expressions for the energy and gradients are provided, as well as a description of the integration of the model into existing QM/MM frameworks, allowing QXD to replace traditional LJ interactions in simulations of reactive condensed phase systems. After initial validation against QM data, the method is demonstrated by capturing the solvation free energies of a series of small, chlorine-containing compounds that have varying charge on the chlorine atom. The model is further tested on the S{sub N}2 attack of a chloride anion on methylchloride. Results suggest that the QXD model, unlike the traditional LJ model, is able to simultaneously obtain accurate solvation free energies for a range of compounds while at the same time closely reproducing the experimental reaction free energy barrier. The QXD interaction model allows explicit coupling of atomic charge with many-body exchange and dispersion interactions that are related to atomic size and provides a more accurate and robust representation of non-electrostatic non-bonded QM

  4. Transport, charge exchange and loss of energetic heavy ions in the earth's radiation belts - Applicability and limitations of theory

    NASA Technical Reports Server (NTRS)

    Spjeldvik, W. N.

    1981-01-01

    Computer simulations of processes which control the relative abundances of ions in the trapping regions of geospace are compared with observations from discriminating ion detectors. Energy losses due to Coulomb collisions between ions and exospheric neutrals are considered, along with charge exchange losses and internal charge exchanges. The time evolution of energetic ion fluxes of equatorially mirroring ions under radial diffusion is modelled to include geomagnetic and geoelectric fluctutations. Limits to the validity of diffusion transport theory are discussed, and the simulation is noted to contain provisions for six ionic charge states and the source effect on the radiation belt oxygen ion distributions. Comparisons are made with ion flux data gathered on Explorer 45 and ISEE-1 spacecraft and results indicate that internal charge exchanges cause the radiation belt ion charge state to be independent of source charge rate characteristics, and relative charge state distribution is independent of the radially diffusive transport rate below the charge state redistribution zone.

  5. Cometary X-ray emission: theoretical cross sections following charge exchange by multiply charged ions of astrophysical interest

    SciTech Connect

    Otranto, S; Olson, R E; Beiersdorfer, P

    2007-02-13

    The CTMC method is used to calculate emission cross sections following charge exchange collisions involving highly charged ions of astrophysical interest and typical cometary targets. Comparison is made to experimental data obtained on the EBIT machine at Lawrence Livermore National Laboratory (LLNL) for O{sup 8+} projectiles impinging on different targets at a collision energy of 10 eV/amu. The theoretical cross sections are used together with ion abundances measured by the Advanced Composition Explorer as well as those obtained by a fitting procedure using laboratory emission cross sections in order to reproduce the x-ray spectrum of comet C/LINEAR S4 measured on July 14th 2001.

  6. Observations of solar wind ion charge exchange in the comet Halley coma

    NASA Technical Reports Server (NTRS)

    Fuselier, S. A.; Shelley, E. G.; Goldstein, B. E.; Goldstein, R.; Neugebauer, M.; Ip, W.-H.; Balsiger, H.; Reme, H.

    1991-01-01

    Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) observations of solar wind ions show charge exchange effects and solar wind compositional changes in the coma of comet Halley. As the comet was approached, the He(++) to proton density ratio increased until about 1 hour before closest approach after which time it decreased. Abrupt increases in this ratio were also observed in the beginning and near the end of the so-called Mystery Region (8.6 - 5.5(10)(exp 5) km from the comet along the spacecraft trajectory). These abrupt increases in the density ratio were well correlated with enhanced fluxes of keV electrons as measured by the Giotto plasma electron spectrometer. The general increase and then decrease of the He(++) to proton density ratio is quantitatively consistent with a combination of the addition of protons of cometary origin to the plasma and loss of plasma through charge exchange of protons and He(++). In general agreement with the solar wind proton and He(++) observations, solar wind oxygen and carbon ions were observed to charge exchange from higher to lower charge states with decreasing distance to the comet. The more abrupt increases in the He(++) to proton and the He(++) to O(6+) density ratios in the mystery region require a change in the solar wind ion composition in this region while the correlation with energetic electrons indicates processes associated with the comet.

  7. Absolute Charge Exchange Cross Sections for ^3He^2+ Collisions with ^4He and H_2

    NASA Astrophysics Data System (ADS)

    Mawhorter, R. J.; Greenwood, J.; Smith, S. J.; Chutjian, A.

    2002-05-01

    The JPL charge exchange beam-line(J.B. Greenwood, et al., Phys. Rev A 63), 062707 (2001) was modified to increase the forward acceptance angle and enable the measurement of total charge-exchange cross sections for slow, light, highly-charged ion collisions with neutral targets(R. E. Olson and M. Kimura, J. Phys. B 15), 4231 (1982). Data are presented for single charge exchange cross sections for ^3He^2+ nuclei scattered by ^4He and H2 in the energy range 0.33-4.67 keV/amu. For both targets there is good agreement with Kusakabe, et al.(T. Kusakabe, et al., J. Phys. Soc. Japan 59), 1218 (1990). Angular collection is studied by a comparison with differential measurements(D. Bordenave-Montesquieu and R. Dagnac, J. Phys. B 27), 543 (1994), as well as with earlier JPL results(J.B. Greenwood, et al., Ap. J. 533), L175 (2000), ibid. 529, 605 (2000) using heavier projectiles and targets. This work was carried out at JPL/Caltech, and was supported through contract with NASA. RJM thanks the NRC for a Senior Associateship at JPL.

  8. Charge Exchange Cross Sections for Multiply-Charged Ions Colliding with Water

    SciTech Connect

    Otranto, S.; Olson, R. E.

    2009-03-10

    The classical trajectory Monte Carlo method is used to calculate total and state selective nl-electron capture cross sections for highly charged ions Z = 4-10, 14, 18 and 26 colliding with water. The initialization for the 1B1 and 3A1 orbitals of the water molecule is based on a Slater orbital expansion. The Z-dependence of the calculated total cross sections is in reasonable agreement with recent data. The K-shell x-ray emission cross sections are determined from the calculated state-selective electron capture results.

  9. Dynamics of the fully stripped ion-hydrogen atom charge exchange process in dense quantum plasmas

    SciTech Connect

    Zhang, Ling-yu; Wan, Jiang-feng; Zhao, Xiao-ying; Xiao, Guo-qing; Duan, Wen-shan; Qi, Xin; Yang, Lei

    2014-09-15

    The plasma screening effects of dense quantum plasmas on charge exchange processes of a fully stripped ion colliding with a hydrogen atom are studied by the classical trajectory Monte Carlo method. The inter-particle interactions are described by the exponential cosine-screened Coulomb potentials. It is found that in weak screening conditions, cross sections increase with the increase of the ionic charge Z. However, in strong screening conditions, the dependence of cross sections on the ionic charge is related to the incident particle energy. At high energies, cross sections show a linear increase with the increase of Z, whereas at low energies, cross sections for Z≥4 become approximately the same. The He{sup 2+} and C{sup 6+} impacting charge exchange cross sections in dense quantum plasmas are also compared with those in weakly coupled plasmas. The interactions are described by the static screened Coulomb potential. It is found that for both He{sup 2+} and C{sup 6+}, the oscillatory screening effects of dense quantum plasmas are almost negligible in weak screening conditions. However, in strong screening conditions, the oscillatory screening effects enhance the screening effects of dense quantum plasmas, and the enhancement becomes more and more significant with the increase of the screening parameter and the ionic charge.

  10. Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination

    NASA Technical Reports Server (NTRS)

    Wargelin, B.

    2002-01-01

    The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory (LLNL) to study X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in existing experimental and theoretical understanding of this atomic physics process, and are needed to explain all or part of the observed X-ray emission from the soft X-ray background, stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae. Progress made during the first year of the grant is described, as is work planned for the second year.

  11. ({sup 18}O,{sup 18}Ne) double charge-exchange with MAGNEX

    SciTech Connect

    Bondí, M.; Cappuzzello, F.; Nicolosi, D.; Tropea, S.; Agodi, C.; Carbone, D.; Cavallaro, M.; Cunsolo, A.; De Napoli, M.; Foti, A.

    2014-05-09

    An experimental study concerning Double Gamow-Teller (DGT) modes in ({sup 18}O,{sup 18}Ne) Double Charge-Exchange reactions has been very recently performed at INFN-LNS laboratory in Catania. The experiment was performed using a {sup 40}Ca solid target and a {sup 18}O Cyclotron beam at 270 MeV incident energy. Charged ejectiles produced in the reaction were momentum analyzed and identified by MAGNEX spectrometer at very forward angles. Preliminary results are presented in the present paper.

  12. Pionic charge exchange on the proton from 40 to 250 MeV

    NASA Astrophysics Data System (ADS)

    Breitschopf, J.; Bauer, M.; Clement, H.; Cröni, M.; Denz, H.; Friedman, E.; Gibson, E. F.; Meier, R.; Wagner, G. J.

    2006-08-01

    The total cross sections for pionic charge exchange on hydrogen were measured using a transmission technique on thin CH2 and C targets. Data were taken for π- lab energies from 39 to 247 MeV with total errors of typically 2% over the Δ-resonance and up to 10% at the lowest energies. Deviations from the predictions of the SAID phase shift analysis in the 60-80 MeV region are interpreted as evidence for isospin-symmetry breaking in the s-wave amplitudes. The charge dependence of the Δ-resonance properties appears to be smaller than previously reported.

  13. Polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent counterions: a Monte Carlo simulation study.

    PubMed

    Luque-Caballero, Germán; Martín-Molina, Alberto; Quesada-Pérez, Manuel

    2014-05-07

    Both experiments and theory have evidenced that multivalent cations can mediate the interaction between negatively charged polyelectrolytes and like-charged objects, such as anionic lipoplexes (DNA-cation-anionic liposome complexes). In this paper, we use Monte Carlo simulations to study the electrostatic interaction responsible for the trivalent-counterion-mediated adsorption of polyelectrolytes onto a like-charged planar surface. The evaluation of the Helmholtz free energy allows us to characterize both the magnitude and the range of the interaction as a function of the polyelectrolyte charge, surface charge density, [3:1] electrolyte concentration, and cation size. Both polyelectrolyte and surface charge favor the adsorption. It should be stressed, however, that the adsorption will be negligible if the surface charge density does not exceed a threshold value. The effect of the [3:1] electrolyte concentration has also been analyzed. In certain range of concentrations, the counterion-mediated attraction seems to be independent of this parameter, whereas very high concentrations of salt weaken the adsorption. If the trivalent cation diameter is doubled the adsorption moderates due to the excluded volume effects. The analysis of the integrated charge density and ionic distributions suggests that a delicate balance between charge inversion and screening effects governs the polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent cations.

  14. Electronic structure of Fe-doped In2O3 magnetic semiconductor with oxygen vacancies: Evidence for F-center mediated exchange interaction

    NASA Astrophysics Data System (ADS)

    Hu, Shu-jun; Yan, Shi-shen; Lin, Xue-ling; Yao, Xin-xin; Chen, Yan-xue; Liu, Guo-lei; Mei, Liang-mo

    2007-12-01

    Based on the first-principles calculations, the electronic structure and magnetic properties of Fe-doped In2O3 were theoretically investigated. The presence of the predominating defects in oxide, i.e., oxygen vacancies, can lead to strong ferromagnetic coupling between the nearest neighboring Fe cations. Spin density and band-projected charge distribution in the vicinity of the oxygen vacancies reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Fe :3d and Fe :4s electrons trapped in oxygen vacancies. Such results provide direct evidence for the F-center mediated exchange interaction in oxide-based magnetic semiconductors.

  15. Experimental evidence of charge exchange recombination of highly ionized iron and titanium in Princeton Large Torus

    SciTech Connect

    Suckewer, S.; Hinnov, E.; Bitter, M.; Hulse, R.; Post, D.

    1980-02-01

    The observed behavior of the emissivitives of boron-like FeXXIII, lithium-like FeXXIV and TiXX, and the helium-like FeXXV ions in the PLT tokamak during highpower neutral (H/sup 0/ or D/sup 0/) beam heating is described. A substantial lowering of the dominant ionization state in the center of the discharge while the electron temperature is rising, is attributed primarily to increased recombination rate of the ions through charge exchange with neutral hydrogen. This interpretation is supported by the different space and time behavior of the lithium-like annd boron-like ions of comparable ionization potentials, and by comparisons of neutral beam heating of the plasma with ion cyclotron resonance heating, which does not appreciably change the neutral hydrogen concentration. The observations are compared with approximate zero-dimensional model calculations, using experimental plasma conditions and estimated charge exchange rates.

  16. ROSAT Observations of Solar Wind Charge Exchange with the Lunar Exosphere

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Snowden, S. L.; Benna, M.; Carter, J. A.; Cravens, T. E.; Hills, H. Kent; Hodges, R. R.; Kuntz, K. D.; Porter, F. Scott; Read, A.; Robertson, I. P.; Sembay, S. F.; Sibeck, D. G.; Stubbs, Timothy J.; Travnicek, P.

    2012-01-01

    We analyze the ROSAT PSPC soft X-ray image of the Moon taken on 29 June 1990 by examining the radial profile of the count rate in three wedges, two wedges (one north and one south) 13-32 degrees off (19 degrees wide) the terminator towards the dark side and one wedge 38 degrees wide centered on the anti-solar direction. The radial profiles of both the north and the south wedges show substantial limb brightening that is absent in the 38 degree wide antisolar wedge. An analysis of the count rate increase associated with the limb brightening shows that its magnitude is consistent with that expected due to solar wind charge exchange (SWCX) with the tenuous lunar atmosphere. Along with Mars, Venus, and Earth, the Moon represents another solar system body at which solar wind charge exchange has been observed. This technique can be used to explore the solar wind-lunar interaction.

  17. Tailoring of ion species composition in complex plasmas with charge exchange collisions

    NASA Astrophysics Data System (ADS)

    Ostrikov, K.

    2005-06-01

    A generic approach towards tailoring of ion species composition in reactive plasmas used for nanofabrication of various functional nanofilms and nanoassemblies, based on a simplified model of a parallel-plate rf discharge, is proposed. The model includes an idealized reactive plasma containing two neutral and two ionic species interacting via charge exchange collisions in the presence of a microdispersed solid component. It is shown that the number densities of the desired ionic species can be efficiently managed by adjusting the dilution of the working gas in a buffer gas, rates of electron impact ionization, losses of plasma species on the discharge walls, and surfaces of fine particles, charge exchange rates, and efficiency of three-body recombination processes in the plasma bulk. The results are relevant to the plasma-aided nanomanufacturing of ordered patterns of carbon nanotip and nanopyramid microemitters.

  18. Charge exchange contamination of CRIT-II barium CIV experiment. [critical ionization velocity in ionosphere

    NASA Technical Reports Server (NTRS)

    Swenson, G. R.; Mende, S. B.; Meyerott, R. E.; Rairden, R. L.

    1991-01-01

    Experiments have been recently performed which attempted to confirm critical ionization velocity (CIV) ionization by deploying chemicals at high velocity in the ionosphere. Specifically, the CRIT-II rocket performed a barium release in the ionosphere, where observations of Ba(+) resonant emissions following the release are believed to have resulted from the CIV process. Calculations are presented which suggest a significant fraction (if not all) of the Ba(+) observed likely resulted from charge exchange with the thermosphere ions and not through CIV processes. The results presented here are pertinent to other CIV experiments performed in the ionosphere. It is recommended that laboratory measurements should be made of the charge exchange cross section between O(+) and Ba as well as other metal vapors used in CIV experiments.

  19. Charge exchange and ionization cross sections of H{sup +}+H collision in dense quantum plasmas

    SciTech Connect

    Zhang, Ling-yu; Qi, Xin; Zhao, Xiao-ying; Meng, Dong-yuan; Xiao, Guo-qing; Duan, Wen-shan; Yang, Lei

    2013-11-15

    The plasma screening effects of dense quantum plasmas on H{sup +}+H charge exchange and ionization cross sections are calculated by the classical trajectory Monte Carlo method. For charge exchange cross sections, it is found that the screening effects reduce cross sections slightly in weak screening conditions. However, cross sections are reduced substantially in strong screening conditions. For ionization cross sections, with the increase of screening effects, cross sections for low energies increase more rapidly than those for high energies. When the screening effects are strong enough, it is found that ionization cross sections decrease with the increase of incident H{sup +} energy. In addition, the cross sections have been compared with those in weakly coupled plasmas. It is found that in weak screening conditions, plasma screening effects in the two plasmas are approximately the same, while in strong screening conditions, screening effects of dense quantum plasmas are stronger than those of weakly coupled plasmas.

  20. Competition between charge exchange and chemical reaction - The D2/+/ + H system

    NASA Technical Reports Server (NTRS)

    Preston, R. K.; Cross, R. J., Jr.

    1973-01-01

    Study of the special features of molecular charge exchange and its competition with chemical reaction in the case of the D2(+) + H system. The trajectory surface hopping (TSH) model proposed by Tully and Preston (1971) is used to study this competition for a number of reactions involving the above system. The diatomics-in-molecules zero-overlap approximation is used to calculate the three adiabatic surfaces - one triplet and two singlet - which are needed to describe this system. One of the significant results of this study is that the chemical reaction and charge exchange are strongly coupled. It is also found that the number of trajectories passing into the chemical regions of the three surfaces depends very strongly on the surface crossings.-

  1. Charge-exchange erosion studies of accelerator grids in ion thrusters

    NASA Technical Reports Server (NTRS)

    Peng, Xiaohang; Ruyten, Wilhelmus M.; Keefer, Dennis

    1993-01-01

    A particle simulation model is developed to study the charge-exchange grid erosion in ion thrusters for both ground-based and space-based operations. Because the neutral gas downstream from the accelerator grid is different for space and ground operation conditions, the charge-exchange erosion processes are also different. Based on an assumption of now electric potential hill downstream from the ion thruster, the calculations show that the accelerator grid erosion rate for space-based operating conditions should be significantly less than experimentally observed erosion rates from the ground-based tests conducted at NASA Lewis Research Center (LeRC) and NASA Jet Propulsion Laboratory (JPL). To resolve this erosion issue completely, we believe that it is necessary to accurately measure the entire electric potential field downstream from the thruster.

  2. Influence of resonant charge exchange on the viscosity of partially ionized plasma in a magnetic field

    SciTech Connect

    Zhdanov, V. M. Stepanenko, A. A.

    2013-12-15

    The influence of resonant charge exchange for ion-atom interaction on the viscosity of partially ionized plasma embedded in the magnetic field is investigated. The general system of equations used to derive the viscosity coefficients for an arbitrary plasma component in the 21-moment approximation of Grad’s method is presented. The expressions for the coefficients of total and partial viscosities of a multicomponent partially ionized plasma in the magnetic field are obtained. As an example, the coefficients of the parallel and transverse viscosities for the ionic and neutral components of the partially ionized hydrogen plasma are calculated. It is shown that the account for resonant charge exchange can lead to a substantial change of the parallel and transverse viscosity of the plasma components in the region of low degrees of ionization on the order of 0.1.

  3. Nuclear fragmentation and charge-exchange reactions induced by pions in the Δ -resonance region

    NASA Astrophysics Data System (ADS)

    Feng, Zhao-Qing

    2016-11-01

    The dynamics of the nuclear fragmentations and the charge exchange reactions in pion-nucleus collisions near the Δ (1232) resonance energies has been investigated within the Lanzhou quantum molecular dynamics transport model. An isospin-, momentum-, and density-dependent pion-nucleon potential is implemented in the model, which influences the pion dynamics, in particular the kinetic energy spectra, but weakly impacts the fragmentation mechanism. The absorption process in pion-nucleon collisions to form the Δ (1232) resonance dominates the heating mechanism of the target nucleus. The excitation energy transferred to the target nucleus increases with the pion kinetic energy and is similar for both π-- and π+-induced reactions. The magnitude of fragmentation of the target nucleus weakly depends on the pion energy. The isospin ratio in the pion double-charge exchange is influenced by the isospin ingredient of target nucleus.

  4. Energy-loss cross sections for inclusive charge-exchange reactions at intermediate energies

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.; Townsend, Lawrence W.; Dubey, Rajendra R.

    1993-01-01

    Charge-exchange reactions for scattering to the continuum are considered in a high-energy multiple scattering model. Calculations for (p,n) and (He-3,H-3) reactions are made and compared with experimental results for C-12, O-16, and Al-27 targets. Coherent effects are shown to lead to an important role for inelastic multiple scattering terms when light projectiles are considered.

  5. Charge Exchange and Ablation Rates of a Titanium Wire Plasma Corona

    SciTech Connect

    Terry, Robert E.

    2009-01-21

    Wire ablation rates are important features in any examination of precursors or transparent mode implosions of wire arrays. When ion temperatures in a Ti wire plasma corona exceed a few eV, the process of resonant charge exchange competes with elastic scattering. Ions pushed into the corona from an anode bias wire array can be expected to drive a fast neutral wind into the surrounding volume, while a cathode bias wire array would not show the strong neutral wind.

  6. USING KAPPA FUNCTIONS TO CHARACTERIZE OUTER HELIOSPHERE PROTON DISTRIBUTIONS IN THE PRESENCE OF CHARGE-EXCHANGE

    SciTech Connect

    Zirnstein, E. J.; McComas, D. J. E-mail: dmccomas@swri.edu

    2015-12-10

    Kappa functions have long been used in the analysis and modeling of suprathermal particles in various space plasmas. In situ observations of the supersonic solar wind show its distribution contains a cold ion core and power-law tail, which is well-represented by a kappa function. In situ plasma observations by Voyager, as well as observations of energetic neutral atom (ENA) spectra by the Interstellar Boundary Explorer (IBEX), showed that the compressed and heated inner heliosheath (IHS) plasma beyond the termination shock can also be represented by a kappa function. IBEX exposes the IHS plasma properties through the detection of ENAs generated by charge-exchange in the IHS. However, charge-exchange modifies the plasma as it flows through the IHS, and makes it difficult to ascertain the parent proton distribution. In this paper we investigate the evolution of proton distributions, initially represented by a kappa function, that experience losses due to charge-exchange in the IHS. In the absence of other processes, it is no longer representable by a single kappa function due to the energy-dependent, charge-exchange process. While one can still fit a kappa function to the evolving proton distribution over limited energy ranges, this yields fitting parameters (pseudo-density, pseudo-temperature, pseudo-kappa index) that depend on the energy range of the fit. We discuss the effects of fitting a kappa function to the IHS proton distribution over limited energy ranges, its dependence on the initial proton distribution properties at the termination shock, and implications for understanding the observations.

  7. Measurement of pion double charge exchange on carbon-13, carbon-14, magnesium-26, and iron-56

    SciTech Connect

    Seidl, P.A.

    1985-02-01

    Cross sections for the /sup 13,14/C,/sup 26/Mg,/sup 56/Fe(..pi../sup +/,..pi../sup -/)/sup 13,14/O,/sup 26/Si,/sup 56/Ni reactions were measured with the Energetic Pion Channel and Spectrometer at the Clinton P. Anderson Meson Physics Facility for 120 less than or equal to T/sub ..pi../ less than or equal to 292 MeV and 0 less than or equal to theta less than or equal to 50. The double isobaric analog states (DIAS) are of primary interest. In addition, cross sections for transitions to /sup 14/O(0/sup +/, 5.92 MeV), /sup 14/O(2/sup +/, 7.77 MeV), /sup 56/Ni(gs), /sup 13/O(gs), and /sup 13/O(4.21 MeV) are presented. The /sup 13/O(4.21 MeV) state is postulated to have J/sup ..pi../ = 1/2/sup -/. The data are compared to previously measured double-charge-exchange cross sections on other nuclei, and the systematics of double charge exchange on T greater than or equal to 1 target nuclei leading to the DIAS are studied. Near the ..delta../sub 33/ resonance, cross sections for the DIAS transitions are in disagreement with calculations in which the reaction is treated as sequential charge exchange through the free pion-nucleon amplitude, while for T/sub ..pi../ > 200 MeV the anomalous features of the 164 MeV data are not apparent. This is evidence for significant higher order contributions to the double-charge-exchange amplitude near the reasonable energy. Two theoretical approaches that include two nucleon processes are applied to the DIAS data. 64 references.

  8. Polyoxometalate active charge-transfer material for mediated redox flow battery

    DOEpatents

    Anderson, Travis Mark; Hudak, Nicholas; Staiger, Chad; Pratt, Harry

    2017-01-17

    Redox flow batteries including a half-cell electrode chamber coupled to a current collecting electrode are disclosed herein. In a general embodiment, a separator is coupled to the half-cell electrode chamber. The half-cell electrode chamber comprises a first redox-active mediator and a second redox-active mediator. The first redox-active mediator and the second redox-active mediator are circulated through the half-cell electrode chamber into an external container. The container includes an active charge-transfer material. The active charge-transfer material has a redox potential between a redox potential of the first redox-active mediator and a redox potential of the second redox-active mediator. The active charge-transfer material is a polyoxometalate or derivative thereof. The redox flow battery may be particularly useful in energy storage solutions for renewable energy sources and for providing sustained power to an electrical grid.

  9. Helium escape from the Earth's atmosphere - The charge exchange mechanism revisited

    NASA Technical Reports Server (NTRS)

    Lie-Svendsen, O.; Rees, M. H.; Stamnes, K.

    1992-01-01

    We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.

  10. Experiments with an ion-neutral hybrid trap: cold charge-exchange collisions

    NASA Astrophysics Data System (ADS)

    Smith, W. W.; Goodman, D. S.; Sivarajah, I.; Wells, J. E.; Banerjee, S.; Côté, R.; Michels, H. H.; Mongtomery, J. A.; Narducci, F. A.

    2014-01-01

    Due to their large trap depths (˜1 eV or 10,000 K), versatility, and ease of construction, Paul traps have important uses in high-resolution spectroscopy, plasma physics, and precision measurements of fundamental constants. An ion-neutral hybrid trap consisting of two separate but spatially concentric traps [a magneto-optic trap (MOT) for the neutral species and a mass-selective linear Paul trap for the ionic species] is an ideal apparatus for sympathetic cooling. However, over the past few years, hybrid traps have proven most useful in measuring elastic and charge-exchange rate constants of ion-neutral collisions over a wide temperature range from kilo-Kelvin to nano-Kelvin. We report some initially surprising results from a hybrid trap system in our laboratory where we have loaded the Paul trap with Ca+ ions in the presence of a Na MOT (localized dense gas of cold Na atoms). We find a strong loss of Ca+ ions with MOT exposure, attributed to an exothermic, non-resonant ion-neutral charge-exchange process with an activation barrier, which leads to the formation of Na+ ions. We propose a detailed mechanism for this process. We obtain an estimated measure of the rate constant for this charge exchange of ˜2 × 10-11 cm3/s, much less than the Langevin rate, which suggests that the Langevin assumption of unit efficiency in the reaction region is not correct in this case.

  11. The inconsistency between proton charge exchange and the observed ring current decay

    NASA Technical Reports Server (NTRS)

    Lyons, L. R.; Evans, D. S.

    1976-01-01

    The equatorial pitch-angle distributions of ring-current ions observed during a storm recovery phase at L values between 3 and 4 are compared with the pitch-angle distributions predicted by proton charge exchange with neutral hydrogen. Large disagreements are found, and three alternative explanations are explored. (1) A strong proton source acts to mask the effects of charge exchange. It is believed that the required strong continual source with a unique pitch-angle and energy dependence is unrealistic at these low L values. (2) Presently accepted neutral hydrogen density models have densities well over an order of magnitude too large for a storm recovery phase. No evidence is known to support the required large errors in the densities. (3) The ring current at particle energies not exceeding 50 keV was dominated by some ion species other than protons during the storm recovery phase. Such ions must have much longer lifetimes for charge exchange with hydrogen than do protons. This alternative is strongly favored, with He(+) being an attractive candidate.

  12. Coherent control of charge exchange in strong-field dissociation of LiF

    NASA Astrophysics Data System (ADS)

    Armstrong, Greg; Esry, Brett

    2016-05-01

    The alkali-metal-halides family of molecules are useful prototypes in the study of laser-assisted charge exchange. Typically these molecules possess a field-free crossing between the ionic and covalent diabatic Born-Oppenheimer potential curves, leading to Li+ + F- and Li + F in LiF. These channels are energetically well-separated from higher-lying potentials, and may be easily distinguished experimentally. Moreover, charge exchange involves non-adiabatic transitions between the ionic and covalent channels, thereby allowing the investigation of physics beyond the Born-Oppenheimer approximation. The focus of this work is to control the preference between ionic and covalent dissociative products. We solve the time-dependent Schrödinger equation for the nuclear motion in full dimensionality, and investigate a pump-probe scheme for charge-exchange control. The degree of control is investigated by calculating the kinetic-energy release spectrum as a function of pump-probe delay for the ionic and covalent fragments. This work is supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  13. Wavelength calibration of the charge exchange recombination spectroscopy system on the DIII-D tokamak

    SciTech Connect

    Gohil, P.; Burrell, K.H.; Groebner, R.J.; Holtrop, K.; Kaplan, K.H.; Monier-Garbet, P.

    1998-06-01

    A wavelength calibration of all the detectors on the charge exchange recombination spectroscopy (CER) system is performed after every plasma discharge on the DIII-D tokamak. This is done to insure that the rest wavelength position of the C VI 5290.5 {angstrom} charge exchange line on the detector is accurately known so that the Doppler shift of the spectral line emitted during the discharge can be used for measurements of plasma rotation. In addition, this calibration provides a check on the spectral dispersion needed to determine the ion temperature. The reference spectra for the calibration are Ne I lines created by neon capillary discharge lamps contained within specially designed, diffuse reflectors. The Ne I lines at 3520.4720 {angstrom}, 5274.0393 {angstrom}, 5280.0853 {angstrom}, 5298.1891 {angstrom}, and 5304.7580 {angstrom} are used in this work. The location of these lines on the linear detectors can be determined to an accuracy of 0.1 pixel, which corresponds to a plasma rotation accuracy of 1.2 km/s and 0.7 km/s for the central and edge rotation measurements, respectively. Use of oppositely directed views of the plasma at the same major radius have been used to verify that the nominal 5290.5 {angstrom} wavelength of the C VI (n = 8 {r_arrow} 7) multiplet is the correct wavelength for the line emitted owing to charge exchange excitation.

  14. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    SciTech Connect

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  15. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    DOE PAGES

    Ma, X.; Fang, F.; Li, Q.; ...

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recoverymore » time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.« less

  16. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    PubMed Central

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-01-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation. PMID:26508587

  17. Modeling of protein-anion exchange resin interaction for the human growth hormone charge variants.

    PubMed

    Lapelosa, Mauro; Patapoff, Thomas W; Zarraga, Isidro E

    2015-12-01

    Modeling ion exchange chromatography (IEC) behavior has generated significant interest because of the wide use of IEC as an analytical technique as well as a preparative protein purification process; indeed there is a need for better understanding of what drives the unique behavior of protein charge variants. We hypothesize that a complex protein molecule, which contains both hydrophobic and charged moieties, would interact strongly with an in silico designed resin through charged electrostatic patches on the surface of the protein. In the present work, variants of recombinant human growth hormone that mimic naturally-occurring deamidation products were produced and characterized in silico. The study included these four variants: rhGH, N149D, N152D, and N149D/N152D. Poisson-Boltzmann calculations were used to determine surface electrostatic potential. Metropolis Monte Carlo simulations were carried out with the resulting variants to simulate IEC systems, examining the free energy of the interaction of the protein with an in silico anion exchange column represented by polylysine polypeptide. The results show that the charge variants have different average binding energies and the free energy of interaction can be used to predict the retention time for the different variants.

  18. Charge exchange of medium energy H and He ions emerging from solid surfaces

    NASA Astrophysics Data System (ADS)

    Kitsudo, Y.; Shibuya, K.; Nishimura, T.; Hoshino, Y.; Vickridge, I.; Kido, Y.

    2009-02-01

    Charge exchange of medium energy H and He ions emerging from clean solid surfaces is studied extensively using a toroidal electrostatic analyzer with an excellent energy resolution. The charge distributions of He ions scattered from sub-monolayers near a surface are non-equilibrated, resulting in a surface peak even for poly-crystal solids. By solving simultaneous rate equations numerically, we derive electron capture and loss cross sections for Ni and Au surfaces. Based on a free electron gas model, non-equilibrated He+ fractions dependent on emerging angle reveals uniform electronic surfaces for metals and corrugated surfaces for Si and graphite with covalent bonds. It is also found that equilibrium charge fractions of H+ are independent of surface materials (Z2) and in contrast equilibrium He+ fractions depend pronouncedly on Z2. The data obtained are compared with semi-empirical formulas.

  19. Observed Limits on Charge Exchange Contributions to the Diffuse X-Ray Background

    NASA Technical Reports Server (NTRS)

    Crowder, S. G.; Barger, K. A.; Brandl, D. E.; Eckart, M. E.; Galeazzi, M.; Kelley, R. L.; Kilbourne, C. A.; McCammon, D.; Pfendner, C. G.; Porter, F. S.; Rocks, L.; Szymkowiak, A. E.; Teplin, I. M.

    2012-01-01

    We present a high-resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV for an approximately 1 sr region of the sky centered at l = 90 degrees b = +60 degrees using a 36 pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrum s observed line ratios help separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced by about a factor of four from contamination that occurred early in the flight, limiting the significance of the results. The observed centroid of helium-like O VII is 568 (sup +2 (sub -3) eV at 90% confidence. Since the centroid expected for thermal emission is 568.4 eV and for charge exchange is 564.2 eV, thermal emission appears to dominate for this line complex. The dominance of thermal emission is consistent with much of the high-latitude O VII emission originating in 2-3 x 10(exp 6) K gas in the Galactic halo. On the other hand, the observed ratio of C VI Lygamma to Lyalpha is 0.3 plus or minus 0.2. The expected ratios are 0.04 for thermal emission and 0.24 for charge exchange, indicating that charge exchange must contribute strongly to this line and therefore potentially to the rest of the ROSAT R12 band usually associated with 10(sup 6) K emission from the Local Hot Bubble. The limited statistics of this experiment and systematic uncertainties due to the contamination require only greater than 32% thermal emission for O VII and greater than 20% from charge exchange for C VI at the 90% confidence level. An experimental gold coating on the silicon substrate of the array greatly reduced extraneous signals induced on nearby pixels from cosmic rays passing through the substrate, reducing the triggered event rate by a factor of 15 from a previous flight of the instrument.

  20. Surface charge of gold nanoparticles mediates mechanism of toxicity

    NASA Astrophysics Data System (ADS)

    Schaeublin, Nicole M.; Braydich-Stolle, Laura K.; Schrand, Amanda M.; Miller, John M.; Hutchison, Jim; Schlager, John J.; Hussain, Saber M.

    2011-02-01

    Recently gold nanoparticles (Au NPs) have shown promising biological and military applications due to their unique electronic and optical properties. However, little is known about their biocompatibility in the event that they come into contact with a biological system. In the present study, we have investigated whether modulating the surface charge of 1.5 nm Au NPs induced changes in cellular morphology, mitochondrial function, mitochondrial membrane potential (MMP), intracellular calcium levels, DNA damage-related gene expression, and of p53 and caspase-3 expression levels after exposure in a human keratinocyte cell line (HaCaT). The evaluation of three different Au NPs (positively charged, neutral, and negatively charged) showed that cell morphology was disrupted by all three NPs and that they demonstrated a dose-dependent toxicity; the charged Au NPs displayed toxicity as low as 10 µg ml-1 and the neutral at 25 µg ml-1. Furthermore, there was significant mitochondrial stress (decreases in MMP and intracellular Ca2+ levels) following exposure to the charged Au NPs, but not the neutral Au NPs. In addition to the differences observed in the MMP and Ca2+ levels, up or down regulation of DNA damage related gene expression suggested a differential cell death mechanism based on whether or not the Au NPs were charged or neutral. Additionally, increased nuclear localization of p53 and caspase-3 expression was observed in cells exposed to the charged Au NPs, while the neutral Au NPs caused an increase in both nuclear and cytoplasmic p53 expression. In conclusion, these results indicate that surface charge is a major determinant of how Au NPs impact cellular processes, with the charged NPs inducing cell death through apoptosis and neutral NPs leading to necrosis.Recently gold nanoparticles (Au NPs) have shown promising biological and military applications due to their unique electronic and optical properties. However, little is known about their biocompatibility in the

  1. Trace adsorption of positively charged proteins onto Sepharose FF and Sepharose FF-based anion exchangers.

    PubMed

    Yu, Lin-Ling; Sun, Yan

    2012-08-31

    Agarose-based matrices have been widely used in ion exchange chromatography (IEC). We have herein observed that positively charged proteins (lysozyme and cytochrome c) are adsorbed on the agarose-based anion-exchangers (Q and DEAE Sepharose FF gels) in a capacity of 10-40 μg/mL. In contrast, negatively charged protein (bovine serum albumin) is not adsorbed to Sepharose FF and SP Sepharose FF gels. Elemental analysis of the gel indicated that the residual anionic sulfate groups in agarose would have worked as the cation exchange groups for the positively charged proteins. The trace adsorption behavior of lysozyme onto Sepharose FF and Sepharose FF-based anion exchangers was studied and the effects of NaCl concentration and cation group density on the adsorption were examined for better understanding of the trace adsorption in chromatographic processes. At NaCl concentrations less than 0.05 mol/L, which is the normal adsorption condition in IEC, the trace adsorption kept at a high level, so this trace adsorption cannot be avoided in the ionic strength range of routine IEC operations. Grafting poly(ethylenimine) (PEI) chain of 60 kDa to a cation group density of 700 mmol/L could reduce the adsorption capacity to about 20 μg/mL, but further reduction was not possible by increasing the cation group density to 1200 mmol/L. Therefore, attentions need to be paid to the phenomenon in protein purification practice using agarose-based matrices. The research is expected to call attentions to the trace adsorption on agarose-based matrices and to the importance in the selection of the suitable solid matrices in the production of high-purity protein products in large-scale bioprocesses.

  2. Quantum Plasmonics: Optical Monitoring of DNA-Mediated Charge Transfer in Plasmon Rulers.

    PubMed

    Lerch, Sarah; Reinhard, Björn M

    2016-03-09

    Plasmon coupling between DNA-tethered gold nanoparticles is investigated by correlated single-particle spectroscopy and transmission electron microscopy for interparticle separations between 0.5 and 41 nm. Spectral characterization reveals a weakening of the plasmon coupling due to DNA-mediated charge transfer for separations up to 2.8 nm. Electromagnetic simulations indicate a coherent charge transfer across the DNA.

  3. Perceived Organizational Support as a Mediator between Relational Exchange and Organizational Identification

    ERIC Educational Resources Information Center

    Sluss, David M.; Klimchak, Malayka; Holmes, Jeanne J.

    2008-01-01

    Using cross-level data from 364 supervisor-subordinate dyads, we examined how relational exchange quality, perceived organizational support (POS), and organizational identification interrelate. We found subordinate POS mediates the relationship between leader-member exchange (i.e., LMX) and organizational identification. We also found the…

  4. Toward a predictive understanding of water and charge transport in proton exchange membranes.

    PubMed

    Selvan, Myvizhi Esai; Calvo-Muñoz, Elisa; Keffer, David J

    2011-03-31

    An analytical model for water and charge transport in highly acidic and highly confined systems such as proton exchange membranes of fuel cells is developed and compared to available experimental data. The model is based on observations from both experiment and multiscale simulation. The model accounts for three factors in the system including acidity, confinement, and connectivity. This model has its basis in the molecular-level mechanisms of water transport but has been coarse-grained to the extent that it can be expressed in an analytical form. The model uses the concentration of H(3)O(+) ion to characterize acidity, interfacial surface area per water molecule to characterize confinement, and percolation theory to describe connectivity. Several important results are presented. First, an integrated multiscale simulation approach including both molecular dynamics simulation and confined random walk theory is capable of quantitatively reproducing experimentally measured self-diffusivities of water in the perfluorinated sulfonic acid proton exchange membrane material, Nafion. The simulations, across a range of hydration conditions from minimally hydrated to fully saturated, have an average error for the self-diffusivity of water of 16% relative to experiment. Second, accounting for three factors-acidity, confinement, and connectivity-is necessary and sufficient to understand the self-diffusivity of water in proton exchange membranes. Third, an analytical model based on percolation theory is capable of quantitatively reproducing experimentally measured self-diffusivities of both water and charge in Nafion across a full range of hydration.

  5. Development of Laboratory Experimental System to Clarify Solar Wind Charge Exchange Mechanism with TES Microcalorimeter

    NASA Astrophysics Data System (ADS)

    Enoki, T.; Ishisaki, Y.; Akamatsu, H.; Ezoe, Y.; Ohashi, T.; Kanda, T.; Ishida, T.; Tanuma, H.; Ohashi, H.; Shinozaki, K.; Mitsuda, K.

    2012-06-01

    Significant fraction of the cosmic diffuse soft X-ray emission (0.1-1 keV) is caused by the Solar Wind Charge eXchange (SWCX) process between the solar wind ion (C q+, N q+, O q+ etc.) and the interplanetary neutral matter. It is difficult to identify spectral features of SWCX with the spectral resolution of existing X-ray astronomy satellites. We are developing a laboratory experimental system with transition edge sensor (TES) X-ray microcalorimeters, in order to clarify the SWCX mechanism. This experiment is designed to measure Charge eXchange (CX) X-rays using Electron Cyclotron Resonance Ion Source (ECRIS) that generates multi-charged ions. Emission lines (OVIII: 2p→1s; 654 eV) by CX between O8+ and neutral He atom is aimed to be measured with energy resolution better than 10 eV. The TES microcalorimeter is cooled by a double-stage adiabatic demagnetization refrigerator (DADR), however, our TES microcalorimeter are not working potentially due to magnetic field contamination. This paper reports our experimental system, present results, and future prospects.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  7. A comprehensive model of ion diffusion and charge exchange in the cold Io torus

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.; Moreno, M. A.

    1988-01-01

    A comprehensive analytic model of radial diffusion in the cold Io torus is developed. The model involves a generalized molecular cloud theory of SO2 and its dissociation fragments SO, O2, S, and O, which are formed at a relatively large rate by solar UV photodissociation of SO2. The key component of the new theory is SO, which can react with S(+) through a near-resonant charge exchange process that is exothermic. This provides a mechanism for the rapid depletion of singly ionized sulfur in the cold torus and can account for the large decrease in the total flux tube content inward of Io's orbit. The model is used to demonstrate quantitatively the effects of radial diffusion in a charge exchange environment that acts as a combined source and sink for ions in various charge states. A detailed quantitative explanation for the O(2+) component of the cold torus is given, and insight is derived into the workings of the so-called plasma 'ribbon'.

  8. Charge exchange fast neutral measurement with natural diamond detectors in neon plasma on LHD

    NASA Astrophysics Data System (ADS)

    Saida, T.; Sasao, M.; Isobe, M.; Krasilnikov, A. V.

    2003-03-01

    Charge exchange (CX) fast neutral spectra produced by ion cyclotron resonance frequency hydrogen minority heating in neon and helium majority plasmas sustained by neutral beam injection were measured with perpendicular Natural Diamond Detectors during the fifth campaign in 2002 on large helical devices (LHDs). It was observed that there were differences between fast neutral spectra shapes in neon plasma and those in helium of the same discharge condition with similar plasma parameters. Dominant CX processes in neon and helium plasmas were studied for ionization components from outside of the last closed flux surface. High-energy proton spectra were obtained by taking account of each charge state distribution and responsible charge exchange cross sections. The high-energy proton tail formations in both plasmas were similar for the same heating regime. The relaxation time tendencies of the effective temperatures of a high-energy proton have also shown no differences, indicating that the acceleration and confinement of energetic ions in LHDs are similar in neon and helium plasmas.

  9. Charge-exchange plasma environment for an ion drive spacecraft. [a model for describing mercury ion engines and its effect on spacecraft subsystems

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.; Carruth, M. R., Jr.

    1979-01-01

    The charge exchange plasma environment around a spacecraft that uses mercury ion thrusters for propulsion is described. The interactions between the plasma environment and the spacecraft are determined and a model which describes the propagation of the mercury charge exchange plasma is discussed. The model is extended to describe the flow of the molybdenum component of the charge exchange plasma. The uncertainties in the models for various conditions are discussed and current drain to the solar array, charge exchange plasma material deposition, and the effects of space plasma on the charge exchange plasma propagation are addressed.

  10. Possible Charge-Exchange X-Ray Emission in the Cygnus Loop Detected with Suzaku

    NASA Technical Reports Server (NTRS)

    Katsuda, Satoru; Tsunemi, Hiroshi; Mori, Koji; Uchida, Hiroyuki; Kosugi, Hiroko; Kimura, Masashi; Nakajima, Hiroshi; Takakura, Satoru; Petre, Robert; Hewitt. John W.; Yamaguchi, Hiroya

    2011-01-01

    X-ray spectroscopic measurements of the Cygnus Loop supernova remnant indicate that metal abundances throughout most of the remnant s rim are depleted to approx.0.2 times the solar value. However, recent X-ray studies have revealed in some narrow regions along the outermost rim anomalously "enhanced" abundances (up to approx. 1 solar). The reason for these anomalous abundances is not understood. Here, we examine X-ray spectra in annular sectors covering nearly the entire rim of the Cygnus Loop using Suzaku (21 pointings) and XMM-Newton (1 pointing). We find that spectra in the "enhanced" abundance regions commonly show a strong emission feature at approx.0.7 keV. This feature is likely a complex of He-like O K(gamma + delta + epsilon), although other possibilities cannot be fully excluded. The intensity of this emission relative to He-like O K(alpha) appears to be too high to be explained as thermal emission. This fact, as well as the spatial concentration of the anomalous abundances in the outermost rim, leads us to propose an origin from charge-exchange processes between neutrals and H-like O. We show that the presence of charge-exchange emission could lead to the inference of apparently "enhanced" metal abundances using pure thermal emission models. Accounting for charge-exchange emission, the actual abundances could be uniformly low throughout the rim. The overall abundance depletion remains an open question. Subject headings: ISM: abundances ISM: individual objects (Cygnus Loop) ISM: supernova remnants X-rays: ISM atomic processes

  11. Correlation between charge transfer and exchange coupling in carbon-based magnetic materials

    SciTech Connect

    Nguyen, Anh Tuan; Nguyen, Van Thanh; Nguyen, Huy Sinh; Pham, Thi Tuan Anh; Do, Viet Thang; Dam, Hieu Chi

    2015-10-15

    Several forms of carbon-based magnetic materials, i.e. single radicals, radical dimers, and alternating stacks of radicals and diamagnetic molecules, have been investigated using density-functional theory with dispersion correction and full geometry optimization. Our calculated results demonstrate that the C{sub 31}H{sub 15} (R{sub 4}) radical has a spin of ½. However, in its [R{sub 4}]{sub 2} dimer structure, the net spin becomes zero due to antiferromagnetic spin-exchange between radicals. To avoid antiferromagnetic spin-exchange of identical face-to-face radicals, eight alternating stacks, R{sub 4}/D{sub 2m}/R{sub 4} (with m = 3-10), were designed. Our calculated results show that charge transfer (Δn) between R{sub 4} radicals and the diamagnetic molecule D{sub 2m} occurs with a mechanism of spin exchange (J) in stacks. The more electrons that transfer from R{sub 4} to D{sub 2m}, the stronger the ferromagnetic spin-exchange in stacks. In addition, our calculated results show that Δn can be tailored by adjusting the electron affinity (E{sub a}) of D{sub 2m}. The correlation between Δn, E{sub a}, m, and J is discussed. These results give some hints for the design of new ferromagnetic carbon-based materials.

  12. Neutrino nuclear responses for double beta decays and astro neutrinos by charge exchange reactions

    NASA Astrophysics Data System (ADS)

    Ejiri, Hiroyasu

    2014-09-01

    Neutrino nuclear responses are crucial for neutrino studies in nuclei. Charge exchange reactions (CER) are shown to be used to study charged current neutrino nuclear responses associated with double beta decays(DBD)and astro neutrino interactions. CERs to be used are high energy-resolution (He3 ,t) reactions at RCNP, photonuclear reactions via IAR at NewSUBARU and muon capture reactions at MUSIC RCNP and MLF J-PARC. The Gamow Teller (GT) strengths studied by CERs reproduce the observed 2 neutrino DBD matrix elements. The GT and spin dipole (SD) matrix elements are found to be reduced much due to the nucleon spin isospin correlations and the non-nucleonic (delta isobar) nuclear medium effects. Impacts of the reductions on the DBD matrix elements and astro neutrino interactions are discussed.

  13. Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

    NASA Technical Reports Server (NTRS)

    Zhang, M. H. G.; Luhmann, J. G.; Nagy, A. F.; Spreiter, J. R.; Stahara, S. S.

    1993-01-01

    Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

  14. Fast time resolution charge-exchange measurements during the fishbone instability in the poloidal divertor experiment

    SciTech Connect

    Beiersdorfer, P.; Kaita, R.; Goldston, R.J.

    1984-01-01

    Measurements of fast ion losses due to the fishbone instability during high ..beta../sub T/q neutral beam heated discharges in the Poloidal Divertor Experiment have been made using two new vertical-viewing charge-exchange analyzers. The measurements show that the instability has an n=1 toroidal mode number, and that it ejects beam ions in a toroidally rotating beacon directed outward along a major radius. Observations of ejected ions with energies up to twice the beam injection energy at R approx. = R/sub 0/ + a indicate the presence of a non-..mu..-conserving acceleration mechanism.

  15. Neutron skin thickness of {sup 90}Zr determined by charge exchange reactions

    SciTech Connect

    Yako, K.; Sakai, H.; Sagawa, H.

    2006-11-15

    Charge exchange spin-dipole (SD) excitations of {sup 90}Zr are studied by the {sup 90}Zr(p,n) and {sup 90}Zr(n,p) reactions at 300 MeV. A multipole decomposition technique is employed to obtain the SD strength distributions in the cross-section spectra. For the first time, a model-independent SD sum rule value is obtained: 148{+-}12 fm{sup 2}. The neutron skin thickness of {sup 90}Zr is determined to be 0.07{+-}0.04 fm from the SD sum rule value.

  16. Laser interferometric measurement of ion electrode shape and charge exchange erosion

    NASA Technical Reports Server (NTRS)

    Macrae, Gregory S.; Mercer, Carolyn R.

    1991-01-01

    A projected fringe profilometry system was applied to surface contour measurements of an accelerator electrode from an ion thrustor. The system permitted noncontact, nondestructive evaluation of the fine and gross structure of the electrode. A 3-D surface map of a dished electrode was generated without altering the electrode surface. The same system was used to examine charge exchange erosion pits near the periphery of the electrode to determine the depth, location, and volume of material lost. This electro-optical measurement system allowed rapid, nondestructive, digital data acquisition coupled with automated computer data processing. In addition, variable sensitivity allowed both coarse and fine measurements of objects having various surface finishes.

  17. Simulations of ion velocity distribution functions taking into account both elastic and charge exchange collisions

    NASA Astrophysics Data System (ADS)

    Wang, Huihui; Sukhomlinov, Vladimir S.; Kaganovich, Igor D.; Mustafaev, Alexander S.

    2017-02-01

    Based on accurate representation of the He+-He angular differential scattering cross sections consisting of both elastic and charge exchange collisions, we performed detailed numerical simulations of the ion velocity distribution functions (IVDF) by Monte Carlo collision method (MCC). The results of simulations are validated by comparison with the experimental data of the ion mobility and the transverse diffusion. The IVDF simulation study shows that due to significant effect of scattering in elastic collisions IVDF cannot be separated into product of two independent IVDFs in the transverse and parallel to the electric field directions.

  18. X-Ray Emission Cross Sections following Charge Exchange by Multiply-Charged Ions of Astrophysical Interest

    SciTech Connect

    Otranto, S; Olson, R E; Beiersdorfer, P

    2005-09-19

    State selective nl-electron capture cross sections are presented for highly charged ions with Z = 6-10 colliding with atoms and molecules. The energy range investigated was from 1 eV/amu (v = 0.006 a.u.) to 100 keV/amu (v =2.0 a.u.). The energy dependence of the l-level populations is investigated. The K-shell x-ray emission cross sections are determined by using the calculated state-selective electron capture results as input and then applying hydrogenic branching and cascading values for the photon emission. A major shift in the line emission from being almost solely Lyman-{alpha} transitions at the highest collisions energies to strong high-n to 1s transitions at the lowest energies is observed. The calculated cross sections are in reasonable accord with measurements made by Greenwood et al, Phys. Rev. A 63, 062707 (2001), using O{sup 8+} and Ne{sup 10+} on various targets at 3 keV/amu. The calculations are also in accord with x-ray emission cross section data obtained on the EBIT machine at LLNL where O{sup 8+} and Ne{sup 10+} high resolution measurements were made at a temperature of 10 eV/amu for a series of targets with varying ionization potentials. The Ne{sup 10+} data clearly shows the contribution from multiple capture followed by Auger autoionization in the line emission spectra. Our calculated line emission cross sections are used to provide an ab initio determination of the soft x-ray spectrum of comet C/Linear 1999 S4 that was observed on the Chandra X-ray Observatory. The calculations show that the spectrum is due to charge exchange of the neutral gases in the comet's coma with the ions of the slow solar wind.

  19. Metal-ion-specific screening of charge effects in protein amide H/D exchange and the Hofmeister series.

    PubMed

    Abdolvahabi, Alireza; Gober, Jennifer L; Mowery, Richard A; Shi, Yunhua; Shaw, Bryan F

    2014-10-21

    In this study, protein charge ladders and mass spectrometry were used to quantify how metal cations in the Hofmeister series (Na(+), K(+), Li(+), Mg(2+), and Ca(2+)) permute the effects of lysine acetylation on the rate of amide H/D exchange in a representative protein (myoglobin, Mb). The successive acetylation of up to 18 Lys-ε-NH3(+) groups in Mb caused a linear decrease in its global rate of amide H/D exchange (as measured by mass spectrometry), despite also decreasing the thermostability of Mb by >10 °C. The ability of a metal cation to screen kinetic electrostatic effects during H/D exchange-and to abolish the protective effect of acetylation against H/D exchange-was found to depend on the position of the cation in the Hofmeister series. Na(+) and K(+) cations did not fully equalize the rates of H/D exchange among each "rung" of the charge ladder, whereas Mg(2+) and Ca(2+) did equalize rates without eliminating the hydrophobic core of the protein (i.e., without unfolding Mb); Li(+) exhibited intermediate effects. The ability of Mg(2+) and Ca(2+) to completely screen electrostatic effects associated with the H/D exchange of charge isomers of Mb suggests that Mg(2+) or Ca(2+) (but not Na(+) or K(+)) can be used to quantify the magnitude by which electrostatic charge contributes to the observed rates of amide H/D exchange in proteins.

  20. Predicting Salt Permeability Coefficients in Highly Swollen, Highly Charged Ion Exchange Membranes.

    PubMed

    Kamcev, Jovan; Paul, Donald R; Manning, Gerald S; Freeman, Benny D

    2017-02-01

    This study presents a framework for predicting salt permeability coefficients in ion exchange membranes in contact with an aqueous salt solution. The model, based on the solution-diffusion mechanism, was tested using experimental salt permeability data for a series of commercial ion exchange membranes. Equilibrium salt partition coefficients were calculated using a thermodynamic framework (i.e., Donnan theory), incorporating Manning's counterion condensation theory to calculate ion activity coefficients in the membrane phase and the Pitzer model to calculate ion activity coefficients in the solution phase. The model predicted NaCl partition coefficients in a cation exchange membrane and two anion exchange membranes, as well as MgCl2 partition coefficients in a cation exchange membrane, remarkably well at higher external salt concentrations (>0.1 M) and reasonably well at lower external salt concentrations (<0.1 M) with no adjustable parameters. Membrane ion diffusion coefficients were calculated using a combination of the Mackie and Meares model, which assumes ion diffusion in water-swollen polymers is affected by a tortuosity factor, and a model developed by Manning to account for electrostatic effects. Agreement between experimental and predicted salt diffusion coefficients was good with no adjustable parameters. Calculated salt partition and diffusion coefficients were combined within the framework of the solution-diffusion model to predict salt permeability coefficients. Agreement between model and experimental data was remarkably good. Additionally, a simplified version of the model was used to elucidate connections between membrane structure (e.g., fixed charge group concentration) and salt transport properties.

  1. High spatial and temporal resolution charge exchange recombination spectroscopy on the HL-2A tokamak

    SciTech Connect

    Wei, Y. L.; Yu, D. L. Liu, L.; Cao, J. Y.; Sun, A. P.; Ma, Q.; Chen, W. J.; Liu, Yi; Yan, L. W.; Yang, Q. W.; Duan, X. R.; Liu, Yong; Ida, K.; Hellermann, M. von

    2014-10-01

    A 32/64-channel charge exchange recombination spectroscopy (CXRS) diagnostic system is developed on the HL-2A tokamak (R = 1.65 m, a = 0.4 m), monitoring plasma ion temperature and toroidal rotation velocity simultaneously. A high throughput spectrometer (F/2.8) and a pitch-controlled fiber bundle enable the temporal resolution of the system up to 400 Hz. The observation geometry and an optimized optic system enable the highest radial resolution up to ~1 cm at the plasma edge. The CXRS system monitors the carbon line emission (C VI, n = 8–7, 529.06 nm) whose Doppler broadening and Doppler shift provide ion temperature and plasma rotation velocity during the neutral beam injection. The composite CX spectral data are analyzed by the atomic data and analysis structure charge exchange spectroscopy fitting (ADAS CXSFIT) code. First experimental results are shown for the case of HL-2A plasmas with sawtooth oscillations, electron cyclotron resonance heating, and edge transport barrier during the high-confinement mode (H-mode)

  2. Ionosphere-exosphere coupling through charge exchange and momentum transfer in hydrogen-proton collisions

    NASA Technical Reports Server (NTRS)

    Hodges, R. R., Jr.; Breig, E. L.

    1991-01-01

    The implications of a traditional assumption of exospheric physics, that collisions of hydrogen atoms and protons preferentially result in charge exchange with negligible momentum transfer are examined. Initially adopted as a necessary convenience to accommodate limited computer resources in exosphere model calculations, this approximation results in a direct transformation of the proton velocity distribution into a hot component of neutral hydrogen. With expanding computational facilities, the need for the approximation has passed. As the first step toward its replacement with a realistic, quantum mechanical model of the H - H(+) collision process, differential and cumulative cross sections were calculated for quantum elastic scattering of indistinguishable nuclei for a fine grid of encounter energies and scattering angles. These data are used to study the nature of ionosphere-exosphere coupling through H - H(+) collisions, and to demonstrate that the distribution of velocities of scattered H produced in the traditional exospheric charge exchange approximation, as well as that arising from an alternative, fluid dynamic approach, leads to unacceptable abundances of coronal atoms in long-term, highly elliptic trajectories.

  3. Charge Exchange Contribution to the Decay of the Ring Current, Measured by Energetic Neutral Atoms (ENAs)

    NASA Technical Reports Server (NTRS)

    Jorgensen, A. M.; Henderson, M. G.; Roelof, E. C.; Reeves, G. D.; Spence, H. E.

    2001-01-01

    In this paper we calculate the contribution of charge exchange to the decay of the ring current. Past works have suggested that charge exchange of ring current protons is primarily responsible for the decay of the ring current during the late recovery phase, but there is still much debate about the fast decay of the early recovery phase. We use energetic neutral atom (ENA) measurements from Polar to calculate the total ENA energy escape. To get the total ENA escape we apply a forward modeling technique, and to estimate the total ring current energy escape we use the Dessler-Parker-Sckopke relationship. We find that during the late recovery phase of the March 10, 1998 storm ENAs with energies greater than 17.5 keV can account for 75% of the estimated energy loss from the ring current. During the fast recovery the measured ENAs can only account for a small portion of the total energy loss. We also find that the lifetime of the trapped ions is significantly shorter during the fast recovery phase than during the late recovery phase, suggesting that different processes are operating during the two phases.

  4. High spatial and temporal resolution charge exchange recombination spectroscopy on the HL-2A tokamak.

    PubMed

    Wei, Y L; Yu, D L; Liu, L; Ida, K; von Hellermann, M; Cao, J Y; Sun, A P; Ma, Q; Chen, W J; Liu, Yi; Yan, L W; Yang, Q W; Duan, X R; Liu, Yong

    2014-10-01

    A 32/64-channel charge exchange recombination spectroscopy (CXRS) diagnostic system is developed on the HL-2A tokamak (R = 1.65 m, a = 0.4 m), monitoring plasma ion temperature and toroidal rotation velocity simultaneously. A high throughput spectrometer (F/2.8) and a pitch-controlled fiber bundle enable the temporal resolution of the system up to 400 Hz. The observation geometry and an optimized optic system enable the highest radial resolution up to ∼1 cm at the plasma edge. The CXRS system monitors the carbon line emission (C VI, n = 8-7, 529.06 nm) whose Doppler broadening and Doppler shift provide ion temperature and plasma rotation velocity during the neutral beam injection. The composite CX spectral data are analyzed by the atomic data and analysis structure charge exchange spectroscopy fitting (ADAS CXSFIT) code. First experimental results are shown for the case of HL-2A plasmas with sawtooth oscillations, electron cyclotron resonance heating, and edge transport barrier during the high-confinement mode (H-mode).

  5. CHARGE-EXCHANGE LIMITS ON LOW-ENERGY {alpha}-PARTICLE FLUXES IN SOLAR FLARES

    SciTech Connect

    Hudson, H. S.; Fletcher, L.; MacKinnon, A. L.; Woods, T. N.

    2012-06-20

    This paper reports on a search for flare emission via charge-exchange radiation in the wings of the Ly{alpha} line of He II at 304 A, as originally suggested for hydrogen by Orrall and Zirker. Via this mechanism a primary {alpha} particle that penetrates into the neutral chromosphere can pick up an atomic electron and emit in the He II bound-bound spectrum before it stops. The Extreme-ultraviolet Variability Experiment on board the Solar Dynamics Observatory gives us our first chance to search for this effect systematically. The Orrall-Zirker mechanism has great importance for flare physics because of the essential roles that particle acceleration plays; this mechanism is one of the few proposed that would allow remote sensing of primary accelerated particles below a few MeV nucleon{sup -1}. We study 10 events in total, including the {gamma}-ray events SOL2010-06-12 (M2.0) and SOL2011-02-24 (M3.5) (the latter a limb flare), seven X-class flares, and one prominent M-class event that produced solar energetic particles. The absence of charge-exchange line wings may point to a need for more complete theoretical work. Some of the events do have broadband signatures, which could correspond to continua from other origins, but these do not have the spectral signatures expected from the Orrall-Zirker mechanism.

  6. Influence of a wick lining on the evaporation rate of lithium from a charge exchange canal

    NASA Astrophysics Data System (ADS)

    Thampi, N. S.; Berger, S.; Dworschak, F.

    1992-02-01

    A wick lining is used with a lithium charge exchange canal for reducing the consumption of lithium. The wick helps to condense the lithium vapour more effectively and to make it flow back to the main oven. For its efficient functioning, the temperature gradient along the wick has to be properly maintained. The present studies were carried out to assess the extent of reduction in lithium loss when using the wick and to determine the optimum temperature settings. The evaporation rate of lithium vapour from a charge exchange canal (General Ionex Model-712) has been investigated in the temperature range from 470 to 575° C. The measurements were carried out with and without a stainless steel wire mesh wick lining, inside the canal. A quartz crystal oscillator type rate meter was used for monitoring the evaporation rate. The results indicate that, when the wick lining is inserted, the reduction in evaporation rate of lithium is only 20%. This differs much from the result of Greenway [Report 85/11, Oxford University, Nuclear Physics Laboratory (1985)] who reported a reduction by a factor of 8. The evaporation rate is also found to depend on the canal end heater temperature, maintained high enough to keep the condensing vapour in liquid state. The optimum temperature settings for the end heaters have been found to be 300 ° C. The experimental arrangements and results are presented in this paper.

  7. A high etendue spectrometer suitable for core charge eXchange recombination spectroscopy on ITER

    SciTech Connect

    Jaspers, R. J. E.; Scheffer, M.; Kappatou, A.; Valk, N. C. J. van der; Durkut, M.; Snijders, B.; Marchuk, O.; Biel, W.; Pokol, G. I.; Erdei, G.; Zoletnik, S.; Dunai, D.

    2012-10-15

    A feasibility study for the use of core charge exchange recombination spectroscopy on ITER has shown that accurate measurements on the helium ash require a spectrometer with a high etendue of 1mm{sup 2}sr to comply with the measurement requirements [S. Tugarinov et al., Rev. Sci. Instrum. 74, 2075 (2003)]. To this purpose such an instrument has been developed consisting of three separate wavelength channels (to measure simultaneously He/Be, C/Ne, and H/D/T together with the Doppler shifted direct emission of the diagnostic neutral beam, the beam emission (BES) signal), combining high dispersion (0.02 nm/pixel), sufficient resolution (0.2 nm), high efficiency (55%), and extended wavelength range (14 nm) at high etendue. The combined measurement of the BES along the same sightline within a third wavelength range provides the possibility for in situ calibration of the charge eXchange recombination spectroscopy signals. In addition, the option is included to use the same instrument for measurements of the fast fluctuations of the beam emission intensity up to 2 MHz, with the aim to study MHD activity.

  8. DXL: A sounding rocket mission measuring Solar Wind Charge eXchange properties

    NASA Astrophysics Data System (ADS)

    Galeazzi, Massimiliano

    2016-04-01

    Solar Wind interacts with the interstellar neutrals via charge exchange mechanism to produce spatially and temporally varying x-rays making it difficult to separate from other diffuse sources. The Diffuse X-rays from the Local Galaxy (DXL) mission measured the spatial signature of Solar Wind Charge eXchange (SWCX) emission due to the helium focusing cone. The mission used 2 large area proportional counters and was able to separate the SWCX contribution from Local Hot Bubble emission. The data from the mission provide a robust estimate of the SWCX contribution to the ROSAT maps, measuring the compound SWCX cross section with He in all ROSAT bands. The results showed that the total SWCX contribution in the ¼ keV band is, on average, ~27%. A new mission, DXL-2, was launched on December 4, 2015 with two new counters for a better understanding of the energy distribution of heliospheric SWCX photons, by using a multi-band approach. A dedicated scan to accurately measure the cone position and solve the IBEX controversy was also performed. The talk will discuss the DXL mission, the results from the first flight, and the preliminary results from the latest flight.Submitted for the DXL Collaboration

  9. High spatial and temporal resolution charge exchange recombination spectroscopy on the HL-2A tokamak

    NASA Astrophysics Data System (ADS)

    Wei, Y. L.; Yu, D. L.; Liu, L.; Ida, K.; von Hellermann, M.; Cao, J. Y.; Sun, A. P.; Ma, Q.; Chen, W. J.; Liu, Yi; Yan, L. W.; Yang, Q. W.; Duan, X. R.; Liu, Yong

    2014-10-01

    A 32/64-channel charge exchange recombination spectroscopy (CXRS) diagnostic system is developed on the HL-2A tokamak (R = 1.65 m, a = 0.4 m), monitoring plasma ion temperature and toroidal rotation velocity simultaneously. A high throughput spectrometer (F/2.8) and a pitch-controlled fiber bundle enable the temporal resolution of the system up to 400 Hz. The observation geometry and an optimized optic system enable the highest radial resolution up to ˜1 cm at the plasma edge. The CXRS system monitors the carbon line emission (C VI, n = 8-7, 529.06 nm) whose Doppler broadening and Doppler shift provide ion temperature and plasma rotation velocity during the neutral beam injection. The composite CX spectral data are analyzed by the atomic data and analysis structure charge exchange spectroscopy fitting (ADAS CXSFIT) code. First experimental results are shown for the case of HL-2A plasmas with sawtooth oscillations, electron cyclotron resonance heating, and edge transport barrier during the high-confinement mode (H-mode).

  10. Upgrade of the Edge Charge Exchange Diagnostic on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    McDermott, Rachael; Lipschultz, Bruce; Marr, Kenneth

    2006-10-01

    The current edge Charge Exchange Spectroscopy system is being upgraded to include both a beam viewing and a background viewing toroidal periscope. The beam viewing periscope will be focused on the center of the DNB and will cover a 4cm radial region at the edge of the plasma starting a few centimeters in from and extending up to 1centimeter outside of the last closed flux surface. The background periscope will view the same radial region but will be displaced toroidally by 36 degrees. Each periscope has 20 chordal views with a radial resolution of 2.5-3mm. The presence of a background periscope obviates the need for a chopped DNB by providing time synchronized background B^+4 spectral data that can be subtracted directly from the active beam-derived B^+4 line-shapes. This system has been designed to work in conjunction with the current poloidal Charge Exchange periscope which has 25 fibers focused in the same region with equivalent radial resolution. The new toroidal system will enable concurrent measurements of the poloidal and toroidal velocity as well as the temperature and density of the B^+5 ions in the edge pedestal region; a measurement that currently does not exist on C-Mod. This information will then be used to calculate radial electric field profiles and study edge physics phenomena.

  11. Observations of solar wind ion charge exchange in the Comet Halley coma

    NASA Technical Reports Server (NTRS)

    Fuselier, S. A.; Shelley, E. G.; Goldstein, B. E.; Goldstein, R.; Neugebauer, M.; Ip, W.-H.; Balsiger, H.; Reme, H.

    1991-01-01

    Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) observations of solar wind ions show charge exchange effects and solar wind compositional changes in the coma of Comet Halley. As the comet was approached, the He(2+) to proton density ratio increased from 2.5 percent in the solar wind to about 4 percent about 1 hr before closest approach after which time it decreased to about 1 percent. Abrupt increases in this ratio from 2.5 to 4.5 percent were also observed in the beginning and near the end of the so-called Mystery Region. These abrupt increases in the density ratio were well correlated with enhanced fluxes of keV electrons as measured by the Giotto plasma electron spectrometer. The general increase and then decrease of the He(2+) to proton density ratio is quantitatively consistent with a combination of the addition of protons of Cometary origin to the plasma and loss of plasma through charge exchange of protons and He(2+).

  12. Ne X X-ray emission due to charge exchange in M82

    NASA Astrophysics Data System (ADS)

    Cumbee, R. S.; Liu, L.; Lyons, D.; Schultz, D. R.; Stancil, P. C.; Wang, J. G.; Ali, R.

    2016-06-01

    Recent X-ray observations of star-forming galaxies such as M82 have shown the Ly β/Ly α line ratio of Ne X to be in excess of predictions for thermal electron impact excitation. Here, we demonstrate that the observed line ratio may be due to charge exchange and can be used to constrain the ion kinetic energy to be ≲ 500 eV/u. This is accomplished by computing spectra and line ratios via a range of theoretical methods and comparing these to experiments with He over astrophysically relevant collision energies. The charge exchange emission spectra calculations were performed for Ne10++ H and Ne10++ He using widely applied approaches including the atomic orbital close coupling, classical trajectory Monte Carlo, and multichannel Landau-Zener (MCLZ) methods. A comparison of the results from these methods indicates that for the considered energy range and neutrals (H, He) the so-called low-energy ℓ-distribution MCLZ method provides the most likely reliable predictions.

  13. First measurement of the edge charge exchange recombination spectroscopy on EAST tokamak.

    PubMed

    Li, Y Y; Yin, X H; Fu, J; Jiang, D; Feng, S Y; Lyu, B; Shi, Y J; Yi, Y; Zhou, X J; Hu, C D; Ye, M Y; Wan, B N

    2016-11-01

    An edge toroidal charge exchange recombination spectroscopy (eCXRS) diagnostic, based on a heating neutral beam injection (NBI), has been deployed recently on the Experimental Advanced Superconducting Tokamak (EAST). The eCXRS, which aims to measure the plasma ion temperature and toroidal rotation velocity in the edge region simultaneously, is a complement to the exiting core CXRS (cCXRS). Two rows with 32 fiber channels each cover a radial range from ∼2.15 m to ∼2.32 m with a high spatial resolution of ∼5-7 mm. Charge exchange emission of Carbon VI CVI at 529.059 nm induced by the NBI is routinely observed, but can be tuned to any interested wavelength in the spectral range from 400 to 700 nm. Double-slit fiber bundles increase the number of channels, the fibers viewing the same radial position are binned on the CCD detector to improve the signal-to-noise ratio, enabling shorter exposure time down to 5 ms. One channel is connected to a neon lamp, which provides the real-time wavelength calibration on a shot-to-shot basis. In this paper, an overview of the eCXRS diagnostic on EAST is presented and the first results from the 2015 experimental campaign will be shown. Good agreements in ion temperature and toroidal rotation are obtained between the eCXRS and cCXRS systems.

  14. Recent Advances in Computational Studies of Charge Exchange X-ray Emission

    NASA Astrophysics Data System (ADS)

    Cumbee, Renata

    2016-06-01

    Interest in astrophysical sources of charge exchange (CX) has grown since X-ray emission from comet Hyakutake was first observed, the origin of which is primarily due to CX processes between neutral species in the comet’s atmosphere and highly charged ions from the solar wind. More recent observations have shown that CX may have a significant contribution to the X-ray emission spectra of a wide variety of environments within our solar system including solar wind charge exchange (SWCX) with neutral gases in the heliosphere and in planetary atmospheres, as well as beyond the solar system in galaxy clusters, supernova remnants, and star forming galaxies.While the basic process of CX has been studied for many decades, the reliability of the existing data is not uniform, and the coverage of the astrophysically important projectile and target combinations and collisional velocities is insufficient. The need for reliable and robust CX X-ray emission models will only be amplified with the with the high resolution X-ray spectra expected from the soft X-ray imaging calorimeter spectrometer (SXS) onboard the Hitomi X-ray observatory. In this talk, I will discuss recent advances in theoretical CX cross sections and X-ray modeling with a focus on CX diagnostics. The need for experimental X-ray spectra and cross sections for benchmarking current theory will also be highlighted. This work was performed in collaboration with David Lyons, Patrick Mullen, David Schultz, Phillip Stancil, and Robin Shelton. Work at UGA was partially supported by NASA grant NNX09AC46G.

  15. Study of multi-electron ionization and charge exchange in HIBF

    NASA Astrophysics Data System (ADS)

    Wu, Linchun

    Beam ion stripping on background gases or plasma in a Heavy Ion Beam Fusion (HIBF) chamber increases the charge state of the beam and the diameter of the focus, complicating the final focusing on the focusing target. To model beam transport in the chamber, it is necessary to know the beam charge-state evolution, including both ionization and charge exchange dynamics. The main objective of this research is to explore theoretical approaches including scaling law. Improved models are developed to calculate multi-electron loss, especially ion stripping and charge exchange cross sections, for both near-term experiments and future power plant scale HIBF research. First, a new space-charge neutralization approach that uses electron injection is proposed for the ion beam transport in HIBF chamber. An analytical study was performed to illustrate the plasma dynamics and final neutralization effects with this technique. The results examine the effect of different injected electron profiles. Next, to improve the accuracy of such simulations, methods to improve cross sections of ionization and charge exchange are studied. Both classical and quantum mechanical approaches are examined. Attention is focused on the interaction by low-charge-state heavy ions. Multi-electron processes for dressed ions, including screening and anti-screening effects, internuclear forces, are given special attention, This analysis is complex and requires a combining several different theoretical approaches. Finally, a Classic Trajectory Monte Carlo (CTMC) model based on an improvement of Olson's n-body CTMC method is presented. This model solves the n-body ion-atom ionization problem in a regime of intent to HIBF. In the paper, a new and complete computational module for these interactions has been developed. The cross section data for Xe, Cs, and Bi ions colliding with various background gases (Xe, N2, Ar and Flibe) is presented. After the calculation of the cross section data, the predicted energy

  16. Charge Noise Spectroscopy Using Coherent Exchange Oscillations in a Singlet-Triplet Qubit

    NASA Astrophysics Data System (ADS)

    Dial, O. E.; Shulman, M. D.; Harvey, S. P.; Bluhm, H.; Umansky, V.; Yacoby, A.

    2013-04-01

    Two level systems that can be reliably controlled and measured hold promise as qubits both for metrology and for quantum information science. Since a fluctuating environment limits the performance of qubits in both capacities, understanding environmental coupling and dynamics is key to improving qubit performance. We show measurements of the level splitting and dephasing due to the voltage noise of a GaAs singlet-triplet qubit during exchange oscillations. Unexpectedly, the voltage fluctuations are non-Markovian even at high frequencies and exhibit a strong temperature dependence. This finding has impacts beyond singlet-triplet qubits since nearly all solid state qubits suffer from some kind of charge noise. The magnitude of the fluctuations allows the qubit to be used as a charge sensor with a sensitivity of 2×10-8e/Hz, 2 orders of magnitude better than a quantum-limited rf single electron transistor. Based on these measurements, we provide recommendations for improving qubit coherence, allowing for higher fidelity operations and improved charge sensitivity.

  17. Design of a strong cation exchange methodology for the evaluation of charge heterogeneity in glatiramer acetate.

    PubMed

    Campos-García, Víctor R; López-Morales, Carlos A; Benites-Zaragoza, Eleuterio; Jiménez-Miranda, Armando; Espinosa-de la Garza, Carlos E; Herrera-Fernández, Daniel; Padilla-Calderón, Jesús; Pérez, Néstor O; Flores-Ortiz, Luis F; Medina-Rivero, E

    2017-01-05

    Complex pharmaceuticals are in demand of competent analytical methods able to analyze charge heterogeneity as a critical quality attribute (CQA), in compliance with current regulatory expectations. A notorious example is glatiramer acetate (GA), a complex polypeptide mixture useful for the treatment of relapsing-remitting multiple sclerosis. This pharmaceutical challenges the current state of analytical technology in terms of the capacity to study their constituent species. Thus, a strong cation exchange methodology was designed under the lifecycle approach to support the establishment of GA identity, trough the evaluation of its chromatographic profile, which acts as a charge heterogeneity fingerprint. In this regard, a maximum relative margin of error of 5% for relative retention time and symmetry factor were proposed for the analytical target profile. The methodology met the proposed requirements after precision and specificity tests results, the former comprised of sensitivity and selectivity. Subsequently, method validation was conducted and showed that the method is able to differentiate between intact GA and heterogeneity profiles coming from stressed, fractioned or process-modified samples. In summary, these results provide evidence that the method is adequate to assess charge heterogeneity as a CQA of this complex pharmaceutical.

  18. The velocity dependence of X-ray emission due to Charge Exchange in the Cygnus Loop

    NASA Astrophysics Data System (ADS)

    Cumbee, Renata; Lyons, David; Mullen, Patrick Dean; Shelton, Robin L.; Stancil, Phillip C.; Schultz, David R.

    2016-01-01

    The fundamental collisional process of charge exchange (CX) has been been established as a primary source of X-ray emission from the heliosphere [1], planetary exospheres [2], and supernova remnants [3,4]. In this process, X-ray emission results from the capture of an electron by a highly charged ion from a neutral atom or molecule, to form a highly-excited, high charge state ion. As the captured electron cascades down to the lowest energy level, photons are emitted, including X-rays.To provide reliable CX-induced X-ray spectral models to realistically simulate these environments, line ratios and spectra are computed using theoretical CX cross-sections obtained with the multi-channel Landau-Zener, atomic-orbital close-coupling, and classical-trajectory Monte Carlo methods for various collisional velocities relevant to astrophysics for collisions of bare and H-like C to Al ions with H, He, and H2. Using these line ratios, XSPEC models of CX emission in the northeast rim of the Cygnus Loop supernova remnant will be shown as an example with ion velocity dependence.[1] Henley, D. B. & Shelton, R. L. 2010, ApJSS, 187, 388[2] Dennerl, K. et al. 2002, A&A 386, 319[3] Katsuda, S. et al. 2011, ApJ 730 24[4] Cumbee, R. S. et al. 2014, ApJ 787 L31This work was partially supported by NASA grant NNX09AC46G.

  19. Supervisors' upward exchange relationships and subordinate outcomes: testing the multilevel mediation role of empowerment.

    PubMed

    Zhou, Le; Wang, Mo; Chen, Gilad; Shi, Junqi

    2012-05-01

    This study empirically examined the proposition that supervisors' exchange relationships with their own supervisors (i.e., leader-leader exchange, or LLX) are related to their subordinates' work-related outcomes through 3 mechanisms: (a) leaders modeling their LLX to develop and maintain their exchange relationships with their subordinates (i.e., leader-member exchange, or LMX), (b) motivating the team and its members, captured by team and individual empowerment, and (c) facilitating the relationships between LMX and individual outcomes. Analyses of multisource and lagged data from 104 team supervisors and 577 subordinates showed that LMX mediated the positive relationship of LLX on subordinates' individual empowerment. Furthermore, team empowerment and individual empowerment sequentially mediated the positive relationships between LLX and subordinates' job satisfaction and job performance. The authors also found that the indirect relationships of LMX with job satisfaction and job performance via individual empowerment were stronger when LLX was higher. Theoretical and practical implications of these findings are discussed.

  20. X-Ray Emission Cross Sections following Charge Exchange by Multiply-Charged Ions of Astrophysical Interest

    NASA Astrophysics Data System (ADS)

    Olson, Ronald

    2006-05-01

    State selective nl-electron capture cross sections are presented for highly charged ions with Z = 6-10 colliding with molecules. The energy range investigated was from 1 eV/amu (v = 1.4x10^6 cm/s) to 100 keV/amu (v = 4.4x10^8 cm/s). The K-shell x-ray emission cross sections are determined by using the calculated state-selective electron capture results as input and then applying the branching and cascading values for the photon emission. A major shift in the line emission from being almost solely Lyman-alpha transitions at the highest collisions energies to strong high-n to 1s transitions at the lowest energies is observed. The calculated emission cross sections are in reasonable accord with measurements made by Greenwood et al^1 for O^8+ and Ne^10+ on various targets at 3 keV/amu. The calculations are also in accord with x-ray emission cross section data obtained on the EBIT machine at LLNL where O^8+ and Ne^10+ high resolution measurements were made at a temperature of 10 eV/amu for a series of targets with varying ionization potentials. The Ne^10+ data clearly show the contribution from multiple capture followed by Auger autoionization in the line emission spectra. Our calculated line emission cross sections are used to provide an ab initio determination of the soft x-ray spectrum of comet C/Linear 1999 S4 that was observed on the Chandra X-ray Observatory. The calculations reproduce the measured spectrum and show that it is due to charge exchange of the neutral gases in the comet's coma with the ions of the slow solar wind. Details of the calculations are presented in a recent paper by Otranto et al^2. 1. J. B. Greenwood, I. D. Williams, S. J. Smith and A. Chutjian, Phys. Rev. A 63, 062707 (2001). 2. S. Otranto, R. E. Olson, and P. Beiersdorfer, Phys. Rev. A (in press).

  1. Role of hydrophobicity and solvent-mediated charge-charge interactions in stabilizing alpha-helices.

    PubMed Central

    Vila, J A; Ripoll, D R; Villegas, M E; Vorobjev, Y N; Scheraga, H A

    1998-01-01

    A theoretical study to identify the conformational preferences of lysine-based oligopeptides has been carried out. The solvation free energy and free energy of ionization of the oligopeptides have been calculated by using a fast multigrid boundary element method that considers the coupling between the conformation of the molecule and the ionization equilibria explicitly, at a given pH value. It has been found experimentally that isolated alanine and lysine residues have somewhat small intrinsic helix-forming tendencies; however, results from these simulations indicate that conformations containing right-handed alpha-helical turns are energetically favorable at low values of pH for lysine-based oligopeptides. Also, unusual patterns of interactions among lysine side chains with large hydrophobic contacts and close proximity (5-6 A) between charged NH3+ groups are observed. Similar arrangements of charged groups have been seen for lysine and arginine residues in experimentally determined structures of proteins available from the Protein Data Bank. The lowest-free-energy conformation of the sequence Ac-(LYS)6-NMe from these simulations showed large pKalpha shifts for some of the NH3+ groups of the lysine residues. Such large effects are not observed in the lowest-energy conformations of oligopeptide sequences with two, three, or four lysine residues. Calculations on the sequence Ac-LYS-(ALA)4-LYS-NMe also reveal low-energy alpha-helical conformations with interactions of one of the LYS side chains with the helix backbone in an arrangement quite similar to the one described recently by (Proc. Natl. Acad. Sci. U.S.A. 93:4025-4029). The results of this study provide a sound basis with which to discuss the nature of the interactions, such as hydrophobicity, charge-charge interaction, and solvent polarization effects, that stabilize right-handed alpha-helical conformations. PMID:9826588

  2. The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions

    SciTech Connect

    Krinichnyi, V. I. Yudanova, E. I.; Denisov, N. N.

    2014-07-28

    Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′, 3′-benzothiadiazole)]:-[6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PCDTBT:PC{sub 61}BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix.

  3. Scrape-off layer modeling with kinetic or diffusion description of charge-exchange atoms

    NASA Astrophysics Data System (ADS)

    Tokar, M. Z.

    2016-12-01

    Hydrogen isotope atoms, generated by charge-exchange (c-x) of neutral particles recycling from the first wall of a fusion reactor, are described either kinetically or in a diffusion approximation. In a one-dimensional (1-D) geometry, kinetic calculations are accelerated enormously by applying an approximate pass method for the assessment of integrals in the velocity space. This permits to perform an exhaustive comparison of calculations done with both approaches. The diffusion approximation is deduced directly from the velocity distribution function of c-x atoms in the limit of charge-exchanges with ions occurring much more frequently than ionization by electrons. The profiles across the flux surfaces of the plasma parameters averaged along the main part of the scrape-off layer (SOL), beyond the X-point and divertor regions, are calculated from the one-dimensional equations where parallel flows of charged particles and energy towards the divertor are taken into account as additional loss terms. It is demonstrated that the heat losses can be firmly estimated from the SOL averaged parameters only; for the particle loss the conditions in the divertor are of importance and the sensitivity of the results to the so-called "divertor impact factor" is investigated. The coupled 1-D models for neutral and charged species, with c-x atoms described either kinetically or in the diffusion approximation, are applied to assess the SOL conditions in a fusion reactor, with the input parameters from the European DEMO project. It is shown that the diffusion approximation provides practically the same profiles across the flux surfaces for the plasma density, electron, and ion temperatures, as those obtained with the kinetic description for c-x atoms. The main difference between the two approaches is observed in the characteristics of these species themselves. In particular, their energy flux onto the wall is underestimated in calculations with the diffusion approximation by 20 % - 30

  4. Rapid biologically mediated oxygen isotope exchange between water and phosphate

    NASA Astrophysics Data System (ADS)

    Paytan, Adina; Kolodny, Yehoshua; Neori, Amir; Luz, Boaz

    2002-03-01

    In order to better constrain the rate of oxygen isotope exchange between water and phosphate via biochemical reactions a set of controlled experiments were conducted in 1988 at the Aquaculture Plant in Elat, Israel. Different species of algae and other organisms were grown in seawater tanks under controlled conditions, and the water temperature and oxygen isotopic composition (δ18Ow) were monitored. The oxygen isotopic composition of phosphate (δ18Op) in the organisms' food source, tissues, and the δ18Op of dissolved inorganic phosphate (DIP) were measured at different stages of the experiments. Results indicate that intracellular oxygen isotope exchange between phosphorus compounds and water is very rapid and occurs at all levels of the food chain. Through these reactions the soft tissue δ18Op values become 23-26‰ higher than δ18Ow, and δ18Op values of DIP become ~20‰ higher than δ18Ow. No correlation between δ18Op values and either temperature or P concentrations in these experiments was observed. Our data imply that biogenic recycling and intracellular phosphorus turnover, which involves kinetic fractionation effects, are the major parameters controlling the δ18Op values of P compounds dissolved in aquatic systems. This information is fundamental to any application of δ18Op of dissolved organic or inorganic phosphate to quantify the dynamics of phosphorus cycling in aquatic systems.

  5. High resolution main-ion charge exchange spectroscopy in the DIII-D H-mode pedestal

    SciTech Connect

    Grierson, B. A.; Burrell, K. H.; Chrystal, C.; Groebner, R. J.; Haskey, S. R.; Kaplan, D. H.

    2016-09-12

    A new high spatial resolution main-ion (deuterium) charge-exchange spectroscopy system covering the tokamak boundary region has been installed on the DIII-D tokamak. Sixteen new edge main-ion charge-exchange recombination sightlines have been combined with nineteen impurity sightlines in a tangentially viewing geometry on the DIII-D midplane with an interleaving design that achieves 8 mm inter-channel radial resolution for detailed profiles of main-ion temperature, velocity, charge-exchange emission, and neutral beam emission. At the plasma boundary, we find a strong enhancement of the main-ion toroidal velocity that exceeds the impurity velocity by a factor of two. Furthermore, the unique combination of experimentally measured main-ion and impurity profiles provides a powerful quasi-neutrality constraint for reconstruction of tokamak H-mode pedestals.

  6. High resolution main-ion charge exchange spectroscopy in the DIII-D H-mode pedestal

    NASA Astrophysics Data System (ADS)

    Grierson, B. A.; Burrell, K. H.; Chrystal, C.; Groebner, R. J.; Haskey, S. R.; Kaplan, D. H.

    2016-11-01

    A new high spatial resolution main-ion (deuterium) charge-exchange spectroscopy system covering the tokamak boundary region has been installed on the DIII-D tokamak. Sixteen new edge main-ion charge-exchange recombination sightlines have been combined with nineteen impurity sightlines in a tangentially viewing geometry on the DIII-D midplane with an interleaving design that achieves 8 mm inter-channel radial resolution for detailed profiles of main-ion temperature, velocity, charge-exchange emission, and neutral beam emission. At the plasma boundary, we find a strong enhancement of the main-ion toroidal velocity that exceeds the impurity velocity by a factor of two. The unique combination of experimentally measured main-ion and impurity profiles provides a powerful quasi-neutrality constraint for reconstruction of tokamak H-mode pedestals.

  7. High resolution main-ion charge exchange spectroscopy in the DIII-D H-mode pedestal

    DOE PAGES

    Grierson, B. A.; Burrell, K. H.; Chrystal, C.; ...

    2016-09-12

    A new high spatial resolution main-ion (deuterium) charge-exchange spectroscopy system covering the tokamak boundary region has been installed on the DIII-D tokamak. Sixteen new edge main-ion charge-exchange recombination sightlines have been combined with nineteen impurity sightlines in a tangentially viewing geometry on the DIII-D midplane with an interleaving design that achieves 8 mm inter-channel radial resolution for detailed profiles of main-ion temperature, velocity, charge-exchange emission, and neutral beam emission. At the plasma boundary, we find a strong enhancement of the main-ion toroidal velocity that exceeds the impurity velocity by a factor of two. Furthermore, the unique combination of experimentally measuredmore » main-ion and impurity profiles provides a powerful quasi-neutrality constraint for reconstruction of tokamak H-mode pedestals.« less

  8. Strain-mediated multiferroic control of spontaneous exchange bias in Ni-NiO heterostructures

    NASA Astrophysics Data System (ADS)

    Domann, John P.; Sun, Wei-Yang; Schelhas, Laura T.; Carman, Greg P.

    2016-10-01

    This paper presents the measurement of strain-mediated multiferroic control of spontaneous exchange bias (SEB) in magnetostrictive nickel/nickel oxide (Ni/NiO) bilayers on ferroelectric lead magnesium niobate-lead titanate (PMN-PT). Electric field control of a positive to negative exchange bias shift was measured, with an overall shift of 40.5 Oe, corresponding to a 325% change. Observed changes in coercivity are also reported and provide insight into the role of competing anisotropies in these structures. The findings in this paper provide evidence that magnetoelastic anisotropy can be utilized to control spontaneous exchange bias (SEB). This control of SEB is accomplished by modifying a bulk anisotropy (magnetoelasticity) that adjusts the mobility of interfacial anti-ferromagnetic spins and, therefore, the magnitude of the exchange bias. The demonstrated magnetoelastic control of exchange bias provides a useful tool in the creation of future magnetoelectric devices.

  9. Tolerance of DNA Mismatches in Dmc1 Recombinase-mediated DNA Strand Exchange.

    PubMed

    Borgogno, María V; Monti, Mariela R; Zhao, Weixing; Sung, Patrick; Argaraña, Carlos E; Pezza, Roberto J

    2016-03-04

    Recombination between homologous chromosomes is required for the faithful meiotic segregation of chromosomes and leads to the generation of genetic diversity. The conserved meiosis-specific Dmc1 recombinase catalyzes homologous recombination triggered by DNA double strand breaks through the exchange of parental DNA sequences. Although providing an efficient rate of DNA strand exchange between polymorphic alleles, Dmc1 must also guard against recombination between divergent sequences. How DNA mismatches affect Dmc1-mediated DNA strand exchange is not understood. We have used fluorescence resonance energy transfer to study the mechanism of Dmc1-mediated strand exchange between DNA oligonucleotides with different degrees of heterology. The efficiency of strand exchange is highly sensitive to the location, type, and distribution of mismatches. Mismatches near the 3' end of the initiating DNA strand have a small effect, whereas most mismatches near the 5' end impede strand exchange dramatically. The Hop2-Mnd1 protein complex stimulates Dmc1-catalyzed strand exchange on homologous DNA or containing a single mismatch. We observed that Dmc1 can reject divergent DNA sequences while bypassing a few mismatches in the DNA sequence. Our findings have important implications in understanding meiotic recombination. First, Dmc1 acts as an initial barrier for heterologous recombination, with the mismatch repair system providing a second level of proofreading, to ensure that ectopic sequences are not recombined. Second, Dmc1 stepping over infrequent mismatches is likely critical for allowing recombination between the polymorphic sequences of homologous chromosomes, thus contributing to gene conversion and genetic diversity.

  10. High-resolution Studies of Charge Exchange in Supernova Remnants with Magellan, XMM-Newton, and Micro-X

    NASA Astrophysics Data System (ADS)

    Heine, Sarah N.; Figueroa-Feliciano, Enectali; Castro, Daniel

    2015-01-01

    Charge exchange, the semi-resonant transfer of an electron from a neutral atom to an excited state in an energetic ion, can occur in plasmas where energetic ions are incident on a cold, at least partially neutral gas. Supernova remnants, especially in the immediate shock region, provide conditions conducive to charge exchange. The emission from post charge-exchange ions as the captured electron cascades down to the ground state, can shed light on the physical conditions of the shock and the immediate post-shock material, providing an important tool to understanding supernova explosions and their aftermath.I present a study of charge exchange in the galactic supernova remnant G296.1-0.5 in two bands: the optical and the X-ray. The optical study, performed using both imaging and spectroscopy from the IMACS instrument on the Magellan Baade Telescope at Las Companas Observatory, seeks to identify `Balmer-dominated shocks' in the remnant, which occur when charge exchange occurs between hot, post-shock protons and colder neutral hydrogen in the environment. The X-ray study probes line ratios in dispersed spectral data obtained with XMM-Newton RGS from an X-ray lobe in the NW of the remnant to hunt for signatures of charge exchange. The dispersed data are degraded by the extended nature of the source, blending many of the lines.We are working towards the future of spectroscopic studies in the X-ray for such extended sources with Micro-X: a sounding rocket-borne, high energy resolution X-ray telescope, utilizing an array of microcalorimeters to achieve high energy resolution for extended sources. I describe the design and commissioning of the payload and the steps toward launch, which is anticipated in the summer of 2015.

  11. Production of vibrationally excited H(2)O from charge exchange of H(3)O(+) with cesium.

    PubMed

    Mann, Jennifer E; Xie, Zhen; Savee, John D; Bowman, Joel M; Continetti, Robert E

    2009-01-28

    The center-of-mass kinetic energy release for the dissociation of H(3)O following charge exchange of H(3)O(+) with cesium has been studied experimentally and modeled using quasiclassical trajectory calculations based on an ab initio potential energy surface for H(3)O(+) and "direct dynamics" for H(3)O. Branching fractions for the H(2)O+H and OH+H(2) dissociation channels have been measured and compared to the calculations. The dominant channel is found to be H(2)O+H and the experimental kinetic energy release spectrum reveals that H(2)O is formed with a vibrational inversion in stretching vibrations, coupled with low bending and rotational excitation.

  12. Observation of Solar Wind Charge Exchange Emission from Exospheric Material in and Outside Earth's Magnetosheath

    NASA Technical Reports Server (NTRS)

    Snowden, S. L.; Collier, M. R.; Cravens, T.; Kuntz, K. D.; Lepri, S. T.; Robertson, I.; Tomas, L.

    2008-01-01

    A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth s magnetosheath. The light curve of the O VII (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.36). The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

  13. Charge-exchange QRPA with the Gogny Force for Axially-symmetric Deformed Nuclei

    SciTech Connect

    Martini, M.; Goriely, S.; Péru, S.

    2014-06-15

    In recent years fully consistent quasiparticle random-phase approximation (QRPA) calculations using finite range Gogny force have been performed to study electromagnetic excitations of several axially-symmetric deformed nuclei up to the {sup 238}U. Here we present the extension of this approach to the charge-exchange nuclear excitations (pnQRPA). In particular we focus on the Isobaric Analog and Gamow-Teller resonances. A comparison of the predicted GT strength distribution with existing experimental data is presented. The role of nuclear deformation is shown. Special attention is paid to β-decay half-lives calculations for which experimental data exist and for specific isotone chains of relevance for the r-process nucleosynthesis.

  14. Inference of the ring current ion composition by means of charge exchange decay

    NASA Technical Reports Server (NTRS)

    Smith, P. H.; Bewtra, N. K.; Hoffman, R. A.

    1978-01-01

    The analysis of the measured ion fluxes during the several day storm recovery period and the assumption that beside hydrogen other ions were present and that the decays were exponential in nature, it was possible to establish three separate lifetimes for the ions. These fitted decay lifetimes are in excellent agreement with the expected charge exchange decay lifetimes for H(+), O(+), and He(+) in the energy and L-value range of the data. This inference technique, thus, establishes the presence of measurable and appreciable quantities of oxygen and helium ions as well as protons in the storm-time ring current. Indications that He(+) may also be present under these same conditions were found.

  15. Corrections to charge exchange spectroscopic measurements in TFTR due to energy-dependent excitation rates

    SciTech Connect

    Howell, R.B.; Fonck, R.J.; Knize, R.J.; Jaehnig, K.P.

    1988-08-01

    The use of charge exchange spectrocopy to determine plasma rotation speeds and ion temperature is complicated by the energy dependence of the excitation cross sections. The Doppler-broadened spectral line shape is distorted by the relative velocity between the neutral hydrogen atoms of the injected beam and impurity ions. The asymmetric nature of the energy dependence of this cross section causes a non-motional shift of the line center and a non-thermal change in the line width. These effects vary with the angles between the beam direction, rotation velocity direction, and direction of the viewing sightline. When viewing two neutral beams at different angles on TFTR, the two measurements of v/sub phi/(r) show discrepancies about 20 to 30% with each other. The calculation of the spectral intensity profiles, using the excitation rates available, overcorrects these discrepancies and indicates the need for better excitation coefficients. 10 refs., 5 figs.

  16. Scaling for state-selective charge exchange due to collisions of multicharged ions with hydrogen

    NASA Astrophysics Data System (ADS)

    Jorge, A.; Illescas, Clara; Miraglia, J. E.; Gravielle, M. S.

    2015-12-01

    In this article we evaluate state-resolved charge exchange cross sections for Be{}4+, {{{B}}}5+, {{{C}}}6+, {{{N}}}7+, and {{{O}}}8+ projectiles colliding with atomic hydrogen employing two different methods: the classical trajectory Monte Carlo and the eikonal impulse approximations. These cross sections are used to extend previously derived scaling laws for n-, nl-, and nlm-distributions to highly excited final levels with 4≤slant n≤slant 9, covering energies in the range 50-2000 {{keV}}/ amu. Present total and partial capture cross sections are in agreement with available experimental and theoretical data for these collision systems. Besides, the proposed scaling rules are also verified by other theories, becoming a useful instrument for plasma research.

  17. Scaling for state-selective charge exchange due to collisions of multicharged ions with hydrogen

    NASA Astrophysics Data System (ADS)

    Jorge, A.; Illescas, Clara; Miraglia, J. E.; Gravielle, M. S.

    2014-12-01

    In this article we evaluate state-resolved charge exchange cross sections for Be{}4+, {{{B}}}5+, {{{C}}}6+, {{{N}}}7+, and {{{O}}}8+ projectiles colliding with atomic hydrogen employing two different methods: the classical trajectory Monte Carlo and the eikonal impulse approximations. These cross sections are used to extend previously derived scaling laws for n-, nl-, and nlm-distributions to highly excited final levels with 4≤slant n≤slant 9, covering energies in the range 50-2000 {{keV}}/ amu. Present total and partial capture cross sections are in agreement with available experimental and theoretical data for these collision systems. Besides, the proposed scaling rules are also verified by other theories, becoming a useful instrument for plasma research.

  18. Correlation of Resonance Charge Exchange Cross-Section Data in the Low-Energy Range

    NASA Technical Reports Server (NTRS)

    Sheldon, John W.

    1962-01-01

    During the course of a literature survey concerning resonance charge exchange, an unusual degree of agreement was noted between an extrapolation of the data reported by Kushnir, Palyukh, and Sena and the data reported by Ziegler. The data of Kushnir et al. are for ion-atom relative energies from 10 to 1000 ev, while the data of Ziegler are for a relative energy of about 1 ev. Extrapolation of the data of Kushnir et al. was made in accordance with Holstein's theory, 3 which is a combination of time-dependent perturbation methods and classical orbit theory. The results of this theory may be discussed in terms of a critical impact parameter b(sub c).

  19. Development of the charge exchange recombination spectroscopy and the beam emission spectroscopy on the EAST tokamak

    SciTech Connect

    Li, Y. Y.; Fu, J.; Lyu, B.; Du, X. W.; Li, C. Y.; Yu, Y.; Wang, Q. P.; Zhang, Y.; Yin, X. H.; Ye, M. Y.; Wan, B. N.; Hellermann, M. von; Shi, Y. J.

    2014-11-15

    Charge eXchange Recombination Spectroscopy (CXRS) and Beam Emission Spectroscopy (BES) diagnostics based on a heating neutral beam have recently been installed on EAST to provide local measurements of ion temperature, velocity, and density. The system design features common light collection optics for CXRS and BES, background channels for the toroidal views, multi-chord viewing sightlines, and high throughput lens-based spectrometers with good signal to noise ratio for high time resolution measurements. Additionally, two spectrometers each has a tunable grating to observe any wavelength of interest are used for the CXRS and one utilizes a fixed-wavelength grating to achieve higher diffraction efficiency for the BES system. A real-time wavelength correction is implemented to achieve a high-accuracy wavelength calibration. Alignment and calibration are performed. Initial performance test results are presented.

  20. PLASMA INSTABILITIES AS A RESULT OF CHARGE EXCHANGE IN THE DOWNSTREAM REGION OF SUPERNOVA REMNANT SHOCKS

    SciTech Connect

    Ohira, Yutaka; Takahara, Fumio; Terasawa, Toshio

    2009-09-20

    Halpha emission from supernova remnants (SNRs) implies the existence of neutral hydrogen in the circumstellar medium. Some of the neutral particles penetrating the shock are ionized by the charge-exchange process and make a cold ion beam in the shock downstream region. We perform linear analyses of collisionless plasma instabilities between the cold beam and the hot downstream plasma. We find that, under typical SNR conditions, either the resonant instability or the Weibel instability is the most unstable. This mechanism may amplify the magnetic field to more than 100 muG and changes the shock structure. As a result, the radio spectrum and the large magnetic field can be explained, apart from the widely discussed Bell's mechanism.

  1. Charge-exchange recombination spectroscopy of the plasma ion temperature at the T-10 tokamak

    SciTech Connect

    Krupin, V. A.; Tugarinov, S. N.; Barsukov, A. G.; Dnestrovskij, A. Yu.; Klyuchnikov, L. A.; Korobov, K. V.; Krasnyanskii, S. A.; Naumenko, N. N.; Nemets, A. R.; Sushkov, A. V.; Tilinin, G. N.

    2013-08-15

    Charge-exchange recombination spectroscopy (CXRS) based on a diagnostic neutral beam has been developed at the T-10 tokamak. The diagnostics allows one to measure the ion temperature profile in the cross section of the plasma column. In T-10 experiments, the measurement technique was adjusted and the elements of the CXRS diagnostics for ITER were tested. The used spectroscopic equipment makes it possible to reliably determine the ion temperature from the Doppler broadening of impurity lines (helium, carbon), as well as of the spectral lines of the working gas. The profiles of the plasma ion temperature in deuterium and helium discharges were measured at different plasma currents and densities, including with the use of active Doppler measurements of lines of different elements. The validity and reliability of ion temperature measurements performed by means of the developed CXRS diagnostics are analyzed.

  2. Cobalt(II) and Nickel(II) Transfer through Charged Polysulfonated Cation Exchange Membranes.

    PubMed

    Ersoz; Kara

    2000-12-15

    The transport of Co(II) and Ni(II) ions through charged polysulfonated ion exchange membranes under Donnan dialysis conditions has been studied as a function of pH gradient at 25 degrees C. In the Donnan dialysis process, the membrane is bounded by two electrolyte solutions, the one side (donor phase) initially containing metal salts and the other H(2)SO(4) with no external potential field applied. The transport of metal ions through membranes was correlated with the flux data as well as with estimated diffusion coefficients and was found to depend on the interaction between the fixed groups in the membrane and the metal ions. It was observed that the pH gradient influences the transport of metals and the flux of ions increases with H ion concentration in the receiver phase. Copyright 2000 Academic Press.

  3. Spin dipole nuclear matrix elements for double beta decay nuclei by charge-exchange reactions

    NASA Astrophysics Data System (ADS)

    Ejiri, H.; Frekers, D.

    2016-11-01

    Spin dipole (SD) strengths for double beta-decay (DBD) nuclei were studied experimentally for the first time by using measured cross sections of (3He, t) charge-exchange reactions (CERs). Then SD nuclear matrix elements (NMEs) {M}α ({{SD}}) for low-lying 2- states were derived from the experimental SD strengths by referring to the experimental α = GT (Gamow-Teller) and α = F (Fermi) strengths. They are consistent with the empirical NMEs M({{SD}}) based on the quasi-particle model with the empirical effective SD coupling constant. The CERs are used to evaluate the SD NME, which is associated with one of the major components of the neutrino-less DBD NME.

  4. Design of charge exchange recombination spectroscopy for the joint Texas experimental tokamak.

    PubMed

    Chi, Y; Zhuang, G; Cheng, Z F; Hou, S Y; Cheng, C; Li, Z; Wang, J R; Wang, Z J

    2014-11-01

    The old diagnostic neutral beam injector first operated at the University of Texas at Austin is ready for rejoining the joint Texas experimental tokamak (J-TEXT). A new set of high voltage power supplies has been equipped and there is no limitation for beam modulation or beam pulse duration henceforth. Based on the spectra of fully striped impurity ions induced by the diagnostic beam the design work for toroidal charge exchange recombination spectroscopy (CXRS) system is presented. The 529 nm carbon VI (n = 8 - 7 transition) line seems to be the best choice for ion temperature and plasma rotation measurements and the considered hardware is listed. The design work of the toroidal CXRS system is guided by essential simulation of expected spectral results under the J-TEXT tokamak operation conditions.

  5. Design of charge exchange recombination spectroscopy for the joint Texas experimental tokamak

    SciTech Connect

    Chi, Y.; Zhuang, G. Cheng, Z. F.; Hou, S. Y.; Cheng, C.; Li, Z.; Wang, J. R.; Wang, Z. J.

    2014-11-15

    The old diagnostic neutral beam injector first operated at the University of Texas at Austin is ready for rejoining the joint Texas experimental tokamak (J-TEXT). A new set of high voltage power supplies has been equipped and there is no limitation for beam modulation or beam pulse duration henceforth. Based on the spectra of fully striped impurity ions induced by the diagnostic beam the design work for toroidal charge exchange recombination spectroscopy (CXRS) system is presented. The 529 nm carbon VI (n = 8 − 7 transition) line seems to be the best choice for ion temperature and plasma rotation measurements and the considered hardware is listed. The design work of the toroidal CXRS system is guided by essential simulation of expected spectral results under the J-TEXT tokamak operation conditions.

  6. Design of charge exchange recombination spectroscopy for the joint Texas experimental tokamaka)

    NASA Astrophysics Data System (ADS)

    Chi, Y.; Zhuang, G.; Cheng, Z. F.; Hou, S. Y.; Cheng, C.; Li, Z.; Wang, J. R.; Wang, Z. J.

    2014-11-01

    The old diagnostic neutral beam injector first operated at the University of Texas at Austin is ready for rejoining the joint Texas experimental tokamak (J-TEXT). A new set of high voltage power supplies has been equipped and there is no limitation for beam modulation or beam pulse duration henceforth. Based on the spectra of fully striped impurity ions induced by the diagnostic beam the design work for toroidal charge exchange recombination spectroscopy (CXRS) system is presented. The 529 nm carbon VI (n = 8 - 7 transition) line seems to be the best choice for ion temperature and plasma rotation measurements and the considered hardware is listed. The design work of the toroidal CXRS system is guided by essential simulation of expected spectral results under the J-TEXT tokamak operation conditions.

  7. Localized description of surface energy gap effects in the resonant charge exchange between atoms and surfaces.

    PubMed

    Iglesias-García, A; García, Evelina A; Goldberg, E C

    2011-02-02

    The resonant charge exchange between atoms and surfaces is described by considering a localized atomistic view of the solid within the Anderson model. The presence of a surface energy gap is treated within a simplified tight-binding model of the solid, and a proper calculation of the Hamiltonian terms based on a LCAO expansion of the solid eigenstates is performed. It is found that interference terms jointly with a surface projected gap maximum at the Γ point and the Fermi level inside it, lead to hybridization widths negligible around the Fermi level. This result can explain experimental observations related to long-lived adsorbate states and anomalous neutral fractions of low energy ions in alkali/Cu(111) systems.

  8. Charge exchange and cluster formation in an rf Paul trap: interaction of alkali atoms with C +60

    NASA Astrophysics Data System (ADS)

    Pollack, Stuart; Cameron, Douglas; Rokni, Mordechai; Hill, Winfield; Parks, J. H.

    1996-06-01

    A Paul ion trap was used to study the formation of clusters under controlled temperature and pressure conditions. Exposure of cold C +60 ions to Li flux leads to the formation of Li nC +60 clusters ( n = 1-18) occurring by the sequential association of Li atoms. Cluster formation dependence on He pressure displayed a competition between vibrational relaxation and unimolecular dissociation. Collisions with Na, K, Rb and Cs atoms resulted in dissociative charge exchange. Decay rates of C +60 ions resulting from these low-energy charge exchange collisions were consistent with Langevin capture rates.

  9. What can be Learned from X-ray Spectroscopy Concerning Hot Gas in Local Bubble and Charge Exchange Processes?

    NASA Technical Reports Server (NTRS)

    Snowden, Steve

    2007-01-01

    What can be learned from x-ray spectroscopy in observing hot gas in local bubble and charge exchange processes depends on spectral resolution, instrumental grasp, instrumental energy band, signal-to-nose, field of view, angular resolution and observatory location. Early attempts at x-ray spectroscopy include ROSAT; more recently, astronomers have used diffuse x-ray spectrometers, XMM Newton, sounding rocket calorimeters, and Suzaku. Future observations are expected with calorimeters on the Spectrum Roentgen Gamma mission, and the Solar Wind Charge Exchange (SWCX). The Geospheric SWCX may provide remote sensing of the solar wind and magnetosheath and remote observations of solar CMEs moving outward from the sun.

  10. Cyclooxygenase Isoform Exchange Blocks Brain-Mediated Inflammatory Symptoms

    PubMed Central

    Mirrasekhian, Elahe; Zajdel, Joanna; Kumar Singh, Anand; Engblom, David

    2016-01-01

    Cyclooxygenase-2 (COX-2) is the main source of inducible prostaglandin E2 production and mediates inflammatory symptoms including fever, loss of appetite and hyperalgesia. COX-1 is dispensable for fever, anorexia and hyperalgesia but is important for several other functions both under basal conditions and during inflammation. The differential functionality of the COX isoforms could be due to differences in the regulatory regions of the genes, leading to different expression patterns, or to differences in the coding sequence, resulting in distinct functional properties of the proteins. To study the molecular underpinnings of the functional differences between the two isoforms in the context of inflammatory symptoms, we used mice in which the coding sequence of COX-2 was replaced by the corresponding sequence of COX-1. In these mice, COX-1 mRNA was induced by inflammation but COX-1 protein expression did not fully mimic inflammation-induced COX-2 expression. Just like mice globally lacking COX-2, these mice showed a complete lack of fever and inflammation-induced anorexia as well as an impaired response to inflammatory pain. However, as previously reported, they displayed close to normal survival rates, which contrasts to the high fetal mortality in COX-2 knockout mice. This shows that the COX activity generated from the hybrid gene was strong enough to allow survival but not strong enough to mediate the inflammatory symptoms studied, making the line an interesting alternative to COX-2 knockouts for the study of inflammation. Our results also show that the functional differences between COX-1 and COX-2 in the context of inflammatory symptoms are not only dependent on the features of the promoter regions. Instead they indicate that there are fundamental differences between the isoforms at translational or posttranslational levels. PMID:27861574

  11. Scaling of submonolayer island growth with reversible adatom exchange in surfactant-mediated epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Daimu; Wang, Zhuping; Zhu, Hui

    2007-08-01

    Surfactant-mediated epitaxial growth is studied with a realistic model, which includes three main kinetic processes: diffusion of adatoms on the surfactant terrace, exchange of adatoms with their underneath surfactant atoms, and reexchange in which an exchanged adatom resurfaces to the top of the surfactant layer. The scaling behavior of nucleus density and island size distributions in the initial stage of growth is investigated by using kinetic Monte Carlo simulations. The results show that the temperature dependence of nucleus density and island size distributions governed by the reexchanging-controlled nucleation at high temperatures exhibits similar scaling behavior to that obtained by the standard diffusion-mediated nucleation at low temperatures. However, at intermediate temperatures, the exchanging-controlled nucleation leads to an increase of nucleus density with temperature, while the island size distribution scales to a monotonically decreasing function, showing nonstandard scaling behavior.

  12. Temperature dependence of the rate coefficient for charge exchange of metastable O/+//2D/ with N2. [in atmosphere

    NASA Technical Reports Server (NTRS)

    Torr, M. R.; Torr, D. G.

    1980-01-01

    Using a data base of aeronomical parameters measured on board the Atmosphere Explorer-C satellite, temperature dependence of the reaction rate coefficient is deduced for the charge exchange of O(+)(2D) with N2. The results indicate the Explorer values determined over the temperature range from 700 to 1900 K are not in conflict with laboratory measurements made at higher temperatures.

  13. Synthesis and mannose receptor-mediated uptake of clustered glycomimetics by human dendritic cells: effect of charge.

    PubMed

    Angyalosi, Gerhild; Grandjean, Cyrille; Lamirand, Mélanie; Auriault, Claude; Gras-Masse, Hélène; Melnyk, Oleg

    2002-10-07

    Effect of charge and shape of multivalent lysine-based cluster glycomimetics on their mannose receptor-mediated uptake by human dendritic cells has been evaluated: The capture is strongly affected by the shape of the ligands. The effect of charge is less pronounced although positive charges on the ligands seem to favor non-specific endocytosis capture.

  14. Observation and modeling of geocoronal charge exchange X-ray emission during solar wind gusts

    SciTech Connect

    Wargelin, B. J.; Kornbleuth, M.; Juda, M.; Martin, P. L.

    2014-11-20

    Solar wind charge exchange (SWCX) X-rays are emitted when highly charged solar wind ions such as O{sup 7{sup +}} collide with neutral gas, including the Earth's tenuous outer atmosphere (exosphere or geocorona) and hydrogen and helium from the local interstellar medium drifting through the heliosphere. This geocoronal and heliospheric emission comprises a significant and varying fraction of the soft X-ray background (SXRB) and is seen in every X-ray observation, with the intensity dependent on solar wind conditions and observation geometry. Under the right conditions, geocoronal emission can increase the apparent SXRB by roughly an order of magnitude for an hour or more. In this work, we study a dozen occasions when the near-Earth solar wind flux was exceptionally high. These gusts of wind lead to abrupt changes in SWCX X-ray emission around Earth, which may or may not be seen by X-ray observatories depending on their line of sight. Using detailed three-dimensional magnetohydrodynamical simulations of the solar wind's interaction with the Earth's magnetosphere, and element abundances and ionization states measured by ACE, we model the time-dependent brightness of major geocoronal SWCX emission lines during those gusts and compare with changes in the X-ray background measured by the Chandra X-ray Observatory. We find reasonably good agreement between model and observation, with measured geocoronal line brightnesses averaged over 1 hr of up to 136 photons s{sup –1} cm{sup –2} sr{sup –1} in the O VII Kα triplet around 564 eV.

  15. Multiproduct high-resolution monoclonal antibody charge variant separations by pH gradient ion-exchange chromatography.

    PubMed

    Farnan, Dell; Moreno, G Tony

    2009-11-01

    In the biotechnology industry, ion-exchange chromatography is widely used for profiling the charge heterogeneity of proteins, including monoclonal antibodies. Ionic strength based ion exchange separations, while having excellent resolving power and robustness, are product specific and time-consuming to develop. In the present work, a pH gradient based separation using a cation exchange column is described and shown to be a multiproduct charge sensitive separation method for monoclonal antibodies. Simple mixtures of defined buffer components were used to generate the pH-gradients that separate closely related antibody species. The form of the pH gradient was controlled and optimized by the pump as well as the buffer composition if necessary. During this work, the buffer compositions for the separation were optimized in parallel for several MAbs. The data shows that the multiproduct method is optimal for all of the MAbs studied. Operational aspects of the separation such as column chemistry, column length, and sample matrix indicate a very robust method. The pH gradient ion-exchange method is demonstrated to have significant resolving power and peak capacities far in excess of what we would expect for ionic strength elution ion-exchange. Data obtained demonstrates that the separation is relatively insensitive to column length. Direct analysis (no buffer exchange) of samples in matrixes consistent with in-process manufacturing pools is demonstrated. Such a capability is extremely useful for the high throughput evaluation of in-process and final product samples.

  16. Mechanistic modeling of ion-exchange process chromatography of charge variants of monoclonal antibody products.

    PubMed

    Kumar, Vijesh; Leweke, Samuel; von Lieres, Eric; Rathore, Anurag S

    2015-12-24

    Ion-exchange chromatography (IEX) is universally accepted as the optimal method for achieving process scale separation of charge variants of a monoclonal antibody (mAb) therapeutic. These variants are closely related to the product and a baseline separation is rarely achieved. The general practice is to fractionate the eluate from the IEX column, analyze the fractions and then pool the desired fractions to obtain the targeted composition of variants. This is, however, a very cumbersome and time consuming exercise. A mechanistic model that is capable of simulating the peak profile will be a much more elegant and effective way to make a decision on the pooling strategy. This paper proposes a mechanistic model, based on the general rate model, to predict elution peak profile for separation of the main product from its variants. The proposed approach uses inverse fit of process scale chromatogram for estimation of model parameters using the initial values that are obtained from theoretical correlations. The packed bed column has been modeled along with the chromatographic system consisting of the mixer, tubing and detectors as a series of dispersed plug flow and continuous stirred tank reactors. The model uses loading ranges starting at 25% to a maximum of 70% of the loading capacity and hence is applicable to process scale separations. Langmuir model has been extended to include the effects of salt concentration and temperature on the model parameters. The extended Langmuir model that has been proposed uses one less parameter than the SMA model and this results in a significant ease of estimating the model parameters from inverse fitting. The proposed model has been validated with experimental data and has been shown to successfully predict peak profile for a range of load capacities (15-28mg/mL), gradient lengths (10-30CV), bed heights (6-20cm), and for three different resins with good accuracy (as measured by estimation of residuals). The model has been also

  17. The loss rates of O{sup +} in the inner magnetosphere caused by both magnetic field line curvature scattering and charge exchange reactions

    SciTech Connect

    Ji, Y.; Shen, C.

    2014-03-15

    With consideration of magnetic field line curvature (FLC) pitch angle scattering and charge exchange reactions, the O{sup +} (>300 keV) in the inner magnetosphere loss rates are investigated by using an eigenfunction analysis. The FLC scattering provides a mechanism for the ring current O{sup +} to enter the loss cone and influence the loss rates caused by charge exchange reactions. Assuming that the pitch angle change is small for each scattering event, the diffusion equation including a charge exchange term is constructed and solved; the eigenvalues of the equation are identified. The resultant loss rates of O{sup +} are approximately equal to the linear superposition of the loss rate without considering the charge exchange reactions and the loss rate associated with charge exchange reactions alone. The loss time is consistent with the observations from the early recovery phases of magnetic storms.

  18. Spectroscopic evidence of charge exchange X-ray emission from galaxies

    NASA Astrophysics Data System (ADS)

    Wang, Q. D.; Liu, J.

    2012-04-01

    What are the origins of the soft X-ray line emission from non-AGN galaxies? XMM-Newton RGS spectra of nearby non-AGN galaxies (including starforming ones: M82, NGC 253, M51, M83, M61, NGC 4631, M94, NGC 2903, and the Antennae galaxies, as well as the inner bulge of M31) have been analyzed. In particular, the K\\alpha triplet of O VII shows that the resonance line is typically weaker than the forbidden and/or inter-combination lines. This suggests that a substantial fraction of the emission may not arise directly from optically thin thermal plasma, as commonly assumed, and may instead originate at its interface with neutral gas via charge exchange. This latter origin naturally explains the observed spatial correlation of the emission with various tracers of cool gas in some of the galaxies. However, alternative scenarios, such as the resonance scattering by the plasma and the relic photo-ionization by AGNs in the recent past, cannot be ruled out, at least in some cases, and are being examined. Such X-ray spectroscopic studies are important to the understanding of the relationship of the emission to various high-energy feedback processes in galaxies.

  19. Charge-exchange reactions and nuclear matrix elements for {beta}{beta} decay

    SciTech Connect

    Frekers, D.

    2009-11-09

    Charge-exchange reactions of (n, p) and (p, n) type at intermediate energies are a powerful tool for the study of nuclear matrix element in {beta}{beta} decay. The present paper reviews some of the most recent experiments in this context. Here, the (n, p) type reactions are realized through (d, {sup 2}He), where {sup 2}He refers to two protons in a singlet {sup 1}S{sub 0} state and where both of these are momentum analyzed and detected by the same spectrometer and detector. These reactions have been developed and performed exclusively at KVI, Groningen (NL), using an incident deuteron energy of 183 MeV. Final state resolutions of about 100 keV have routinely been available. On the other hand, the ({sup 3}He, t) reaction is of (p, n) type and was developed at the RCNP facility in Osaka (JP). Measurements with an unprecedented high resolution of 30 keV at incident energies of 420 MeV are now readily possible. Using both reaction types one can extract the Gamow-Teller transition strengths B(GT{sup +}) and B(GT{sup -}), which define the two ''legs'' of the {beta}{beta} decay matrix elements for the 2v{beta}{beta} decay The high resolution available in both reactions allows a detailed insight into the excitations of the intermediate odd-odd nuclei and, as will be shown, some unexpected features are being unveiled.

  20. X-ray emission from the local hot bubble and solar wind charge exchange

    NASA Astrophysics Data System (ADS)

    Uprety, Youaraj

    DXL (Diffuse X-rays from the Local galaxy) is a sounding rocket mission to quantify the Solar Wind Charge Exchange (SWCX) X-ray emission in the interplanetary medium, and separate its contribution from the Local Hot Bubble (LHB) emission. The first launch of DXL took place in December 2012. This thesis will describe the DXL instrumentation and calibrations, and discuss the results obtained. The mission uses two large area proportional counters to scan through the Helium Focusing Cone (HFC), a high helium density region in the solar system emitting excess X-rays due to SWCX. Using well determined models of the interplanetary neutral distribution and comparing the DXL results with data from the same region obtained by the ROSAT satellite away from the cone, we calculated that SWCX contributes at most 36% to the ¼ keV ROSAT band and 13% to the ¾ keV ROSAT band, in the galactic plane. This provides a firm proof for existence of a LHB which dominates the Diffuse X-ray Background (DXB) at ¼ keV, while raising new questions on the origin of the ¾ keV emission.

  1. Inference of the ring current ion composition by means of charge exchange decay

    SciTech Connect

    Smith, P.H.; Bewtra, N.K.; Hoffman, R.A.

    1981-05-01

    The analysis of data from the Explorer 45 (S/sup 3/-A) electrostatic analyzer in the energy range 5--30 keV has provided some new results of the ring current ion composition. It has been well established that the storm time ring current has a decay time of several days, during which the particle fluxes decrease nearly monotonically. In the past, ring current studies have assumed or stated that hydrogen was the dominant ion in the earth's ring current. By analyzing the measured ion fluxes during the several day storm recovery period and assuming that beside hydrogen other ions were present and that the decays were exponential in nature, we were able to establish three separate lifetimes for the ions. These fitted decay lifetimes are in excellent agreement with the expected charge exchange decay lifetimes for H/sup +/, O/sup +/, and He/sup +/ in the energy and L value of the data. This inference technique thus establishes the presence of measureable and appreciable quantities of oxygen and helium ions as well as protons in the storm time ring current; we also find indicatons that He/sup + +/ may also be present under these same conditions. The existence of additional ions is not rules out by this technique.

  2. Temperatures of individual ion species and heating due to charge exchange in the ionosphere of Venus

    NASA Technical Reports Server (NTRS)

    Kim, Jhoon; Nagy, Andrew F.; Cravens, Thomas E.; Shinagawa, Hiroyuki

    1990-01-01

    The coupled electron and multispecies ion energy equations were solved for daytime conditions in the Venus ionosphere. The heating rates due to charge exchange between hot oxygen atoms and thermal oxygen ions were calculated and incorporated into the energy equations. The combination of the traditional EUV heating and this hot oxygen energy source leads to calculated electron and individual ion temperatures significantly lower than the measured values during solar cycle maximum conditions. Calculations were also carried out for solar cycle minimum conditions, which led to considerably lower temperatures; no data are available which would allow direct comparisons of these results with measurements. In order to obtain calculated temperature values consistent with the observed ones, for solar cycle maximum conditions, topside heat inflows into the ion and electron gases have to be introduced or the thermal conductivity must be reduced by considering the effect of steady and fluctuating magnetic fields, as was done in previous studies. The addition of hot oxygen heating leads to minor increases in the calculated ion temperatures except for the case of reduced thermal conductivities. Separate temperatures were calculated for each ion species for a number of different conditions and in general the differences were found to be relatively small.

  3. Suzaku and XMM-Newton observations of the North Polar Spur: Charge exchange or ISM absorption?

    NASA Astrophysics Data System (ADS)

    Gu, Liyi; Mao, Junjie; Costantini, Elisa; Kaastra, Jelle

    2016-10-01

    By revisiting the Suzaku and XMM-Newton data of the North Polar Spur, we discovered that the spectra are inconsistent with the traditional model consisting of pure thermal emission and neutral absorption. The most prominent discrepancies are the enhanced O vii and Ne ix forbidden-to-resonance ratios, and a high O viii Lyβ line relative to other Lyman series. A collisionally ionized absorption model can naturally explain both features, while a charge exchange component can only account for the former. By including the additional ionized absorption, the plasma in the North Polar Spur can be described by a single-phase collisional ionization equilibrium (CIE) component with a temperature of 0.25 keV, and nitrogen, oxygen, neon, magnesium, and iron abundances of 0.4-0.8 solar. The abundance pattern of the North Polar Spur is well in line with those of the Galactic halo stars. The high nitrogen-to-oxygen ratio reported in previous studies can be migrated to the large transmission of the O viii Lyα line. The ionized absorber is characterized by a balance temperature of 0.17-0.20 keV and a column density of 3-5 × 1019 cm-2. Based on the derived abundances and absorption, we speculate that the North Polar Spur is a structure in the Galactic halo, so that the emission is mostly absorbed by the Galactic interstellar medium in the line of sight.

  4. On charge exchange and knock-on processes in the exosphere of Io

    NASA Technical Reports Server (NTRS)

    Ip, W.-H.

    1982-01-01

    One direct consequence of magnetospheric interaction of Io is the strong dynamical coupling of its neutral atmosphere with the corotating plasma. The absorption of the thermal ions and the associated neutral injection is an improtant issue not yet explored. As far as nonthermal escape of the neutral atmosphere is concerned, three processes stand out. That is, apart from sputtering, exospheric interactions like atom-ion knock-on collision and charge exchange recombination could be a significant source of the neutral clouds in the Jovian system. Using a current electrodynamic model of Io, both the absorption rate of the corotating thermal plasma and the production rates of new exospheric ions and the fast neutrals are considered. It is found that the source strength of the neutral atoms and molecules with speeds of about 100 km/sec could amount to 10 to the 26th/sec whereas exospheric neutrals emitted at lower speed (of about 10 km/sec) amounts to 4 x 10 to the 25th/sec. The generation of the new ions in connection with the streaming of the magnetospheric plasma around Io could also produce an asymmetric sputtering with a neutral flux of about 10 to the 27th/sec emitted from the region of Io which faces Jupiter. These results may be related to a number of sodium observations.

  5. The Relationship between Psychological Contract Breach and Organizational Commitment: Exchange Imbalance as a Moderator of the Mediating Role of Violation

    ERIC Educational Resources Information Center

    Cassar, Vincent; Briner, Rob B.

    2011-01-01

    This study tested the mediating role of violation in the relationship between breach and both affective and continuance commitment and the extent to which this mediating role is moderated by exchange imbalance amongst a sample of 103 sales personnel. Results suggest that violation mediated the relationship between breach and commitment. Also,…

  6. Evaluation of Surface State Mediated Charge Recombination in Anatase and Rutile TiO2

    PubMed Central

    2016-01-01

    In nanostructured thin films, photogenerated charge carriers can access the surface more easily than in dense films and thus react more readily. However, the high surface area of these films has also been associated with enhanced recombination losses via surface states. We herein use transient absorption spectroscopy to compare the ultrafast charge carrier kinetics in dense and nanostructured TiO2 films for its two most widely used polymorphs: anatase and rutile. We find that nanostructuring does not enhance recombination rates on ultrafast time scales, indicating that surface state mediated recombination is not a key loss pathway for either TiO2 polymorph. Rutile shows faster, and less intensity-dependent recombination than anatase, which we assign to its higher doping density. For both polymorphs, we conclude that bulk rather than surface recombination is the primary determinant of charge carrier lifetime. PMID:27564137

  7. Role stressors and job attitudes: a mediated model of leader-member exchange.

    PubMed

    Zhang, Rui-Ping; Tsingan, Li; Zhang, Long-Ping

    2013-01-01

    Workers with high levels of role stressors have been known to report low job satisfaction and high turnover intention. However, how the role stressors-job attitudes relationship is influenced by leader-member exchange has hardly been studied. This study examined the effect of leader-member exchange (leader support) on the relationship between chronic role stressors (i.e., role ambiguity and role conflict) and job attitudes (i.e., job satisfaction and turnover intention). Employees (N = 162) who enrolled in weekend psychology courses were investigated. The results showed that leader-member exchange mediated the effects of role stressors on job satisfaction and turnover intention. Implications of these results are discussed and directions for future research are suggested.

  8. Sulfate transport mediated by the mammalian anion exchangers in reconstituted proteoliposomes.

    PubMed

    Sekler, I; Lo, R S; Mastrocola, T; Kopito, R R

    1995-05-12

    The kinetic properties of sulfate transport mediated by the anion exchangers AE1 and AE2 have been examined. Microsomes isolated from HEK cells transiently overexpressing either protein were reconstituted in unilamellar, 200-600-nm diameter proteoliposomes. Transport mediated by the exchangers was monitored by loading the reconstituted proteoliposomes with the slowly transportable anion SO4(2-) using [35S]SO4(2-) as a tracer and performing [35S]SO4(2-)/SO4(2-) exchange. The following data suggest that AE1 and AE2 have been functionally reconstituted: (i) the rate of SO4(2-) transport in AE1 and AE2 containing proteoliposomes was 10-20 times higher than in proteoliposomes derived from control microsomes; (ii) the transport of SO4(2-) was strongly dependent on the presence of a trans anion; and (iii) the anion exchanger inhibitors, 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) and 4,4'-dinitrostilbene-2,2'-di-sulfonate (DIDS) totally abolished SO4(2-) transport. furthermore, DIDS inhibits SO4(2-) transport only when occluded inside the vesicles, indicating a uniform, asymmetrical, inside-out orientation of the reconstituted exchangers. The Ki values of the stilbene disulfonate compound DNDS were 2.5 and 4 microM for AE1 and AE2, respectively, suggesting that the two exchangers possess similar high affinity sites for stilbene compounds. Both AE1 and AE2 showed the same steep pH dependence of sulfate transport, which was maximal at pH 5.5 and reduced to less than 10% (of the value at pH 5.5) at pH 8.5, suggesting that an acidic residue shared by AE1 and AE2 participates in the pH regulation of sulfate transport.

  9. Protein adsorption on ion exchange resins and monoclonal antibody charge variant modulation.

    PubMed

    Guélat, Bertrand; Khalaf, Rushd; Lattuada, Marco; Costioli, Matteo; Morbidelli, Massimo

    2016-05-20

    A novel multicomponent adsorption equilibrium model for proteins on ion-exchange resins is developed on a statistical thermodynamic basis including surface coverage effects and protein-resin and protein-protein interactions. The resulting model exhibits a general competitive Langmuirian behavior and was applied to the study and optimization of the separation of monoclonal antibody charge variants on two strong cation exchangers. The model accounts explicitly for the effect of both pH and salt concentration, and its parameters can be determined in diluted conditions, that is, through physically sound assumptions, all model parameters can be obtained using solely experiments in diluted conditions, and be used to make predictions in overloaded conditions. The parameterization of the model and optimization of the separation is based on a two-step approach. First, gradient experiments in diluted conditions are undertaken in order to determine the model parameters. Based on these experiments and on information about the proteins of interest and the stationary phase used, all the model parameters can be estimated. Second, using the parameterized model, an initial Pareto optimization is undertaken where overloaded operating conditions are investigated. Experiments from this Pareto set are then used to refine the estimation of the model parameters. A second Pareto optimization can then be undertaken, this time with the refined parameters. This can be repeated until a satisfactory set of model parameters is found. This iterative approach is shown to be extremely efficient and to provide large amounts of knowledge based on only a few experiments. It is shown that due to the strong physical foundation of the model and the very low number of adjustable parameters, the number of iterations is expected to be at most two or three. Furthermore, the model based tool is improved as more experimental knowledge is provided, allowing for better estimations of the chromatographic

  10. Quantification of strain and charge co-mediated magnetoelectric coupling on ultra-thin Permalloy/PMN-PT interface.

    PubMed

    Nan, Tianxiang; Zhou, Ziyao; Liu, Ming; Yang, Xi; Gao, Yuan; Assaf, Badih A; Lin, Hwaider; Velu, Siddharth; Wang, Xinjun; Luo, Haosu; Chen, Jimmy; Akhtar, Saad; Hu, Edward; Rajiv, Rohit; Krishnan, Kavin; Sreedhar, Shalini; Heiman, Don; Howe, Brandon M; Brown, Gail J; Sun, Nian X

    2014-01-14

    Strain and charge co-mediated magnetoelectric coupling are expected in ultra-thin ferromagnetic/ferroelectric multiferroic heterostructures, which could lead to significantly enhanced magnetoelectric coupling. It is however challenging to observe the combined strain charge mediated magnetoelectric coupling, and difficult in quantitatively distinguish these two magnetoelectric coupling mechanisms. We demonstrated in this work, the quantification of the coexistence of strain and surface charge mediated magnetoelectric coupling on ultra-thin Ni0.79Fe0.21/PMN-PT interface by using a Ni0.79Fe0.21/Cu/PMN-PT heterostructure with only strain-mediated magnetoelectric coupling as a control. The NiFe/PMN-PT heterostructure exhibited a high voltage induced effective magnetic field change of 375 Oe enhanced by the surface charge at the PMN-PT interface. Without the enhancement of the charge-mediated magnetoelectric effect by inserting a Cu layer at the PMN-PT interface, the electric field modification of effective magnetic field was 202 Oe. By distinguishing the magnetoelectric coupling mechanisms, a pure surface charge modification of magnetism shows a strong correlation to polarization of PMN-PT. A non-volatile effective magnetic field change of 104 Oe was observed at zero electric field originates from the different remnant polarization state of PMN-PT. The strain and charge co-mediated magnetoelectric coupling in ultra-thin magnetic/ferroelectric heterostructures could lead to power efficient and non-volatile magnetoelectric devices with enhanced magnetoelectric coupling.

  11. Effects of exchanged cation and layer charge on the sorption of water and EGME vapors on montmorillonite clays

    USGS Publications Warehouse

    Chiou, C.T.; Rutherford, D.W.

    1997-01-01

    The effects of exchanged cation and layer charge on the sorption of water and ethylene glycol monoethyl ether (EGME) vapors on montmorillonite have been studied on SAz-1 and SWy-1 source clays, each exchanged respectively with Ca, Na, K, Cs and tetramethylammonium (TMA) cations. The corresponding lattice expansions were also determined, and the corresponding N2 adsorption data were provided for comparison. For clays exchanged with cations of low hydrating powers (such as K, Cs and TMA), water shows a notably lower uptake than does N2 at low relative pressures (P/P0). By contrast, EGME shows higher uptakes than N2 on all exchanged clays at all P/P0. The anomaly for water is attributed to its relatively low attraction for siloxane surfaces of montmorillonite because of its high cohesive energy density. In addition to solvating cations and expanding interlayers, water and EGME vapors condense into small clay pores and interlayer voids created by interlayer expansion. The initial (dry) interlayer separation varies more significantly with cation type than with layer charge; the water-saturated interlayer separation varies more with cation type than the EGME-saturated interlayer separation. Because of the differences in surface adsorption and interlayer expansion for water and EGME, no general correspondence is found between the isotherms of water and EGME on exchanged clays, nor is a simple relation observed between the overall uptake of either vapor and the cation solvating power. The excess interlayer capacities of water and of EGME that result from lattice expansion of the exchanged clays are estimated by correcting for amounts of vapor adsorption on planar clay surfaces and of vapor condensation into intrinsic clay pores. The resulting data follow more closely the relative solvating powers of the exchanged cations.

  12. Semiautomated pH gradient ion-exchange chromatography of monoclonal antibody charge variants.

    PubMed

    Talebi, Mohammad; Shellie, Robert A; Hilder, Emily F; Lacher, Nathan A; Haddad, Paul R

    2014-10-07

    A new approach using a chromatography system equipped with isocratic pumps and an electrolytic eluent generator (EG) is introduced, replacing external pH gradient delivery using conventional gradient systems, in which bottled buffers with preadjusted pH are mixed using a gradient pump. The EG is capable of generating high purity base or acid required for online preparation of the buffer at the point of use, utilizing deionized water as the only carrier stream. Typically, the buffer was generated from online titration of a reagent composed of low molecular weight amines. The reagent was delivered isocratically into a static mixing tee, where it was titrated to the required pH with electrolytically generated base or acid. The required pH gradient was thus conveniently generated by electrically controlling the concentration of titrant. Also, since the pH was adjusted at the point of use, this approach offered enhanced throughput in terms of eluent preparation time and labor, and with a more reproducible pH profile. The performance of the system was demonstrated by running pH gradients ranging from pH 8.2 to 10.9 on a polymer monolith cation-exchange column for high throughput profiling of charge heterogeneity of intact, basic therapeutic monoclonal antibodies. A high degree of flexibility in modulating the key parameters of the pH gradient, including the buffer concentration, the pH gradient slope and the operating pH range was demonstrated. This enabled fine-tuning of the separation conditions for each individual antibody in order to enhance the chromatographic resolution.

  13. Spectral modeling of the charge-exchange X-ray emission from M82

    SciTech Connect

    Zhang, Shuinai; Ji, Li; Zhou, Xin; Wang, Q. Daniel; Smith, Randall K.; Foster, Adam R.

    2014-10-10

    It has been proposed that the charge-exchange (CX) process at the interface between hot and cool interstellar gases could contribute significantly to the observed soft X-ray emission in star-forming galaxies. We analyze the XMM-Newton/reflection grating spectrometer (RGS) spectrum of M82 using a newly developed CX model combined with a single-temperature thermal plasma to characterize the volume-filling hot gas. The CX process is largely responsible for not only the strongly enhanced forbidden lines of the Kα triplets of various He-like ions but also good fractions of the Lyα transitions of C VI (∼87%), O VIII, and N VII (≳50%) as well. In total about a quarter of the X-ray flux in the RGS 6-30 Å band originates in the CX. We infer an ion incident rate of 3 × 10{sup 51} s{sup –1} undergoing CX at the hot and cool gas interface and an effective area of the interface of ∼2 × 10{sup 45} cm{sup 2} that is one order of magnitude larger than the cross section of the global biconic outflow. With the CX contribution accounted for, the best-fit temperature of the hot gas is 0.6 keV, and the metal abundances are approximately solar. We further show that the same CX/thermal plasma model also gives an excellent description of the EPIC-pn spectrum of the outflow Cap, projected at 11.6 kpc away from the galactic disk of M82. This analysis demonstrates that the CX is potentially an important contributor to the X-ray emission from starburst galaxies and also an invaluable tool to probe the interface astrophysics.

  14. Solar Wind Charge Exchange Contribution to the ROSAT All Sky Survey Maps

    NASA Astrophysics Data System (ADS)

    Uprety, Y.; Chiao, M.; Collier, M. R.; Cravens, T.; Galeazzi, M.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Lepri, S. T.; Liu, W.; McCammon, D.; Morgan, K.; Porter, F. S.; Prasai, K.; Snowden, S. L.; Thomas, N. E.; Ursino, E.; Walsh, B. M.

    2016-10-01

    DXL (Diffuse X-ray emission from the Local Galaxy) is a sounding rocket mission designed to estimate the contribution of solar wind charge eXchange (SWCX) to the diffuse X-ray background and to help determine the properties of the Local Hot Bubble. The detectors are large area thin-window proportional counters with a spectral response that is similar to that of the PSPC used in the ROSAT All Sky Survey (RASS). A direct comparison of DXL and RASS data for the same part of the sky viewed from quite different vantage points in the solar system, and the assumption of approximate isotropy for the solar wind, allowed us to quantify the SWCX contribution to all six RASS bands (R1-R7, excluding R3). We find that the SWCX contribution at l=140^\\circ ,b=0^\\circ , where the DXL path crosses the Galactic plane, is 33 % +/- 6 % ({statistical})+/- 12 % ({systematic}) for R1, 44 % +/- 6 % +/- 5 % for R2, 18 % +/- 12 % +/- 11 % for R4, 14 % +/- 11 % +/- 9 % for R5, and negligible for the R6 and R7 bands. Reliable models for the distribution of neutral H and He in the solar system permit estimation of the contribution of interplanetary SWCX emission over the the whole sky and correction of the RASS maps. We find that the average SWCX contribution in the whole sky is 26 % +/- 6 % +/- 13 % for R1, 30 % +/- 4 % +/- 4 % for R2, 8 % +/- 5 % +/- 5 % for R4, 6 % +/- 4 % +/- 4 % for R5, and negligible for R6 and R7.

  15. The TFTR E Parallel B Spectrometer for Mass and Energy Resolved Multi-Ion Charge Exchange Diagnostics

    SciTech Connect

    A.L. Roquemore; S.S. Medley

    1998-01-01

    The Charge Exchange Neutral Analyzer diagnostic for the Tokamak Fusion Test Reactor was designed to measure the energy distributions of both the thermal ions and the supra thermal populations arising from neutral-beam injection and ion cyclotron radio-frequency heating. These measurements yield the plasma ion temperature, as well as several other plasma parameters necessary to provide an understanding of the plasma condition and the performance of the auxiliary heating methods. For this application, a novel charge-exchange spectrometer using a dee-shaped region of parallel electric and magnetic fields was developed at the Princeton Plasma Physics Laboratory. The design and performance of this spectrometer is described in detail, including the effects of exposure of the microchannel plate detector to magnetic fields, neutrons, and tritium.

  16. Heavy-ion double charge exchange reactions: A tool toward 0 νββ nuclear matrix elements

    NASA Astrophysics Data System (ADS)

    Cappuzzello, F.; Cavallaro, M.; Agodi, C.; Bondì, M.; Carbone, D.; Cunsolo, A.; Foti, A.

    2015-11-01

    The knowledge of the nuclear matrix elements for the neutrinoless double beta decay is fundamental for neutrino physics. In this paper, an innovative technique to extract information on the nuclear matrix elements by measuring the cross section of a double charge exchange nuclear reaction is proposed. The basic point is that the initial- and final-state wave functions in the two processes are the same and the transition operators are similar. The double charge exchange cross sections can be factorized in a nuclear structure term containing the matrix elements and a nuclear reaction factor. First pioneering experimental results for the 40Ca(18O,18Ne)40Ar reaction at 270 MeV incident energy show that such cross section factorization reasonably holds for the crucial 0+ → 0+ transition to 40Args, at least at very forward angles.

  17. Upper-limit charge exchange cross sections for mercury (plus) on molybdenum and cesium (plus) on aluminum

    NASA Technical Reports Server (NTRS)

    Dugan, J. V., Jr.

    1972-01-01

    Upper-limit charge exchange cross sections are calculated for Hg(+) on Mo and Cs(+) on Al. The cross sections are calculated from the polarization interaction at low ion energies (1 to 500 eV) and by assuming favorable curve crossings with a hard-core reaction radius at higher energies (500 eV to 10 keV). The cross sections for Hg(+) on Mo becomes greater than corresponding Hg Hg(+) resonance values at ion energies below 2 eV, whereas the Cs(+) Al values remain considerably lower than the Cs(+)Cs resonance value at all ion energies. It is also shown that charge exchange of slow Hg(+) with Mo may be important for spacecraft with electron bombardment thrusters.

  18. Method for decomposing observed line shapes resulting from multiple causes - Application to plasma charge-exchange-neutral spectra

    NASA Technical Reports Server (NTRS)

    Patch, R. W.

    1979-01-01

    A method is given for decomposing the widths of observed spectral lines resulting from unresolved line splitting, additive kinetic processes of different types, instrumental broadening (slit function), Doppler broadening, etc. all superimposed. The second moments are used as measures of the various widths involved. The method is not applicable if dispersion type (Lorentz) broadening occurs. Application is made to plasma charge-exchange-neutral spectra of hydrogen, deuterium, and helium.

  19. High-resolution Crystal Spectroscopy of Charge-Exchange Produced K-shell X-ray Emission Lines

    NASA Astrophysics Data System (ADS)

    Beiersdorfer, P.; Bitter, M.; Olson, R.; Marion, M.

    2005-05-01

    Charge-exchange spectral models needed to describe and predict the X-ray emission of cometary and planetary atmospheres interacting with solar wind heavy ions are under development and require laboratory data for guidance. The relative intensity of the four K-shell emission lines in heliumlike ions is particularly uncertain, as the individual lines have not yet been fully resolved in charge-exchange-produced spectra. Using a high-resolution crystal spectrometer, we have measured the charge exchange induced K-shell X-ray emission from Ar16+ following the interaction of Ar17+ ions with fast, 40 keV/amu deuterium atoms. The measurement was performed on the National Spherical Torus Experiment (NSTX). The Ar17+ ions were constituents of the plasma, while deuterium was injected via a 80 keV neutral beam. During the brief, 20 ms neutral beam injection emission from electron-impact collisions ceases, and X-ray line emission is solely due to charge exchange. The measurement fully resolves the resonance, intercombination, and forbidden lines. We have constructed a complete radiative cascade model of Ar16+ that includes electron capture into levels as high as n=29 and all E1, M1, E2, and M2 radiative transitions. We find excellent agreement between the model and the NSTX crystyal spectrum. We will present these findings as well as our predictions of the emission in other spectral bands from the optical and extreme ultraviolet to the soft X-ray region. This work was performed under the auspices of the U.S. DOE by UC-LLNL under contract W-7405-Eng-48, by UMR under contract DE-FG02-84ER53175, and by PPPL under contract DE-AC02-76CHO3073.

  20. Charge-Exchange Excitation of the Isobaric Analog State and Implication for the Nuclear Symmetry Energy and Neutron Skin

    NASA Astrophysics Data System (ADS)

    Khoa, Dao T.; Loc, Bui Minh; Zegers, R. G. T.

    The charge-exchange (p, n) or (3He,t) reaction can be considered as elastic scattering of proton or 3He by the isovector term of the optical potential that flips the projectile isospin. Therefore, the accurately measured charge-exchange scattering cross section for the isobaric analog states can be a good probe of the isospin dependence of the optical potential, which is determined exclusively within the folding model by the difference between the neutron and proton densities and isospin dependence of the nucleon-nucleon interaction. On the other hand, the same isospin- and density-dependent nucleon-nucleon interaction can also be used in a Hartree-Fock calculation of asymmetric nuclear matter, to estimate the nuclear matter energy and its asymmetry part. As a result, the fine-tuning of the isospin dependence of the effective nucleon-nucleon interaction against the measured (p, n) or (3He,t) cross sections should allow us to make some realistic prediction of the nuclear symmetry energy and its density dependence. Moreover, given the neutron skin of the target related directly to the neutron-proton difference of the ground-state density, it can be well probed in the analysis of the charge-exchange (3He,t) reactions at medium energies when the two-step processes can be neglected and the t-matrix interaction can be used in the folding calculation.

  1. Boltzmann-BCA Analysis on the Role of Charge Exchange in Microscopic Erosion of Fusion-Relevant Plasma Facing Components

    NASA Astrophysics Data System (ADS)

    Keniley, Shane; Curreli, Davide

    2016-10-01

    Charge-exchange is expected to play an important role in microscopic erosion of plasma facing components under fusion-relevant conditions. In this work we present a set of detailed Boltzmann simulations of the near-wall plasma including surface response, with the goal of highlighting the relative role of charge exchange against ion-induced erosion. The simulations reveal that the charge-exchange processes occurring in the collisional presheath release energetic neutrals toward the wall with angular distributions ranging from grazing to normal incidence; the ions accelerated across the collisional and magnetic presheath acts as a dominant factor in affecting the initial phase of the neutral population reaching the wall, and ultimately its energy-angle distribution at the surface. The effect on erosion rates, plasma sheath/presheath structure, and moments of the distributions are highlighted. The study has been made possible thanks to a newly-developed dynamically-coupled Boltzmann-BCA model retaining the effects of both the plasma and the material erosion. Material based on work supported by the U.S. Department of Energy, Office of Advanced Scientific Computing Research through the SciDAC project on Plasma-Surface Interactions, Award No. DE-SC0008875.

  2. Surface Tension Mediated Under-Water Adhesion of Rigid Spheres on Soft, Charged Surfaces

    NASA Astrophysics Data System (ADS)

    Sinha, Shayandev; Das, Siddhartha

    2015-11-01

    Understanding the phenomenon of surface-tension-mediated under-water adhesion is necessary for studying a plethora of physiological and technical phenomena, such as the uptake of bacteria or nanoparticle by cells, attachment of virus on bacterial surfaces, biofouling on large ocean vessels and marine devices, etc. This adhesion phenomenon becomes highly non-trivial in case the soft surface where the adhesion occurs is also charged. Here we propose a theory for analyzing such an under-water adhesion of a rigid sphere on a soft, charged surface, represented by a grafted polyelectrolyte layer (PEL). We develop a model based on the minimization of free energy that, in addition to considering the elastic and the surface-tension-mediated adhesion energies, also accounts for the PEL electric double layer (EDL) induced electrostatic energies. We show that in the presence of surface charges, adhesion gets enhanced. This can be explained by the fact that the increase in the elastic energy is better balanced by the lowering of the EDL energy associated with the adhesion process. The entire behaviour is further dictated by the surface tension components that govern the adhesion energy.

  3. Guanine nucleotide exchange factor Dock7 mediates HGF-induced glioblastoma cell invasion via Rac activation

    PubMed Central

    Murray, D W; Didier, S; Chan, A; Paulino, V; Van Aelst, L; Ruggieri, R; Tran, N L; Byrne, A T; Symons, M

    2014-01-01

    Background: Glioblastoma multiforme (GBM), a highly invasive primary brain tumour, remains an incurable disease. Rho GTPases and their activators, guanine nucleotide exchange factors (GEFs), have central roles in GBM invasion. Anti-angiogenic therapies may stimulate GBM invasion via HGF/c-Met signalling. We aim to identify mediators of HGF-induced GBM invasion that may represent targets in a combination anti-angiogenic/anti-invasion therapeutic paradigm. Methods: Guanine nucleotide exchange factor expression was measured by microarray analysis and western blotting. Specific depletion of proteins was accomplished using siRNA. Cell invasion was determined using matrigel and brain slice assays. Cell proliferation and survival were monitored using sulforhodamine B and colony formation assays. Guanine nucleotide exchange factor and GTPase activities were determined using specific affinity precipitation assays. Results: We found that expression of Dock7, a GEF, is elevated in human GBM tissue in comparison with non-neoplastic brain. We showed that Dock7 mediates serum- and HGF-induced glioblastoma cell invasion. We also showed that Dock7 co-immunoprecipitates with c-Met and that this interaction is enhanced upon HGF stimulation in a manner that is dependent on the adaptor protein Gab1. Dock7 and Gab1 also co-immunoprecipitate in an HGF-dependent manner. Furthermore, Gab1 is required for HGF-induced Dock7 and Rac1 activation and glioblastoma cell invasion. Conclusions: Dock7 mediates HGF-induced GBM invasion. Targeting Dock7 in GBM may inhibit c-MET-mediated invasion in tumours treated with anti-angiogenic regimens. PMID:24518591

  4. Charge exchange produced K-shell x-ray emission from Ar16+ in a tokamak plasma with neutral beam injection

    SciTech Connect

    Beiersdorfer, P; Bitter, M; Marion, M; Olson, R E

    2004-12-27

    High-resolution spectroscopy of hot tokamak plasma seeded with argon ions and interacting with an energetic, short-pulse neutral hydrogen beam was used to obtain the first high-resolution K-shell x-ray spectrum formed solely by charge exchange. The observed K-shell emission of Ar{sup 16+} is dominated by the intercombination and forbidden lines, providing clear signatures of charge exchange. Results from an ab initio atomic cascade model provide excellent agreement, validating a semiclassical approach for calculating charge exchange cross sections.

  5. Charge exchange spectroscopy of multiply charged ions for the development of the EUV light source for the next generation photo lithography

    NASA Astrophysics Data System (ADS)

    Tanuma, Hajime

    2015-09-01

    As a candidate of an extreme ultra-violet (EUV) light source for a next generation lithography, laser produced plasmas (LPP) of Xe and Sn have been investigated intensively in this decade because these plasmas have a strong emission around 13.5 nm which had been determined as the wavelength for the EUV lithography. This emission was considered to be due to multiply charged Xe and Sn ions in hot plasmas. However, the detail atomic spectroscopic data of these multiply charged heavy ions had not been reported yet. To provide atomic data for the understanding and development of the LPP as the EUV light source, we have observed the EUV emission spectra from individual charge states of Xe and Sn ions by means of a charge exchange spectroscopy method. Multiply charged Xeq+ (q = 7-23) and Snq+ (q = 5-21) ions were produced with a 14.25 GHz electron cyclotron resonance ion source, and a charge-selected ion beam was directed into a collision chamber, where the ion interact with a target gas of He and Xe. EUV emissions from the collision center were observed with a compact flat-field grazing-incident spectrometer equipped with a liquid nitrogen cooled CCD camera. In experiments using Xe ions, we have found only Xe XI has a strong UTA (unresolved transition array) around 13.5 nm. On the other hand, various charge states of Sn from VIII to XIV contribute to the 13.5 nm emission. Identification of the transition lines was carried out by calculations using the Hebrew university Livermore laboratory atomic physics code and the Cowan code. Most of the emissions in the EUV region are attributed to the 4p-4d and 4d- nl (nl = 4f, 5p, and 5f) transitions. However, the 4d-4f transitions have approximately constant differences of about 0.5 nm between the experimental and theoretical results. This can be explained by considering the strong configuration interactions in the n=4 subshells. Using the experimental transition wavelengths of multiply charged Sn ions, theoretical modeling of

  6. Removing Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charged Exchange Recombination

    NASA Technical Reports Server (NTRS)

    Wargelin, Brad

    2004-01-01

    Our research uses the electron beam ion trap (EBIT) at the Lawrence Livermore National Laboratory to study X-ray emission from the charge exchange (CX) of highly charged ions with neutral gases. The resulting data help to fill a void in existing experimental and theoretical understanding of this atomic physics process, and are needed to explain all or part of the observed X-ray emission from the soft X-ray background, stellar winds, the Galactic Center and Galactic Ridge, supernova ejecta, and photoionized nebulae. Appreciation of the astrophysical relevance of our work continues to grow with the publication of roughly a dozen papers in the past four years describing Chandra and XMM observations of geocoronal and heliospheric CX emission, the temporal variation of such emission and correlation with X-ray emission enhancements observed by ROSAT, the theoretical spatial distribution of that emission, and CX emission around other stars. A similar number of papers were also published during that time describing CX emission from planets and comets. We expect that the launch of ASTRSE2, with its second-generation XRS microcalo- (with 6-eV resolution), will reveal even more clearly the contributions of CX to astrophysical emission. In our EBIT work we collected CX spectra from such ions as H-like and He-like Ne, Ar, and Fe. Our early measurements were made with a high-purity Ge detector, but during the second year we began operation of the first-generation XRS microcalorimeter (a twin of the XRS on ASTRO-E) and greatly improved the resolution of our measurements from roughly 150 eV (FWHM) with the Ge detectors to 10 eV with the XRS. We found that saturation of the XRS counting apparatus, which we described in our proposal as a potential concern, is not a problem for studying CX. During the course of our research, we expanded the number of injection gases permitted by the LLNL safety team, purchased and eventually operated an atomic H source, and clearly demonstrated the

  7. Solar Wind Charge Exchange Contribution To The ROSAT Sky Survey Maps

    NASA Technical Reports Server (NTRS)

    Uprety, Y.; Chiao, M.; Collier, M. R.; Cravens, T.; Galeazzi, M.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Lepri, S. T.; Liu, W.; McCammon, D.; Morgan, K.; Porter, F. S.; Prasai, K.; Snowden, S. L.; Thomas, N. E.; Ursino, E.; Walsh, B. M.

    2016-01-01

    DXL (Diffuse X-ray emission from the Local Galaxy) is a sounding rocket mission designed to estimate the contribution of solar wind charge eXchange (SWCX) to the diffuse X-ray background and to help determine the properties of the Local Hot Bubble. The detectors are large area thin-window proportional counters with a spectral response that is similar to that of the PSPC (Position Sensitive Proportional Counters) used in the ROSAT All Sky Survey (RASS). A direct comparison of DXL and RASS data for the same part of the sky viewed from quite different vantage points in the solar system, and the assumption of approximate isotropy for the solar wind, allowed us to quantify the SWCX contribution to all six RASS bands (R1-R7, excluding R3). We find that the SWCX contribution at l = 140 degrees, b = 0 degrees, where the DXL path crosses the Galactic plane, is 33 percent plus or minus 6 percent (statistical) plus or minus 12 percent (systematic) for R1, 44 percent plus or minus 6 percent plus or minus 5 percent for R2, 18 percent plus or minus 12 percent plus or minus 11 percent for R4, 14 percent plus or minus 11 percent plus or minus 9 percent for R5, and negligible for the R6 and R7 bands. Reliable models for the distribution of neutral H and He in the solar system permit estimation of the contribution of interplanetary SWCX emission over the the whole sky and correction of the RASS maps. We find that the average SWCX contribution in the whole sky is 26 percent plus or minus 6 percent plus or minus 13 percent for R1, 30 percent plus or minus 4 percent plus or minus 4 percent for R2, 8 percent plus or minus 5 percent plus or minus 5 percent for R4, 6 percent plus or minus 4 percent plus or minus 4 percent for R5, and negligible for R6 and R7.

  8. Calcium activation of Ras mediated by neuronal exchange factor Ras-GRF.

    PubMed

    Farnsworth, C L; Freshney, N W; Rosen, L B; Ghosh, A; Greenberg, M E; Feig, L A

    1995-08-10

    Tyrosine kinase receptors stimulate the Ras signalling pathway by enhancing the activity of the SOS nucleotide-exchange factor. This occurs, at least in part, by the recruitment of an SOS-GRB2 complex to Ras in the plasma membrane. Here we describe a different signalling pathway to Ras that involves activation of the Ras-GRF exchange factor in response to Ca2+ influx. In particular, we show that the ability of Ras-GRF to activate Ras in vivo is markedly enhanced by raised Ca2+ concentrations. Activation is mediated by calmodulin binding to an IQ motif in Ras-GRF, because substitutions in conserved amino acids in this motif prevent both calmodulin binding to Ras-GRF and Ras-GRF activation in vivo. So far, full-length Ras-GRF has been detected only in brain neurons. Our findings implicate Ras-GRF in the regulation of neuronal functions that are influenced by Ca2+ signals.

  9. HLA-DM mediates peptide exchange by interacting transiently and repeatedly with HLA-DR1

    PubMed Central

    Narayan, Kedar; Su, Katherine W.; Chou, Chih-Ling; Khoruzhenko, Stanislav

    2009-01-01

    The peptide editor HLA-DM (DM) catalyzes the exchange of peptides bound to MHC class II molecules within antigen presenting cells by generating a “peptide-receptive” MHC class II conformation (MHCreceptive) to which peptides readily bind and rapidly unbind. While recent work has uncovered the determinants of DM recognition and effector functions, the nature of MHCreceptive and its interaction with DM remains unclear. Here, we show that DM induces but does not stabilize MHCreceptive in the absence of peptides. We demonstrate that DM is out-competed by certain superantigens, and increasing solvent viscosity inhibits DM-induced peptide association. We suggest that DM mediates peptide exchange by interacting transiently and repeatedly with MHC class II molecules, continually generating MHCreceptive. The simultaneous presence of peptide and DM in the milieu is thus crucial for the efficient generation of specific peptide-MHC class II complexes over time. PMID:19647320

  10. Stable Recombinase-Mediated Cassette Exchange in Arabidopsis Using Agrobacterium tumefaciens1

    PubMed Central

    Louwerse, Jeanine D.; van Lier, Miranda C.M.; van der Steen, Dirk M.; de Vlaam, Clementine M.T.; Hooykaas, Paul J.J.; Vergunst, Annette C.

    2007-01-01

    Site-specific integration is an attractive method for the improvement of current transformation technologies aimed at the production of stable transgenic plants. Here, we present a Cre-based targeting strategy in Arabidopsis (Arabidopsis thaliana) using recombinase-mediated cassette exchange (RMCE) of transferred DNA (T-DNA) delivered by Agrobacterium tumefaciens. The rationale for effective RMCE is the precise exchange of a genomic and a replacement cassette both flanked by two heterospecific lox sites that are incompatible with each other to prevent unwanted cassette deletion. We designed a strategy in which the coding region of a loxP/lox5171-flanked bialaphos resistance (bar) gene is exchanged for a loxP/lox5171-flanked T-DNA replacement cassette containing the neomycin phosphotransferase (nptII) coding region via loxP/loxP and lox5171/lox5171 directed recombination. The bar gene is driven by the strong 35S promoter, which is located outside the target cassette. This placement ensures preferential selection of RMCE events and not random integration events by expression of nptII from this same promoter. Using root transformation, during which Cre was provided on a cotransformed T-DNA, 50 kanamycin-resistant calli were selected. Forty-four percent contained a correctly exchanged cassette based on PCR analysis, indicating the stringency of the selection system. This was confirmed for the offspring of five analyzed events by Southern-blot analysis. In four of the five analyzed RMCE events, there were no additional T-DNA insertions or they easily segregated, resulting in high-efficiency single-copy RMCE events. Our approach enables simple and efficient selection of targeting events using the advantages of Agrobacterium-mediated transformation. PMID:17921337

  11. Reduced exchange narrowing caused by gate-induced charge carriers in high-mobility donor-acceptor copolymers

    NASA Astrophysics Data System (ADS)

    Tsutsumi, Jun'ya; Matsuoka, Satoshi; Osaka, Itaru; Kumai, Reiji; Hasegawa, Tatsuo

    2017-03-01

    Variations in exciton absorption resulting from charge accumulation in various semiconducting donor-acceptor (DA) copolymer thin films were systematically investigated by gate modulation (GM) spectroscopy by using the field-effect transistor device structure. The GM spectra obtained for high-mobility DA copolymer thin films exhibited second-derivative like line shapes due to an effect of spectral broadening of ordinary exciton absorption spectra by accumulated charges. In contrast, the GM spectra obtained for relatively low-mobility DA copolymer thin films exhibited simple bleaching of exciton absorption spectra, as well as observed for non-DA-type polymers like poly(3-hexylthiophene-2,5-diyl) (P3HT). From a systematic comparison of the GM spectra with temperature-dependent absorption spectra for the polymers in solution, we found that the spectral broadening observed in the GM spectra can be attributed to a reduced effect on the exchange narrowing where excitonic transitions of individual polymer chains are coherently coupled within highly ordered crystalline domains in the polymer thin films. We discuss that the gate-induced charge accumulation in the polymer films effects to suppress the exciton coherence length, which contributes to the reduced exchange narrowing. We also discuss that the whole feature of the GM spectra can be understood in terms of a decomposition into ordered and disordered polymers and that the GM spectra can be used as fine probes for a degree of structural ordering in semiconductor channels of polymer field-effect transistors.

  12. Design and operation of the pellet charge exchange diagnostic for measurement of energetic confined alphas and tritons on TFTR

    SciTech Connect

    Medley, S.S.; Duong, H.H.; Fisher, R.K.

    1996-05-01

    Radially-resolved energy and density distributions of the energetic confined alpha particles in D-T experiments on TFTR are being measured by active neutral particle analysis using low-Z impurity pellet injection. When injected into a high temperature plasma, an impurity pellet (e.g. Lithium or Boron) rapidly ablates forming an elongated cloud which is aligned with the magnetic field and moves with the pellet. This ablation cloud provides a dense target with which the alpha particles produced in D-T fusion reactions can charge exchange. A small fraction of the alpha particles incident on the pellet ablation cloud will be converted to helium neutrals whose energy is essentially unchanged by the charge transfer process. By measuring the resultant helium neutrals escaping from the plasma using a mass and energy resolving charge exchange analyzer, this technique offers a direct measurement of the energy distribution of the incident high-energy alpha particles. Other energetic ion species can be detected as well, such as tritons generated in D-D plasmas and H or He{sup 3} RF-driven minority ion tails. The diagnostic technique and its application on TFTR are described in detail.

  13. An ion-exchange nanomembrane sensor for detection of nucleic acids using a surface charge inversion phenomenon.

    PubMed

    Senapati, Satyajyoti; Slouka, Zdenek; Shah, Sunny S; Behura, Susanta K; Shi, Zonggao; Stack, M Sharon; Severson, David W; Chang, Hsueh-Chia

    2014-10-15

    We present a novel low-cost biosensor for rapid, sensitive and selective detection of nucleic acids based on an ionic diode feature of an anion exchange nanoporous membrane under DC bias. The ionic diode feature is associated with external surface charge inversion on the positively charged anion exchange nanomembrane upon hybridization of negatively charged nucleic acid molecules to single-stranded oligoprobes functionalized on the membrane surface resulting in the formation of a cation selective monolayer. The resulting bipolar membrane causes a transition from electroconvection-controlled to water-splitting controlled ion conductance, with a large ion current signature that can be used to accurately quantify the hybridized nucleic acids. The platform is capable of distinguishing two base-pair mismatches in a 22-base pairing segment of microRNAs associated with oral cancer, as well as serotype-specific detection of dengue virus. We also show the sensor' capability to selectively capture target nucleic acids from a heterogeneous mixture. The limit of detection is 1 pM for short 27 base target molecules in a 15-min assay. Similar hybridization results are shown for short DNA molecules as well as RNAs from Brucella and Escherichia coli. The versatility and simplicity of this low-cost biosensor should enable point-of-care diagnostics in food, medical and environmental safety markets.

  14. A semi-interpenetrating network approach for dimensionally stabilizing highly-charged anion exchange membranes for alkaline fuel cells.

    PubMed

    He, Steve S; Strickler, Alaina L; Frank, Curtis W

    2015-04-24

    There is a delicate balance between ion exchange capacity (IEC), conductivity, and dimensional stability in anion exchange membranes as higher charge content can lead to increased water uptake, causing excessive swelling and charge dilution. Using highly-charged benzyltrimethylammonium polysulfone (IEC=2.99 mEq g(-1) ) as a benchmark (which ruptured in water even at room temperature), we report the ability to dramatically decrease water uptake using a semi-interpenetrating network wherein we reinforced the linear polyelectrolyte with a crosslinked poly(styrene-co-divinylbenzene) network. These membranes show enhanced dimensional stability as a result of lower water uptake (75 % vs. 301 % at 25 °C) while maintaining excellent hydroxide conductivity (up to 50 mS cm(-1) at 25 °C). These improvements produced an enhanced alkaline fuel cell capable of generating 236 mW cm(-2) peak power density at 80 °C. This method is easily adaptable and can be a viable strategy for stabilizing existing systems.

  15. Cometary Solar Wind Charge Exchange Line Ratios: Source of X-rays in Comet C/2000 WM1 (linear)

    NASA Astrophysics Data System (ADS)

    Mullen, Patrick Dean; Cumbee, Renata; Lyons, David; Gu, Liyi; Kaastra, Jelle S.; Shelton, Robin L.; Stancil, Phillip C.

    2016-06-01

    Cometary solar wind charge exchange (C-SWCX) occurs when highly charged projectile ions present in solar wind capture an electron from a target neutral species present in the cometary atmosphere. The availability of atomic and molecular data necessary for the X-ray emission modeling due to C-SWCX is limited; therefore, we apply multi-channel Landau-Zener (MCLZ) theory (Mullen et al. 2016) to generate cross section data and theoretical X-ray line ratios for a variety of bare and non-bare ion single electron capture (SEC) collisions. Namely, we consider collisions between the solar wind constituent H-like and He-like ions of C, N, O, Ne, Na, Al, and Si and the cometary neutrals H, H2O, CO, CO2, OH, and O. To exemplify the application of this data, we model the X-ray emission of comet C/2000 WM1 (linear) using the charge exchange package in SPEX (Gu et al. 2015) and find excellent agreement with observations made with the XMM-RGS detector. Our analyses show that the X-ray intensity is dominated by C-SWCX with H.Work at UGA was partially funded by NASA grant NNX13AF31G.References:Gu et al. 2016, A&A, accepted 22 January 2016Mullen et al. 2016, ApJS, in press

  16. A Multiplexed, Two-Electrode Platform for Biosensing based on DNA-Mediated Charge Transport

    PubMed Central

    Furst, Ariel L.; Hill, Michael G.; Barton, Jacqueline K.

    2015-01-01

    We have developed a thin layer, multiplexed biosensing platform that features two working-electrode arrays for detecting small molecules, nucleic acid sequences, and DNA-binding proteins. DNA duplexes are patterned onto the primary electrode array, while a secondary electrode array is used both to initiate DNA monolayer formation, and for electrochemical readout via DNA-mediated charge transport (DNA CT) chemistry. Electrochemical reduction of Cu(phendione)22+ (phendione is 1,10-phenanthroline-5,6-dione) at the secondary electrodes induces covalent attachment via click chemistry of ethynyl-labeled DNA probe duplexes onto the primary electrodes that have been treated with azide-terminated alkythiols. Electrochemical impedance spectroscopy and cyclic voltammetry confirm that catalyst activation at the secondary electrode is essential to maintain the integrity of the DNA monolayer. Electrochemical readout of DNA CT processes that occur at the primary electrode is accomplished at the secondary electrode. The two-electrode system enables the platform to function as a collector-generator using either ferrocyanide or ferricyanide as mediators with methylene blue and DNA charge transport. Electrochemical measurements at the secondary electrode eliminate the need for large background corrections. The resulting sensitivity of this platform enables the reliable and simultaneous detection of femtomoles of the transcription factors TATA-binding protein and CopG on a single multiplexed device. PMID:26042916

  17. X-ray Emission Cross Sections following Charge Exchange by Multiply-Charged Ions of Astrophysical Interest.

    NASA Astrophysics Data System (ADS)

    Otranto, Sebastian; Olson, Ronald; Beiersdorfer, Peter

    2006-05-01

    State selective nl-electron capture cross sections calculated using the classical trajectory Monte Carlo (CTMC) model are presented for highly charged ions with Z = 6-10 colliding with atoms and molecules. The energy dependence of the l-level populations is investigated. The calculated cross sections are compared with measurements made by Greenwood et al [1], using O^8+ and Ne^10+ on various targets at 3 keV/amu, and with recent x-ray emission cross sections measured with the EBIT machine at LLNL using O^8+ and Ne^9+,10+ on different targets at 10 eV/amu. We use the calculated cross sections to present an ab initio determination of the soft x-ray spectrum of comet C/Linear 1999 S4 that was observed on the Chandra X-ray Observatory [2]. [1] J. B. Greenwood, I. D. Williams, S. J. Smith and A. Chutjian, Phys. Rev. A 63, 062707 (2001). [2] C. M. Lisse, D. J. Christian, K. Dennerl, K. J. Meech, R. Petre, H. A. Weaver and S. J. Wolk, Science 292, 1343 (2001).

  18. Charge exchange and x-ray emission cross sections for multiply charged ions colliding with H{sub 2}O

    SciTech Connect

    Otranto, S.; Olson, R. E.

    2008-02-15

    Total and state selective nl-electron capture cross sections are presented for highly charged ions Z=4-10, 14, 18, and 26 colliding with water molecules. The energy range investigated was from 10 eV/amu (v=0.02 a.u.) to 100 keV/amu (v=2 a.u.). An initialization for the 1B1 and 3A1 orbitals of the water molecule is introduced based on the one center expansion of Moccia and compared to our previous studies based on a hydrogenic approximation within the microcanonical ensemble. The Z dependence of the calculated total cross sections is in reasonable agreement with the recent data of Mawhorter et al. [Phys. Rev. A 75, 032704 (2007)] and is improved over previous results. The energy dependence of the n- and l-level populations is investigated. The K-shell x-ray emission cross sections are determined by using the calculated state-selective electron capture results as input and then applying hydrogenic branching and cascading values for the photon emission. Our results compare favorably with experimental data from the KVI-Groningen, Jet Propulsion Laboratory and Lawrence Livermore National Laboratory groups.

  19. Monolayer optical memory cells based on artificial trap-mediated charge storage and release

    NASA Astrophysics Data System (ADS)

    Lee, Juwon; Pak, Sangyeon; Lee, Young-Woo; Cho, Yuljae; Hong, John; Giraud, Paul; Shin, Hyeon Suk; Morris, Stephen M.; Sohn, Jung Inn; Cha, Seungnam; Kim, Jong Min

    2017-03-01

    Monolayer transition metal dichalcogenides are considered to be promising candidates for flexible and transparent optoelectronics applications due to their direct bandgap and strong light-matter interactions. Although several monolayer-based photodetectors have been demonstrated, single-layered optical memory devices suitable for high-quality image sensing have received little attention. Here we report a concept for monolayer MoS2 optoelectronic memory devices using artificially-structured charge trap layers through the functionalization of the monolayer/dielectric interfaces, leading to localized electronic states that serve as a basis for electrically-induced charge trapping and optically-mediated charge release. Our devices exhibit excellent photo-responsive memory characteristics with a large linear dynamic range of ~4,700 (73.4 dB) coupled with a low OFF-state current (<4 pA), and a long storage lifetime of over 104 s. In addition, the multi-level detection of up to 8 optical states is successfully demonstrated. These results represent a significant step toward the development of future monolayer optoelectronic memory devices.

  20. Monolayer optical memory cells based on artificial trap-mediated charge storage and release.

    PubMed

    Lee, Juwon; Pak, Sangyeon; Lee, Young-Woo; Cho, Yuljae; Hong, John; Giraud, Paul; Shin, Hyeon Suk; Morris, Stephen M; Sohn, Jung Inn; Cha, SeungNam; Kim, Jong Min

    2017-03-24

    Monolayer transition metal dichalcogenides are considered to be promising candidates for flexible and transparent optoelectronics applications due to their direct bandgap and strong light-matter interactions. Although several monolayer-based photodetectors have been demonstrated, single-layered optical memory devices suitable for high-quality image sensing have received little attention. Here we report a concept for monolayer MoS2 optoelectronic memory devices using artificially-structured charge trap layers through the functionalization of the monolayer/dielectric interfaces, leading to localized electronic states that serve as a basis for electrically-induced charge trapping and optically-mediated charge release. Our devices exhibit excellent photo-responsive memory characteristics with a large linear dynamic range of ∼4,700 (73.4 dB) coupled with a low OFF-state current (<4 pA), and a long storage lifetime of over 10(4) s. In addition, the multi-level detection of up to 8 optical states is successfully demonstrated. These results represent a significant step toward the development of future monolayer optoelectronic memory devices.

  1. EXCHANGE

    SciTech Connect

    Boltz, J.C.

    1992-09-01

    EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

  2. Simplified dark matter models with charged mediators: prospects for direct detection

    NASA Astrophysics Data System (ADS)

    Sandick, Pearl; Sinha, Kuver; Teng, Fei

    2016-10-01

    We consider direct detection prospects for a class of simplified models of fermionic dark matter (DM) coupled to left and right-handed Standard Model fermions via two charged scalar mediators with arbitrary mixing angle α. DM interactions with the nucleus are mediated by higher electromagnetic moments, which, for Majorana DM, is the anapole moment. After giving a full analytic calculation of the anapole moment, including its α dependence, and matching with limits in the literature, we compute the DM-nucleon scattering cross-section and show the LUX and future LZ constraints on the parameter space of these models. We then compare these results with constraints coming from F ermi-LAT continuum and line searches. Results in the supersymmetric limit of these simplified models are provided in all cases. We find that future direct detection experiments will be able to probe most of the parameter space of these models for O (100 - 200) GeV DM and lightest mediator mass ≲ O (5%) larger than the DM mass. The direct detection prospects dwindle for larger DM mass and larger mass gap between the DM and the lightest mediator mass, although appreciable regions are still probed for O (200) GeV DM and lightest mediator mass ≲ O (20%) larger than the DM mass. The direct detection bounds are also attenuated near certain "blind spots" in the parameter space, where the anapole moment is severely suppressed due to cancellation of different terms. We carefully study these blind spots and the associated F ermi-LAT signals in these regions.

  3. Critical validity assessment of theoretical models: charge-exchange at intermediate and high energies

    NASA Astrophysics Data System (ADS)

    Belkić, Dževad

    1999-06-01

    Exact comprehensive computations are carried out by means of four leading second-order approximations yielding differential cross sections dQ/ dΩ for the basic charge exchange process H ++H(1s)→H(1s)+H + at intermediate and high energies. The obtained extensive set of results is thoroughly tested against all the existing experimental data with the purpose of critically assessing the validity of the boundary corrected second-Born (CB2), continuum-distorted wave (CDW), impulse approximation (IA) and the reformulated impulse approximation (RIA). The conclusion which emerges from this comparative study clearly indicates that the RIA agrees most favorably with the measurements available over a large energy range 25 keV-5 MeV. Such a finding reaffirms the few-particle quantum scattering theory which imposes several strict conditions on adequate second-order methods. These requirements satisfied by the RIA are: (i) normalisations of all the scattering wave functions, (ii) correct boundary conditions in both entrance and exit channels, (iii) introduction of a mathematically justified two-center continuum state for the sum of an attractive and a repulsive Coulomb potential with the same interaction strength, (iv) inclusion of the multiple scattering effects neglected in the IA, (v) a proper description of the Thomas double scattering in good agreement with the experiments and without any unobserved peak splittings. Nevertheless, the performed comparative analysis of the above four approximations indicates that none of the methods is free from some basic shortcomings. Despite its success, the RIA remains essentially a high-energy model like the other three methods under study. More importantly, their perturbative character leaves virtually no room for further systematic improvements, since the neglected higher-order terms are prohibitively tedious for practical purposes and have never been computed exactly. To bridge this gap, we presently introduce the variational Pad

  4. Positively charged and pH self-buffering quantum dots for efficient cellular uptake by charge mediation and monitoring cell membrane permeability.

    PubMed

    Wang, Suhua; Song, Haipeng; Ong, Wei Yi; Han, Ming Yong; Huang, Dejian

    2009-10-21

    Positively charged and pH self-buffering quantum dots (Tren-QDs) were achieved by surface functionalization with tris(2-aminoethyl)amine (Tren) derivatives, which are attached to the inorganic cores of QDs through bidentate chelating of dithiocarbamates. The Tren-QDs exhibit pH buffering capability by absorbing or releasing protons due to the surface polyamine groups as the surrounding pH fluctuates. Such self-buffering capability stabilizes the photoluminescence of the Tren-QDs against acid. The Tren-QDs bear positive charges through protonation of the surface polyamine groups under physiological conditions and the surface positive charges improve their cellular uptake efficiency by charge mediation, which has been demonstrated by BV-2 microglia cells. The photoluminescence of Tren-QDs shows a selective Stern-Volmer response to copper ions and this property has been preliminarily evaluated for investigating the BV-2 cell membrane structure by monitoring the photoluminescence of intracellular Tren-QDs.

  5. Positively charged and pH self-buffering quantum dots for efficient cellular uptake by charge mediation and monitoring cell membrane permeability

    NASA Astrophysics Data System (ADS)

    Wang, Suhua; Song, Haipeng; Ong, Wei Yi; Han, Ming Yong; Huang, Dejian

    2009-10-01

    Positively charged and pH self-buffering quantum dots (Tren-QDs) were achieved by surface functionalization with tris(2-aminoethyl)amine (Tren) derivatives, which are attached to the inorganic cores of QDs through bidentate chelating of dithiocarbamates. The Tren-QDs exhibit pH buffering capability by absorbing or releasing protons due to the surface polyamine groups as the surrounding pH fluctuates. Such self-buffering capability stabilizes the photoluminescence of the Tren-QDs against acid. The Tren-QDs bear positive charges through protonation of the surface polyamine groups under physiological conditions and the surface positive charges improve their cellular uptake efficiency by charge mediation, which has been demonstrated by BV-2 microglia cells. The photoluminescence of Tren-QDs shows a selective Stern-Volmer response to copper ions and this property has been preliminarily evaluated for investigating the BV-2 cell membrane structure by monitoring the photoluminescence of intracellular Tren-QDs.

  6. Calculating field emission current in nanodiodes—A multi-group formalism with space charge and exchange-correlation effects

    SciTech Connect

    Biswas, Debabrata; Kumar, Raghwendra

    2014-03-21

    Inclusion of electron-electron interaction is essential in nano-diodes to understand the underlying physical phenomenon and tailor devices accordingly. However, both space charge and exchange-correlation interaction involve electrons at different energies and hence a self-consistent multi-energy-group solution of the Schrödinger-Poisson system is required. It is shown here that the existence of a limiting density-dependent potential at low applied voltages allows calculation of the field emission current. Despite additional interactions, a Fowler-Nordheim behaviour is observed. It is also found that the exchange-correlation potential dominates at these voltages in nanogaps and possibly leads to a higher turn-on voltage.

  7. Determination of 16O and 18O sensitivity factors and charge-exchange processes in low-energy ion scattering

    NASA Astrophysics Data System (ADS)

    Téllez, H.; Chater, R. J.; Fearn, S.; Symianakis, E.; Brongersma, H. H.; Kilner, J. A.

    2012-10-01

    Quantitative analysis in low-energy ion scattering (LEIS) requires an understanding of the charge-exchange processes to estimate the elemental sensitivity factors. In this work, the neutralization of He+ scattered by 18O-exchanged silica at energies between 0.6 and 7 keV was studied. The process is dominated by Auger neutralization for Ei < 0.8 keV. An additional mechanism starts above the reionization threshold. This collision-induced neutralization becomes the dominant mechanism for Ei > 2 keV. The ion fractions P+ were determined for Si and O using the characteristic velocity method to quantify the surface density. The 18O/16O sensitivity ratio indicates an 18% higher sensitivity for the heavier O isotope.

  8. Investigation of Anion-Exchange and Immunoaffinity Particle-Loaded Membranes for the Isolation of Charged Organic Analytes from Water

    USGS Publications Warehouse

    Dombrowski, T.R.; Wilson, G.S.; Thurman, E.M.

    1998-01-01

    Anion-exchange and immunoaffinity particle loaded membranes (PLMs) were investigated as a mechanism for the isolation of charged organic analytes from water. Kinetic properties determined theoretically included dynamic capacity, pressure drop (??P), residence and diffusion times (Tr, Td), and total membrane porosity (???T). These properties were confirmed through experimental evaluation, and the PLM method showed significant improvement over conventional solid-phase extraction (SPE) and ion-exchange formats. Recoveries of more than 90% were observed for a variety of test compounds at flow rates up to 70 mL/min (equipment-limited maximum flow rate). A fast-flow immunoaffinity column was developed using antibodies (Abs) attached to the PLMs. Reproducible recoveries (88% ?? 4%) were observed at flow rates up to 70 mL/min for the antibody (Ab)-loaded PLMs. Findings indicate increased selectivity over anion-exchange PLMs and conventional SPE or ion-exchange methods and rapid Ab-antigen binding rates given the excellent mass-transfer characteristics of the PLMs.

  9. A Novel Kinetic Assay of Mitochondrial ATP-ADP Exchange Rate Mediated by the ANT

    PubMed Central

    Chinopoulos, Christos; Vajda, Szilvia; Csanády, László; Mándi, Miklós; Mathe, Katalin; Adam-Vizi, Vera

    2009-01-01

    A novel method exploiting the differential affinity of ADP and ATP to Mg2+ was developed to measure mitochondrial ADP-ATP exchange rate. The rate of ATP appearing in the medium after addition of ADP to energized mitochondria, is calculated from the measured rate of change in free extramitochondrial [Mg2+] reported by the membrane-impermeable 5K+ salt of the Mg2+-sensitive fluorescent indicator, Magnesium Green, using standard binding equations. The assay is designed such that the adenine nucleotide translocase (ANT) is the sole mediator of changes in [Mg2+] in the extramitochondrial volume, as a result of ADP-ATP exchange. We also provide data on the dependence of ATP efflux rate within the 6.8–7.8 matrix pH range as a function of membrane potential. Finally, by comparing the ATP-ADP steady-state exchange rate to the amount of the ANT in rat brain synaptic, brain nonsynaptic, heart and liver mitochondria, we provide molecular turnover numbers for the known ANT isotypes. PMID:19289073

  10. Flipase-mediated cassette exchange in Sf9 insect cells for stable gene expression.

    PubMed

    Fernandes, Fabiana; Vidigal, João; Dias, Mafalda M; Prather, Kristala L J; Coroadinha, Ana S; Teixeira, Ana P; Alves, Paula M

    2012-11-01

    Site-specific DNA integration allows predictable heterologous gene expression and circumvents extensive clone screening. Herein, the establishment of a Flipase (Flp)-mediated cassette exchange system in Sf9 insect cells for targeted gene integration is described. A tagging cassette harboring a reporter dsRed gene was randomly introduced into the cell genome after screening different transfection protocols. Single-copy integration clones were then co-transfected with both Flp-containing plasmid and an EGFP-containing targeting cassette. Successful cassette exchange was suggested by emergence of G418-resistant green colonies and confirmed by PCR analysis, showing the absence of the tagging cassette and single integration of the targeting cassette in the same locus. Upon cassette exchange, uniform EGFP expression between clones derived from the same integration site was obtained. Moreover, the resulting cell clones exhibited the expression properties of the parental cell line. EGFP production titers over 40 mg/L were of the same order of magnitude as those achieved through baculovirus infection. This Sf9 master cell line constitutes a versatile and re-usable platform to produce multiple recombinant proteins for fundamental and applied research.

  11. Quantification of charge-to-strain mediated interface coupling transfiguration in FE/FSMA multiferroic heterostructures

    NASA Astrophysics Data System (ADS)

    Singh, Kirandeep; Kaur, Davinder

    2016-01-01

    Thickness modulated direct, local measurement of magnetoelectric (ME) coupling was executed in a high quality sputter deposited PZT/Ni-Mn-In bilayer system grown on Si(1 0 0) substrate. The additive temperature and magnetic-field-driven shape-memory behavior of bottom ferromagnetic (FM) Ni-Mn-In layer, which vanish at ultra-low regime (8 nm), induce fluctuations in the dielectric and ferroelectric (FE) characteristic of PZT. The prominent magnetic-field-modulated P-E loops registered at room temperature in  ±400 kV cm-1 electric field range illustrate the presence of giant strain-mediated direct ME coupling in bilayers. This giant strain-mediated direct ME coupling in bilayers can be imputed to magnetic-field-actuated shape-memory behavior of Ni-Mn-In film. The I-V characteristic depicts that the PZT/Ni-Mn-In bilayer endures transition from Ohmic conduction (dominant at low field) to interface-limited Fowler-Nordheim (FN) tunneling prevailing at high electric field. Magnetic measurements of the bilayer revealed that voltage-attuned magnetic anisotropy variation was strongly dependent on the thickness of the bilayer. The normalized magnetization (M/M s) versus electric field (ME) plots was sketched to cognize the origin of interfacial converse ME coupling. The occurrence of butterfly-shaped ME loops showed the dominance of strain-mediated coupling in the (200 nm/220 nm) bilayer, in contrast to (40 nm/8 nm) heterostructure coupling which was purely charge mediated. The co-existence of charge- and strain-mediated ME coupling in (80 nm/30 nm) structure was evident from quite asymmetric features of ME curves. In 80 nm/30 nm multiferroic heterostructure two reversible and stable magnetic field states of Ni-Mn-In were observed at zero electric field. Such a non-volatile switching of magnetization accomplished by reversing the electric field could prove useful in future MERAM devices.

  12. Influence of self-assembling redox mediators on charge transfer at hydrophobic electrodes.

    PubMed

    Smith, Timothy J; Wang, Chenxuan; Abbott, Nicholas L

    2015-10-06

    We report an investigation of the influence of reversible self-assembly of amphiphilic redox-mediators on interfacial charge transfer at chemically functionalized electrodes. Specifically, we employed (11-ferrocenylundecyl)-trimethylammonium bromide (FTMA) as a model self-assembling redox mediator and alkanethiol-modified gold films as hydrophobic electrodes. By performing cyclic voltammetry (CV, 10 mV/s) in aqueous solutions containing FTMA above its critical micellar concentration (CMC), we measured anodic (Ia) and cathodic (Ic) peak current densities of 18 ± 3 and 1.1 ± 0.1 μA/cm(2), respectively, revealing substantial current rectification (Ia/Ic= 17) at the hydrophobic electrodes. In contrast, hydroxymethyl ferrocene (a non-self-assembling redox mediator) at hydrophobic electrodes and FTMA at bare gold electrodes, yielded relatively low levels of rectification (Ia/Ic= 1.7 and 2.3, respectively). Scan-rate-dependent measurements revealed Ia of FTMA to arise largely from the diffusion of FTMA from bulk solution to the hydrophobic electrode whereas Ic was dominated by adsorbed FTMA, leading to the proposal that current rectification observed with FTMA is mediated by interfacial assemblies of reduced FTMA that block access of oxidized FTMA to the hydrophobic electrode. Support for this proposal was obtained by using atomic force microscopy and quartz crystal microbalance measurements to confirm the existence of interfacial assemblies of reduced FTMA (1.56 ± 0.2 molecules/nm(2)). Additional characterization of a mixed surfactant system containing FTMA and dodecyltrimethylammonium bromide (DTAB) revealed that interfacial assemblies of DTAB also block access of oxidized FTMA to hydrophobic electrodes; this system exhibited Ia/Ic > 80. These results and others reported in this paper suggest that current rectification occurs in this system because oxidized FTMA does not mix with interfacial assemblies of reduced FTMA or DTAB formed at hydrophobic electrodes. More

  13. NUMEN Project @ LNS : Heavy ions double charge exchange reactions towards the 0νββ nuclear matrix element determination

    SciTech Connect

    Agodi, C. Calabretta, L.; Calanna, A.; Carbone, D.; Cavallaro, M.; Colonna, M.; Cuttone, G.; Finocchiaro, P.; Pandola, L.; Rifuggiato, D.; Tudisco, S.; Cappuzzello, F.; Greco, V.; Bonanno, D. L.; Bongiovanni, D. G.; Longhitano, F.; Branchina, V.; Foti, A.; Lo Presti, D.; Lanzalone, G.; and others

    2015-10-28

    In the NUMEN Project it is proposed an innovative technique to access the nuclear matrix elements entering in the expression of the life-time of the neutrinoless double beta decay, using relevant cross sections of double charge exchange reactions. A key aspect is the use of MAGNEX large acceptance magnetic spectrometer, for the detection of the ejectiles, and of the INFN Laboratori Nazionali del Sud (LNS) K800 Superconducting Cyclotron (CS), for the acceleration of the required high resolution and low emittance heavy-ion beams.

  14. A three-dimensional, quantum mechanical study of exchange and charge transfer processes in the (Ar+H2) + system

    NASA Astrophysics Data System (ADS)

    Baer, Michael; Nakamura, Hiroki

    1987-10-01

    A three-dimensional quantum mechanical study of the (Ar+H2)+ system was carried out within the reactive infinite order sudden approximation. All three arrangement channels for exchange and charge transfer were treated simultaneously. Steric factors, opacity functions, angular distributions, and integral cross sections were calculated. Whenever possible, these were compared with both experimental and trajectory surface hopping (TSH) results. Whereas the fit with the TSH results was reasonable, the fit obtained with the experiment was less satisfactory. The reason for that can be attributed at least partially to the semiempirical DIM potential employed in the calculation.

  15. Measurement of derivative of ion temperature using high spatial resolution charge exchange spectroscopy with space modulation optics

    SciTech Connect

    Ida, K.; Yoshinuma, M.; Inagaki, S.; Kobuchi, T.; Sakamoto, Y.; Matsunaga, G.; Koide, Y.

    2008-05-15

    A new technique to measure the first and second derivatives of the ion temperature profile has been developed by using a charge exchange spectroscopy system with space modulation optics. The space observed is scanned up to {+-}3 cm with a cosine wave modulation frequency up to 30 Hz by shifting the object lens in front of the optical fiber bundle by 0.5 mm with a piezoelement. The first and second derivatives of ion temperature are derived from the modulation component of the ion temperature measured by using Fourier series expansion.

  16. Quantification of strain and charge co-mediated magnetoelectric coupling on ultra-thin Permalloy/PMN-PT interface

    PubMed Central

    Nan, Tianxiang; Zhou, Ziyao; Liu, Ming; Yang, Xi; Gao, Yuan; Assaf, Badih A.; Lin, Hwaider; Velu, Siddharth; Wang, Xinjun; Luo, Haosu; Chen, Jimmy; Akhtar, Saad; Hu, Edward; Rajiv, Rohit; Krishnan, Kavin; Sreedhar, Shalini; Heiman, Don; Howe, Brandon M.; Brown, Gail J.; Sun, Nian X.

    2014-01-01

    Strain and charge co-mediated magnetoelectric coupling are expected in ultra-thin ferromagnetic/ferroelectric multiferroic heterostructures, which could lead to significantly enhanced magnetoelectric coupling. It is however challenging to observe the combined strain charge mediated magnetoelectric coupling, and difficult in quantitatively distinguish these two magnetoelectric coupling mechanisms. We demonstrated in this work, the quantification of the coexistence of strain and surface charge mediated magnetoelectric coupling on ultra-thin Ni0.79Fe0.21/PMN-PT interface by using a Ni0.79Fe0.21/Cu/PMN-PT heterostructure with only strain-mediated magnetoelectric coupling as a control. The NiFe/PMN-PT heterostructure exhibited a high voltage induced effective magnetic field change of 375 Oe enhanced by the surface charge at the PMN-PT interface. Without the enhancement of the charge-mediated magnetoelectric effect by inserting a Cu layer at the PMN-PT interface, the electric field modification of effective magnetic field was 202 Oe. By distinguishing the magnetoelectric coupling mechanisms, a pure surface charge modification of magnetism shows a strong correlation to polarization of PMN-PT. A non-volatile effective magnetic field change of 104 Oe was observed at zero electric field originates from the different remnant polarization state of PMN-PT. The strain and charge co-mediated magnetoelectric coupling in ultra-thin magnetic/ferroelectric heterostructures could lead to power efficient and non-volatile magnetoelectric devices with enhanced magnetoelectric coupling. PMID:24418911

  17. Effect of dense plasmas on exchange-energy shifts in highly charged ions: An alternative approach for arbitrary perturbation potentials

    SciTech Connect

    Rosmej, F.; Bennadji, K.; Lisitsa, V. S.

    2011-09-15

    An alternative method of calculation of dense plasma effects on exchange-energy shifts {Delta}E{sub x} of highly charged ions is proposed which results in closed expressions for any plasma or perturbation potential. The method is based on a perturbation theory expansion for the inner atomic potential produced by charged plasma particles employing the Coulomb Green function method. This approach allows us to obtain analytic expressions and scaling laws with respect to the electron temperature T, density n{sub e}, and nuclear charge Z. To demonstrate the power of the present method, two specific models were considered in detail: the ion sphere model (ISM) and the Debye screening model (DSM). We demonstrate that analytical expressions can be obtained even for the finite temperature ISM. Calculations have been carried out for the singlet 1s2p{sup 1} P{sub 1} and triplet 1s2p{sup 3} P{sub 1} configurations of He-like ions with charge Z that can be observed in dense plasmas via the He-like resonance and intercombination lines. Finally we discuss recently available purely numerical calculations and experimental data.

  18. Fast charge exchange ions in high power impulse magnetron sputtering of titanium as probes for the electrical potential

    NASA Astrophysics Data System (ADS)

    Breilmann, W.; Maszl, C.; von Keudell, A.

    2017-03-01

    High power impulse magnetron sputtering (HiPIMS) plasmas exhibit a high ionization fraction of the sputtered material and ions with high kinetic energies, which produce thin films with superior quality. These ion energy distribution functions (IEDF) contain energetic peaks, which are believed to be linked to a distinct electrical potential hump {{Δ }}{{{Φ }}}{{ionization}{{zone}}} inside rotating localized ionization zones, so called spokes, at target power densities above 1 kW cm‑2. Any direct measurement of this electrical potential structure is, however, very difficult due to the dynamic nature of the spokes and the very high local power density, which hampers the use of conventional emissive probes. Instead, we use a careful analysis of the IEDFs for singly and doubly charged titanium ions from a HiPIMS plasma at varying target power density. The energy peaks in the IEDFs measured at the substrate depend on the point of ionization and any charge exchange collisions on the path between ionization and impact at the substrate. Thereby, the IEDFs contain a convoluted information about the electrical potential structure inside the plasma. The analysis of these IEDFs reveal that higher ionization states originate at high target power densities from the central part of the plasma spoke, whereas singly charged ions originate from the perimeter of the plasma spoke. Consequently, we observe different absolute ion energies with the energy of Ti2+ being slightly higher than two times the energy of Ti+. Additional peaks are observed in the IEDFs of Ti+ originating from charge exchange reactions from Ti2+ and Ti3+ with titanium neutrals. Based on this analysis of the IEDFs, the structure of the electrical potential inside a spoke is inferred yielding {{Δ }}{{{Φ }}}{{ionization}{{zone}}} = 25 V above the plasma potential, irrespective of target power density.

  19. Chiral anion exchangers applied to capillary electrochromatography enantioseparation of oppositely charged chiral analytes: investigation of stationary and mobile phase parameters.

    PubMed

    Lämmerhofer, M; Tobler, E; Lindner, W

    2000-07-28

    Weak anion-exchange (WAX) type chiral stationary phases (CSPs) based on tert.-butyl carbamoyl quinine as chiral selector (SO) and different types of silica particles (porous and non-porous) as chromatographic support are evaluated in packed capillary electrochromatography (CEC). Their ability to resolve the enantiomers of negatively charged chiral analytes, e.g., N-derivatized amino acids, in the anion-exchange mode and their electrochromatographic characteristics are described in dependence of several mobile phase parameters (pH, buffer type and concentration, organic modifier type and concentration) and other experimental variables (electric field strength, capillary temperature). The inherent "zwitterionic" surface character of such silica-based WAX type CSPs (positively charged SO and negatively charged residual silanols) allows the reversal of the electroosmotic flow (EOF) towards the anode at pH values below the isoelectric point (pI) of the modified surface, whereas a cathodic EOF results at pH values above the pI. Since for negatively charged analytes also an electrophoretic transport increment has to be considered, which can be either in or against the EOF direction, several distinct modes of elution have been observed under different stationary phase and mobile phase conditions: (i) co-electrophoretic elution of the negatively charged solutes with the anodic EOF in the negative polarity mode, (ii) counter-electrophoretic elution with the cathodic EOF in the positive polarity mode, and (iii) electrophoretically dominated elution in the negative polarity mode with a cathodic EOF directed to the injection end of the capillary. Useful enantioseparations of chiral acids have been obtained with all three modes. Enantioselectivity values as high as under pressure-driven conditions and theoretical plate numbers up to 120000 per meter could be achieved under electrically driven conditions. A repeatability study yielded RSD values below 2% for retention times and

  20. Charge Profile Analysis Reveals That Activation of Pro-apoptotic Regulators Bax and Bak Relies on Charge Transfer Mediated Allosteric Regulation

    PubMed Central

    Ionescu, Crina-Maria; Svobodová Vařeková, Radka; Prehn, Jochen H. M.; Huber, Heinrich J.; Koča, Jaroslav

    2012-01-01

    The pro-apoptotic proteins Bax and Bak are essential for executing programmed cell death (apoptosis), yet the mechanism of their activation is not properly understood at the structural level. For the first time in cell death research, we calculated intra-protein charge transfer in order to study the structural alterations and their functional consequences during Bax activation. Using an electronegativity equalization model, we investigated the changes in the Bax charge profile upon activation by a functional peptide of its natural activator protein, Bim. We found that charge reorganizations upon activator binding mediate the exposure of the functional sites of Bax, rendering Bax active. The affinity of the Bax C-domain for its binding groove is decreased due to the Arg94-mediated abrogation of the Ser184-Asp98 interaction. We further identified a network of charge reorganizations that confirms previous speculations of allosteric sensing, whereby the activation information is conveyed from the activation site, through the hydrophobic core of Bax, to the well-distanced functional sites of Bax. The network was mediated by a hub of three residues on helix 5 of the hydrophobic core of Bax. Sequence and structural alignment revealed that this hub was conserved in the Bak amino acid sequence, and in the 3D structure of folded Bak. Our results suggest that allostery mediated by charge transfer is responsible for the activation of both Bax and Bak, and that this might be a prototypical mechanism for a fast activation of proteins during signal transduction. Our method can be applied to any protein or protein complex in order to map the progress of allosteric changes through the proteins' structure. PMID:22719244

  1. Use of the TFTR prototype charge exchange neutral analyzer for fast He/sub 3//sup + +/ diagnostics during ICRF heating on PLT

    SciTech Connect

    Medley, S.S.

    1981-07-01

    The Charge Exchange Neutral Analyzer (CENA) for TFTR is designed to measure singly charged ion species of atomic mass A = 1, 2, and 3 simultaneously with up to 75 energy channels per mass and an energy range of 0.5 < AE < 600, where AE is in units of AMU.keV. Plans to test the prototype analyzer on PLT prior to installation on TFTR are discussed. The capability of the analyzer to simultaneously measure singly reionized H, D, and He/sub 3/ charge exchange neutrals makes the analyzer of particular interest for recently proposed fast He/sub 3//sup + +/ diagnostics during ICRF heating on PLT.

  2. Charge transfer and momentum exchange in exospheric D-H(+) and H-D(+) collisions

    NASA Technical Reports Server (NTRS)

    Hodges, R. R., Jr.; Breig, E. L.

    1993-01-01

    Mechanisms that control the escape of deuterium from planetary exospheres include the acceleration of D(+) in the polar wind, and the production of suprathermal D atoms through nonthermal collisions. In this paper we examine the effects of neutral-ion interactions involving deuterium and hydrogen on the velocity distribution of neutral D. A two-center scattering approximation is used as the basis for calculations of the differential cross sections for charge transfer and elastic scatter in collision of H with D(+) and of D with H(+) for ionosphere-exosphere collision energies below 10 e V. These data are used to derive temperature dependent rate coefficients for the charge transfer branches of these interactions, and to determine the effects of ion-neutral temperature differences on the rate of generation of suprathermal D through charge transfer and elastic scatter.

  3. The effect of the charge exchange source on the velocity and 'temperature' distributions and their anisotropies in the earth's exosphere

    NASA Astrophysics Data System (ADS)

    Hodges, R. R., Jr.; Rohrbaugh, R. P.; Tinsley, B. A.

    1981-08-01

    The velocity distribution of atomic hydrogen in the earth's exosphere is calculated as a function of altitude and direction taking into account both the classic exobase source and the higher-altitude plasmaspheric charge exchange source. Calculations are performed on the basis of a Monte Carlo technique in which random ballistic trajectories of individual atoms are traced through a three-dimensional grid of audit zones, at which relative concentrations and momentum or energy fluxes are obtained. In the case of the classical exobase source alone, the slope of the velocity distribution is constant only for the upward radial velocity component and increases dramatically with altitude for the incoming radial and transverse velocity components, resulting in a temperature decrease. The charge exchange source, which produces the satellite hydrogen component and the hot ballistic and escape components of the exosphere, is found to enhance the wings of the velocity distributions, however this effect is not sufficient to overcome the temperature decreases at altitudes above one earth radius. The resulting global model of the hydrogen exosphere may be used as a realistic basis for radiative transfer calculations.

  4. The effect of the charge exchange source on the velocity and 'temperature' distributions and their anisotropies in the earth's exosphere

    NASA Technical Reports Server (NTRS)

    Hodges, R. R., Jr.; Rohrbaugh, R. P.; Tinsley, B. A.

    1981-01-01

    The velocity distribution of atomic hydrogen in the earth's exosphere is calculated as a function of altitude and direction taking into account both the classic exobase source and the higher-altitude plasmaspheric charge exchange source. Calculations are performed on the basis of a Monte Carlo technique in which random ballistic trajectories of individual atoms are traced through a three-dimensional grid of audit zones, at which relative concentrations and momentum or energy fluxes are obtained. In the case of the classical exobase source alone, the slope of the velocity distribution is constant only for the upward radial velocity component and increases dramatically with altitude for the incoming radial and transverse velocity components, resulting in a temperature decrease. The charge exchange source, which produces the satellite hydrogen component and the hot ballistic and escape components of the exosphere, is found to enhance the wings of the velocity distributions, however this effect is not sufficient to overcome the temperature decreases at altitudes above one earth radius. The resulting global model of the hydrogen exosphere may be used as a realistic basis for radiative transfer calculations.

  5. Nongeminate Radiative Recombination of Free Charges in Cation-Exchanged PbS Quantum Dot Films

    SciTech Connect

    Marshall, Ashley R.; Beard, Matthew C.; Johnson, Justin C.

    2016-06-01

    Using photoluminescence (PL) spectroscopy we explore the radiative recombination pathways in PbS quantum dots (QDs) synthesized by two methods. We compare conventionally synthesized PbS from a PbO precursor to PbS synthesized using cation-exchange from CdS QDs. We show that strongly coupled films of PbS QDs from the cation-exchange luminesce with significant efficiency at room temperature. This is in stark contrast to conventional PbS QDs, which have exceedingly weak room temperature emission. Moreover, the power dependence of the emission is quadratic, indicating bimolecular radiative recombination that is reasonably competitive with trap-assisted recombination, a feature previously unreported in coupled PbS QD films. We interpret these results in terms of a greatly reduced defect concentration for cation-exchanged QDs that mitigates the influence of trap-assisted recombination. Cation-exchanged QDs have recently been employed in highly efficient and air-stable lead chalcogenide QD devices, and the reduced number of trap states inferred here may lead to improved current collection and higher open circuit voltage.

  6. Charge-assisted bond N(+)H mediates the gelation of amorphous lurasidone hydrochloride during dissolution.

    PubMed

    Qian, Shuai; Wang, Shanshan; Li, Zhen; Wang, Xiaojie; Ma, Di; Liang, Shujun; Gao, Yuan; Zhang, Jianjun; Wei, Yuanfeng

    2017-02-25

    Lurasidone hydrochloride (LH), the hydrochloride form of lurasidone with a charge-assisted bond N(+)H, is an atypical antipsychotropic agent for the treatment of schizophrenia. As a BCS class II drug, LH has a low oral bioavailability mainly due to its poor water solubility and low dissolution. In order to improve its solubility, amorphization of LH was performed and characterized. Unexpectedly, the dissolution rate of amorphous LH was much lower than that of crystalline LH. In addition, the amorphous LH powders quickly aggregated when contacting the dissolution media (water, 37°C), and formed a sticky gel adhering on the paddle. The follow-up polarized light microscope, XRPD, DSC, and FTIR analysis found that amorphous LH transformed to crystalline LH during dissolution. On the other hand, no such gelation phenomenon of amorphous lurasidone was observed under the same dissolution condition. However, the gel would reform when dropping concentrated hydrochloric acid slowly into the bottom of the medium during the dissolution of amorphous lurasidone, and XRPD/DSC/FTIR results indicated that the regenerated gel was consisted of crystalline LH, suggesting that the charge-assisted bond N(+)H in the structure of LH mediated the gel formation of amorphous LH during its dissolution process.

  7. Charge-signal multiplication mediated by urea wires inside Y-shaped carbon nanotubes

    SciTech Connect

    Lv, Mei; Liu, Zengrong; He, Bing; Xiu, Peng E-mail: ystu@shu.edu.cn; Tu, Yusong E-mail: ystu@shu.edu.cn

    2014-07-28

    In previous studies, we reported molecular dynamics (MD) simulations showing that single-file water wires confined inside Y-shaped single-walled carbon nanotubes (Y-SWNTs) held strong and robust capability to convert and multiply charge signals [Y. S. Tu, P. Xiu, R. Z. Wan, J. Hu, R. H. Zhou, and H. P. Fang, Proc. Natl. Acad. Sci. U.S.A. 106, 18120 (2009); Y. Tu, H. Lu, Y. Zhang, T. Huynh, and R. Zhou, J. Chem. Phys. 138, 015104 (2013)]. It is fascinating to see whether the signal multiplication can be realized by other kinds of polar molecules with larger dipole moments (which make the experimental realization easier). In this article, we use MD simulations to study the urea-mediated signal conversion and multiplication with Y-SWNTs. We observe that when a Y-SWNT with an external charge of magnitude 1.0 e (the model of a signal at the single-electron level) is solvated in 1 M urea solutions, urea can induce drying of the Y-SWNT and fill its interiors in single-file, forming Y-shaped urea wires. The external charge can effectively control the dipole orientation of the urea wire inside the main channel (i.e., the signal can be readily converted), and this signal can further be multiplied into 2 (or more) output signals by modulating dipole orientations of urea wires in bifurcated branch channels of the Y-SWNT. This remarkable signal transduction capability arises from the strong dipole-induced ordering of urea wires under extreme confinement. We also discuss the advantage of urea as compared with water in the signal multiplication, as well as the robustness and biological implications of our findings. This study provides the possibility for multiplying signals by using urea molecules (or other polar organic molecules) with Y-shaped nanochannels and might also help understand the mechanism behind signal conduction in both physical and biological systems.

  8. Calculation of total cross sections for charge exchange in molecular collisions

    NASA Technical Reports Server (NTRS)

    Ioup, J.

    1979-01-01

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

  9. Ion-exchange molecularly imprinted polymer for the extraction of negatively charged acesulfame from wastewater samples.

    PubMed

    Zarejousheghani, Mashaalah; Schrader, Steffi; Möder, Monika; Lorenz, Pierre; Borsdorf, Helko

    2015-09-11

    Acesulfame is a known indicator that is used to identify the introduction of domestic wastewater into water systems. It is negatively charged and highly water-soluble at environmental pH values. In this study, a molecularly imprinted polymer (MIP) was synthesized for negatively charged acesulfame and successfully applied for the selective solid phase extraction (SPE) of acesulfame from influent and effluent wastewater samples. (Vinylbenzyl)trimethylammonium chloride (VBTA) was used as a novel phase transfer reagent, which enhanced the solubility of negatively charged acesulfame in the organic solvent (porogen) and served as a functional monomer in MIP synthesis. Different molecularly imprinted polymers were synthesized to optimize the extraction capability of acesulfame. The different materials were evaluated using equilibrium rebinding experiments, selectivity experiments and scanning electron microscopy (SEM). The most efficient MIP was used in a molecularly imprinted-solid phase extraction (MISPE) protocol to extract acesulfame from wastewater samples. Using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) analysis, detection and quantification limits were achieved at 0.12μgL(-1) and 0.35μgL(-1), respectively. Certain cross selectivity for the chemical compounds containing negatively charged sulfonamide functional group was observed during selectivity experiments.

  10. Polycation-exchanged clays as sorbents for organic pollutants: Influence of layer charge on pollutant sorption capacity

    SciTech Connect

    Breen, C.; Watson, R.

    1998-12-15

    The uptake curves for the adsorption of a polycation ([CH{sub 2}CH(OH)CH{sub 2}N(CH{sub 3}){sub 2}]{sub n}{sup n+}(Cl){sub n}{sup n{minus}}) onto a low iron Texas bentonite, WL, have been determined and compared with those onto two source smectites, SWy-1 and SAz-1. The polycation exhibited a marked affinity for all the smectite surfaces but polycation uptake was maximized on the fine fractions of Na{sup +}-WL. Variable temperature X-ray diffraction of the clay polycation complexes showed that the polycation was segregated into different interlayers at loadings below 30% of the CEC. The adsorption of benzene onto TMA{sup +}-exchanged SWy-1, SAz-1, and WL showed that, despite having a comparable layer charge to SWy-1, WL was as poor a sorbent for benzene as SAz-1, which has a much higher layer charge. The adsorption of p-nitrophenol (PNP) from aqueous solution onto the TMA{sup +}-exchanged sorbents exhibited the same trends, although a smaller amount was adsorbed due to the greater size of PNP. The amount of PNP adsorbed by polycation-treated SWy-1 depended upon the polycation loading, and PNP uptake maximized at loadings of 28 and 46 mg/(g clay). At higher loadings (80, 102, and 147 mg/(g clay)) the uptake curves became linear and the PNP uptake decreased with increased polycation loading. No polycation-treated clay was as effective as TMA{sup +}-exchanged SWy-1 for the removal of PNP from water.

  11. Exchange bias effect in Au-Fe3O4 dumbbell nanoparticles induced by the charge transfer from gold

    SciTech Connect

    Feygenson, Mikhail; Bauer, John C.; Gai, Zheng; Marques, Carlos; Aronson, Meigan C.; Teng, Xiaowei; Su, Dong; Stanic, Vesna; Urban, Volker S.; Beyer, Kevin A.; Dai, Sheng

    2015-08-10

    We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron-scattering, synchrotron x-ray diffraction, and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wustite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatch between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into the FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed, presumably across the interface to accommodate an excess of oxygen released during the reduction of magnetite

  12. Exchange bias effect in Au-Fe3O4 dumbbell nanoparticles induced by the charge transfer from gold

    DOE PAGES

    Feygenson, Mikhail; Bauer, John C; Gai, Zheng; ...

    2015-08-10

    We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron scattering, synchrotron x-ray diffraction and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wüstite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatchmore » between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed across the interface to accommodate an excess of oxygen released during the reduction of magnetite.« less

  13. Ion Mobility Spectrometry-Hydrogen Deuterium Exchange Mass Spectrometry of Anions: Part 2. Assessing Charge Site Location and Isotope Scrambling.

    PubMed

    Khakinejad, Mahdiar; Kondalaji, Samaneh Ghassabi; Donohoe, Gregory C; Valentine, Stephen J

    2016-03-01

    Ion mobility spectrometry (IMS) coupled with gas-phase hydrogen deuterium exchange (HDX)-mass spectrometry (MS) and molecular dynamic simulations (MDS) has been used for structural investigation of anions produced by electrospraying a sample containing a synthetic peptide having the sequence KKDDDDDIIKIIK. In these experiments the potential of the analytical method for locating charge sites on ions as well as for utilizing collision-induced dissociation (CID) to reveal the degree of deuterium uptake within specific amino acid residues has been assessed. For diffuse (i.e., more elongated) [M - 2H](2-) ions, decreased deuterium content along with MDS data suggest that the D4 and D6 residues are charge sites, whereas for the more diffuse [M - 3H](3-) ions, the data suggest that the D4, D7, and the C-terminus are deprotonated. Fragmentation of mobility-selected, diffuse [M - 2H](2-) ions to determine deuterium uptake at individual amino acid residues reveals a degree of deuterium retention at incorporation sites. Although the diffuse [M - 3H](3-) ions may show more HD scrambling, it is not possible to clearly distinguish HD scrambling from the expected deuterium uptake based on a hydrogen accessibility model. The capability of the IMS-HDX-MS/MS approach to provide relevant details about ion structure is discussed. Additionally, the ability to extend the approach for locating protonation sites on positively-charged ions is presented.

  14. Ion Mobility Spectrometry-Hydrogen Deuterium Exchange Mass Spectrometry of Anions: Part 2. Assessing Charge Site Location and Isotope Scrambling

    NASA Astrophysics Data System (ADS)

    Khakinejad, Mahdiar; Ghassabi Kondalaji, Samaneh; Donohoe, Gregory C.; Valentine, Stephen J.

    2016-03-01

    Ion mobility spectrometry (IMS) coupled with gas-phase hydrogen deuterium exchange (HDX)-mass spectrometry (MS) and molecular dynamic simulations (MDS) has been used for structural investigation of anions produced by electrospraying a sample containing a synthetic peptide having the sequence KKDDDDDIIKIIK. In these experiments the potential of the analytical method for locating charge sites on ions as well as for utilizing collision-induced dissociation (CID) to reveal the degree of deuterium uptake within specific amino acid residues has been assessed. For diffuse (i.e., more elongated) [M - 2H]2- ions, decreased deuterium content along with MDS data suggest that the D4 and D6 residues are charge sites, whereas for the more diffuse [M - 3H]3- ions, the data suggest that the D4, D7, and the C-terminus are deprotonated. Fragmentation of mobility-selected, diffuse [M - 2H]2- ions to determine deuterium uptake at individual amino acid residues reveals a degree of deuterium retention at incorporation sites. Although the diffuse [M - 3H]3- ions may show more HD scrambling, it is not possible to clearly distinguish HD scrambling from the expected deuterium uptake based on a hydrogen accessibility model. The capability of the IMS-HDX-MS/MS approach to provide relevant details about ion structure is discussed. Additionally, the ability to extend the approach for locating protonation sites on positively-charged ions is presented.

  15. Shorting time of magnetically insulated reflex-ion diodes from the neutral-atom charge-exchange mechanism

    SciTech Connect

    Strobel, G.

    1981-10-01

    In a magnetically insulated diode, collision-free electrons return to the cathode and no electron current is present at the anode. Electron transport to the anode is studied in this paper. Steady-state space-charge-limited flow is assumed initially. Breakdown of ion flow occurs when static neutral atoms at the anode undergo charge exchange, which results in neutral atoms drifting across the diode. These are subsequently ionized by reflexing ions producing electrons trapped in Larmor orbits throughout the diode. These electrons drift to the anode via ionization and inelastic collisions with other neutral atoms. Model calculations compare the effects of foil and mesh cathodes. Steady-state space-charge-limited ion current densities are calculated. The neutral atom density at the cathode is determined as a function of time. The shorting time of the diode is scaled versus the electrode separation d, the diode potential V/sub 0/, the magnetic field, and the initial concentration of static neutron atoms.

  16. The velocity dependence of X-ray emission due to Charge Exchange: Applications in the Cygnus Loop

    NASA Astrophysics Data System (ADS)

    Cumbee, Renata; Lyons, David; Mullen, Patrick; Shelton, Robin L.; Stancil, Phillip C.; Schultz, David R.

    2016-04-01

    The fundamental collisional process of charge exchange (CX) has been been established as a primary source of X-ray emission from the heliosphere [1], planetary exospheres [2], and supernova remnants [3,4]. In this process, X-ray emission results from the capture of an electron by a highly charged ion from a neutral atom or molecule, to form a highly-excited, high charge state ion. As the captured electron cascades down to the lowest energy level, photons are emitted, including X-rays.To provide reliable CX-induced X-ray spectral models to realistically simulate high-energy astrophysical environments, line ratios and spectra are computed using theoretical CX cross-sections obtained with the multi-channel Landau-Zener, atomic-orbital close-coupling, and classical-trajectory Monte Carlo methods for various collisional velocities. Collisions of bare and H-like C to Al ions with H, He, and H2 are considered. Using these line ratios, XSPEC models of CX emission in the northeast rim of the Cygnus Loop supernova remnant will be shown as an example with ion velocity dependence.[1] Henley, D. B. & Shelton, R. L. 2010, ApJSS, 187, 388[2] Dennerl, K. et al. 2002, A&A 386, 319[3] Katsuda, S. et al. 2011, ApJ 730 24[4] Cumbee, R. S. et al. 2014, ApJ 787 L31

  17. Conjugation-mediated plasmid exchange between bacteria grown under space flight conditions

    NASA Astrophysics Data System (ADS)

    De Boever, P.; Mergeay, M.; Ilyin, V.; Forget-Hanus, D.; Van der Auwera, G.; Mahillon, J.

    2007-09-01

    Mobile genetic elements (MGE) such as phages, plasmids and transposons play a crucial role in bacterial adaptation and evolution. These MGE mobilize and reorganize genes within a given genome or between bacterial cells. The impact of space flight conditions on these processes is largely unknown. The Mobilisatsia/Plasmida experiment was set up to investigate the impact of space flight conditions on plasmid-mediated conjugation. The experiment was done aboard the International Space Station during the Soyuz Mission 8S (April 19th until April 30th 2004). An experiment was performed with the Gram-positive Bacillus thuringiensis AND931 (carrying the conjugative plasmid pXO 16), B. thuringiensis 4Q7 (with mobilizable plasmid pC194) andB. thuringiensis GBJ002 (final recipient). A second experiment was carried out with the Gram-negative Escherichia coli CM140 (carrying the conjugative plasmid RP4), E. coli CM1962 (with the mobilizable plasmid pMOL222) and Cupriavidus metallidurans AE815 (final recipient). It was observed by selective platings that plasmid exchange between the Gram-positive bacterial strains occurred in the space flight experiment. It is speculated that the latter plasmid exchange occurs more efficient than in the ground control experiment. No significant differences could be observed between space flight and ground control for the Gram-negative bacteria. The data indicate that plasmid exchange between microorganisms is occurring under space flight conditions. Since microorganisms are endogenous to any spacecraft and their presence considered as a possible jeopardy for manned space exploration, more experiments are needed to evaluate the occurrence and implications of microbial adaptation and evolution via MGE.

  18. Ionization and Charge Exchange Reactions in Neutral Entrainment of a Field Reversed Configuration Thruster

    DTIC Science & Technology

    2012-07-16

    exchange and ionization rates for neon are plotted in Fig. 3 (right). The recombination rate is not shown as it was found, similar to helium , to be much...temperature for light gas, helium are shown in Fig. 2 (left). It can be concluded that at those temperatures and a number density on the order of 1018 m−3...process in a helium -based FRC thruster may be expected to be fairly efficient, especially for lower plasma temperatures. Note however that for

  19. Site-specific recombination in the chicken genome using Flipase recombinase-mediated cassette exchange.

    PubMed

    Lee, Hong Jo; Lee, Hyung Chul; Kim, Young Min; Hwang, Young Sun; Park, Young Hyun; Park, Tae Sub; Han, Jae Yong

    2016-02-01

    Targeted genome recombination has been applied in diverse research fields and has a wide range of possible applications. In particular, the discovery of specific loci in the genome that support robust and ubiquitous expression of integrated genes and the development of genome-editing technology have facilitated rapid advances in various scientific areas. In this study, we produced transgenic (TG) chickens that can induce recombinase-mediated gene cassette exchange (RMCE), one of the site-specific recombination technologies, and confirmed RMCE in TG chicken-derived cells. As a result, we established TG chicken lines that have, Flipase (Flp) recognition target (FRT) pairs in the chicken genome, mediated by piggyBac transposition. The transgene integration patterns were diverse in each TG chicken line, and the integration diversity resulted in diverse levels of expression of exogenous genes in each tissue of the TG chickens. In addition, the replaced gene cassette was expressed successfully and maintained by RMCE in the FRT predominant loci of TG chicken-derived cells. These results indicate that targeted genome recombination technology with RMCE could be adaptable to TG chicken models and that the technology would be applicable to specific gene regulation by cis-element insertion and customized expression of functional proteins at predicted levels without epigenetic influence.

  20. Oxidative stress-mediated hemolytic activity of solvent exchange-prepared fullerene (C60) nanoparticles

    NASA Astrophysics Data System (ADS)

    Trpkovic, Andreja; Todorovic-Markovic, Biljana; Kleut, Duska; Misirkic, Maja; Janjetovic, Kristina; Vucicevic, Ljubica; Pantovic, Aleksandar; Jovanovic, Svetlana; Dramicanin, Miroslav; Markovic, Zoran; Trajkovic, Vladimir

    2010-09-01

    The present study investigated the hemolytic properties of fullerene (C60) nanoparticles prepared by solvent exchange using tetrahydrofuran (nC60THF), or by mechanochemically assisted complexation with macrocyclic oligosaccharide gamma-cyclodextrin (nC60CDX) or the copolymer ethylene vinyl acetate-ethylene vinyl versatate (nC60EVA-EVV). The spectrophotometrical analysis of hemoglobin release revealed that only nC60THF, but not nC60CDX or nC60EVA-EVV, was able to cause lysis of human erythrocytes in a dose- and time-dependent manner. Atomic force microscopy revealed that nC60THF-mediated hemolysis was preceded by erythrocyte shrinkage and increase in cell surface roughness. A flow cytometric analysis confirmed a decrease in erythrocyte size and demonstrated a significant increase in reactive oxygen species production in red blood cells exposed to nC60THF. The nC60THF-triggered hemolytic activity was efficiently reduced by the antioxidants N-acetylcysteine and butylated hydroxyanisole, as well as by serum albumin, the most abundant protein in human blood plasma. These data indicate that nC60THF can cause serum albumin-preventable hemolysis through oxidative stress-mediated damage of the erythrocyte membrane.

  1. Gold nanoparticles produced in situ mediate bioelectricity and hydrogen production in a microbial fuel cell by quantized capacitance charging.

    PubMed

    Kalathil, Shafeer; Lee, Jintae; Cho, Moo Hwan

    2013-02-01

    Oppan quantized style: By adding a gold precursor at its cathode, a microbial fuel cell (MFC) is demonstrated to form gold nanoparticles that can be used to simultaneously produce bioelectricity and hydrogen. By exploiting the quantized capacitance charging effect, the gold nanoparticles mediate the production of hydrogen without requiring an external power supply, while the MFC produces a stable power density.

  2. Neutralizing positive charges at the surface of a protein lowers its rate of amide hydrogen exchange without altering its structure or increasing its thermostability.

    PubMed

    Shaw, Bryan F; Arthanari, Haribabu; Narovlyansky, Max; Durazo, Armando; Frueh, Dominique P; Pollastri, Michael P; Lee, Andrew; Bilgicer, Basar; Gygi, Steven P; Wagner, Gerhard; Whitesides, George M

    2010-12-15

    This paper combines two techniques--mass spectrometry and protein charge ladders--to examine the relationship between the surface charge and hydrophobicity of a representative globular protein (bovine carbonic anhydrase II; BCA II) and its rate of amide hydrogen-deuterium (H/D) exchange. Mass spectrometric analysis indicated that the sequential acetylation of surface lysine-ε-NH3(+) groups--a type of modification that increases the net negative charge and hydrophobicity of the surface of BCA II without affecting its secondary or tertiary structure--resulted in a linear decrease in the aggregate rate of amide H/D exchange at pD 7.4, 15 °C. According to analysis with MS, the acetylation of each additional lysine generated between 1.4 and 0.9 additional hydrogens that are protected from H/D exchange during the 2 h exchange experiment at 15 °C, pD 7.4. NMR spectroscopy demonstrated that none of the hydrogen atoms which became protected upon acetylation were located on the side chain of the acetylated lysine residues (i.e., lys-ε-NHCOCH3) but were instead located on amide NHCO moieties in the backbone. The decrease in rate of exchange associated with acetylation paralleled a decrease in thermostability: the most slowly exchanging rungs of the charge ladder were the least thermostable (as measured by differential scanning calorimetry). This observation--that faster rates of exchange are associated with slower rates of denaturation--is contrary to the usual assumptions in protein chemistry. The fact that the rates of H/D exchange were similar for perbutyrated BCA II (e.g., [lys-ε-NHCO(CH2)2CH3]18) and peracetylated BCA II (e.g., [lys-ε-NHCOCH3]18) suggests that the electrostatic charge is more important than the hydrophobicity of surface groups in determining the rate of H/D exchange. These electrostatic effects on the kinetics of H/D exchange could complicate (or aid) the interpretation of experiments in which H/D exchange methods are used to probe the structural

  3. Charge exchange ionization in collision cells as a method to detect the presence of long-lived excited electronic states of polyatomic ions.

    PubMed

    Kwon, C H; Kim, M S; Choe, J C

    2001-10-01

    Charge exchange ionization in collision cells installed in a double focusing mass spectrometer with reversed geometry has been used to detect the presence of a long-lived excited electronic state of benzene ion. In particular, the first collision cell located between the ion source and the magnetic sector was modified to serve as an ion source for the reagent ion generated by charge exchange with the primary ion. Strong reagent ion signals were observed when the ionization energies of the reagents (1,3-C4H6, CS2, CH3Cl) were lower than the recombination energy (approximately 11.5 eV) of the excited state benzene ion, while the signals were negligible for reagents (CH3F,CH4) with higher ionization energy. The fact that a strong signal is observable only for electronically exoergic charge exchange is useful for detecting the presence of a long-lived electronically excited state.

  4. Cationic-anionic mediated charge compensation on La2Ti2O7 for visible light photocatalysis.

    PubMed

    Liu, Peng; Nisar, Jawad; Pathak, Biswarup; Ahuja, Rajeev

    2013-10-28

    The cationic-anionic mediated charge compensation effect was studied in the layered perovskite La2Ti2O7 for the visible light photocatalysis. Our screened hybrid density functional study shows that the electronic structure of La2Ti2O7 can be tuned by the cationic (V, Nb, Ta)/anionic (N) mono- and co-doping. Such mono-doping creates impurity states in the band gap which helps the electron-hole recombination. But if the charge compensation is made by the cationic-anionic mediated co-doping then such impurity states can be removed and can be a promising strategy for visible light photocatalysis. The absolute band edge position of the doped La2Ti2O7 has been aligned with respect to the water oxidation/reduction potential. The calculated defect formation energy shows the stability of the co-doping system is improved due to the coulomb interactions and charge compensations effect.

  5. FISH-MEDIATED NUTRIENT AND ENERGY EXCHANGE BETWEEN A LAKE SUPERIOR COASTAL WETLAND AND ITS ADJACENT BAY

    EPA Science Inventory

    Little has been done to quantify fluxes of organisms, nutrients, and energy between freshwater coastal habitats and adjacent offshore waters or to evaluate the ecological implications of these exchanges on a whole-lake basis. To test the hypothesis that fish-mediated transport m...

  6. A simple polymerase chain reaction-based method for the construction of recombinase-mediated cassette exchange donor vectors.

    PubMed

    Bateman, Jack R; Wu, C-ting

    2008-11-01

    Here we describe a simple method for generating donor vectors suitable for targeted transgenesis via recombinase-mediated cassette exchange (RMCE) using the PhiC31 integrase. This PCR-based strategy employs small attB "tails" on the primers used to amplify a sequence of interest, permitting the rapid creation of transgenes for in vivo analysis.

  7. Symmetric Resonance Charge Exchange Cross Section Based on Impact Parameter Treatment

    NASA Technical Reports Server (NTRS)

    Omidvar, Kazem; Murphy, Kendrah; Atlas, Robert (Technical Monitor)

    2002-01-01

    Using a two-state impact parameter approximation, a calculation has been carried out to obtain symmetric resonance charge transfer cross sections between nine ions and their parent atoms or molecules. Calculation is based on a two-dimensional numerical integration. The method is mostly suited for hydrogenic and some closed shell atoms. Good agreement has been obtained with the results of laboratory measurements for the ion-atom pairs H+-H, He+-He, and Ar+-Ar. Several approximations in a similar published calculation have been eliminated.

  8. Mechanism of charged pollutants removal in an ion exchange membrane bioreactor: drinking water denitrification.

    PubMed

    Velizarov, S; Rodrigues, C M; Reis, M A; Crespo, J G

    The mechanism of anionic pollutant removal in an ion exchange membrane bioreactor (IEMB) was studied for drinking water denitrification. This hybrid process combines continuous ion exchange transport (Donnan dialysis) of nitrate and its simultaneous bioreduction to gaseous nitrogen. A nonporous mono-anion permselective membrane precludes direct contact between the polluted water and the denitrifying culture and prevents secondary pollution of the treated water with dissolved nutrients and metabolic products. Complete denitrification may be achieved without accumulation of NO3(-) and NO2(-) ions in the biocompartment. Focus was given to the effect of the concentration of co-ions, counterions, and ethanol on the IEMB performance. The nitrate overall mass transfer coefficient in this hybrid process was found to be 2.8 times higher compared to that in a pure Donnan dialysis process without denitrification. Furthermore, by adjusting the ratio of co-ions between the biocompartment and the polluted water compartment, the magnitude and direction of each individual anion flux can be easily regulated, allowing for flexible process operation and control. Synthetic groundwater containing 135-350 mg NO3(-) L(-1) was treated in the IEMB system. A surface denitrification rate of 33 g NO3(-) per square meter of membrane per day was obtained at a nitrate loading rate of 360 g NO3(-) m(-3)d(-1), resulting in a nitrate removal efficiency of 85%.

  9. Energy exchange between a laser beam and charged particles using inverse transition radiation and method for its use

    DOEpatents

    Kimura, Wayne D.; Romea, Richard D.; Steinhauer, Loren C.

    1998-01-01

    A method and apparatus for exchanging energy between relativistic charged particles and laser radiation using inverse diffraction radiation or inverse transition radiation. The beam of laser light is directed onto a particle beam by means of two optical elements which have apertures or foils through which the particle beam passes. The two apertures or foils are spaced by a predetermined distance of separation and the angle of interaction between the laser beam and the particle beam is set at a specific angle. The separation and angle are a function of the wavelength of the laser light and the relativistic energy of the particle beam. In a diffraction embodiment, the interaction between the laser and particle beams is determined by the diffraction effect due to the apertures in the optical elements. In a transition embodiment, the interaction between the laser and particle beams is determined by the transition effect due to pieces of foil placed in the particle beam path.

  10. Forward sum rule for the 2 γ -exchange correction to the charge-radius extraction from elastic electron scattering

    NASA Astrophysics Data System (ADS)

    Gorchtein, Mikhail

    2014-11-01

    Two-photon-exchange (TPE) contributions to elastic electron-proton scattering in the forward regime in leading logarithmic ˜t ln|t | approximation in the momentum transfer t are considered. The imaginary part of the TPE amplitude in the forward kinematics is related to the total photoabsorption cross section. The real part of the TPE amplitude is obtained from an unsubtracted fixed-t dispersion relation. This allows a clean prediction of the real part of the TPE amplitude at forward angles with the leading term ˜t ln|t | . Numerical estimates are comparable with or exceed the experimental precision in extracting the charge radius from the experimental data.

  11. Charge-exchange x-ray spectra: Evidence for significant contributions from radiative decays of doubly excited states

    NASA Astrophysics Data System (ADS)

    Ali, R.; Beiersdorfer, P.; Harris, C. L.; Neill, P. A.

    2016-01-01

    Charge-exchange collisions of slow Ne+10 ions with He, Ne, and Ar targets were studied with simultaneous x-ray and cold-target recoil-ion-momentum spectroscopy proving the contribution of several mechanisms to the radiative stabilization of apparent (4,4) doubly excited states for He and Ne targets and of (5,6) states for Ar. In particular, the stabilization efficiency of the mechanism of dynamic auto-transfer to Rydberg states is confirmed. Moreover, we present evidence for direct radiative decays of (4,4) states populated in collisions with He, which is an experimental indication of the population of so-called unnatural-parity states in such collisions. These mechanisms lead to the emission of x-rays that have considerably higher energies than those predicted by current spectral models and may explain recent observations of anomalously large x-ray emission from Rydberg levels.

  12. Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide: Power-law decay of the charge density exchange

    SciTech Connect

    Wen, Rui-Tao Granqvist, Claes G.; Niklasson, Gunnar A.

    2014-10-20

    Ni-oxide-based thin films were produced by reactive direct-current magnetron sputtering and were characterized by X-ray diffraction and Rutherford backscattering spectroscopy. Intercalation of Li{sup +} ions was accomplished by cyclic voltammetry (CV) in an electrolyte of LiClO{sub 4} in propylene carbonate, and electrochromism was documented by spectrophotometry. The charge density exchange, and hence the optical modulation span, decayed gradually upon repeated cycling. This phenomenon was accurately described by an empirical power law, which was valid for at least 10{sup 4} cycles when the applied voltage was limited to 4.1 V vs Li/Li{sup +}. Our results allow lifetime assessments for one of the essential components in an electrochromic device such as a “smart window” for energy-efficient buildings.

  13. Monte Carlo simulation of ion-neutral charge exchange collisions and grid erosion in an ion thruster

    NASA Technical Reports Server (NTRS)

    Peng, Xiaohang; Ruyten, Wilhelmus M.; Keefer, Dennis

    1991-01-01

    A combined particle-in-cell (PIC)/Monte Carlo simulation model has been developed in which the PIC method is used to simulate the charge exchange collisions. It is noted that a number of features were reproduced correctly by this code, but that its assumption of two-dimensional axisymmetry for a single set of grid apertures precluded the reproduction of the most characteristic feature of actual test data; namely, the concentrated grid erosion at the geometric center of the hexagonal aperture array. The first results of a three-dimensional code, which takes into account the hexagonal symmetry of the grid, are presented. It is shown that, with this code, the experimentally observed erosion patterns are reproduced correctly, demonstrating explicitly the concentration of sputtering between apertures.

  14. Observation of Solar Wind Charge Exchange Emission From Exospheric Material in and Outside Earth's Magnetosheath 2008 September 25

    NASA Technical Reports Server (NTRS)

    Snowden, S. L.; Collier, M. R.; Cravens, T.; Kuntz, K. D.; Lepri, S. T.; Robertson, I.; Tomas, L.

    2009-01-01

    A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth's magnetosheath. The light curve of the O vii (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.5). In addition, an average value of the SWCX O vii emission from the magnetosheath over the observation of 2.6 +/- 0.5 LU is derived. The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

  15. Charge-exchange and fusion reaction measurements during compression experiments with neutral beam heating in the Tokamak Fusion Test Reactor

    SciTech Connect

    Kaita, R.; Heidbrink, W.W.; Hammett, G.W.; Chan, A.A.; England, A.C.; Hendel, H.W.; Medley, S.S.; Nieschmidt, E.; Roquemore, A.L.; Scott, S.D.

    1986-04-01

    Adiabatic toroidal compression experiments were performed in conjunction with high power neutral beam injection in the Tokamak Fusion Test Reactor (TFTR). Acceleration of beam ions to energies nearly twice the injection energy was measured with a charge-exchange neutral particle analyzer. Measurements were also made of 2.5 MeV neutrons and 15 MeV protons produced in fusion reactions between the deuterium beam ions and the thermal deuterium and /sup 3/He ions, respectively. When the plasma was compressed, the d(d,n)/sup 3/He fusion reaction rate increased a factor of five, and the /sup 3/He(d,p)/sup 4/He rate by a factor of twenty. These data were simulated with a bounce-averaged Fokker-Planck program, which assumed conservation of angular momentum and magnetic moment during compression. The results indicate that the beam ion acceleration was consistent with adiabatic scaling.

  16. Optimization of a compact multicusp He{sup +} ion source for double-charge-exchanged He{sup -} beam

    SciTech Connect

    Shinto, K.; Sugawara, H.; Takenaga, M.; Takeuchi, S.; Tanaka, N.; Okamoto, A.; Kitajima, S.; Sasao, M.; Nishiura, M.; Wada, M.

    2006-03-15

    Preliminary test bench results to study the beam quality extracted from a compact multicusp He{sup +} ion source for He{sup -} beam production are reported. The bench is a part of the beam diagnostic system equipped with energy analyzers, emittance meters, focusing beam optics, an alkali-metal charge-exchange cell, a neutral particle energy analyzer, a double focusing magnetic momentum analyzer, a postaccelerator, and a drift tube. Utilizing the front end of the bench, the transverse emittance and the energy distribution function of a He{sup +} beam extracted from a multi-line-cusp magnetic-field ion source 8 cm in diameter and 9 cm in length were measured. The results indicated that improvements in both formation of the plasma meniscus and reinforcement of pumping in the extraction region are necessary to produce a higher brightness He{sup +} beam.

  17. Exchange-Induced Negative-U Charge Order in N-Doped WO3: A Spin-Peierls-Like System

    SciTech Connect

    Huda, M. N.; Yan, Y.; Wei, S.-H.; Al-Jassim, M. M.

    2009-01-01

    An unconventional spin-Peierls-type distortion was found in a nonmagnetic atom N doped pseudo-one-dimensional WO{sub 3} system. The periodicity of the initial ferromagnetic WO{sub 3}:N is doubled in one direction, and the band gap opens up due to this distortion. The magnetic moment at the N site is asymmetric in the distorted system, and the interaction between the localized spin is very weak. We show that the large exchange interaction of the nitrogen 2p atomic orbital and the pseudo-one-dimensional W-O-W chain in monoclinic WO{sub 3} structure is the origin of this spin-Peierls-like transition that leads to the stabilization of an unusual negative-U charge-ordered system.

  18. THE ION-INDUCED CHARGE-EXCHANGE X-RAY EMISSION OF THE JOVIAN AURORAS: MAGNETOSPHERIC OR SOLAR WIND ORIGIN?

    SciTech Connect

    Hui Yawei; Schultz, David R.; Kharchenko, Vasili A.; Stancil, Phillip C.; Cravens, Thomas E.; Lisse, Carey M. E-mail: schultzd@ornl.gov E-mail: stancil@physast.uga.edu E-mail: carey.lisse@jhuapl.edu

    2009-09-10

    A new and more comprehensive model of charge-exchange induced X-ray emission, due to ions precipitating into the Jovian atmosphere near the poles, has been used to analyze spectral observations made by the Chandra X-ray Observatory. The model includes for the first time carbon ions, in addition to the oxygen and sulfur ions previously considered, in order to account for possible ion origins from both the solar wind and the Jovian magnetosphere. By comparing the model spectra with newly reprocessed Chandra observations, we conclude that carbon ion emission provides a negligible contribution, suggesting that solar wind ions are not responsible for the observed polar X-rays. In addition, results of the model fits to observations support the previously estimated seeding kinetic energies of the precipitating ions ({approx}0.7-2 MeV u{sup -1}), but infer a different relative sulfur-to-oxygen abundance ratio for these Chandra observations.

  19. The Ion-induced Charge-exchange X-ray Emission of the Jovian Auroras: Magnetospheric or Solar Wind Origin?

    SciTech Connect

    Hui, Yawei; Schultz, David Robert; Kharchenko, Vasili A; Stancil, Phillip C.; Cravens, Thomas E. E.; Lisse, Carey M.; Dalgarno, A.

    2009-01-01

    A new and more comprehensive model of charge-exchange induced X-ray emission, due to ions precipitating into the Jovian atmosphere near the poles, has been used to analyze spectral observations made by the Chandra X-ray Observatory. The model includes for the first time carbon ions, in addition to the oxygen and sulfur ions previously considered, in order to account for possible ion origins from both the solar wind and the Jovian magnetosphere. By comparing the model spectra with newly reprocessed Chandra observations, we conclude that carbon ion emission provides a negligible contribution, suggesting that solar wind ions are not responsible for the observed polar X-rays. In addition, results of the model fits to observations support the previously estimated seeding kinetic energies of the precipitating ions ( 0.7-2 MeV/u), but infer a different relative sulfur to oxygen abundance ratio for these Chandra observations.

  20. Analysis of x-ray emission spectra in charge-exchange collisions of C6 + with He and H2

    NASA Astrophysics Data System (ADS)

    Leung, Anthony C. K.; Kirchner, Tom

    2016-05-01

    Charge exchange in C6 +-He and -H2 collisions followed by x-ray emission is examined using the two-center basis generator method for low to intermediate projectile energies. Within the independent electron model, we calculate capture cross sections and perform a radiative cascade analysis to obtain Lyman line-emission ratios. Single capture is considered for the C6 +-He system, while both single capture and autoionizing double capture are considered for the C6 +-H2 system. Effects of a time-dependent screening potential that models target response on the l distribution of capture cross sections and the line-emission ratios are examined as well. Calculated line-emission ratios based on the no-response approximation are in satisfactory agreement with previous measurements.

  1. Inclusive measurement of (p,. pi. /sup -/xn) double charge exchange reactions on bismuth from threshold to 800 MeV

    SciTech Connect

    Dombsky, M.; D'Auria, J.M.; Kelson, I.; Yavin, A.I.; Ward, T.E.; Clark, J.L.; Ruth, T.; Sheffer, G.

    1985-07-01

    The energy dependence of the total angle-integrated cross section for the production of astatine isotopes from (p,..pi../sup -/xn) double charge exchange reactions on bismuth (/sup 209/Bi) was measured from 120 to 800 MeV using activation and radiochemical techniques. Chemical yields were estimated by direct radioassaying of /sup 211/At activity in thin (approx.1 mg/cm/sup 2/), irradiated bismuth targets. Calculations of the contributions of secondary (two-step) reactions to these measured astatine yields were performed, based partially upon the observed /sup 211/At activity although even at the highest energies, the contribution to products lighter than /sup 207/At was negligible. These data for products with as many as seven neutrons removed from the doubly coherent product (/sup 210/At) display nearly Gaussian shapes for the mass distributions of the astatine residues, with the maximum occurring for about /sup 204/At. The most probable momentum transfer deduced from these distributions for the initial ..pi../sup -/ production step was 335 MeV/c. The observed excitation functions display a behavior similar to that observed for the yield of /sup 210/Po from a (p,..pi../sup 0/) reaction on /sup 209/Bi, but radically different from that observed for inclusive ..pi../sup -/ reactions on a heavy nucleus. These data are discussed in terms of recent theoretical approaches to negative pion production from bismuth. In addition, a simple, schematic model is developed to treat the rapidly decreasing percentage of the total inclusive ..pi../sup -/ emission which is observed for this double charge exchange reaction. This model reflects the opacity of a nucleus to a source of internal energetic protons.

  2. Optimization and application of cooled avalanche photodiodes for spectroscopic fluctuation measurements with ultra-fast charge exchange recombination spectroscopy

    NASA Astrophysics Data System (ADS)

    Truong, D. D.; Fonck, R. J.; McKee, G. R.

    2016-11-01

    The Ultra-Fast Charge Exchange Recombination Spectroscopy (UF-CHERS) diagnostic is a highly specialized spectroscopic instrument with 2 spatial channels consisting of 8 spectral channels each and a resolution of ˜0.25 nm deployed at DIII-D to measure turbulent ion temperature fluctuations. Charge exchange emissions are obtained between 528 and 530 nm with 1 μs time resolution to study plasma instabilities. A primary challenge of extracting fluctuation measurements from raw UF-CHERS signals is photon and electronic noise. In order to reduce dark current, the Avalanche Photodiode (APD) detectors are thermo-electrically cooled. State-of-the-art components are used for the signal amplifiers and conditioners to minimize electronic noise. Due to the low incident photon power (≤1 nW), APDs with a gain of up to 300 are used to optimize the signal to noise ratio. Maximizing the APDs' gain while minimizing the excess noise factor (ENF) is essential since the total noise of the diagnostic sets a floor for the minimum level of detectable broadband fluctuations. The APDs' gain should be high enough that photon noise dominates electronic noise, but not excessive so that the ENF overwhelms plasma fluctuations. A new generation of cooled APDs and optimized preamplifiers exhibits significantly enhanced signal-to-noise compared to a previous generation. Experiments at DIII-D have allowed for characterization and optimization of the ENF vs. gain. A gain of ˜100 at 1700 V is found to be near optimal for most plasma conditions. Ion temperature and toroidal velocity fluctuations due to the edge harmonic oscillation in quiescent H-mode plasmas are presented to demonstrate UF-CHERS' capabilities.

  3. The Production of Energetic Atomic Beams via Charge Exchange for the Simulation of the Low-Earth Orbit Environment.

    NASA Astrophysics Data System (ADS)

    Ketsdever, Andrew David

    The interactions of energetic atoms with solid materials and other gases are important to a wide range of engineering disciplines. The interactions between low -Earth orbit (LEO) atomic oxygen and spacecraft surfaces, outgassed molecules, rocket exhaust plume species and other atmospheric gases are of great interest to the aerospace engineering community. The approach taken in this study was to design a facility which can be used to understand the physics of energetic gas-gas and gas-surface collisions. The type of facility needed to accomplish this requires a continuous, high energy (5-100eV) atomic beam with a low energy spread and a moderate flux. The flux of atoms from this facility, although estimated to be several orders of magnitude lower than LEO conditions, is sufficient to gain qualitative and quantitative insight into LEO environmental interactions. In the pilot scale true energy atmospheric simulator (TEAS) developed in this research, ion engine technology is incorporated to produce a beam of energetic ions. Because the ion source discharges can be operated on several gases, simulation of any atmospheric species can be achieved; however, atomic oxygen is the species of interest in this study. The ions are accelerated to the desired energy range and undergo a charge exchange process in molecular hydrogen to produce the energetic atomic beam Molecular hydrogen is chosen as the charge exchange gas because of the relatively large cross section for the reaction and the small scattering angle per collision. An electrostatic energy analyzer, a mass spectrometer and thin silver reaction films are used to diagnose the beams produced by the TEAS.

  4. Understanding the charge transport and polarities in organic donor-acceptor mixed-stack crystals: molecular insights from the super-exchange couplings.

    PubMed

    Geng, Hua; Zheng, Xiaoyan; Shuai, Zhigang; Zhu, Lingyun; Yi, Yuanping

    2015-02-25

    Charge transport and polarity in organic D-A mixed-stack crystals are examined in terms of super-exchange electronic couplings. When the super-exchange coupling is dominated by the interaction between donor HOMO and acceptor LUMO, ambipolar transport is achieved. Otherwise, involvement of other bridge orbitals can lead to unbalanced, even to unipolar transport in a special case that the HOMO-LUMO interaction vanishes.

  5. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Intense charge exchange of laser-plasma ions with the atoms of a pulsed gas jet

    NASA Astrophysics Data System (ADS)

    Antonov, V. M.; Boyarintsev, Y. L.; Melekhov, A. V.; Posukh, V. G.; Ponomarenko, A. G.; Shaikhislamov, I. F.

    2007-09-01

    The results of experiments on the interaction of a laser plasma with a pulsed gas jet are presented. The charge exchange of ions with neutral particles was realised for the first time under controllable conditions for a density of the reagents of no less than 1016 cm-3. The resonance pumping of the C3+ ion level with n=3 was observed by spectral methods. The structure of the region of intense charge exchange was determined from plasma photographs. The data obtained suggest that experiments on soft X-ray lasing at a C5+ ion transition are promising.

  6. Charge exchange between two nearest neighbour ions immersed in a dense plasma

    NASA Astrophysics Data System (ADS)

    Sauvan, P.; Angelo, P.; Derfoul, H.; Leboucher-Dalimier, E.; Devdariani, A.; Calisti, A.; Talin, B.

    1999-04-01

    In dense plasmas the quasimolecular model is relevant to describe the radiative properties: two nearest neighbor ions remain close to each other during a time scale of the order of the emission time. Within the frame of a quasistatic approach it has been shown that hydrogen-like spectral line shapes can exhibit satellite-like features. In this work we present the effect on the line shapes of the dynamical collision between the two ions exchanging transiently their bound electron. This model is suitable for the description of the core, the wings and the red satellite-like features. It is post-processed to the self consistent code (IDEFIX) giving the adiabatic transition energies and the oscillator strengths for the transient molecule immersed in a dense free electron bath. It is shown that the positions of the satellites are insensitive to the dynamics of the ion-ion collision. Results for fluorine Lyβ are presented.

  7. Charge exchange transition probability for collisions between unlike ions and atoms within the adiabatic approximation

    NASA Technical Reports Server (NTRS)

    Xu, Y. J.; Khandelwal, G. S.; Wilson, John W.

    1989-01-01

    A simple formula for the transition probability for electron exchange between unlike ions and atoms is established within the adiabatic approximation by employing the Linear Combination of Atomic Orbitals (LCAO) method. The formula also involves an adiabatic parameter, introduced by Massey, and thus the difficulties arising from the internal energy defect and the adiabatic approximation are avoided. Specific reactions Li(+++) + H to Li(++) + H(+) and Be(4+) + H to Be(3+) + H(+) are considered as examples. The calculated capture cross section results of the present work are compared with the experimental data and with the calculation of other authors over the velocity range of 10(7) cm/sec to 10(8) cm/sec.

  8. Sorption of doubly charged metal ions from ammonium fluoride solutions by KFP-23 cation-exchange resin

    SciTech Connect

    Ganyaev, V.P.; Pimneva, L.A.; Pakholkov, V.S.

    1982-10-20

    This report examines the results of a study of sorption of a number of doubly charged cations by the macroporous cation-exchange KFP-12 from 0.1 N MeF/sub 2/ solutions containing NH/sub 4/F in concentrations from 0 to 3.0 M. As the result of an investigation of the sorption, under dynamic conditions, of copper, zinc, cadmium, manganese, cobalt, and nickel ions from ammonium fluoride solutions by KFP-12 cation-exchange resin in the influence of the ionic form (H/sup +/ or NH/sub 4//sup +/) of the resin and of the NH/sub 4/F concentration on the degree of sorption and on the breakthrough capacity was established. The character of bonding and coordination of the sorbed cations with the ionic groups of the resin has been established. The possibilty of thorough purification of ammonium fluoride and (NH/sub 4/)/sub 2/BeF/sub 4/ solutions with the aid of KFP-12 resin in NH/sub 4//sup +/ form has been demonstrated. The purification co-efficients were calculated.

  9. Experimental investigation of the reaction of helium ions with dimethyl ether: stereodynamics of the dissociative charge exchange process.

    PubMed

    Cernuto, Andrea; Tosi, Paolo; Martini, Luca Matteo; Pirani, Fernando; Ascenzi, Daniela

    2017-03-09

    The fate of dimethyl ether (DME, CH3OCH3) in collisions with He(+) ions is of high relevance for astrochemical models aimed at reproducing the abundances of complex organic molecules in the interstellar medium. Here we report an investigation on the reaction of He(+) ions with DME carried out using a Guided Ion Beam Mass Spectrometer (GIB-MS), which allows the measurement of reactive cross-sections and branching ratios (BRs) as a function of the collision energy. We obtain insights into the dissociative charge (electron) exchange mechanism by investigating the nature of the non-adiabatic transitions between the relevant potential energy surfaces (PESs) in an improved Landau-Zener approach. We find that the large interaction anisotropy could induce a pronounced orientation of the polar DME molecule in the electric field generated by He(+) so that at short distances the collision complex is confined within pendular states, a particular case of bending motion, which gives rise to intriguing stereodynamic effects. The positions of the intermolecular potential energy curve crossings indicate that He(+) captures an electron from an inner valence orbital of DME, thus causing its dissociation. In addition to the crossing positions, the symmetry of the electron density distribution of the involved DME orbitals turns out to be a further major point affecting the probability of electron transfer. Thus, the anisotropy of the intermolecular interaction and the electron densities of the orbitals involved in the reaction are the key "ingredients" for describing the dynamics of this dissociative charge transfer.

  10. A Cold Atom Measurement of Charge Exchange Collisions between Trapped Yb^+ and Yb

    NASA Astrophysics Data System (ADS)

    Grier, Andrew; Cetina, Marko; Orucevic, Fedja; Vuletic, Vladan

    2008-05-01

    We measure the collisional cross-section and rate constant of the ^174Yb and ^172Yb^+ charge-transfer process. The neutral atoms are trapped in a magneto-optical trap (MOT) resonant with their 399 nm, ^1S0->^1P1 transition and are near the Doppler-limited temperature of 680 μK. The ions are confined in a planar Paul trap with a secular frequency of 39 kHz, Doppler cooled, and spatially overlapped with the neutral atoms. The collisional energy is varied from 4 meV to 100s of neV by varying the micromotion energy of the ions by displacement from the center of the Paul trap. We report the rate constant in comparison to that derived from the Langevin cross-section.

  11. Quantum-mechanical interference in charge exchange between hydrogen and graphene-like surfaces.

    PubMed

    Romero, M; Iglesias-García, A; Goldberg, E C

    2012-02-01

    The neutral to negative charge fluctuation of a hydrogen atom in front of a graphene surface is calculated by using the Anderson model within an infinite intra atomic Coulomb repulsion approximation. We perform an ab initio calculation of the Anderson hybridization function that allows investigation of the effect of quantum-mechanical interference related to the Berry phase inherent to the graphene band structure. We find that consideration of the interaction of hydrogen on top of many C atoms leads to a marked asymmetry of the imaginary part of the hybridization function with respect to the Fermi level. Consequently, Fano factors larger than one and strongly dependent on the energy around the Fermi level are predicted. Moreover, the suppression of the hybridization for energies above the Fermi level can explain the unexpected large negative ion formation measured in the scattering of protons by graphite-like surfaces.

  12. The Uranian corona as a charge exchange cascade of plasma sheet protons

    NASA Astrophysics Data System (ADS)

    Herbert, F.

    1993-03-01

    The paper uses models of magnetic convection and interparticle interactions to examine the collisional interactions between atmospheric neutral hydrogen and magnetospheric charged particles observed by Voyager to be convecting through the Uranian magnetosphere. The e(-)-H collisional ionization process, continually reenergized by compressional heating of the electrons as they drift toward Uranus, produces a cascade of new plasma. This process has been suggested elsewhere as the source of the warm (10 eV at L = 5) plasma and is found in the present study to continue in a cascade to even cooler and more abundant plasma. This newly created plasma consists almost entirely of electrons and protons because He and H2 are nearly absent from the uppermost layers of the atmosphere. If this plasma crosses the dayside magnetopause and mixes with magnetopause boundary layers such as the plasma mantle, there to be swept back along the magnetotail, reincorporated into the magnetotail by the same processes postulated for solar wind plasma entry, and reenergized in the magnetotail current sheet, it would constitute an important source for the hot plasma observed by Voyager.

  13. Structural basis of omalizumab therapy and omalizumab-mediated IgE exchange

    SciTech Connect

    Pennington, Luke F.; Tarchevskaya, Svetlana; Brigger, Daniel; Sathiyamoorthy, Karthik; Graham, Michelle T.; Nadeau, Kari Christine; Eggel, Alexander; Jardetzky, Theodore S.

    2016-05-19

    Omalizumab is a widely used therapeutic anti-IgE antibody. Here we report the crystal structure of the omalizumab–Fab in complex with an IgE-Fc fragment. This structure reveals the mechanism of omalizumab-mediated inhibition of IgE interactions with both high- and low-affinity IgE receptors, and explains why omalizumab selectively binds free IgE. The structure of the complex also provides mechanistic insight into a class of disruptive IgE inhibitors that accelerate the dissociation of the high-affinity IgE receptor from IgE. We use this structural data to generate a mutant IgE-Fc fragment that is resistant to omalizumab binding. Treatment with this omalizumab-resistant IgE-Fc fragment, in combination with omalizumab, promotes the exchange of cell-bound full-length IgE with omalizumab-resistant IgE-Fc fragments on human basophils. Furthermore, this combination treatment also blocks basophil activation more efficiently than either agent alone, providing a novel approach to probe regulatory mechanisms underlying IgE hypersensitivity with implications for therapeutic interventions.

  14. Structural basis of omalizumab therapy and omalizumab-mediated IgE exchange

    PubMed Central

    Pennington, Luke F.; Tarchevskaya, Svetlana; Brigger, Daniel; Sathiyamoorthy, Karthik; Graham, Michelle T.; Nadeau, Kari Christine; Eggel, Alexander; Jardetzky, Theodore S.

    2016-01-01

    Omalizumab is a widely used therapeutic anti-IgE antibody. Here we report the crystal structure of the omalizumab–Fab in complex with an IgE-Fc fragment. This structure reveals the mechanism of omalizumab-mediated inhibition of IgE interactions with both high- and low-affinity IgE receptors, and explains why omalizumab selectively binds free IgE. The structure of the complex also provides mechanistic insight into a class of disruptive IgE inhibitors that accelerate the dissociation of the high-affinity IgE receptor from IgE. We use this structural data to generate a mutant IgE-Fc fragment that is resistant to omalizumab binding. Treatment with this omalizumab-resistant IgE-Fc fragment, in combination with omalizumab, promotes the exchange of cell-bound full-length IgE with omalizumab-resistant IgE-Fc fragments on human basophils. This combination treatment also blocks basophil activation more efficiently than either agent alone, providing a novel approach to probe regulatory mechanisms underlying IgE hypersensitivity with implications for therapeutic interventions. PMID:27194387

  15. Exchange factors directly activated by cAMP mediate melanocortin 4 receptor-induced gene expression

    PubMed Central

    Glas, Evi; Mückter, Harald; Gudermann, Thomas; Breit, Andreas

    2016-01-01

    Gs protein-coupled receptors regulate many vital body functions by activation of cAMP response elements (CRE) via cAMP-dependent kinase A (PKA)-mediated phosphorylation of the CRE binding protein (CREB). Melanocortin 4 receptors (MC4R) are prototypical Gs-coupled receptors that orchestrate the hypothalamic control of food-intake and metabolism. Remarkably, the significance of PKA for MC4R-induced CRE-dependent transcription in hypothalamic cells has not been rigorously interrogated yet. In two hypothalamic cell lines, we observed that blocking PKA activity had only weak or no effects on reporter gene expression. In contrast, inhibitors of exchange factors directly activated by cAMP-1/2 (EPAC-1/2) mitigated MC4R-induced CRE reporter activation and mRNA induction of the CREB-dependent genes c-fos and thyrotropin-releasing hormone. Furthermore, we provide first evidence that extracellular-regulated kinases-1/2 (ERK-1/2) activated by EPACs and not PKA are the elusive CREB kinases responsible for MC4R-induced CREB/CRE activation in hypothalamic cells. Overall, these data emphasize the pivotal role of EPACs rather than PKA in hypothalamic gene expression elicited by a prototypical Gs-coupled receptor. PMID:27612207

  16. Structural basis of omalizumab therapy and omalizumab-mediated IgE exchange

    DOE PAGES

    Pennington, Luke F.; Tarchevskaya, Svetlana; Brigger, Daniel; ...

    2016-05-19

    Omalizumab is a widely used therapeutic anti-IgE antibody. Here we report the crystal structure of the omalizumab–Fab in complex with an IgE-Fc fragment. This structure reveals the mechanism of omalizumab-mediated inhibition of IgE interactions with both high- and low-affinity IgE receptors, and explains why omalizumab selectively binds free IgE. The structure of the complex also provides mechanistic insight into a class of disruptive IgE inhibitors that accelerate the dissociation of the high-affinity IgE receptor from IgE. We use this structural data to generate a mutant IgE-Fc fragment that is resistant to omalizumab binding. Treatment with this omalizumab-resistant IgE-Fc fragment, inmore » combination with omalizumab, promotes the exchange of cell-bound full-length IgE with omalizumab-resistant IgE-Fc fragments on human basophils. Furthermore, this combination treatment also blocks basophil activation more efficiently than either agent alone, providing a novel approach to probe regulatory mechanisms underlying IgE hypersensitivity with implications for therapeutic interventions.« less

  17. Mediated Cross-Cultural Learning through Exchange in Higher Agricultural Education

    ERIC Educational Resources Information Center

    Wals, Arjen E. J.; Sriskandarajah, Nadarajah

    2010-01-01

    This article reports on the long-term impact of an intensive European Union-Australia student exchange programme that took place in 2004 and 2005. The programme, Learning through Exchange about Agriculture, Food Systems and Environment (LEAFSE), was designed to facilitate exchange of post-graduate students on a pilot scale between four…

  18. New Measurements of the Solar Wind Charge Exchange, Local Bubble, and Halo 3/4 keV Emission from XMM-Newton and Suzaku Shadowing Observations

    NASA Astrophysics Data System (ADS)

    Shelton, Robin L.; Henley, David

    2016-06-01

    We report on the analyses of XMM-Newton and/or Suzaku observations of 6 on-cloud and off-cloud shadowing pairs. This study provides the first analysis of two of these pairs and the first uniform analysis of the larger dataset. For every shadowing pair, we determined the foreground and halo components by simultaneously fitting the spectra from both members of the pair with a model that included a foreground component and an absorbed background component. In the past, foreground X-ray emission was thought to come from the Local Bubble of hot gas surrounding the solar neighborhood and so thermal spectral models were used. Now that solar wind charge exchange is recognized as a source of foreground X-ray photons, it is appropriate to consider charge exchange models as well. For this reason, we repeated the analyses using one of 3 possible foreground models: a charge exchange spectral model whose line ratios come from atomic physics calculations and are presented in Cumbee et al. (2014), a charge exchange model based on the AtomDB Charge Exchange code, or a thermal spectrum. The analyses of the larger dataset enabled us to place an upper limit on the Local Bubble's O VII contribution, provide measurements of the local and halo contributions in the 0.4 to 1.0 keV band, comment on the abilities of the various solar wind models to fit the data, and comment on the sensitivity of the fit parameters to the choice of foreground model, metal abundance tables, and X-ray observatory.

  19. Charge Exchange-induced X-Ray Emission of Fe xxv and Fe xxvI via a Streamlined Model

    NASA Astrophysics Data System (ADS)

    Mullen, P. D.; Cumbee, R. S.; Lyons, D.; Stancil, P. C.

    2016-06-01

    Charge exchange (CX) is an important process for the modeling of X-ray spectra obtained by the Chandra, XMM-Newton, and Suzaku X-ray observatories, as well as the anticipated Astro-H mission. The understanding of the observed X-ray spectra produced by many astrophysical environments is hindered by the current incompleteness of available atomic and molecular data—especially for CX. Here, we implement a streamlined program set that applies quantum defect methods and the Landau-Zener theory to generate total, n-resolved, and n{\\ell }S-resolved cross sections for any given projectile ion/target CX collision. By using these data in a cascade model for X-ray emission, theoretical spectra for such systems can be predicted. With these techniques, Fe25+ and Fe26+ CX collisions with H, He, H2, N2, H2O, and CO are studied for single-electron capture (SEC). These systems have been selected because they illustrate computational difficulties for high projectile charges. Furthermore, Fe xxv and Fe xxvi emission lines have been detected in the Galactic center and Galactic ridge. Theoretical X-ray spectra for these collision systems are compared to experimental data generated by an electron-beam ion trap study. Several ℓ-distribution models have been tested for Fe25+ and Fe26+ SEC. Such analyses suggests that commonly used ℓ-distribution models struggle to accurately reflect the true distribution of electron capture as understood by more advanced theoretical methods.

  20. Microstructure defects mediated charge transport in Nb-doped epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhou, Jian; Jing, Xiaosai; Alexe, Marin; Dai, Jiyan; Qin, Minghui; Wu, Sujuan; Zeng, Min; Gao, Jinwei; Lu, Xubing; Liu, J.-M.

    2016-05-01

    Nb-doped BaTiO3 (BNTO) films were deposited on MgO substrates at different substrate temperatures by pulsed laser deposition. The temperature dependence of their resistivity, carrier mobility and carrier concentration were systematically investigated. It reveals that the BNTO films deposited at lower temperature show higher resistivity and lower carrier mobility, and only show semiconductor characteristics at measurement temperatures ranging from 10 to 400 K. There is a metal-semiconductor transition at about 20 K for the films grown at relatively higher temperature. The intrinsic mechanism responsible for the different charge transport behavior was revealed by microstructure studies. Low crystal quality and high density of microstructure defects, observed for BNTO films grown at low temperatures, are, in particular, massively affecting the charge transport behavior of the BNTO films. The mediated charge transport of the microstructure defects is dominated by the thermal excitation process.

  1. Systems Based Study of the Therapeutic Potential of Small Charged Molecules for the Inhibition of IL-1 Mediated Cartilage Degradation

    PubMed Central

    Kar, Saptarshi; Smith, David W.; Gardiner, Bruce S.; Grodzinsky, Alan J.

    2016-01-01

    Inflammatory cytokines are key drivers of cartilage degradation in post-traumatic osteoarthritis. Cartilage degradation mediated by these inflammatory cytokines has been extensively investigated using in vitro experimental systems. Based on one such study, we have developed a computational model to quantitatively assess the impact of charged small molecules intended to inhibit IL-1 mediated cartilage degradation. We primarily focus on the simplest possible computational model of small molecular interaction with the IL-1 system—direct binding of the small molecule to the active site on the IL-1 molecule itself. We first use the model to explore the uptake and release kinetics of the small molecule inhibitor by cartilage tissue. Our results show that negatively charged small molecules are excluded from the negatively charged cartilage tissue and have uptake kinetics in the order of hours. In contrast, the positively charged small molecules are drawn into the cartilage with uptake and release timescales ranging from hours to days. Using our calibrated computational model, we subsequently explore the effect of small molecule charge and binding constant on the rate of cartilage degradation. The results from this analysis indicate that the small molecules are most effective in inhibiting cartilage degradation if they are either positively charged and/or bind strongly to IL-1α, or both. Furthermore, our results showed that the cartilage structural homeostasis can be restored by the small molecule if administered within six days following initial tissue exposure to IL-1α. We finally extended the scope of the computational model by simulating the competitive inhibition of cartilage degradation by the small molecule. Results from this model show that small molecules are more efficient in inhibiting cartilage degradation by binding directly to IL-1α rather than binding to IL-1α receptors. The results from this study can be used as a template for the design and

  2. Charging and exciton-mediated decharging of metal nanoparticles in organic semiconductor matrices

    SciTech Connect

    Ligorio, Giovanni; Vittorio Nardi, Marco Christodoulou, Christos; Florea, Ileana; Ersen, Ovidiu; Monteiro, Nicolas-Crespo; Brinkmann, Martin; Koch, Norbert

    2014-04-21

    Gold nanoparticles (Au-NPs) were deposited on the surface of n- and p-type organic semiconductors to form defined model systems for charge storage based electrically addressable memory elements. We used ultraviolet photoelectron spectroscopy to study the electronic properties and found that the Au-NPs become positively charged because of photoelectron emission, evidenced by spectral shifts to higher binding energy. Upon illumination with light that can be absorbed by the organic semiconductors, dynamic charge neutrality of the Au-NPs could be re-established through electron transfer from excitons. The light-controlled charge state of the Au-NPs could add optical addressability to memory elements.

  3. Transient energetic charge exchange flux enhancement observed in NSTX neutral-beam-heated H-mode discharges

    NASA Astrophysics Data System (ADS)

    Medley, S. S.; Kramer, G. J.; Bell, R. E.; Belova, E.; Fredrickson, E. D.; Gerhardt, S. P.; Leblanc, B. P.; Podestá, M.; Ren, Y.; Roquemore, A. L.; Crocker, N. A.; NSTX Team

    2011-10-01

    Large increases in the E | | B Neutral Particle Analyzer (NPA) charge exchange neutral flux localized at the Neutral Beam Injection (NBI) full energy are observed in the National Spherical Torus Experiment (NSTX). Termed the High-Energy Feature (HEF), it appears only at the NBI full energy, exhibits growth times ~ 20-80 ms, seldom develops a slowing down distribution and arises only in discharges where NTM modes (f < 30 kHz) are absent, TAE activity (f ~ 30-150 kHz) is weak and GAE/CAE activity (f ~ 400-1200 kHz) is robust. The HEF occurs only in H-mode discharges with Pb >= 3 MW and v||/v ~ 0.7-0.9; i.e. only for passing ions. The HEF appears to be caused by a GAE wave-particle interaction that modifies of the NB fast ion distribution, fi(E,v||/v,r). This proposed mechanism was studied using the SPIRAL code that imports a TRANSP-calculated fi(E,v||/v,r) distribution and evolves it under drive from GAE wave-particle resonances. Supported by U.S. DoE Contract Nos. DE-AC02-09CH11466, DE-FG02-99ER54527.

  4. Charge-exchange X-ray emission of M82: Kα triplets of O VII, Ne IX and Mg XI

    NASA Astrophysics Data System (ADS)

    Liu, Jiren; Mao, Shude; Wang, Q. Daniel

    2011-07-01

    Starburst galaxies are primary feedback sources of mechanical energy and metals, which are generally measured from associated X-ray emission lines, assuming that they are from the thermal emission of the outflowing hot gas. Such line emission, however, can also arise from the charge-exchange X-ray emission (CXE) between highly ionized ions and neutral species. To understand the feedback of energy and metals, it is crucial to determine the origin of the X-ray emission lines and to distinguish the contributions from the CXE and the thermal emission. The origin of the lines can be diagnosed by the Kα triplets of He-like ions, because the CXE favours the intercombination and forbidden lines, while the thermal emission favours the resonance line. We analyse the triplets of O VII, Ne IX and Mg XI observed in the XMM-Newton reflection grating spectra of the starburst galaxy M82. The flux contribution of the CXE is 90, 50 and 30 per cent to the O VII, Ne IX and Mg XI triplets, respectively. Averaged over all the three triplets, the contribution of the CXE is ˜50 per cent of the total observed triplet flux. To correctly understand the hot outflow of starburst galaxies, it is necessary to include the CXE. Based on the measured CXE fluxes of the O VII, Ne IX and Mg XI triplets, we estimate the relative abundances of O, Ne and Mg of the outflow and find they are similar to the solar ratios.

  5. Analysis of x-ray emission in charge-exchange collisions of C6+ ions with He and H2

    NASA Astrophysics Data System (ADS)

    Leung, Anthony C. K.; Kirchner, T.

    2016-05-01

    Charge exchange in C6+-He and - H2 collisions followed by x-ray emission is examined using the two-center basis generator method within the independent electron model. The analysis examines the two collision systems for low to intermediate projectile energies. We perform capture cross section and radiative cascade calculations to obtain Lyman line emission ratios which can be compared to measurements that were carried out at the Oak Ridge National Laboratory Multicharged Ion Research Facility. Single-electron capture is considered for the C6+-He system while both single and autoionizing double capture are considered for the C6+- H2 system. We also examine the effects of a time-dependent screening potential that models target response on the l distribution of the capture cross sections and the emission ratios. Calculated line emission ratios based on the no-response approximation are found to be in satisfactory agreement with the measurements. Work supported by SHARCNET, OGS, and NSERC, Canada

  6. Using (18)O/(16)O exchange to probe an equilibrium space-charge layer at the surface of a crystalline oxide: method and application.

    PubMed

    De Souza, Roger A; Martin, Manfred

    2008-05-07

    The use of an (18)O/(16)O exchange experiment as a means for probing surface space-charge layers in oxides is examined theoretically and experimentally. On the basis of a theoretical treatment, isotope penetration profiles are calculated for (18)O/(16)O exchange across a gas-solid interface and subsequent diffusion of the labelled isotope through an equilibrium space-charge layer depleted of mobile oxygen vacancies and into a homogeneous bulk phase. Profiles calculated for a range of conditions all have a characteristic shape: a sharp drop in isotope fraction close to the surface followed by a normal bulk diffusion profile. Experimental (18)O profiles in an exchanged (001) oriented single crystal of Fe-doped SrTiO(3) were measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). By extracting the space-charge potential from such profiles, we demonstrate that this method allows the spatially resolved characterization of space-charge layers at the surfaces of crystalline oxides under thermodynamically well-defined conditions.

  7. Validation of a pH gradient-based ion-exchange chromatography method for high-resolution monoclonal antibody charge variant separations.

    PubMed

    Rea, Jennifer C; Moreno, G Tony; Lou, Yun; Farnan, Dell

    2011-01-25

    Ion-exchange chromatography is widely used for profiling the charge heterogeneity of proteins, including monoclonal antibodies. Despite good resolving power and robustness, ionic strength-based ion-exchange separations are product-specific and time-consuming to develop. We have previously reported a novel pH-based separation of proteins by cation exchange chromatography that was multi-product, high-resolution, and robust against variations in sample matrix salt concentration and pH. In this study, a pH gradient-based separation method using cation exchange chromatography was evaluated in a mock validation. This method was shown to be robust for monoclonal antibodies and suitable for its intended purpose of charge heterogeneity analysis. Simple mixtures of defined buffer components were used to generate the pH gradients that separated closely related antibody species. Validation characteristics, such as precision and linearity, were evaluated. Robustness to changes in protein load, buffer pH and column oven temperature was demonstrated. The stability-indicating capability of this method was determined using thermally stressed antibody samples. In addition, intermediate precision was demonstrated using multiple instruments, multiple analysts, multiple column lots, and different column manufacturers. Finally, the precision for this method was compared to conventional ion-exchange chromatography and imaged capillary isoelectric focusing. These results demonstrate the superior precision and robustness of this multi-product method, which can be used for the high-throughput evaluation of in-process and final product samples.

  8. Dirac dark matter with a charged mediator: a comprehensive one-loop analysis of the direct detection phenomenology

    SciTech Connect

    Ibarra, Alejandro; Wild, Sebastian

    2015-05-26

    We analyze the direct detection signals of a toy model consisting of a Dirac dark matter particle which couples to one Standard Model fermion via a scalar mediator. For all scenarios, the dark matter particle scatters off nucleons via one loop-induced electromagnetic and electroweak moments, as well as via the one-loop exchange of a Higgs boson. Besides, and depending on the details of the model, the scattering can also be mediated at tree level via the exchange of the scalar mediator or at one loop via gluon-gluon interactions. We show that, for thermally produced dark matter particles, the current limits from the LUX experiment on these scenarios are remarkably strong, even for dark matter coupling only to leptons. We also discuss future prospects for XENON1T and DARWIN and we argue that multi-ton xenon detectors will be able to probe practically the whole parameter space of the model consistent with thermal production and perturbativity. We also discuss briefly the implications of our results for the dark matter interpretation of the Galactic GeV excess.

  9. Dirac dark matter with a charged mediator: a comprehensive one-loop analysis of the direct detection phenomenology

    SciTech Connect

    Ibarra, Alejandro; Wild, Sebastian E-mail: sebastian.wild@ph.tum.de

    2015-05-01

    We analyze the direct detection signals of a toy model consisting of a Dirac dark matter particle which couples to one Standard Model fermion via a scalar mediator. For all scenarios, the dark matter particle scatters off nucleons via one loop-induced electromagnetic and electroweak moments, as well as via the one-loop exchange of a Higgs boson. Besides, and depending on the details of the model, the scattering can also be mediated at tree level via the exchange of the scalar mediator or at one loop via gluon-gluon interactions. We show that, for thermally produced dark matter particles, the current limits from the LUX experiment on these scenarios are remarkably strong, even for dark matter coupling only to leptons. We also discuss future prospects for XENON1T and DARWIN and we argue that multi-ton xenon detectors will be able to probe practically the whole parameter space of the model consistent with thermal production and perturbativity. We also discuss briefly the implications of our results for the dark matter interpretation of the Galactic GeV excess.

  10. Sialic acid mediates the initial binding of positively charged inorganic particles to alveolar macrophage membranes.

    PubMed

    Gallagher, J E; George, G; Brody, A R

    1987-06-01

    Pulmonary macrophages phagocytize inhaled particles and are postulated to play a role in the development of pulmonary interstitial fibrogenesis. The basic biologic mechanisms through which inhaled particles bind to macrophage membranes and subsequently are phagocytized remain unclear. We hypothesize that positively charged particles bind to negatively charged sialic acid (SA) residues on macrophage membranes. Alveolar Macrophages (AM) were collected by saline lavage from normal rat lungs. The cells adhered to plastic coverslips in serum-free phosphate buffered saline at 37 degrees C for 45 min and then were maintained at 4 degrees C for the binding experiments. Even distribution of SA groups on AM surfaces was demonstrated by scanning electron microscopy of wheat germ agglutinin (WGA) conjugated to 50 nm gold spheres. The WGA is a lectin that binds specifically to sialic acid, and pretreatment of AM with this lectin prevented the binding of positively charged carbonyl iron (C-Fe) spheres, aluminum (Al) spheres, and chrysotile asbestos fibers to AM surfaces. Limulus protein, another lectin with binding specificity for SA, similarly blocked the binding of positively charged spheres and chrysotile asbestos fibers but not negatively charged glass spheres or crocidolite asbestos fibers. Con A and ricin, lectins that bind to mannose and galactose residues, respectively, did not block particle binding. When both positively charged iron spheres and negatively charged glass spheres were prebound to AM membranes, subsequent treatment with WGA displaced only the positively charged spheres from macrophage surfaces. Con A and ricin had no effect on prebound positively charged C-Fe and Al spheres.(ABSTRACT TRUNCATED AT 250 WORDS)

  11. Multifluid Modeling of the Partially Ionized Chromosphere with Effects of Impact Ionization, Radiative Recombination and Charge Exchange

    NASA Astrophysics Data System (ADS)

    Maneva, Y. G.; Poedts, D. S.; Alvarez Laguna, A.; Lani, A.

    2015-12-01

    Neutrals play an important role in the evolution of the weakly ionized solar chromosphere where the number density of neutrals can vastly exceed the number density of protons. Therefore modeling the neutral-ion interactions and studying the effect of neutrals on the ambient plasma properties is an important task for better understanding the observed emission lines and the propagation of disturbances from the photosphere to the transition region and the corona. To pursue this goal we have developed two-fluid and three-fluid simulation setups to study the interaction between electrons, ions and neutrals in a reactive gravitationally stratified collisional media. The model considers the electrons and ions within the resistive MHD approach with Coulomb collisions and anisotropic heat flux determined by Braginskii's transport coefficients. The electromagnetic fields are evolved according to the full Maxwell equations, allowing for propagation of higher frequency waves neglected by the standard MHD approximation. Separate mass, momentum and energy conservation equations are considered for the neutrals and the interaction between the different fluids is determined by the chemical reactions, such as impact ionization, radiative recombination and charge exchange, provided as additional source terms. To initialize the system we consider an ideal gas equation of state with equal initial temperatures for the electrons, ions and the neutrals and different density profiles. The initial temperature and density profiles are height-dependent and follow VAL C atmospheric model for the solar chromosphere. We have searched for a chemical and collisional equilibrium between the ions and the neutrals in the hydrostatic case to avoid unphysical outflows and artificial heating induced by initial pressure imbalances. Next we consider ion-neutral interactions in magnetized plasma with an initial magnetic profile, corresponding to emerging magnetic funnel. Finally we include an external

  12. Core-ion temperature measurement of the ADITYA tokamak using passive charge exchange neutral particle energy analyzer.

    PubMed

    Pandya, Santosh P; Ajay, Kumar; Mishra, Priyanka; Dhingra, Rajani D; Govindarajan, J

    2013-02-01

    Core-ion temperature measurements have been carried out by the energy analysis of passive charge exchange (CX) neutrals escaping out of the ADITYA tokamak plasma (minor radius, a = 25 cm and major radius, R = 75 cm) using a 45° parallel plate electrostatic energy analyzer. The neutral particle analyzer (NPA) uses a gas cell configuration for re-ionizing the CX-neutrals and channel electron multipliers (CEMs) as detectors. Energy calibration of the NPA has been carried out using ion-source and ΔE∕E of high-energy channel has been found to be ∼10%. Low signal to noise ratio (SNR) due to VUV reflections on the CEMs was identified during the operation of the NPA with ADITYA plasma discharges. This problem was rectified by upgrading the system by incorporating the additional components and arrangements to suppress VUV radiations and improve its VUV rejection capabilities. The noise rejection capability of the NPA was experimentally confirmed using a standard UV-source and also during the plasma discharges to get an adequate SNR (>30) at the energy channels. Core-ion temperature Ti(0) during flattop of the plasma current has been measured to be up to 150 eV during ohmically heated plasma discharges which is nearly 40% of the average core-electron temperature (typically Te(0) ∼ 400 eV). The present paper describes the principle of tokamak ion temperature measurement, NPA's design, development, and calibration along with the modifications carried out for minimizing the interference of plasma radiations in the CX-spectrum. Performance of the NPA during plasma discharges and experimental results on the measurement of ion-temperature have also been reported here.

  13. Ultra-fast charge exchange spectroscopy for turbulent ion temperature fluctuation measurements on the DIII-D tokamak (invited)

    SciTech Connect

    Uzun-Kaymak, I. U.; Fonck, R. J.; McKee, G. R.

    2012-10-15

    A novel two-channel, high throughput, high efficiency spectrometer system has been developed to measure impurity ion temperature and toroidal velocity fluctuations associated with long-wavelength turbulence and other plasma instabilities. The spectrometer observes the emission of the n= 8-7 hydrogenic transition of C{sup +5} ions ({lambda}{sub air}= 529.06 nm) resulting from charge exchange reactions between deuterium heating beams and intrinsic carbon. Novel features include a large, prism-coupled high-dispersion, volume-phase-holographic transmission grating and high-quantum efficiency, high-gain, low-noise avalanche photodiode detectors that sample emission at 1 MHz. This new diagnostic offers an order-of-magnitude increase in sensitivity compared to earlier ion thermal turbulence measurements. Increased sensitivity is crucial for obtaining enough photon statistics from plasmas with much less impurity content. The irreducible noise floor set by photon statistics sets the ultimate sensitivity to plasma fluctuations. Based on the measured photon flux levels for the entire spectral line, photon noise levels for T(tilde sign){sub i}/T{sub i} and V(tilde sign){sub i}/V{sub i} of {approx}1% are expected, while statistical averaging over long data records enables reduction in the detectable plasma fluctuation levels to values less than that. Broadband ion temperature fluctuations are observed to near 200 kHz in an L-mode discharge. Cross-correlation with the local beam emission spectroscopy measurements demonstrates a strong coupling of the density and temperature fields, and enables the cross-phase measurements between density and ion temperature fluctuations.

  14. X-ray emission cross sections following Ar{sup 18+} charge-exchange collisions on neutral argon: The role of the multiple electron capture

    SciTech Connect

    Otranto, S.; Olson, R. E.

    2011-03-15

    X-ray emission originating in charge-exchange collisions between Ar{sup 18+} and neutral argon is studied at impact energies of 5-4000 eV/amu by means of the classical trajectory Monte Carlo method (CTMC). Line emission and charge-exchange cross sections obtained from different CTMC versions based on the one-active electron approximation are contrasted among themselves and against the results obtained by means of a three-active electron code that lets us infer the role of multiple electron capture. The present results are compared to the recent experimental data available from the EBIT groups operating at Livermore, NIST, and Berlin. We were not able to reconcile the major difference in x-ray emission cross sections obtained from in situ measurements made in EBIT, versus those made in an exterior, field-free collision chamber using ions extracted from the EBIT. Our calculations support the extracted beam results.

  15. Laboratory Measurements Compellingly Support a Charge-exchange Mechanism for the ’Dark Matter’ ~3.5 keV X-Ray Line

    NASA Astrophysics Data System (ADS)

    Shah, Chintan; Dobrodey, Stepan; Bernitt, Sven; Steinbrügge, René; Crespo López-Urrutia, José R.; Gu, Liyi; Kaastra, Jelle

    2016-12-01

    The reported observations of an unidentified X-ray line feature at ∼3.5 keV have driven a lively discussion about its possible dark matter origin. Motivated by this, we have measured the K-shell X-ray spectra of highly ionized bare sulfur ions following charge exchange with gaseous molecules in an electron beam ion trap, as a source of or a contributor to this X-ray line. We produced S16+ and S15+ ions and let them capture electrons in collision with those molecules with the electron beam turned off while recording X-ray spectra. We observed a charge-exchange-induced X-ray feature at the Lyman series limit (3.47 ± 0.06 keV). The inferred X-ray energy is in full agreement with the reported astrophysical observations and supports the novel scenario proposed by Gu et al.

  16. Differences in Electronic Exchanges in Synchronous and Asynchronous Computer-Mediated Communication: The Effect of Culture as a Mediating Variable

    ERIC Educational Resources Information Center

    Angeli, Charoula; Schwartz, Neil H.

    2016-01-01

    Two hundred and eighty undergraduates from universities in two countries were asked to read didactic material, and then think and write about potential solutions to an ill-defined problem. The writing was conducted within a synchronous or asynchronous computer-mediated communication (CMC) environment. Asynchronous CMC took the form of email…

  17. Effects of island-edge exchange barrier on 2D pattern formation in surfactant-mediated epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Dai-mu; Sun, Xia; Wu, Zi-qin

    2001-11-01

    The nucleation and growth of two-dimensional islands in a surfactant-mediated epitaxy system have been studied by computer simulation. To improve the recent results published in the literature, we use a configuration-dependent energy barrier for the exchange process at the island edge in our model. The simulations produce fractal islands at high temperatures or low deposition fluxes and a transition to regular compact islands occurs at lower temperatures or higher fluxes, in good agreement with the recent experimental results. The barrier for the island-edge exchange has quite a strong effect on the island density as a function of temperature and flux. A small change of the island-edge exchange barrier induces a large variation of the island density in the low-temperature or high-flux region. The flux-dependent island density shows a clear scaling-law behaviour in the intermediate-flux region. The scaling exponent increases evidently as the island-edge exchange barrier increases.

  18. Experimental test of the single adatom exchange model in surfactant-mediated growth of Ge on Si(100)

    NASA Astrophysics Data System (ADS)

    Bailes, A. A., III; Boshart, M. A.; Seiberling, L. E.

    1998-03-01

    We have tested the single adatom exchange model for surfactant-mediated growth. Using two samples with different coverages of Ge on Sb-terminated Si(100), we generated energy distributions of scattered MeV ions from transmission ion channeling experiments. We studied the system both after room temperature deposition of Ge and after annealing at 350°C. We then compared simulated energy distributions for the single adatom exchange model to the experimental energy distributions. No combination of temperature and coverage produced a good fit between data and simulations of this model. Before annealing, however, a model having Ge in dimer-like sites on top of undisturbed Sb dimers describes the data well for both Ge coverages.

  19. Defect mediated desorption of the KBr(001) surface induced by single highly charged ion impact.

    PubMed

    Heller, R; Facsko, S; Wilhelm, R A; Möller, W

    2008-08-29

    The individual impacts of slow (300 eV/amu) highly charged Xe ions induce nanometer sized pitlike structures on the KBr (001) surface. The volume of these structures shows a strong dependence on the ions potential energy. Total potential sputter yields from atomically flat (001) terraces are determined by imaging single ion impact sites. The dependence of the sputter yield on the ions initial charge state combined with structure formation at low and high-fluence irradiations indicates that agglomeration of defects into complex centers plays a major role in the desorption process induced by the potential energy.

  20. Theoretical description of pump/probe experiments in electron-mediated charge-density-wave insulators

    NASA Astrophysics Data System (ADS)

    Freericks, J. K.; Matveev, O. P.; Shen, Wen; Shvaika, A. M.; Devereaux, T. P.

    2017-03-01

    In this review, we develop the formalism employed to describe charge-density-wave insulators in pump/probe experiments that use ultrashort driving pulses of light. The theory emphasizes exact results in the simplest model for a charge-density-wave insulator (given by a noninteracting system with two bands and a gap) and employs nonequilibrium dynamical mean-field theory to solve the Falicov–Kimball model in its ordered phase. We show how to develop the formalism and how the solutions behave. Care is taken to describe the details behind these calculations and to show how to verify their accuracy via sum-rule constraints.

  1. Ag-mediated charge transport during metal-assisted chemical etching of silicon nanowires.

    PubMed

    Geyer, Nadine; Fuhrmann, Bodo; Leipner, Hartmut S; Werner, Peter

    2013-05-22

    The charge transport mechanism during metal-assisted chemical etching of Si nanowires with contiguous metal films has been investigated. The experiments give a better insight how the charges and reaction products can penetrate to the etching front. The formation of a layer of porous Si between the metal film and the bulk Si is a prerequisite for the etching process. The electronic holes (positive charges) necessary for the etching of porous Si are generated at the surface of the metal in contact with the oxidative agent. Because of the insulating character of the thin walls of the porous Si, the transport of the electronic holes through this layer is not possible. Instead, it is found that the transport of electronic holes proceeds primarily by means of the Ag/Ag(+) redox pair circulating in the electrolyte and diffusing through the etched pores in the Si. The charge transport occurs without the ionic contribution at the positions where the metal is in direct contact with the Si. Here, an electropolishing process takes place, leading to an extensive removal of the Si and sinking in of the film into the Si substrate.

  2. Metal-organic charge transfer can produce biradical states and is mediated by conical intersections

    PubMed Central

    Tishchenko, Oksana; Li, Ruifang; Truhlar, Donald G.

    2010-01-01

    The present paper illustrates key features of charge transfer between calcium atoms and prototype conjugated hydrocarbons (ethylene, benzene, and coronene) as elucidated by electronic structure calculations. One- and two-electron charge transfer is controlled by two sequential conical intersections. The two lowest electronic states that undergo a conical intersection have closed-shell and open-shell dominant configurations correlating with the 4s2 and 4s13d1 states of Ca, respectively. Unlike the neutral-ionic state crossing in, for example, hydrogen halides or alkali halides, the path from separated reactants to the conical intersection region is uphill and the charge-transferred state is a biradical. The lowest-energy adiabatic singlet state shows at least two minima along a single approach path of Ca to the π system: (i) a van der Waals complex with a doubly occupied highest molecular orbital, denoted , and a small negative charge on Ca and (ii) an open-shell singlet (biradical) at intermediate approach (Ca⋯C distance ≈2.5–2.7 Å) with molecular orbital structure ϕ1ϕ2, where ϕ2 is an orbital showing significant charge transfer form Ca to the π-system, leading to a one-electron multicentered bond. A third minimum (iii) at shorter distances along the same path corresponding to a closed-shell state with molecular orbital structure has also been found; however, it does not necessarily represent the ground state at a given Ca⋯C distance in all three systems. The topography of the lowest adiabatic singlet potential energy surface is due to the one- and two-electron bonding patterns in Ca-π complexes. PMID:21037111

  3. Revealing the effect of plasmon transmutation on charge transfer plasmons in substrate-mediated metallodielectric aluminum clusters

    NASA Astrophysics Data System (ADS)

    Nooshnab, Vida; Golmohammadi, Saeed

    2017-01-01

    Aluminum nanoparticle nanocomplexes have extensively been utilized for sustaining ultrastrong plasmonic bonding and antibonding resonant modes across the ultraviolet to visible spectrum. In this study, we analyze the plasmon response for two conventional symmetric heptamer and antisymmetric octamer antennas mediated by conductive film as a substrate to induce very sharp Fano-resonant mode at the high energy states. Besides, presence of an underlying conductive film in touching regime with the plasmonic nanoantennas leads to formation of charge transfer plasmons (CTPs) across the deep-UV band. It is also shown that presence of dielectric carbon nanospheres in the gap spots between proximal nanodisks gives rise to breaking the symmetry of the assemblies, while the new magnetic multipolar modes are induced and divided the Fano dip in two parts as well as formation of a couple of charge transfer plasmon resonant shoulders. The compactness and geometries of the clusters allow for inducing substantially strong resonant modes across the deep-UV domain. Our investigations provide new pathways and features for designing multifunctional molecular probes, biochemical sensors, and cathodoluminescence antennas across the UV spectrum. The proposed analysis were done using a blend of Finite-Difference Time-Domain (FDTD) calculations and transfer of plasmonic charges in nanoscale systems.

  4. Charge-dependent model for many-body polarization, exchange, and dispersion interactions in hybrid quantum mechanical/molecular mechanical calculations.

    PubMed

    Giese, Timothy J; York, Darrin M

    2007-11-21

    This work explores a new charge-dependent energy model consisting of van der Waals and polarization interactions between the quantum mechanical (QM) and molecular mechanical (MM) regions in a combined QMMM calculation. van der Waals interactions are commonly treated using empirical Lennard-Jones potentials, whose parameters are often chosen based on the QM atom type (e.g., based on hybridization or specific covalent bonding environment). This strategy for determination of QMMM nonbonding interactions becomes tedious to parametrize and lacks robust transferability. Problems occur in the study of chemical reactions where the "atom type" is a complex function of the reaction coordinate. This is particularly problematic for reactions, where atoms or localized functional groups undergo changes in charge state and hybridization. In the present work we propose a new model for nonelectrostatic nonbonded interactions in QMMM calculations that overcomes many of these problems. The model is based on a scaled overlap model for repulsive exchange and attractive dispersion interactions that is a function of atomic charge. The model is chemically significant since it properly correlates atomic size, softness, polarizability, and dispersion terms with minimal one-body parameters that are functions of the atomic charge. Tests of the model are examined for rare-gas interactions with neutral and charged atoms in order to demonstrate improved transferability. The present work provides a new framework for modeling QMMM interactions with improved accuracy and transferability.

  5. Cation exchange surface-mediated denaturation of an aglycosylated immunoglobulin (IgG1).

    PubMed

    Gillespie, Ron; Nguyen, Thao; Macneil, Sean; Jones, Laurie; Crampton, Shon; Vunnum, Suresh

    2012-08-17

    Cation exchange chromatography of an aglycosylated IgG1 resulted in two distinct peaks during gradient elution. The early eluting peak contained <1% high molecular weight (HMW) species, while the later peak contained 23% HMW species. Analysis by hydrogen-deuterium exchange and Fourier transform infrared spectroscopy (FTIR) indicated that aggregate formation and generation of the second peak were caused by antibody denaturation on the resin surface. Denaturation and HMW generation was increased by the use of strong cation exchange media, by increasing antibody residence time on the exchanger, or increasing temperature. Denaturation and HMW generation was reduced by increasing pH or ionic strength, by the use of preferentially excluded solutes such as citrate or glycine and controlled entirely by addition of 125 mM arginine to the process buffers. This leads to the hypothesis that denaturation and HMW generation of this antibody can be managed by reducing the strength of binding, by increasing its conformational stability, or by suppressing non-native protein-protein interactions. The glycosylated version of this antibody exhibited less than 2% denatured form, suggesting that glycosylation contributes significantly to the stability of this antibody. These findings may be helpful in managing aggregation in other antibodies, and particularly useful in developing purification processes for aglycosylated antibodies.

  6. Computer-Mediated Corrective Feedback and Language Accuracy in Telecollaborative Exchanges

    ERIC Educational Resources Information Center

    Vinagre, Margarita; Munoz, Beatriz

    2011-01-01

    Recent studies illustrate the potential that intercultural telecollaborative exchanges entail for language development through the use of corrective feedback from collaborating partners (Kessler, 2009; Lee, 2008; Sauro, 2009; Ware & O'Dowd, 2008). We build on this growing body of research by presenting the findings of a three-month-long…

  7. Evidence and implications of direct charge excitation as the dominant mechanism in plasmon-mediated photocatalysis

    DOE PAGES

    Boerigter, Calvin; Campana, Robert; Morabito, Matthew; ...

    2016-01-28

    Plasmonic metal nanoparticles enhance chemical reactions on their surface when illuminated with light of particular frequencies. It has been shown that these processes are driven by excitation of localized surface plasmon resonance (LSPR). The interaction of LSPR with adsorbate orbitals can lead to the injection of energized charge carriers into the adsorbate, which can result in chemical transformations. The mechanism of the charge injection process (and role of LSPR) is not well understood. Here we shed light on the specifics of this mechanism by coupling optical characterization methods, mainly wavelength-dependent Stokes and anti-Stokes SERS, with kinetic analysis of photocatalytic reactionsmore » in an Ag nanocube–methylene blue plasmonic system. We propose that localized LSPR-induced electric fields result in a direct charge transfer within the molecule–adsorbate system. Lastly, these observations provide a foundation for the development of plasmonic catalysts that can selectively activate targeted chemical bonds, since the mechanism allows for tuning plasmonic nanomaterials in such a way that illumination can selectively enhance desired chemical pathways.« less

  8. Evidence and implications of direct charge excitation as the dominant mechanism in plasmon-mediated photocatalysis

    SciTech Connect

    Boerigter, Calvin; Campana, Robert; Morabito, Matthew; Linic, Suljo

    2016-01-28

    Plasmonic metal nanoparticles enhance chemical reactions on their surface when illuminated with light of particular frequencies. It has been shown that these processes are driven by excitation of localized surface plasmon resonance (LSPR). The interaction of LSPR with adsorbate orbitals can lead to the injection of energized charge carriers into the adsorbate, which can result in chemical transformations. The mechanism of the charge injection process (and role of LSPR) is not well understood. Here we shed light on the specifics of this mechanism by coupling optical characterization methods, mainly wavelength-dependent Stokes and anti-Stokes SERS, with kinetic analysis of photocatalytic reactions in an Ag nanocube–methylene blue plasmonic system. We propose that localized LSPR-induced electric fields result in a direct charge transfer within the molecule–adsorbate system. Lastly, these observations provide a foundation for the development of plasmonic catalysts that can selectively activate targeted chemical bonds, since the mechanism allows for tuning plasmonic nanomaterials in such a way that illumination can selectively enhance desired chemical pathways.

  9. Evidence and implications of direct charge excitation as the dominant mechanism in plasmon-mediated photocatalysis

    PubMed Central

    Boerigter, Calvin; Campana, Robert; Morabito, Matthew; Linic, Suljo

    2016-01-01

    Plasmonic metal nanoparticles enhance chemical reactions on their surface when illuminated with light of particular frequencies. It has been shown that these processes are driven by excitation of localized surface plasmon resonance (LSPR). The interaction of LSPR with adsorbate orbitals can lead to the injection of energized charge carriers into the adsorbate, which can result in chemical transformations. The mechanism of the charge injection process (and role of LSPR) is not well understood. Here we shed light on the specifics of this mechanism by coupling optical characterization methods, mainly wavelength-dependent Stokes and anti-Stokes SERS, with kinetic analysis of photocatalytic reactions in an Ag nanocube–methylene blue plasmonic system. We propose that localized LSPR-induced electric fields result in a direct charge transfer within the molecule–adsorbate system. These observations provide a foundation for the development of plasmonic catalysts that can selectively activate targeted chemical bonds, since the mechanism allows for tuning plasmonic nanomaterials in such a way that illumination can selectively enhance desired chemical pathways. PMID:26817619

  10. Structure/function relationships in RecA protein-mediated homology recognition and strand exchange.

    PubMed

    Prentiss, Mara; Prévost, Chantal; Danilowicz, Claudia

    2015-01-01

    RecA family proteins include RecA, Rad51, and Dmc1. These recombinases are responsible for homology search and strand exchange. Homology search and strand exchange occur during double-strand break repair and in eukaryotes during meiotic recombination. In bacteria, homology search begins when RecA binds an initiating single-stranded DNA (ssDNA) in the primary DNA-binding site to form the presynaptic filament. The filament is a right-handed helix, where the initiating strand is bound deep within the filament. Once the presynaptic filament is formed, it interrogates nearby double-stranded DNA (dsDNA) to find a homologous sequence; therefore, we provide a detailed discussion of structural features of the presynaptic filament that play important functional roles. The discussion includes many diagrams showing multiple filament turns. These diagrams illustrate interactions that are not evident in single turn structures. The first dsDNA interactions with the presynaptic filament are insensitive to mismatches. The mismatch insensitive interactions lead to dsDNA deformation that triggers a homology testing process governed by kinetics. The first homology test involves ∼8 bases. Almost all interactions are rejected by this initial rapid test, leading to a new cycle of homology testing. Interactions that pass the initial rapid test proceed to a slower testing stage. That slower stage induces nonhomologous dsDNA to reverse strand exchange and begin a new cycle of homology testing. In contrast, homologous dsDNA continues to extend the heteroduplex strand-exchange product until ATP hydrolysis makes strand exchange irreversible.

  11. Np(V) and Pu(v) ion exchange and surface-mediated reduction mechanisms on montmorillonite.

    PubMed

    Zavarin, Mavrik; Powell, Brian A; Bourbin, Mathilde; Zhao, Pihong; Kersting, Annie B

    2012-03-06

    Due to their ubiquity and chemical reactivity, aluminosilicate clays play an important role in actinide retardation and colloid-facilitated transport in the environment. In this work, Pu(V) and Np(V) sorption to Na-montmorillonite was examined as a function of ionic strength, pH, and time. Np(V) sorption equilibrium was reached within 2 h. Sorption was relatively weak and showed a pH and ionic strength dependence. An approximate NpO(2)(+) → Na(+) Vanselow ion exchange coefficient (Kv) was determined on the basis of Np(V) sorption in 0.01 and 1.0 M NaCl solutions at pH < 5 (Kv ~ 0.3). In contrast to Np(V), Pu(V) sorption equilibrium was not achieved on the time-scale of weeks. Pu(V) sorption was much stronger than Np(V), and sorption rates exhibited both a pH and ionic strength dependence. Differences in Np(V) and Pu(V) sorption behavior are indicative of surface-mediated transformation of Pu(V) to Pu(IV) which has been reported for a number of redox-active and redox-inactive minerals. A model of the pH and ionic strength dependence of Pu(V) sorption rates suggests that H(+) exchangeable cations facilitate Pu(V) reduction. While surface complexation may play a dominant role in Pu sorption and colloid-facilitated transport under alkaline conditions, results from this study suggest that Pu(V) ion exchange and surface-mediated reduction to Pu(IV) can immobilize Pu or enhance its colloid-facilitated transport in the environment at neutral to mildly acidic pHs.

  12. Exchange-mediated spin-lattice relaxation of Fe3+ ions in borate glasses.

    PubMed

    Misra, Sushil K; Pilbrow, John R

    2007-03-01

    Spin-lattice relaxation times (T1) of two borate glasses doped with different concentrations of Fe2O3 were measured using the Electron Spin-Echo (ESE) technique at X-band (9.630 GHz) in the temperature range 2-6K. In comparison with a previous investigation of Fe3+-doped silicate glasses, the relaxation rates were comparable and differed by no more than a factor of two. The data presented here extend those previously reported for borate glasses in the 10-250K range but measured using the amplitude-modulation technique. The T1 values were found to depend on temperature (T) as T(n) with n approximately 1 for the 1% and 0.1% Fe2O3-doped glass samples. These results are consistent with spin-lattice relaxation as effected by exchange interaction of a Fe3+ spin exchange-coupled to another Fe3+ spin in an amorphous material.

  13. Sensitivity Enhancement by Exchange Mediated MagnetizationTransfer of the Xenon Biosensor Signal

    SciTech Connect

    Garcia, Sandra; Chavez, Lana; Lowery, Thomas J.; Han, Song-I.; Wemmer, David E.; Pines, Alexander

    2006-08-31

    Hyperpolarized xenon associated with ligand derivitized cryptophane-A cages has been developed as a NMR based biosensor. To optimize the detection sensitivity we describe use of xenon exchange between the caged and bulk dissolved xenon as an effective signal amplifier. This approach, somewhat analogous to 'remote detection' described recently, uses the chemical exchange to repeatedly transfer spectroscopic information from caged to bulk xenon, effectively integrating the caged signal. After an optimized integration period, the signal is read out by observation of the bulk magnetization. The spectrum of the caged xenon is reconstructed through use of a variable evolution period before transfer and Fourier analysis of the bulk signal as a function of the evolution time.

  14. Measurement of the left-right asymmetry in pion-proton radiative exchange and charge exchange scattering from 301 to 625 MeV/c on a transversely polarized target

    SciTech Connect

    Kim, George Jung-Kwang

    1988-05-01

    The left-right asymmetry A/sub N/ in ..pi../sup /minus//p ..-->.. ..gamma..n has been measured at p/sub ..pi.. = 301, 316, 427, 471, 547, 586, and 625 MeV/c using a transversely polarized target. The final-state neutron and gamma were detected in coincidence by two states of matching neutron and gamma detectors at gamma angles centered around 90/degree and 110/degree/ c.m. A gamma detector consisted of an array of 15 counters, each was 15/times/15/times/25 cm/sup 3/ block of lead-glass. A neutron detector consisted of 15 counters also, each one was a cylindrical plastic scintillator 7.6 cm in diameter and 45.7 cm long. The A/sub N/ results are compared with the predictions from the most recent single-pion photoproduction partial-wave analysis by Arai and Fujii. The agreement is poor, casting doubt on the correctness of the value for the radiative-decay amplitude of the neutral Roper resonance now in use. A comparison is made with the 90/degree/recoil proton polarization data of the inverse reaction derived from ..gamma..d scattering, there are substantial discrepencies. Charge exchange (..pi../sup /minus/p/ ..-->.. ..gamma../degree/n) events were the major yield in this experiment. Very precise values of the charge exchange analyzing power were obtained with an error of typically 3%. The charge exchange results are compared with the predictions from recent ..gamma..n partial wave analyses. At the lower incident energies little difference is seen between the VPI, Karlsruhe-Helsinki, and CMU-LBL analyses, and there is excellent agreement with our experiment. From the onset of the Roper resonance the VPI solution is strongly favored.

  15. A rice tonoplastic calcium exchanger, OsCCX2 mediates Ca2+/cation transport in yeast

    PubMed Central

    Yadav, Akhilesh K.; Shankar, Alka; Jha, Saroj K.; Kanwar, Poonam; Pandey, Amita; Pandey, Girdhar K.

    2015-01-01

    In plant cell, cations gradient in cellular compartments is maintained by synergistic action of various exchangers, pumps and channels. The Arabidopsis exchanger family members (AtCCX3 and AtCCX5) were previously studied and belong to CaCA (calcium cation exchangers) superfamily while none of the rice CCXs has been functionally characterized for their cation transport activities till date. Rice genome encode four CCXs and only OsCCX2 transcript showed differential expression under abiotic stresses and Ca2+ starvation conditions. The OsCCX2 localized to tonoplast and suppresses the Ca2+ sensitivity of K667 (low affinity Ca2+ uptake deficient) yeast mutant under excess CaCl2 conditions. In contrast to AtCCXs, OsCCX2 expressing K667 yeast cells show tolerance towards excess Na+, Li+, Fe2+, Zn2+ and Co2+ and suggest its ability to transport both mono as well as divalent cations in yeast. Additionally, in contrast to previously characterized AtCCXs, OsCCX2 is unable to complement yeast trk1trk2 double mutant suggesting inability to transport K+ in yeast system. These finding suggest that OsCCX2 having distinct metal transport properties than previously characterized plant CCXs. OsCCX2 can be used as potential candidate for enhancing the abiotic stress tolerance in plants as well as for phytoremediation of heavy metal polluted soil. PMID:26607171

  16. Counterion-Mediated Ligand Exchange for PbS Colloidal Quantum Dot Superlattices

    PubMed Central

    2015-01-01

    In the past years, halide capping became one of the most promising strategies to passivate the surface of colloidal quantum dots (CQDs) in thin films to be used for electronic and optoelectronic device fabrication. This is due to the convenient processing, strong n-type characteristics, and ambient stability of the devices. Here, we investigate the effect of three counterions (ammonium, methylammonium, and tetrabutylammonium) in iodide salts used for treating CQD thin films and shed light on the mechanism of the ligand exchange. We obtain two- and three-dimensional square-packed PbS CQD superlattices with epitaxial merging of nearest neighbor CQDs as a direct outcome of the ligand-exchange reaction and show that the order in the layer can be controlled by the nature of the counterion. Furthermore, we demonstrate that the acidity of the environment plays an important role in the substitution of the carboxylates by iodide ions at the surface of lead chalcogenide quantum dots. Tetrabutylammonium iodide shows lower reactivity compared to methylammonium and ammonium iodide due to the nonacidity of the cation, which eventually leads to higher order but also poorer carrier transport due to incomplete removal of the pristine ligands in the QD thin film. Finally, we show that single-step blade-coating and immersion in a ligand exchange solution such as the one containing methylammonium iodide can be used to fabricate well performing bottom-gate/bottom-contact PbS CQD field effect transistors with record subthreshold swing. PMID:26512884

  17. Determination of {sup 16}O and {sup 18}O sensitivity factors and charge-exchange processes in low-energy ion scattering

    SciTech Connect

    Tellez, H.; Chater, R. J.; Fearn, S.; Symianakis, E.; Kilner, J. A.; Brongersma, H. H.

    2012-10-08

    Quantitative analysis in low-energy ion scattering (LEIS) requires an understanding of the charge-exchange processes to estimate the elemental sensitivity factors. In this work, the neutralization of He{sup +} scattered by {sup 18}O-exchanged silica at energies between 0.6 and 7 keV was studied. The process is dominated by Auger neutralization for E{sub i} < 0.8 keV. An additional mechanism starts above the reionization threshold. This collision-induced neutralization becomes the dominant mechanism for E{sub i} > 2 keV. The ion fractions P{sup +} were determined for Si and O using the characteristic velocity method to quantify the surface density. The {sup 18}O/{sup 16}O sensitivity ratio indicates an 18% higher sensitivity for the heavier O isotope.

  18. Effect of ligand exchange of Cu2ZnSnS4 nanocrystals on the charge transport and photovoltaic performance of nanostructured depleted bulk heterojunction solar cell

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuo-Xi; Zhou, Zheng-Ji; Bai, Bing; Liu, Ming-Hua; Zhou, Wen-Hui; Kou, Dong-Xing; Wu, Si-Xin

    2015-12-01

    Cu2ZnSnS4 (CZTS) nanocrystals combining the advantage of feasible solution-phase synthesis and processing are perceived as promising materials for application in efficient, low-cost photovoltaic technology. Herein, we have got surfactant-free CZTS nanocrystals by a novel ligand exchange method, and the obtained CZTS nanocrystals were deposited onto ZnO nanorod arrays to construct depleted bulk heterojunction solar cell. The all-inorganic CZTS nanocrystal solar cells demonstrated a remarkable improvement in J sc (from 8.14 to 13.97 mA/cm2) and power conversion efficiency (from 1.83 to 3.34 %) compared with surfactant-capped CZTS nanocrystals. Using surface photovoltage spectrum, the influence of ligand exchange of CZTS nanocrystals on the charge transport and photovoltaic performance of the nanostructured CZTS solar cells was discussed.

  19. Charge transfer-induced magnetic exchange bias and electron localization in (111)- and (001)-oriented LaNiO3/LaMnO3 superlattices

    NASA Astrophysics Data System (ADS)

    Wei, Haoming; Barzola-Quiquia, Jose Luis; Yang, Chang; Patzig, Christian; Höche, Thomas; Esquinazi, Pablo; Grundmann, Marius; Lorenz, Michael

    2017-03-01

    High-quality lattice-matched LaNiO3/LaMnO3 superlattices with monolayer terrace structure have been grown on both (111)- and (001)-oriented SrTiO3 substrates by pulsed laser deposition. In contrast to the previously reported experiments, a magnetic exchange bias is observed that reproducibly occurs in both (111)- and (001)-oriented superlattices with the thin single layers of 5 and 7 unit cells, respectively. The exchange bias is theoretically explained by charge transfer-induced magnetic moments at Ni atoms. Furthermore, magnetization data at low temperature suggest two magnetic phases in the superlattices, with Néel temperature around 10 K. Electrical transport measurements reveal a metal-insulator transition with strong localization of electrons in the superlattices with the thin LaNiO3 layers of 4 unit cells, in which the electrical transport is dominated by two-dimensional variable range hopping.

  20. Interaction of plasma jets produced from pinch plasma with neutral atoms in order to achieve an effective charge exchange table top X-laser

    SciTech Connect

    Engel, A.; Lebert, R.; Koshelev, K. N.; Sidelnikov, Yu. V.; Churilov, S. S.; Gavrilescu, C.; Neff, W.

    1997-05-05

    Charge exchange recombination is known as an effective scheme to get population inversion in the EUV-range. Highly ionised plasma jets and a neutral target could be very efficient ({sigma}{sub CE}>10{sup -15} cm{sup 2}) to realisation of this atomic scheme. Theoretical estimates and preliminary experiments show that for plasma focus with a stored energy of several kJ one can reach a substantial population inversion for ions of light elements with charge number Z<10. Experimental studies of production of these plasma jets in a 2 kJ plasma focus device is presented. Moreover the optimal properties of possible targets are investigated. Experimental results for the interaction of the plasma jets and targets are presented.

  1. DXL: A Sounding Rocket Mission for the Study of Solar Wind Charge Exchange and Local Hot Bubble X-Ray Emission

    NASA Technical Reports Server (NTRS)

    Galeazzi, M.; Prasai, K.; Uprety, Y.; Chiao, M.; Collier, M. R.; Koutroumpa, D.; Porter, F. S.; Snowden, S.; Cravens, T.; Robertson, I.; Kuntz, K. D.; Lepri, S.; McCammon, D.

    2011-01-01

    The Diffuse X-rays from the Local galaxy (DXL) mission is an approved sounding rocket project with a first launch scheduled around December 2012. Its goal is to identify and separate the X-ray emission generated by solar wind charge exchange from that of the local hot bubble to improve our understanding of both. With 1,000 square centimeters proportional counters and grasp of about 10 square centimeters sr both in the 1/4 and 3/4 keV bands, DXL will achieve in a 5-minute flight what cannot be achieved by current and future X-ray satellites.

  2. Charge exchange in cometary coma: Discovery of H(-) ions in the solar wind close to comet 67P/Churyumov-Gerasimenko.

    PubMed

    Burch, J L; Cravens, T E; Llera, K; Goldstein, R; Mokashi, P; Tzou, C-Y; Broiles, T

    2015-07-16

    As Rosetta was orbiting comet 67P/Churyumov-Gerasimenko, the Ion and Electron Sensor detected negative particles with angular distributions like those of the concurrently measured solar wind protons but with fluxes of only about 10% of the proton fluxes and energies of about 90% of the proton energies. Using well-known cross sections and energy-loss data, it is determined that the fluxes and energies of the negative particles are consistent with the production of H(-) ions in the solar wind by double charge exchange with molecules in the coma.

  3. Measurement of Anomalously Strong Emission from the 1s-9p Transition in the Spectrum of H-like Phosphorus Following Charge Exchange with Molecular Hydrogen

    NASA Technical Reports Server (NTRS)

    Leutenegger, M. A.; Beiersdorfer, P.; Brown, G. V.; Kelley, R. L.; Porter, F. S.

    2010-01-01

    We have measured K-shell x-ray spectra of highly ionized argon and phosphorus following charge exchange with molecular hydrogen at low collision energy in an electron beam ion trap using an x-ray calorimeter array with approx.6 eV resolution. We find that the emission at the high-end of the Lyman series is greater by a factor of two for phosphorus than for argon, even though the measurement was performed concurrently and the atomic numbers are similar. This does not agree with current theoretical models and deviates from the trend observed in previous measurements.

  4. Cross section database for carbon atoms and ions: Electron-impact ionization, excitation, and charge exchange in collisions with hydrogen atoms

    SciTech Connect

    Suno, Hiroya . E-mail: suno@jamstec.go.jp; Kato, Takako

    2006-07-15

    A database has been constructed consisting of the recommended cross sections for electron-impact excitation and ionization of carbon atoms and ions C, C{sup +}-C{sup 5+}, asl as for charge exchange processes between carbon ions C{sup +}-C{sup 6+} and hydrogen atoms. We have collected a large amount of theoretical and experimental cross section data from the literature, and have critically assessed their accuracy. The recommended cross sections, the best values for use, are expressed in the form of simple analytical functions. These are also presented in graphical form.

  5. The effect of N2/+/ recombination on the aeronomic determination of the charge exchange rate coefficient of O/+//2D/ with N2

    NASA Technical Reports Server (NTRS)

    Torr, D. G.; Orsini, N.

    1978-01-01

    The Atmosphere Explorer (AE) data are reexamined in the light of new laboratory measurements of the N2(+) recombination rate coefficient alpha. The new measurements support earlier measurements which yielded values of alpha significantly lower than the AE values. It is found that the values for alpha determined from the satellite data can be reconciled with the laboratory measurements, if the charge exchange rate coefficient for O(+)(2D) with N2 is less than one-quarter of that derived in the laboratory by Rutherford and Vroom (1971).

  6. Charge exchange in cometary coma: Discovery of H− ions in the solar wind close to comet 67P/Churyumov‐Gerasimenko

    PubMed Central

    Cravens, T. E.; Llera, K.; Goldstein, R.; Mokashi, P.; Tzou, C.‐Y.; Broiles, T.

    2015-01-01

    Abstract As Rosetta was orbiting comet 67P/Churyumov‐Gerasimenko, the Ion and Electron Sensor detected negative particles with angular distributions like those of the concurrently measured solar wind protons but with fluxes of only about 10% of the proton fluxes and energies of about 90% of the proton energies. Using well‐known cross sections and energy‐loss data, it is determined that the fluxes and energies of the negative particles are consistent with the production of H− ions in the solar wind by double charge exchange with molecules in the coma. PMID:27656008

  7. Heme biomolecule as redox mediator and oxygen shuttle for efficient charging of lithium-oxygen batteries

    PubMed Central

    Ryu, Won-Hee; Gittleson, Forrest S.; Thomsen, Julianne M.; Li, Jinyang; Schwab, Mark J.; Brudvig, Gary W.; Taylor, André D.

    2016-01-01

    One of the greatest challenges with lithium-oxygen batteries involves identifying catalysts that facilitate the growth and evolution of cathode species on an oxygen electrode. Heterogeneous solid catalysts cannot adequately address the problematic overpotentials when the surfaces become passivated. However, there exists a class of biomolecules which have been designed by nature to guide complex solution-based oxygen chemistries. Here, we show that the heme molecule, a common porphyrin cofactor in blood, can function as a soluble redox catalyst and oxygen shuttle for efficient oxygen evolution in non-aqueous Li-O2 batteries. The heme's oxygen binding capability facilitates battery recharge by accepting and releasing dissociated oxygen species while benefiting charge transfer with the cathode. We reveal the chemical change of heme redox molecules where synergy exists with the electrolyte species. This study brings focus to the rational design of solution-based catalysts and suggests a sustainable cross-link between biomolecules and advanced energy storage. PMID:27759005

  8. Heme biomolecule as redox mediator and oxygen shuttle for efficient charging of lithium-oxygen batteries

    NASA Astrophysics Data System (ADS)

    Ryu, Won-Hee; Gittleson, Forrest S.; Thomsen, Julianne M.; Li, Jinyang; Schwab, Mark J.; Brudvig, Gary W.; Taylor, André D.

    2016-10-01

    One of the greatest challenges with lithium-oxygen batteries involves identifying catalysts that facilitate the growth and evolution of cathode species on an oxygen electrode. Heterogeneous solid catalysts cannot adequately address the problematic overpotentials when the surfaces become passivated. However, there exists a class of biomolecules which have been designed by nature to guide complex solution-based oxygen chemistries. Here, we show that the heme molecule, a common porphyrin cofactor in blood, can function as a soluble redox catalyst and oxygen shuttle for efficient oxygen evolution in non-aqueous Li-O2 batteries. The heme's oxygen binding capability facilitates battery recharge by accepting and releasing dissociated oxygen species while benefiting charge transfer with the cathode. We reveal the chemical change of heme redox molecules where synergy exists with the electrolyte species. This study brings focus to the rational design of solution-based catalysts and suggests a sustainable cross-link between biomolecules and advanced energy storage.

  9. Heme biomolecule as redox mediator and oxygen shuttle for efficient charging of lithium-oxygen batteries.

    PubMed

    Ryu, Won-Hee; Gittleson, Forrest S; Thomsen, Julianne M; Li, Jinyang; Schwab, Mark J; Brudvig, Gary W; Taylor, André D

    2016-10-19

    One of the greatest challenges with lithium-oxygen batteries involves identifying catalysts that facilitate the growth and evolution of cathode species on an oxygen electrode. Heterogeneous solid catalysts cannot adequately address the problematic overpotentials when the surfaces become passivated. However, there exists a class of biomolecules which have been designed by nature to guide complex solution-based oxygen chemistries. Here, we show that the heme molecule, a common porphyrin cofactor in blood, can function as a soluble redox catalyst and oxygen shuttle for efficient oxygen evolution in non-aqueous Li-O2 batteries. The heme's oxygen binding capability facilitates battery recharge by accepting and releasing dissociated oxygen species while benefiting charge transfer with the cathode. We reveal the chemical change of heme redox molecules where synergy exists with the electrolyte species. This study brings focus to the rational design of solution-based catalysts and suggests a sustainable cross-link between biomolecules and advanced energy storage.

  10. Resonance-mode electrochemical impedance measurements of silicon dioxide supported lipid bilayer formation and ion channel mediated charge transport.

    PubMed

    Lundgren, Anders; Hedlund, Julia; Andersson, Olof; Brändén, Magnus; Kunze, Angelika; Elwing, Hans; Höök, Fredrik

    2011-10-15

    A single-chip electrochemical method based on impedance measurements in resonance mode has been employed to study lipid monolayer and bilayer formation on hydrophobic alkanethiolate and SiO(2) substrates, respectively. The processes were monitored by temporally resolving changes in interfacial capacitance and resistance, revealing information about the rate of formation, coverage, and defect density (quality) of the layers at saturation. The resonance-based impedance measurements were shown to reveal significant differences in the layer formation process of bilayers made from (i) positively charged lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine (POEPC), (ii) neutral lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) on SiO(2), and (iii) monolayers made from POEPC on hydrophobic alkanethiolate substrates. The observed responses were represented with an equivalent circuit, suggesting that the differences primarily originate from the presence of a conductive aqueous layer between the lipid bilayers and the SiO(2). In addition, by adding the ion channel gramicidin D to bilayers supported on SiO(2), channel-mediated charge transport could be measured with high sensitivity (resolution around 1 pA).

  11. Molecular orbital (SCF-X-α-SW) theory of Fe2+-Mn3+, Fe3+-Mn2+, and Fe3+-Mn3+ charge transfer and magnetic exchange in oxides and silicates

    USGS Publications Warehouse

    Sherman, David M.

    1990-01-01

    Metal-metal charge-transfer and magnetic exchange interactions have important effects on the optical spectra, crystal chemistry, and physics of minerals. Previous molecular orbital calculations have provided insight on the nature of Fe2+-Fe3+ and Fe2+-Ti4+ charge-transfer transitions in oxides and silicates. In this work, spin-unrestricted molecular orbital calculations on (FeMnO10) clusters are used to study the nature of magnetic exchange and electron delocalization (charge transfer) associated with Fe3+-Mn2+, Fe3+-Mn3+, and Fe2+-Mn3+ interactions in oxides and silicates. 

  12. Nucleotide exchange factor GEF-H1 mediates cross-talk between microtubules and the actin cytoskeleton.

    PubMed

    Krendel, Mira; Zenke, Frank T; Bokoch, Gary M

    2002-04-01

    Regulation of the actin cytoskeleton by microtubules is mediated by the Rho family GTPases. However, the molecular mechanisms that link microtubule dynamics to Rho GTPases have not, as yet, been identified. Here we show that the Rho guanine nucleotide exchange factor (GEF)-H1 is regulated by an interaction with microtubules. GEF-H1 mutants that are deficient in microtubule binding have higher activity levels than microtubule-bound forms. These mutants also induce Rho-dependent changes in cell morphology and actin organization. Furthermore, drug-induced microtubule depolymerization induces changes in cell morphology and gene expression that are similar to the changes induced by the expression of active forms of GEF-H1. Furthermore, these effects are inhibited by dominant-negative versions of GEF-H1. Thus, GEF-H1 links changes in microtubule integrity to Rho-dependent regulation of the actin cytoskeleton.

  13. Measurement of absolute charge-exchange cross sections for He{sup 2+} collisions with He and H{sub 2}

    SciTech Connect

    Mawhorter, R. J.; Greenwood, J. B.; Chutjian, A.; Simcic, J.; Haley, T.; Mitescu, C. D.

    2011-11-15

    Reported are total, absolute charge-exchange cross sections for collisions of {sup 3}He{sup 2+} ions with He and H{sub 2}. Measurements are reported at fixed energies between 0.33 and 4.67 keV/amu. Both the present results and earlier results of others are analyzed in terms of available experimental small-angle differential cross sections as a function of collision energy, and hence the geometry of the exit aperture of the gas-collision cells used by the various experimental groups. In addition, the effective length of gas-collision cells is studied using fluid dynamic and molecular flow simulations to address the density patterns near the cell entrance and exit apertures. When small acceptance-angle corrections were applied, the results of present and previous measurements for the single electron capture in these systems were brought into good accord in the relevant energy ranges. Taken in their entirety, the present data for {sup 3}He{sup 2+} with He and H{sub 2} lend themselves to new theoretical calculations of the multichannel charge-exchange cross sections.

  14. Heterodimers formed through a partial anionic exchange process: scanning tunneling spectroscopy to monitor bands across the junction vis-à-vis photoinduced charge separation.

    PubMed

    Bera, Abhijit; Saha, Sudip K; Pal, Amlan J

    2015-11-07

    We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk-heterojunction solar cells based on the nanostructures in a polymer matrix.

  15. Radiochemical study of the medium energy pion double charge exchange reactions: /sup 209/Bi(pi/sup +/pi/sup -/)/sup 209-x/At

    SciTech Connect

    Clark, J.L.

    1980-01-01

    Carrier-free radiochemical techniques have been used to measure cross sections for the double charge exchange reactions of the type /sup 209/Bi(pi/sup +/, pi/sup -/xn)/sup 209-x/At for 100, 180, and 300 MeV incident pions. The observed formation of astatine products with mass numbers ranging from 208 to 205 is interpreted as evidence of processes in which energy deposited in the initial double charge exchange interaction is subsequently dissipated through neutron evaporation. The excitation functions for these reactions are seen to rise rapidly with decreasing incident pion energy with the maximum results for this study at 100 MeV. The astatine production cross secions measured for these positive pion irradiations of thick bismuth targets must be corrected for secondary processes, particularly the pion induced production of fast alpha particles which can contribute to the total cross sections through reactions like /sup 209/Bi(alpha,xn)/sup 213-x/At. The importance of these secondary contributions was studied through a series of negative pion irradiations of bismuth in which secondary pathways furnish the only means of producing astatine. The failure of evaporation calculations to reproduce the astatine product mass yields observed in these secondary studies suggests that direct mechanisms for energetic complex particle formation are quite important. Values for the alpha decay branches of /sup 207/At, /sup 208/At, and /sup 209/At were determined through a study of the electron capture and alpha decay characteristics of chemically purified astatine fractions.

  16. Design and operation of the pellet charge exchange diagnostic for measurement of energetic confined α particles and tritons on the Tokamak Fusion Test Reactor

    NASA Astrophysics Data System (ADS)

    Medley, S. S.; Mansfield, D. K.; Roquemore, A. L.; Fisher, R. K.; Duong, H. H.; McChesney, J. M.; Parks, P. B.; Petrov, M. P.; Khudoleev, A. V.; Gorelenkov, N. N.

    1996-09-01

    Radially resolved energy and density distributions of the confined α particles in D-T experiments on the Tokamak Fusion Test Reactor (TFTR) are being measured with the pellet charge exchange (PCX) diagnostic. Other energetic ion species can be detected as well, such as tritons produced in D-D plasmas and H, He3, or tritium rf-driven minority ion tails. The ablation cloud formed by injected low-Z impurity pellets provides the neutralization target for this active charge exchange technique. Because the cloud neutralization efficiency is uncertain, the PCX diagnostic is not absolutely calibrated so only relative density profiles are obtained. A mass and energy resolving E∥B neutral particle analyzer (NPA) is used which has eight energy channels covering the energy range of 0.3-3.7 MeV for α particles with energy resolution ranging from 5.8% to 11.3% and a spatial resolution of ˜5 cm. The PCX diagnostic views deeply trapped ions in a narrow pitch angle range around a mean value of v∥/v=-0.048±10-3. For D-T operation, the NPA was shielded by a polyethylene-lead enclosure providing 100× attenuation of ambient γ radiation and 14 MeV neutrons. The PCX diagnostic technique and its application on TFTR are described in detail.

  17. Proton-transfer mediated quenching of pyrene/indole charge-transfer states in isooctane solutions.

    PubMed

    Altamirano, Marcela S; Bohorquez, María del Valle; Previtali, Carlos M; Chesta, Carlos A

    2008-01-31

    The fluorescence quenching of pyrene (Py) by a series of N-methyl and N-H substituted indoles was studied in isooctane at 298 K. The fluorescence quenching rate constants were evaluated by mean of steady-state and time-resolved measurements. In all cases, the quenching process involves a charge-transfer (CT) mechanism. The I(o)/I and tau(o)/tau Stern-Volmer plots obtained for the N-H indoles show a very unusual upward deviation with increasing concentration of the quenchers. This behavior is attributed to the self-quenching of the CT intermediates by the free indoles in solution. The efficiency of quenching of the polyaromatic by the N-H indoles increases abruptly in the presence of small amount of added pyridine (or propanol). A detailed analysis of the experimental data obtained in the presence of pyridine provides unambiguous evidence that the self-quenching process involves proton transfer from the CT states to indoles.

  18. Heme biomolecule as redox mediator and oxygen shuttle for efficient charging of lithium-oxygen batteries

    SciTech Connect

    Ryu, Won-Hee; Gittleson, Forrest S.; Thomsen, Julianne M.; Li, Jinyang; Schwab, Mark J.; Brudvig, Gary W.; Taylor, André D.

    2016-10-19

    One of the greatest challenges with lithium-oxygen batteries involves identifying catalysts that facilitate the growth and evolution of cathode species on an oxygen electrode. Heterogeneous solid catalysts cannot adequately address the problematic overpotentials when the surfaces become passivated. But, there exists a class of biomolecules which have been designed by nature to guide complex solution-based oxygen chemistries. We show that the heme molecule, a common porphyrin cofactor in blood, can function as a soluble redox catalyst and oxygen shuttle for efficient oxygen evolution in non-aqueous Li-O2 batteries. The heme’s oxygen binding capability facilitates battery recharge by accepting and releasing dissociated oxygen species while benefiting charge transfer with the cathode. We reveal the chemical change of heme redox molecules where synergy exists with the electrolyte species. Our study brings focus to the rational design of solution-based catalysts and suggests a sustainable cross-link between biomolecules and advanced energy storage.

  19. Heme biomolecule as redox mediator and oxygen shuttle for efficient charging of lithium-oxygen batteries

    DOE PAGES

    Ryu, Won-Hee; Gittleson, Forrest S.; Thomsen, Julianne M.; ...

    2016-10-19

    One of the greatest challenges with lithium-oxygen batteries involves identifying catalysts that facilitate the growth and evolution of cathode species on an oxygen electrode. Heterogeneous solid catalysts cannot adequately address the problematic overpotentials when the surfaces become passivated. But, there exists a class of biomolecules which have been designed by nature to guide complex solution-based oxygen chemistries. We show that the heme molecule, a common porphyrin cofactor in blood, can function as a soluble redox catalyst and oxygen shuttle for efficient oxygen evolution in non-aqueous Li-O2 batteries. The heme’s oxygen binding capability facilitates battery recharge by accepting and releasing dissociatedmore » oxygen species while benefiting charge transfer with the cathode. We reveal the chemical change of heme redox molecules where synergy exists with the electrolyte species. Our study brings focus to the rational design of solution-based catalysts and suggests a sustainable cross-link between biomolecules and advanced energy storage.« less

  20. Comparison of efficiency between FLPe and Cre for recombinase-mediated cassette exchange in vitro and in adenovirus vector production.

    PubMed

    Takata, Yuki; Kondo, Saki; Goda, Naoki; Kanegae, Yumi; Saito, Izumu

    2011-07-01

    Cre and FLP recombinases mediate not only specific deletions and insertions, but also the recombinase-mediated cassette exchange (RMCE) reaction, which is used in cell biotechnology including ES cells and mouse genetics. However, comparison of efficiencies for Cre and FLP in RMCE has not been made. We here examined the detailed process of RMCE with Cre and FLP in vitro using mutant loxP 2272 and three mutant FRTs (FRT G, FRT H, and FRT F3) and then quantitatively compared the RMCE reactions in vitro. Interestingly, in the in vitro reactions, the RMCE efficiency of Cre reached a plateau level of approximately 5% and did not proceed further, whereas that of FLPe reached approximately 12-13%, showing that FLPe reached a higher level of efficiency than Cre possibly when they were supplied at a very high concentration. Moreover, we quantitatively compared the production efficiency of E1-deleted adenovirus vector using the RMCE method with Cre or FLP. The results showed that FLPe was again found more efficient than Cre in RMCE reaction. Thus, although Cre is considered more active than, or similar to, FLPe, it may not be necessarily true for RMCE reaction. Possible reasons explaining these results are discussed.

  1. Cre/lox-Recombinase-Mediated Cassette Exchange for Reversible Site-Specific Genomic Targeting of the Disease Vector, Aedes aegypti

    PubMed Central

    Häcker, Irina; Harrell II, Robert A.; Eichner, Gerrit; Pilitt, Kristina L.; O’Brochta, David A.; Handler, Alfred M.; Schetelig, Marc F.

    2017-01-01

    Site-specific genome modification (SSM) is an important tool for mosquito functional genomics and comparative gene expression studies, which contribute to a better understanding of mosquito biology and are thus a key to finding new strategies to eliminate vector-borne diseases. Moreover, it allows for the creation of advanced transgenic strains for vector control programs. SSM circumvents the drawbacks of transposon-mediated transgenesis, where random transgene integration into the host genome results in insertional mutagenesis and variable position effects. We applied the Cre/lox recombinase-mediated cassette exchange (RMCE) system to Aedes aegypti, the vector of dengue, chikungunya, and Zika viruses. In this context we created four target site lines for RMCE and evaluated their fitness costs. Cre-RMCE is functional in a two-step mechanism and with good efficiency in Ae. aegypti. The advantages of Cre-RMCE over existing site-specific modification systems for Ae. aegypti, phiC31-RMCE and CRISPR, originate in the preservation of the recombination sites, which 1) allows successive modifications and rapid expansion or adaptation of existing systems by repeated targeting of the same site; and 2) provides reversibility, thus allowing the excision of undesired sequences. Thereby, Cre-RMCE complements existing genomic modification tools, adding flexibility and versatility to vector genome targeting. PMID:28266580

  2. Cre/lox-Recombinase-Mediated Cassette Exchange for Reversible Site-Specific Genomic Targeting of the Disease Vector, Aedes aegypti.

    PubMed

    Häcker, Irina; Harrell Ii, Robert A; Eichner, Gerrit; Pilitt, Kristina L; O'Brochta, David A; Handler, Alfred M; Schetelig, Marc F

    2017-03-07

    Site-specific genome modification (SSM) is an important tool for mosquito functional genomics and comparative gene expression studies, which contribute to a better understanding of mosquito biology and are thus a key to finding new strategies to eliminate vector-borne diseases. Moreover, it allows for the creation of advanced transgenic strains for vector control programs. SSM circumvents the drawbacks of transposon-mediated transgenesis, where random transgene integration into the host genome results in insertional mutagenesis and variable position effects. We applied the Cre/lox recombinase-mediated cassette exchange (RMCE) system to Aedes aegypti, the vector of dengue, chikungunya, and Zika viruses. In this context we created four target site lines for RMCE and evaluated their fitness costs. Cre-RMCE is functional in a two-step mechanism and with good efficiency in Ae. aegypti. The advantages of Cre-RMCE over existing site-specific modification systems for Ae. aegypti, phiC31-RMCE and CRISPR, originate in the preservation of the recombination sites, which 1) allows successive modifications and rapid expansion or adaptation of existing systems by repeated targeting of the same site; and 2) provides reversibility, thus allowing the excision of undesired sequences. Thereby, Cre-RMCE complements existing genomic modification tools, adding flexibility and versatility to vector genome targeting.

  3. Exchange bias effect in Au-Fe3O4 dumbbell nanoparticles induced by the charge transfer from gold

    SciTech Connect

    Feygenson, Mikhail; Bauer, John C; Gai, Zheng; Marques, Carlos; Aronson, Meigan C.; Teng, Xiaowei; Su, Dong; Stanic, Vesna; Urban, Volker S; Kevin, Beyer; Dai, Sheng

    2015-08-10

    We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron scattering, synchrotron x-ray diffraction and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wüstite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatch between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed across the interface to accommodate an excess of oxygen released during the reduction of magnetite.

  4. Charge heterogeneity profiling of monoclonal antibodies using low ionic strength ion-exchange chromatography and well-controlled pH gradients on monolithic columns.

    PubMed

    Talebi, Mohammad; Nordborg, Anna; Gaspar, Andras; Lacher, Nathan A; Wang, Qian; He, Xiaoping Z; Haddad, Paul R; Hilder, Emily F

    2013-11-22

    In this work, the suitability of employing shallow pH gradients generated using single component buffer systems as eluents through cation-exchange (CEX) monolithic columns is demonstrated for the high-resolution separation of monoclonal antibody (mAb) charge variants in three different biopharmaceuticals. A useful selection of small molecule buffer species is described that can be used within very narrow pH ranges (typically 1 pH unit) defined by their buffer capacity for producing controlled and smooth pH profiles when used together with porous polymer monoliths. Using very low ionic strength eluents also enabled direct coupling with electrospray ionisation mass spectrometry. The results obtained by the developed pH gradient approach for the separation of closely related antibody species appear to be consistent with those obtained by imaged capillary isoelectric focusing (iCE) in terms of both resolution and separation profile. Both determinants of resolution, i.e., peak compression and peak separation contribute to the gains in resolution, evidently through the Donnan potential effect, which is increased by decreasing the eluent concentration, and also through the way electrostatic charges are distributed on the protein surface. Retention mechanisms based on the trends observed in retention of proteins at pH values higher than the electrophoretic pI are also discussed using applicable theories. Employing monolithic ion-exchangers is shown to enable fast method development, short analysis time, and high sample throughput owing to the accelerated mass transport of the monolithic media. The possibility of short analysis time, typically less than 15 min, and high sample throughput is extremely useful in the assessment of charge-based changes to the mAb products, such as during manufacturing or storage.

  5. Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for spin I = 1

    NASA Astrophysics Data System (ADS)

    Nilsson, Tomas; Halle, Bertil

    2012-08-01

    The frequency dependence of the longitudinal relaxation rate, known as the magnetic relaxation dispersion (MRD), can provide a frequency-resolved characterization of molecular motions in complex biological and colloidal systems on time scales ranging from 1 ns to 100 μs. The conformational dynamics of immobilized proteins and other biopolymers can thus be probed in vitro or in vivo by exploiting internal water molecules or labile hydrogens that exchange with a dominant bulk water pool. Numerous water 1H and 2H MRD studies of such systems have been reported, but the widely different theoretical models currently used to analyze the MRD data have resulted in divergent views of the underlying molecular motions. We have argued that the essential mechanism responsible for the main dispersion is the exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings when internal water molecules or labile hydrogens escape from orientationally confining macromolecular sites. In the EMOR model, the exchange process is thus not just a means of mixing spin populations but it is also the direct cause of spin relaxation. Although the EMOR theory has been used in several studies to analyze water 2H MRD data from immobilized biopolymers, the fully developed theory has not been described. Here, we present a comprehensive account of a generalized version of the EMOR theory for spin I = 1 nuclides like 2H. As compared to a previously described version of the EMOR theory, the present version incorporates three generalizations that are all essential in applications to experimental data: (i) a biaxial (residual) electric field gradient tensor, (ii) direct and indirect effects of internal motions, and (iii) multiple sites with different exchange rates. In addition, we describe and assess different approximations to the exact EMOR theory that are useful in various regimes. In particular, we consider the experimentally important

  6. Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: longitudinal relaxation dispersion for spin I = 1.

    PubMed

    Nilsson, Tomas; Halle, Bertil

    2012-08-07

    The frequency dependence of the longitudinal relaxation rate, known as the magnetic relaxation dispersion (MRD), can provide a frequency-resolved characterization of molecular motions in complex biological and colloidal systems on time scales ranging from 1 ns to 100 μs. The conformational dynamics of immobilized proteins and other biopolymers can thus be probed in vitro or in vivo by exploiting internal water molecules or labile hydrogens that exchange with a dominant bulk water pool. Numerous water (1)H and (2)H MRD studies of such systems have been reported, but the widely different theoretical models currently used to analyze the MRD data have resulted in divergent views of the underlying molecular motions. We have argued that the essential mechanism responsible for the main dispersion is the exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings when internal water molecules or labile hydrogens escape from orientationally confining macromolecular sites. In the EMOR model, the exchange process is thus not just a means of mixing spin populations but it is also the direct cause of spin relaxation. Although the EMOR theory has been used in several studies to analyze water (2)H MRD data from immobilized biopolymers, the fully developed theory has not been described. Here, we present a comprehensive account of a generalized version of the EMOR theory for spin I = 1 nuclides like (2)H. As compared to a previously described version of the EMOR theory, the present version incorporates three generalizations that are all essential in applications to experimental data: (i) a biaxial (residual) electric field gradient tensor, (ii) direct and indirect effects of internal motions, and (iii) multiple sites with different exchange rates. In addition, we describe and assess different approximations to the exact EMOR theory that are useful in various regimes. In particular, we consider the experimentally

  7. The mechanism of monensin-mediated cation exchange based on real time measurements.

    PubMed

    Nachliel, E; Finkelstein, Y; Gutman, M

    1996-12-04

    Monensin is an ionophore that supports an electroneutral ion exchange across the lipid bilayer. Because of this, under steady-state conditions, no electric signals accompany its reactions. Using the Laser Induced Proton Pulse as a synchronizing event we selectively acidify one face of a black lipid membrane impregnated by monensin. The short perturbation temporarily upsets the acid-base equilibrium on one face of the membrane, causing a transient cycle of ion exchange. Under such conditions the molecular events could be discerned as a transient electric polarization of the membrane lasting approx. 200 microseconds. The proton-driven chemical reactions that lead to the electric signals had been reconstructed by numeric integration of differential rate equations which constitute a maximalistic description of the multi equilibria nature of the system (Gutman, M. and Nachliel, E. (1989) Electrochim. Acta 34, 1801-1806). The analysis of the reactions reveals that the ionic selectivity of the monensin (H+ > Na+ > K+) is due to more than one term. Besides the well established different affinity for the various cations, the selectivity is also derived from a large difference in the rates of cross membranal diffusivities (MoH > MoNa > MoK), which have never been detected before. (v) Quantitative analysis of the membrane's crossing rates of the three neutral complexes reveals a major role of the membranal dipolar field in regulating ion transport. The diffusion of MoH, which has no dipole moment, is hindered only by the viscose drag. On the other hand, the dipolar complexes (MoNa and MoK) are delayed by dipole-dipole interaction with the membrane. (vi) Comparison of the calculated dipoles with those estimated for the crystalline conformation of the [MoNa(H2O)2] and [MoK(H2O)2] complexes reveals that the MoNa may exist in the membrane at its crystal configuration, while the MoK definitely attains a structure having a dipole moment larger than in the crystal.

  8. Sister chromatid exchanges are mediated by homologous recombination in vertebrate cells.

    PubMed

    Sonoda, E; Sasaki, M S; Morrison, C; Yamaguchi-Iwai, Y; Takata, M; Takeda, S

    1999-07-01

    Sister chromatid exchange (SCE) frequency is a commonly used index of chromosomal stability in response to environmental or genetic mutagens. However, the mechanism generating cytologically detectable SCEs and, therefore, their prognostic value for chromosomal stability in mitotic cells remain unclear. We examined the role of the highly conserved homologous recombination (HR) pathway in SCE by measuring SCE levels in HR-defective vertebrate cells. Spontaneous and mitomycin C-induced SCE levels were significantly reduced for chicken DT40 B cells lacking the key HR genes RAD51 and RAD54 but not for nonhomologous DNA end-joining (NHEJ)-defective KU70(-/-) cells. As measured by targeted integration efficiency, reconstitution of HR activity by expression of a human RAD51 transgene restored SCE levels to normal, confirming that HR is the mechanism responsible for SCE. Our findings show that HR uses the nascent sister chromatid to repair potentially lethal DNA lesions accompanying replication, which might explain the lethality or tumorigenic potential associated with defects in HR or HR-associated proteins.

  9. Iron-sulfur cluster exchange reactions mediated by the human Nfu protein.

    PubMed

    Wachnowsky, Christine; Fidai, Insiya; Cowan, J A

    2016-10-01

    Human Nfu is an iron-sulfur cluster protein that has recently been implicated in multiple mitochondrial dysfunctional syndrome (MMDS1). The Nfu family of proteins shares a highly homologous domain that contains a conserved active site consisting of a CXXC motif. There is less functional conservation between bacterial and human Nfu proteins, particularly concerning their Iron-sulfur cluster binding and transfer roles. Herein, we characterize the cluster exchange chemistry of human Nfu and its capacity to bind and transfer a [2Fe-2S] cluster. The mechanism of cluster uptake from a physiologically relevant [2Fe-2S](GS)4 cluster complex, and extraction of the Nfu-bound iron-sulfur cluster by glutathione are described. Human holo Nfu shows a dimer-tetramer equilibrium with a protein to cluster ratio of 2:1, reflecting the Nfu-bridging [2Fe-2S] cluster. This cluster can be transferred to apo human ferredoxins at relatively fast rates, demonstrating a direct role for human Nfu in the process of [2Fe-2S] cluster trafficking and delivery.

  10. Mass transfer of single- and double-charged anions through an MA-41L anion-exchange membrane

    SciTech Connect

    Kulikova, O.M.; Sharkova, O.V.; Kulikov, S.M.

    1995-02-20

    Selective anion transfer through an MA-41L anion-exchange membrane in the Cl{sup -}-F{sup -}, Cl{sup -}-SO{sub 4}{sup 2-}, F{sup -}-SO{sub 4}{sup 2-}, and F{sup -}-CO{sub 3}{sup 2-} systems has been studied. The feasibility of partial anion separation in the chloride-sulfate system has been demonstrated. The separation of fluoride ions from accompanying anions was found to be practically impossible.

  11. X-ray and EUV spectroscopy of various astrophysical and laboratory plasmas: Collisional, photoionization and charge-exchange plasmas

    SciTech Connect

    Liang, G. Y.; Li, F.; Wang, F. L.; Zhong, J. Y.; Zhao, G.; Wu, Y.

    2014-03-10

    Several laboratory facilities were used to benchmark theoretical spectral models that are extensively used by astronomical communities. However, there are still many differences between astrophysical environments and laboratory miniatures that can be archived. Here we setup a spectral analysis system for astrophysical and laboratory plasmas to make a bridge between them, and we investigate the effects from non-thermal electrons and the contributions from a metastable level population on level populations and charge stage distribution for coronal-like, photoionized, and geocoronal plasmas. Test applications to laboratory measurement (i.e., electron beam ion trap plasma) and astrophysical observation (i.e., Comet, Cygnus X-3) are presented. A time evolution of the charge stage and level population are also explored for collisional and photoionized plasmas.

  12. Efficient Recombinase-Mediated Cassette Exchange in hPSCs to Study the Hepatocyte Lineage Reveals AAVS1 Locus-Mediated Transgene Inhibition

    PubMed Central

    Ordovás, Laura; Boon, Ruben; Pistoni, Mariaelena; Chen, Yemiao; Wolfs, Esther; Guo, Wenting; Sambathkumar, Rangarajan; Bobis-Wozowicz, Sylwia; Helsen, Nicky; Vanhove, Jolien; Berckmans, Pieter; Cai, Qing; Vanuytsel, Kim; Eggermont, Kristel; Vanslembrouck, Veerle; Schmidt, Béla Z.; Raitano, Susanna; Van Den Bosch, Ludo; Nahmias, Yaakov; Cathomen, Toni; Struys, Tom; Verfaillie, Catherine M.

    2015-01-01

    Summary Tools for rapid and efficient transgenesis in “safe harbor” loci in an isogenic context remain important to exploit the possibilities of human pluripotent stem cells (hPSCs). We created hPSC master cell lines suitable for FLPe recombinase-mediated cassette exchange (RMCE) in the AAVS1 locus that allow generation of transgenic lines within 15 days with 100% efficiency and without random integrations. Using RMCE, we successfully incorporated several transgenes useful for lineage identification, cell toxicity studies, and gene overexpression to study the hepatocyte lineage. However, we observed unexpected and variable transgene expression inhibition in vitro, due to DNA methylation and other unknown mechanisms, both in undifferentiated hESC and differentiating hepatocytes. Therefore, the AAVS1 locus cannot be considered a universally safe harbor locus for reliable transgene expression in vitro, and using it for transgenesis in hPSC will require careful assessment of the function of individual transgenes. PMID:26455413

  13. Spin exchange dominated by charge fluctuations of the Wigner lattice in the chain cuprate Na5Cu3O6

    NASA Astrophysics Data System (ADS)

    Ali, Naveed Zafar; Sirker, Jesko; Nuss, Jürgen; Horsch, Peter; Jansen, Martin

    2011-07-01

    Na5Cu3O6, a new member of one-dimensional charge-ordered chain cuprates, was synthesized via the azide/nitrate route by reacting NaN3, NaNO3, and CuO. According to single-crystal x-ray analysis, one-dimensional ∞1CuO2n- chains built up from planar, edge-sharing CuO4 squares are a dominant feature of the crystal structure. From the analysis of the Cu-O bond lengths, we find that the system forms a Wigner lattice. The commensurate charge order allows the explicit assignment of the valence states of either +2 or +3 to each copper atom, resulting in a repetition according to Cu2+-Cu3+-Cu2+-Cu2+-Cu3+-Cu2+. Following the theoretical analysis of the previously synthesized compounds Na3Cu2O4 and Na8Cu5O10, the magnetic susceptibility was expected to show a large dimer gap. Surprisingly, this is not the case. To resolve this puzzle, we show that the magnetic couplings in this compound are strongly affected by excitations across the Wigner charge gap. By including these contributions, which are distinct from conventional superexchange in Mott-insulators, we obtain a quantitatively satisfying theoretical description of the magnetic susceptibility data.

  14. Cutting edge: HLA-DM-mediated peptide exchange functions normally on MHC class II-peptide complexes that have been weakened by elimination of a conserved hydrogen bond.

    PubMed

    Ferrante, Andrea; Gorski, Jack

    2010-02-01

    The mechanism by which HLA-DM (DM) promotes exchange of peptides bound to HLA-DR (DR) is still unclear. We have shown that peptide interaction with DR1 can be considered a folding process as evidenced by cooperativity. However, in DM-mediated ligand exchange, prebound peptide release is noncooperative, which could be a function of the breaking of a critical interaction. The hydrogen bond (H-bond) between beta-chain His(81) and the peptide backbone at the -1 position is a candidate for such a target. In this study, we analyze the exchange of peptides bound to a DR1 mutant in which formation of this H-bond is impaired. We observe that DM still functions normally. However, as expected of a cooperative model, this H-bond contributes to the overall energetics of the complex and its disruption impacts the ability of the exchange ligand to fold with the binding groove into a stable complex.

  15. O₂(X³Σg⁻) and O₂(a¹Δg) charge exchange with simple ions.

    PubMed

    Ziółkowski, Marcin; Schatz, George C; Viggiano, A A; Midey, Anthony; Dotan, Itzhak

    2014-06-07

    We present theory and experiments which describe charge transfer from the X³Σg⁻ and a(1)Δg states of molecular oxygen and atomic and molecular cations. Included in this work are new experimental results for O2(a(1)Δg) and the cations O(+), CO(+), Ar(+), and N₂⁺, and new theory based on complete active space self-consistent field method calculations and an extended Langevin model to calculate rate constants for ground and excited O2 reacting with the atomic ions Ar(+), Kr(+), Xe(+), Cl(+), and Br(+). The T-shaped orientation of the (X - O2)(+) potential surface is used for the calculations, including all the low lying states up to the second singlet state of the oxygen molecule b¹Σ(g)⁺. The calculated rate constants for both O₂(X³Σg⁻) and O2(a(1)Δg) show consistent trends with the experimental results, with a significant dependence of rate constant on charge transfer exothermicity that does not depend strongly on the nature of the cation. The comparisons with theory show that partners with exothermicities of about 1 eV have stronger interactions with O2, leading to larger Langevin radii, and also that more of the electronic states are attractive rather than repulsive, leading to larger rate constants. Rate constants for charge transfer involving O2(a(1)Δg) are similar to those for O₂(X³Σg⁻) for a given exothermicity ignoring the electronic excitation of the O2(a(1)Δg) state. This means (and the electronic structure calculations support) that the ground and excited states of O2 have about the same attractive interactions with ions.

  16. The putative guanine nucleotide exchange factor RicA mediates upstream signaling for growth and development in Aspergillus.

    PubMed

    Kwon, Nak-Jung; Park, Hee-Soo; Jung, Seunho; Kim, Sun Chang; Yu, Jae-Hyuk

    2012-11-01

    Heterotrimeric G proteins (G proteins) govern growth, development, and secondary metabolism in various fungi. Here, we characterized ricA, which encodes a putative GDP/GTP exchange factor for G proteins in the model fungus Aspergillus nidulans and the opportunistic human pathogen Aspergillus fumigatus. In both species, ricA mRNA accumulates during vegetative growth and early developmental phases, but it is not present in spores. The deletion of ricA results in severely impaired colony growth and the total (for A. nidulans) or near (for A. fumigatus) absence of asexual sporulation (conidiation). The overexpression (OE) of the A. fumigatus ricA gene (AfricA) restores growth and conidiation in the ΔAnricA mutant to some extent, indicating partial conservation of RicA function in Aspergillus. A series of double mutant analyses revealed that the removal of RgsA (an RGS protein of the GanB Gα subunit), but not sfgA, flbA, rgsB, or rgsC, restored vegetative growth and conidiation in ΔAnricA. Furthermore, we found that RicA can physically interact with GanB in yeast and in vitro. Moreover, the presence of two copies or OE of pkaA suppresses the profound defects caused by ΔAnricA, indicating that RicA-mediated growth and developmental signaling is primarily through GanB and PkaA in A. nidulans. Despite the lack of conidiation, brlA and vosA mRNAs accumulated to normal levels in the ΔricA mutant. In addition, mutants overexpressing fluG or brlA (OEfluG or OEbrlA) failed to restore development in the ΔAnricA mutant. These findings suggest that the commencement of asexual development requires unknown RicA-mediated signaling input in A. nidulans.

  17. Compact, accurate description of diagnostic neutral beam propagation and attenuation in a high temperature plasma for charge exchange recombination spectroscopy analysis.

    PubMed

    Bespamyatnov, Igor O; Rowan, William L; Granetz, Robert S

    2008-10-01

    Charge exchange recombination spectroscopy on Alcator C-Mod relies on the use of the diagnostic neutral beam injector as a source of neutral particles which penetrate deep into the plasma. It employs the emission resulting from the interaction of the beam atoms with fully ionized impurity ions. To interpret the emission from a given point in the plasma as the density of emitting impurity ions, the density of beam atoms must be known. Here, an analysis of beam propagation is described which yields the beam density profile throughout the beam trajectory from the neutral beam injector to the core of the plasma. The analysis includes the effects of beam formation, attenuation in the neutral gas surrounding the plasma, and attenuation in the plasma. In the course of this work, a numerical simulation and an analytical approximation for beam divergence are developed. The description is made sufficiently compact to yield accurate results in a time consistent with between-shot analysis.

  18. Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D

    SciTech Connect

    Haskey, S. R.; Grierson, B. A.; Burrell, K. H.; Chrystal, C.; Groebner, R. J.; Kaplan, D. H.; Pablant, N. A.; Stagner, L.

    2016-09-26

    Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region in H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. Finally, these challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model. Published by AIP Publishing.

  19. Expressions for Form Factors for Inelastic Scattering and Charge Exchange in Plane-Wave, Distorted-Wave, and Coupled-Channels Reaction Formalisms

    SciTech Connect

    Dietrich, F S

    2006-09-25

    This document is intended to facilitate calculation of inelastic scattering and charge-exchange cross sections in a variety of reaction models, including the plane-wave and distorted-wave approximations and the full coupled-channels treatments. Expressions are given for the coupling potentials between the relevant channels in both coordinate and momentum space. In particular, it is expected that the plane-wave calculations should be useful as a check on the correctness of coupled-channels calculations. The Fourier transform methods used to calculate the plane-wave approximation cross sections are also intended to be used to generate the transition potentials for coupled-channels codes, using a folding model with local effective interactions. Specific expressions are given for calculating transition densities for the folding model in the random phase approximation (RPA).

  20. Precision evaluation of the 71Ga(νe,e- ) solar neutrino capture rate from the (3He,t ) charge-exchange reaction

    NASA Astrophysics Data System (ADS)

    Frekers, D.; Adachi, T.; Akimune, H.; Alanssari, M.; Brown, B. A.; Cleveland, B. T.; Ejiri, H.; Fujita, H.; Fujita, Y.; Fujiwara, M.; Gavrin, V. N.; Harakeh, M. N.; Hatanaka, K.; Holl, M.; Iwamoto, C.; Lennarz, A.; Okamoto, A.; Okamura, H.; Suzuki, T.; Tamii, A.

    2015-03-01

    A precision measurement of the 71Ga(3He,t ) 71Ge charge-exchange reaction was performed. By using a rather complete set of theoretical form factors to describe the cross-section angular distributions over a large angular range, the Gamow-Teller strength distribution up to the effective neutron-separation energy in 71Ge was extracted. The data and the analysis constrain the 71Ga(νe,e- ) solar neutrino rate in a neutrino nonoscillation scenario. For nonoscillating neutrinos we report a solar neutrino capture rate of 122.4 ±3.4 (stat ) ±1.1 (sys ) SNU, which is lower than the presently accepted value of 132 ±18 SNU, though not in disagreement given the quoted errors.

  1. Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D

    NASA Astrophysics Data System (ADS)

    Haskey, S. R.; Grierson, B. A.; Burrell, K. H.; Chrystal, C.; Groebner, R. J.; Kaplan, D. H.; Pablant, N. A.; Stagner, L.

    2016-11-01

    Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region in H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. These challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model.

  2. Low energy charge exchange cross sections between sodium and H/sup +/, H/sup +//sub 2/, H/sup +//sub 3/, N/sup +//sub 2/, H/sub 2/O/sup +/, and O/sup +//sub 2/

    SciTech Connect

    Loch, R.; Stengler, R.; Werth, G.

    1989-08-15

    We confined ions of different molecules in a Penning quadrupole ion trap and observed the exponential loss of the stored ion cloud as the result of charge exchange collisions with a Na atomic beam passing through the trap. From the ion loss rates and the Na density we determined the charge exchange cross sections between Na and the ions noted in the title at a mean ion energy of 2 eV. The results are in reasonable agreement with theoretical expectations and other experiments.

  3. Recombinase-mediated cassette exchange (RMCE) and BAC engineering via VCre/VloxP and SCre/SloxP systems.

    PubMed

    Minorikawa, Sachiko; Nakayama, Manabu

    2011-04-01

    Site-specific recombination is a powerful biotechnological tool for genome engineering. We previously reported two novel site-specific recombination systems, VCre/VloxP and SCre/SloxP, that do not cross-react with Cre/loxP and Flp/FRT in culture cells and mouse embryonic stem (ES) cells. In this study, a site-specific recombination assay in Escherichia coli was used to examine the activity of mutant VCre (H314L and Y349F) and mutant SCre (H317L and Y352F), in which both mutated residues lie within the active center of Cre recombination. The site-specific recombination activity of both mutants was significantly decreased. Recombinase-mediated cassette exchange (RMCE) using VloxP and the Vlox2272 mutant site was performed in E. coli by introducing a cassette bearing VloxP and Vlox2272 into a recipient plasmid bearing the same sites. RMCE using SloxP and Slox2272 was also performed by SCre recombinase. Moreover, BAC engineering via Red recombination and VCre/VloxP were demonstrated. First, the DNA cassette for modification was introduced into a BAC clone via Red recombination; second, the antibiotics resistance gene flanked by VloxP was removed from the BAC clone by induction of VCre recombinase. Such site-specific recombination systems may effectively be used in combination with other site-specific recombination systems or engineering tools (e.g., Red recombination).

  4. Production of rotavirus core-like particles in Sf9 cells using recombinase-mediated cassette exchange.

    PubMed

    Fernandes, Fabiana; Dias, Mafalda M; Vidigal, João; Sousa, Marcos F Q; Patrone, Marco; Teixeira, Ana P; Alves, Paula M

    2014-02-10

    A flexible Sf9 insect cell line was recently developed leveraging the recombinase-mediated cassette exchange (RMCE) technology, which competes with the popular baculovirus expression vector system (BEVS) in terms of speed to produce new proteins. Herein, the ability of this cell platform to produce complex proteins, such as rotavirus core-like particles, was evaluated. A gene construct coding for a VP2-GFP fusion protein was targeted to a pre-characterized high recombination efficiency locus flanked by flipase (Flp) recognition target sites and, after three weeks in selection, an isogenic cell population was obtained. Despite the lower cell specific productivities with respect to those obtained by baculovirus infection, the titers of VP2-GFP reached in shake flask batch cultures were comparable as a result of higher cell densities. To further improve the VP2-GFP levels from stable expression, analysis of exhausted medium was undertaken to design feeding strategies enabling higher cell densities as well as increased culture duration. The implementation of the best strategy allowed reaching 20 million cells per ml in bioreactor cultures; the integrity of the rotavirus core-like particles could be confirmed by electron microscopy. Overall, we show that this Sf9-Flp cell platform represents a valuable alternative to the BEVS for producing complex recombinant proteins, such as rotavirus core-like particles.

  5. Fully self-consistent study of charge-exchange resonances and the impact on the symmetry energy parameters

    NASA Astrophysics Data System (ADS)

    Roca-Maza, X.; Cao, Li-Gang; Colò, G.; Sagawa, H.

    2016-10-01

    We have examined within a fully self-consistent theoretical framework the energy difference between the anti-analog giant dipole resonance (AGDR) and the isobaric analog state (IAS), EAGDR-EIAS , as an indicator of the neutron skin and of the density behavior of the symmetry energy. We have improved two specific points in our HF+RPA calculations: (1) the exchange term of the two-body Coulomb interaction is treated exactly without Slater approximation; and (2) the two-parameters spin-orbit interaction is treated in a consistent way within the energy density functional theory. The estimated values for the neutron skin in 208Pb and the slope parameter of symmetry energy are compared with previous analysis available in the literature.

  6. Ion-exchange controls the kinetics of deswelling of polyelectrolyte microgels in solutions of oppositely charged surfactant.

    PubMed

    Nilsson, Peter; Hansson, Per

    2005-12-22

    The kinetics of deswelling of sodium polyacrylate microgels (radius 30-140 microm) in aqueous solutions of dodecyltrimethylammonium bromide is investigated by means of micropipet-assisted light microscopy. The purpose of the study is to test a recent model (J. Phys. Chem. B 2003, 107, 9203) proposing that the rate of the volume change is controlled by the transport of surfactant from the solution to the gel core (ion exchange) via the surfactant-rich surface phase appearing in the gel during the volume transition. Equilibrium swelling characteristics of the gel network in surfactant-free solutions and with various amounts of surfactant present are presented and discussed with reference to related systems. A relationship between gel volume and degree of surfactant binding is determined and used in theoretical predictions of the deswelling kinetics. Experimental data for single gel beads observed during deswelling under conditions of forced convection are presented and compared with model calculations. It is demonstrated that the dependences of the kinetics on initial gel size, the surfactant concentration in the solution, and the liquid flow rate are well accounted for by the model. It is concluded that the deswelling rates of the studied gels are strongly influenced by the mass transport of surfactant between gel and solution (stagnant layer diffusion), but only to a minor extent by the transport through the surface phase. The results indicate that, during the volume transition, swelling equilibrium (network relaxation/transport of water) is established on a relatively short time scale and, therefore, can be treated as independent of the ion-exchange kinetics. Theoretical aspects of the kinetics and mechanisms of surfactant transport through the surface phase are discussed.

  7. Effect of resin charged functional group, porosity, and chemical matrix on the long-term pharmaceutical removal mechanism by conventional ion exchange resins.

    PubMed

    Wang, Wei; Li, Xiaofeng; Yuan, Shengliu; Sun, Jian; Zheng, Shaokui

    2016-10-01

    This study attempted to clarify the long-term pharmaceutical removal mechanism from sewage treatment plant effluent during the cyclical adsorption-regeneration operation of 5 commercial resin-based fixed-bed reactors with the simultaneous occurrence of electrostatic interactions and complex non-electrostatic interactions. It examined 12 pharmaceuticals belonging to 10 therapeutic classes with different predominant existing forms and hydrophobicities. Furthermore, the effect of the resin charged functional group (strong-base vs. strong-acid vs. non-ionic), porosity (macroporous vs. gel), and chemical matrix (polystyrenic vs. polyacrylic) on the mechanism was investigated to optimize resin properties and achieve higher pharmaceutical removal. The results reported herein indicate the importance of non-electrostatic interactions between pharmaceuticals and the resin backbone during short-term cyclical operation (i.e., the 1st adsorption-regeneration cycle). With the development of cyclical operation, however, non-electrostatic interaction-induced pharmaceutical removal generally decreased and even disappeared when equilibrium was achieved between the influent and the resin. Despite pharmaceutical therapeutic class or hydrophilicity, anion (or cation) exchange resin preferentially removed those pharmaceuticals that were predominantly present as organic anions (or cations) by ion exchange process during long-term cyclical operation (i.e., ≥6 adsorption-regeneration cycles). Besides pharmaceuticals predominantly present as undissociated molecules, some amphoteric pharmaceuticals containing large amounts of zwitterions were also difficult to remove by ion exchange resin. Additionally, neither resin porosity nor chemical matrix had any significant effect on the long-term pharmaceutical removal mechanism.

  8. Effects of weakly coupled and dense quantum plasmas environments on charge exchange and ionization processes in Na+ + Rb(5s) atom collisions

    NASA Astrophysics Data System (ADS)

    Pandey, Mukesh Kumar; Lin, Yen-Chang; Ho, Yew Kam

    2017-02-01

    The effects of weakly coupled or classical and dense quantum plasmas environment on charge exchange and ionization processes in Na+ + Rb(5s) atom collision at keV energy range have been investigated using classical trajectory Monte Carlo (CTMC) method. The interaction of three charged particles are described by the Debye-Hückel screen potential for weakly coupled plasma, whereas exponential cosine-screened Coulomb potential have been used for dense quantum plasma environment and the effects of both conditions on the cross sections are compared. It is found that screening effects on cross sections in high Debye length condition is quite small in both plasma environments. However, enhanced screening effects on cross sections are observed in dense quantum plasmas for low Debye length condition, which becomes more effective while decreasing the Debye length. Also, we have found that our calculated results for plasma-free case are comparable with the available theoretical results. These results are analyzed in light of available theoretical data with the choice of model potentials.

  9. Controlling hydrogen scrambling in multiply charged protein ions during collisional activation: implications for top-down hydrogen/deuterium exchange MS utilizing collisional activation in the gas phase.

    PubMed

    Abzalimov, Rinat R; Kaltashov, Igor A

    2010-02-01

    Hydrogen exchange in solution combined with ion fragmentation in the gas phase followed by MS detection emerged in recent years as a powerful tool to study higher order protein structure and dynamics. However, a certain type of ion chemistry in the gas phase, namely, internal rearrangement of labile hydrogen atoms (the so-called hydrogen scrambling), is often cited as a factor limiting the utility of this experimental technique. Although several studies have been carried out to elucidate the roles played by various factors in the occurrence and the extent of hydrogen scrambling, there is still no consensus as to what experimental protocol should be followed to avoid or minimize it. In this study we employ fragmentation of mass-selected subpopulations of protein ions to assess the extent of internal proton mobility prior to dissociation. A unique advantage of tandem MS is that it not only provides a means to map the deuterium content of protein ions whose overall levels of isotope incorporation can be precisely defined by controlling the mass selection window, but also correlates this spatial isotope distribution with such global characteristic as the protein ion charge state. Hydrogen scrambling does not occur when the charge state of the precursor protein ions selected for fragmentation is high. Fragment ions derived from both N- and C-terminal parts of the protein are equally unaffected by scrambling. However, spatial distribution of deuterium atoms obtained by fragmenting low-charge-density protein ions is consistent with a very high degree of scrambling prior to the dissociation events. The extent of hydrogen scrambling is also high when multistage fragmentation is used to probe deuterium incorporation locally. Taken together, the experimental results provide a coherent picture of intramolecular processes occurring prior to the dissociation event and provide guidance for the design of experiments whose outcome is unaffected by hydrogen scrambling.

  10. XMM-Newton Observations of MBM 12: More Constraints on the Solar Wind Charge Exchange and Local Bubble Emissions

    NASA Technical Reports Server (NTRS)

    Koutroumpa, Dimitra; Smith, Randall K.; Edgar, Richard J.; Kuntz, Kip D.; Plucinsky, Paul P.; Snowden, Steven L.

    2010-01-01

    We present the first analysis of an XMM-Newton observation of the nearby molecular cloud MBM 12. We find that in the direction of MBM 12 the total O VII (0.57 keV) triplet emission is 1.8(+0.5/-0.6) photons/sq cm/s/sr (or Line Units - LU) while for the O VIII (0.65 keV) line emission we find a 3(sigma) upper limit of <1 LU. We also use a heliospheric model to calculate the O VII and O VIII emission generated by Solar Wind Charge-eXchange (SWCX) which we compare to the XMM-Newton observations. This comparison provides new constraints on the relative heliospheric and Local Bubble contributions to the local diffuse X-ray background. The heliospheric SWCX model predicts 0.82 LU for O VII, which accounts for approx. 46+/-15% of the observed value, and 0.33 LU for the O VIII line emission consistent with the XMM-Newton observed value. We discuss our results in combination with previous observations of the MBM 12 with CHANDRA and Suzaku.

  11. Development of a laser cleaning method for the first mirror surface of the charge exchange recombination spectroscopy diagnostics on ITER

    SciTech Connect

    Kuznetsov, A. P.; Buzinskij, O. I.; Gubsky, K. L.; Nikitina, E. A.; Savchenkov, A. V.; Tarasov, B. A.; Tugarinov, S. N.

    2015-12-15

    A set of optical diagnostics is expected for measuring the plasma characteristics in ITER. Optical elements located inside discharge chambers are exposed to an intense radiation load, sputtering due to collisions with energetic atoms formed in the charge transfer processes, and contamination due to recondensation of materials sputtered from different parts of the construction of the chamber. Removing the films of the sputtered materials from the mirrors with the aid of pulsed laser radiation is an efficient cleaning method enabling recovery of the optical properties of the mirrors. In this work, we studied the efficiency of removal of metal oxide films by pulsed radiation of a fiber laser. Optimization of the laser cleaning conditions was carried out on samples representing metal substrates polished with optical quality with deposition of films on them imitating the chemical composition and conditions expected in ITER. It is shown that, by a proper selection of modes of radiation exposure to the surface with a deposited film, it is feasible to restore the original high reflection characteristics of optical elements.

  12. Species differences in Cl- affinity and in electrogenicity of SLC26A6-mediated oxalate/Cl- exchange correlate with the distinct human and mouse susceptibilities to nephrolithiasis.

    PubMed

    Clark, Jeffrey S; Vandorpe, David H; Chernova, Marina N; Heneghan, John F; Stewart, Andrew K; Alper, Seth L

    2008-03-01

    The mouse is refractory to lithogenic agents active in rats and humans, and so has been traditionally considered a poor experimental model for nephrolithiasis. However, recent studies have identified slc26a6 as an oxalate nephrolithiasis gene in the mouse. Here we extend our earlier demonstration of different anion selectivities of the orthologous mouse and human SLC26A6 polypeptides to investigate the correlation between species-specific differences in SLC26A6 oxalate/anion exchange properties as expressed in Xenopus oocytes and in reported nephrolithiasis susceptibility. We find that human SLC26A6 mediates minimal rates of Cl(-) exchange for Cl(-), sulphate or formate, but rates of oxalate/Cl(-) exchange roughly equivalent to those of mouse slc2a6. Both transporters exhibit highly cooperative dependence of oxalate efflux rate on extracellular [Cl(-)], but whereas the K(1/2) for extracellular [Cl(-)] is only 8 mM for mouse slc26a6, that for human SLC26A6 is 62 mM. This latter value approximates the reported mean luminal [Cl(-)] of postprandial human jejunal chyme, and reflects contributions from both transmembrane and C-terminal cytoplasmic domains of human SLC26A6. Human SLC26A6 variant V185M exhibits altered [Cl(-)] dependence and reduced rates of oxalate/Cl(-) exchange. Whereas mouse slc26a6 mediates bidirectional electrogenic oxalate/Cl(-) exchange, human SLC26A6-mediated oxalate transport appears to be electroneutral. We hypothesize that the low extracellular Cl(-) affinity and apparent electroneutrality of oxalate efflux characterizing human SLC26A6 may partially explain the high human susceptibility to nephrolithiasis relative to that of mouse. SLC26A6 sequence variant(s) are candidate risk modifiers for nephrolithiasis.

  13. Charge translocation by the Na+/K+-ATPase investigated on solid supported membranes: rapid solution exchange with a new technique.

    PubMed Central

    Pintschovius, J; Fendler, K

    1999-01-01

    Adsorption of Na+/K+-ATPase containing membrane fragments from pig kidney to lipid membranes allows the detection of electrogenic events during the Na+/K+-ATPase reaction cycle with high sensitivity and time resolution. High stability preparations can be obtained using solid supported membranes (SSM) as carrier electrodes for the membrane fragments. The SSMs are prepared using an alkanethiol monolayer covalently linked to a gold surface on a glass substrate. The hydrophobic surface is covered with a lipid monolayer (SAM, self-assembled monolayer) to obtain a double layer system having electrical properties similar to those of unsupported bilayer membranes (BLM). As we have previously shown (, Biophys. J. 64:384-391), the Na+/K+-ATPase on a SSM can be activated by photolytic release of ATP from caged ATP. In this publication we show the first results of a new technique which allows rapid solution exchange at the membrane surface making use of the high mechanical stability of SSM preparations. Especially for substrates, which are not available as a caged substance-such as Na+ and K+-this technique is shown to be capable of yielding new results. The Na+/K+-ATPase was activated by rapid concentration jumps of ATP and Na+ (in the presence of ATP). A time resolution of up to 10 ms was obtained in these experiments. The aim of this paper is to present the new technique together with the first results obtained from the investigation of the Na+/K+-ATPase. A comparison with data taken from the literature shows considerable agreement with our experiments. PMID:9929483

  14. Origins of sequence selectivity in homologous genetic recombination: insights from rapid kinetic probing of RecA-mediated DNA strand exchange.

    PubMed

    Lee, Andrew M; Xiao, Jie; Singleton, Scott F

    2006-07-07

    Despite intense effort over the past 30 years, the molecular determinants of sequence selectivity in RecA-mediated homologous recombination have remained elusive. Here, we describe when and how sequence homology is recognized between DNA strands during recombination in the context of a kinetic model for RecA-mediated DNA strand exchange. We characterized the transient intermediates of the reaction using pre-steady-state kinetic analysis of strand exchange using oligonucleotide substrates containing a single fluorescent G analog. We observed that the reaction system was sensitive to heterology between the DNA substrates; however, such a "heterology effect" was not manifest when functional groups were added to or removed from the edges of the base-pairs facing the minor groove of the substrate duplex. Hence, RecA-mediated recombination must occur without the involvement of a triple helix, even as a transient intermediate in the process. The fastest detectable reaction phase was accelerated when the structure or stability of the substrate duplex was perturbed by internal mismatches or the replacement of G.C by I.C base-pairs. These findings indicate that the sequence specificity in recombination is achieved by Watson-Crick pairing in the context of base-pair dynamics inherent to the extended DNA structure bound by RecA during strand exchange.

  15. Joy of cex: Sharpening the (t,He-3) probe at 345 MeV for the charge-exchange knife drawer

    NASA Astrophysics Data System (ADS)

    Howard, Meredith E.

    This data set represents the first step in a campaign of (t, 3He) charge-exchange experiments at the National Superconducting Cyclotron Laboratory designed explicitly to measure Gamow-Teller strength distributions in the electron capture direction for stable medium-heavy atomic nuclei, with particular interest in reaching the nuclei in the pf -shell or masses up to A=112. The 115 MeV/nucleon secondary triton beam with an average intensity of 4x106 pps on 10 mg/cm2 thick target foils produces 3He that are measured in the focal plane detectors of the S800 magnetic spectrometer. From these data, the scattering angle of the tritons is reconstructed to within 7 mrad and the energy of the recoil nucleus is reconstructed to better then 250 keV. Since there is no comprehensive study of the (t, 3He) probe for triton energies of 100-400 MeV/nucleon, this data is the first step in evaluating the advantages of extracting B(GT) from the (t,3He) probe over other hadronic probes. The first target is a CD2 target used for calibrating cross section. This is the third measurement for the (t, 3He) probe on 12C above 100 MeV/nucleon. The present 12C(t,3He) cross section for the 12B ground state (Jpi = 1 +) is lower than a previous measurement at the NSCL by more than one standard deviation in uncertainty but agrees with 12C( 3He,t)12N. This (t,3He) measurement for 24Mg, the second target, is the first above 100 MeV/nucleon. The B(GT) distribution for 24Na is extracted from differential cross sections as a function of residual nucleus excitation energy up to 7 MeV. For each peak in excitation energy, the differential cross section as a function of reconstructed scattering angle is extrapolated to zero degrees using angular distrubutions calculated with the distorted wave calculations from the code FOLD and transformed to q = 0 zero momentum transfer. Uncertainties in the B(GT) include a calculation of interference to Jpi=1 + expected from DeltaL=2, DeltaS=1 reactions. Comparisons of B

  16. Construction and operation of parallel electric and magnetic field spectrometers for mass/energy resolved multi-ion charge exchange diagnostics on the Tokamak Fusion Test Reactor

    NASA Astrophysics Data System (ADS)

    Medley, S. S.; Roquemore, A. L.

    1998-07-01

    A novel charge exchange spectrometer using a dee-shaped region of parallel electric and magnetic fields was developed at the Princeton Plasma Physics Laboratory for neutral particle diagnostics on the Tokamak Fusion Test Reactor (TFTR). The E∥B spectrometer has an energy range of 0.5⩽A (amu)E (keV)⩽600 and provides mass-resolved energy spectra of H+, D+, and T+ (or 3He+) ion species simultaneously during a single discharge. The detector plane exhibits parallel rows of analyzed ions, each row containing the energy dispersed ions of a given mass-to-charge ratio. The detector consists of a large area microchannel plate (MCP) which is provided with three rectangular, semicontinuous active area strips, one coinciding with each of the mass rows for detection of H+, D+, and T+ (or 3He+) and each mass row has 75 energy channels. To suppress spurious signals attending operation of the plate in the magnetic fringe field of the spectrometer, the MCP was housed in a double-walled iron shield with a wire mesh ion entrance window. Using an accelerator neutron generator, the MCP neutron detection efficiency was measured to be 1.7×10-3 and 6.4×10-3 counts/neutron/cm2 for 2.5 MeV-DD and 14 MeV-DT neutrons, respectively. The design and calibration of the spectrometer are described in detail, including the effect of MCP exposure to tritium, and results obtained during high performance D-D operation on TFTR are presented to illustrate the performance of the E∥B spectrometer. The spectrometers were not used during D-T plasma operation due to the cost of providing the required radiation shielding.

  17. Charge variants characterization of a monoclonal antibody by ion exchange chromatography coupled on-line to native mass spectrometry: Case study after a long-term storage at +5°C.

    PubMed

    Leblanc, Y; Ramon, C; Bihoreau, N; Chevreux, G

    2017-03-24

    Numerous putative post-translational modifications may induce variations of monoclonal antibodies charge distribution that can potentially affect their biological activity. The characterization and the monitoring of these charge variants are critical quality requirements to ensure stability and process consistency. Charge variants are usually characterized by preparative ion exchange chromatography, collection of fractions and subsequent reverse-phase liquid chromatography with mass spectrometry analysis. While this process can be automatized by on-line two-dimensional chromatography, it remains often complex and time consuming. For this reason, a straightforward on-line charge variant analysis method is highly desirable and analytical laboratories are actively pursuing efforts to overcome this challenge. In this study, a mixed mode ion exchange chromatographic method using volatile salts and coupled on-line to native mass spectrometry was developed in association with a middle-up approach for a detailed characterization of monoclonal antibodies charge variants. An aged monoclonal antibody, presenting a complex charge variant profile was successfully investigated by this methodology as a case study. Results demonstrate that deamidation of the heavy chain was the major degradation pathway after long-term storage at 5°C while oxidation was rather low. The method was also very useful to identify all the clipped forms of the antibody.

  18. A Motivation Case Study of English/Japanese Language Exchange Partners Using Computer Mediated Communication and Telecommunication.

    ERIC Educational Resources Information Center

    Long, Robert Harrison

    This case study examines the motivation of two intermediate foreign language learners engaged in a remote language exchange partnership. A learner of English in Japan and a learner of Japanese in Australia completed language exchange activities using the telephone, Internet text chat, and e-mail over 10 weeks. Quantitative and qualitative methods…

  19. On Lunar Exospheric Column Densities and Solar Wind Access Beyond the Terminator from ROSAT Soft X-Ray Observations of Solar Wind Charge Exchange

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Snowden, S. L.; Sarantos, M.; Benna, M.; Carter, J. A.; Cravens, T. E.; Farrell, W. M.; Fatemi, S.; Hills, H. Kent; Hodges, R. R.; Holmstrom, M.; Kuntz, K. D.; Porter, F. Scott; Read, A.; Robertson, I. P.; Sembay, S. F.; Sibeck, D. G.; Stubbs, T. J.; Travnicek, P.; Walsh, B. M.

    2014-01-01

    We analyze the Rontgen satellite (ROSAT) position sensitive proportional counter soft X-ray image of the Moon taken on 29 June 1990 by examining the radial profile of the surface brightness in three wedges: two 19 deg wedges (one north and one south) 13-32 deg off the terminator toward the dark side and one wedge 38 deg wide centered on the antisolar direction. The radial profiles of both the north and the south wedges show significant limb brightening that is absent in the 38 deg wide antisolar wedge. An analysis of the soft X-ray intensity increase associated with the limb brightening shows that its magnitude is consistent with that expected due to solar wind charge exchange (SWCX) with the tenuous lunar atmosphere based on lunar exospheric models and hybrid simulation results of solar wind access beyond the terminator. Soft X-ray imaging thus can independently infer the total lunar limb column density including all species, a property that before now has not been measured, and provide a large-scale picture of the solar wind-lunar interaction. Because the SWCX signal appears to be dominated by exospheric species arising from solar wind implantation, this technique can also determine how the exosphere varies with solar wind conditions. Now, along with Mars, Venus, and Earth, the Moon represents another solar system body at which SWCX has been observed.

  20. Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D

    DOE PAGES

    Haskey, S. R.; Grierson, B. A.; Burrell, K. H.; ...

    2016-09-26

    Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region inmore » H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. Finally, these challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model. Published by AIP Publishing.« less

  1. A diagnostic neutral beam system for the MST reversed-field pinch: Charge-exchange recombination spectroscopy and Rutherford scattering (abstract)

    NASA Astrophysics Data System (ADS)

    Den Hartog, D. J.; Fiksel, G.; Davydenko, V.; Ivanov, A.; Mishagin, V.

    1999-01-01

    A diagnostic neutral beam system is being purchased for the MST reversed-field pinch. Initially, this beam will be used for charge-exchange recombination spectroscopy (CHERS) to measure impurity ion velocity and temperature, both equilibrium and fluctuating. This work is an extension of an existing MST spectroscopic diagnostic which has successfully measured chord-averaged flow with 10 μs time resolution [D. J. Den Hartog and R. J. Fonck, Rev. Sci. Instrum. 65, 3238 (1994)]. CHERS will provide high spatial resolution, critically needed for the investigation of fluctuations associated with the dynamo and transport. This beam will also be applied to Rutherford scattering for local measurements of majority ion velocity and temperature. Ion velocity is determined by the shift of the energy spectrum of the scattered neutral beam; ion temperature by the width of the energy spectrum. The scattered spectrum will be detected by two multichannel neutral particle analyzers. In order to achieve a time resolution of about 10 μs, the neutral beam equivalent current density and current must be high; both of these characteristics are hallmarks of the DINA beam design.

  2. Double-peak elution profile of a monoclonal antibody in cation exchange chromatography is caused by histidine-protonation-based charge variants.

    PubMed

    Luo, Haibin; Cao, Mingyan; Newell, Kelcy; Afdahl, Christopher; Wang, Jihong; Wang, William K; Li, Yuling

    2015-12-11

    We have systemically investigated unusual elution behaviors of an IgG4 (mAb A) in cation exchange chromatography (CEX). This mAb A exhibited two elution peaks under certain conditions when being purified by several strong CEX columns. When either of the two peaks was isolated and re-injected on the same column, the similar pattern was observed again during elution. The protein distribution between the two peaks could be altered by NaCl concentration in the feed, or NaCl concentration in wash buffer, or elution pH, suggesting two pH-associated strong-and-weak binding configurations. The protein distributions under different pH values showed good correlation with protonated/un-protonated fractions of a histidine residue. These results suggest that the double-peak elution profile associates with histidine-protonation-based charge variants. By conducting pepsin digestion, amino-acid specific chemical modifications, peptide mapping, and measuring the effects of elution residence time, a histidine in the variable fragment (Fab) was identified to be the root cause. Besides double-peak pattern, mAb A can also exhibit peak-shouldering or single elution peak on different CEX resins, reflecting different resins' resolving capability on protonated/un-protonated forms. This work characterizes a novel cause for unusual elution behaviors in CEX and also provides alternative avenues of purification development for mAbs with similar behaviors.

  3. Experimental Determination of Mechanisms and Rates of Fe-Mg Exchange Between Spinel Grains Mediated by a Fluid Phase

    NASA Astrophysics Data System (ADS)

    Mueller, T.; Dohmen, R.; Chakraborty, S.

    2008-12-01

    The overall mechanism and kinetics of mineral reactions results from a complex interaction of several processes such as surface reaction kinetics, volume diffusion and net transfer. In order to quantify the kinetics of reactions involving multiple phases in multicomponent systems, it is necessary to understand and characterize the nature and rates of each of these processes. Most laboratory experiments up to now have focused on kinetics of reactions where the reactants and products are in direct physical contact with each other. However, there is abundant textural evidence in rocks that reactions occurred between mineral grains that are physically separated from each other, frequently mediated by a fluid phase. We have devised an experimental setup to study the mechanism and kinetics of such reactions in the laboratory. Polished single crystals of two spinels (synthetic MgAl2O4 and a natural spinel with 44 mol% Hercynite component), 2mm on a side, were placed in a gold capsule (length: 2cm, diameter: 4mm) separated from each other by a 5mm long tube of Au or alumina. The capsule was welded shut after adding distilled water (80-100μl). Such capsules were annealed (2 Kbar, 700-750°C, up to 21 hours) in hydrothermal cold seal vessels. After annealing the crystals were cleaned in an ultrasonic bath in order to rinse them of possible quench products. The surfaces were examined optically and near surface chemistry was determined using Rutherford Backscattering Spectroscopy (RBS). We observe time dependent changes in the morphology as well as the chemistry of the crystals, as follows: After short times, the surface of the Mg spinel shows scattered etch pits while terraces form on the Fe spinel. After longer anneals, the etch pits disappear and the surface of the Mg spinels appear polished. Surface compositions are found to be different, depending on whether a Au or alumina separator was used in the experiments. The Fe rich spinel composition remains unchanged whereas

  4. Exchange of the H(CC) domain mediating double receptor recognition improves the pharmacodynamic properties of botulinum neurotoxin.

    PubMed

    Rummel, Andreas; Mahrhold, Stefan; Bigalke, Hans; Binz, Thomas

    2011-12-01

    The four-domain structure of botulinum neurotoxins (BoNTs) reflects their multistep intoxication process. The high toxicity of BoNTs primarily results from specific binding and uptake into neurons mediated by their 50-kDa cell-binding fragment (H(C) ). X-ray crystallography data have revealed that the H(C) fragment consists of two domains of equal size, named the 25-kDa N-terminal half of H(C) (H(CN) ) and the 25-kDa C-terminal half of H(C) (H(CC) ). In recent years, the ganglioside-binding sites of all seven BoNT serotypes have been allocated to the H(CC) domain. For BoNT/A, BoNT/B and BoNT/G, the protein receptor-binding site has been also been localized to the H(CC) domain. Here, we demonstrate that the H(CC) serotype can modulate the affinity of the H(C) fragment for neuronal membranes as well as the potency of full-length BoNT by replacing the BoNT/A H(CC) domain with the BoNT/B H(CC) , BoNT/C H(CC) and BoNT/E H(CC) domains, which exhibit higher affinity for synaptosomes. Indeed, the hybrids H(C) AB and H(C) AC display a higher affinity than wild-type H(C) A. Furthermore, the potency of a BoNT/A-based full-length hybrid containing the H(CC) B domain (AAAB; letters represent the serotype origin of the four domains) was quadrupled as compared with wild-type BoNT/A. Analogously, exchange of the H(C) fragment (AABB) yielded a neurotoxin with four-fold higher potency. As BoNT/A and BoNT/B are extensively used to treat neurological disorders, thereby facing the problem of BoNT neutralizing antibody formation, a BoNT with increased potency would lower the repeatedly administered protein dosage while maintaining the clinical benefit. Such a lowered protein load will delay the onset of neurotoxin antibody formation in patients.

  5. Exchange bias in Fe/Fe{sub 3}O{sub 4} core-shell magnetic nanoparticles mediated by frozen interfacial spins.

    SciTech Connect

    Ong, Q. K.; Wei, A.; Lin, X.-M.; Center for Nanoscale Materials; Purdue Univ.

    2009-10-01

    The magnetization curves of monodisperse Fe/Fe{sub 3}O{sub 4} core-shell and Fe{sub 3}O{sub 4} hollow-shell nanoparticles reveal an unusual exchange-bias effect. Hysteresis measurements of core-shell particles at 5 K after field cooling exhibit a large loop shift associated with unidirectional anisotropy whereas Fe{sub 3}O{sub 4} hollow-shell nanoparticles support much smaller shifts. Both core-shell and hollow-shell particles exhibit sharp demagnetization jumps at low fields associated with a sudden switching of shell moments. Temperature-dependent magnetization of core-shell particles at high fields shows a deviation between field-cooled and zero-field-cooled curves below 30 K, suggesting the presence of frozen spins at the interface. These frozen interfacial spins play an important role in mediating the exchange coupling between the ferromagnetic core and ferrimagnetic shell.

  6. Charge exchange recombination spectroscopy on a diagnostic hydrogen beam—measuring impurity rotation and radial electric field at the tokamak TEXTOR

    NASA Astrophysics Data System (ADS)

    Coenen, J. W.; Schweer, B.; Clever, M.; Freutel, S.; Schmitz, O.; Stoschus, H.; Samm, U.; Unterberg, B.

    2010-07-01

    In this work we present an overview on the charge exchange recombination spectroscopy (CXRS) diagnostic operated with the modulated diagnostic hydrogen beam at the tokamak TEXTOR. The diagnostic setup combines two observation systems used for the measurement of the poloidal (vpol) and the toroidal (vtor) ion velocity component. At TEXTOR a differential Doppler spectroscopy approach (accurate absolute rotation scale) is combined with the high intensity and spatial resolution of a direct imaging system necessary for accurate poloidal rotation measurements on a shot-by-shot basis. This setup allows the full utilization of a 2D CCD detector in the spectral and radial direction. In the case of the poloidal system this allows spatial resolution in the range of mm to cm depending on the intensity requirements for the velocity. The toroidal system comprises a fibre-optic array. The combination of the two measurements with a low-power diagnostic beam can in principle be operated during any available heating scenario without interfering with the discharge. Time resolution is limited by the necessary averaging process; typically a stable plateau of 3 s during a TETXOR pulse is used. The TEXTOR tokamak has the ability to apply momentum input with two tangential neutral beam heating injectors, allowing for measurements under various heating and momentum input scenarios. With the presented diagnostic half the plasma minor radius at a spatial resolution of {\\sim} 1\\,\\rm cm is covered. With the CVI line at 529.053 nm an accuracy of 0.7\\, \\rm km\\,s^{-1} for the poloidal and ~5 \\rm km\\,s^{-1} for the toroidal system is given. The temperature is measured with an accuracy of a few eV. The presented work illustrates the capability of the system during a toroidal momentum scan, showing the self-consistent determination of the radial electric field from experimental CXRS data based on the radial force balance.

  7. Structural outline of the detailed mechanism for elongation factor Ts-mediated guanine nucleotide exchange on elongation factor Tu.

    PubMed

    Thirup, Søren S; Van, Lan Bich; Nielsen, Tine K; Knudsen, Charlotte R

    2015-07-01

    Translation elongation factor EF-Tu belongs to the superfamily of guanine-nucleotide binding proteins, which play key cellular roles as regulatory switches. All G-proteins require activation via exchange of GDP for GTP to carry out their respective tasks. Often, guanine-nucleotide exchange factors are essential to this process. During translation, EF-Tu:GTP transports aminoacylated tRNA to the ribosome. GTP is hydrolyzed during this process, and subsequent reactivation of EF-Tu is catalyzed by EF-Ts. The reaction path of guanine-nucleotide exchange is structurally poorly defined for EF-Tu and EF-Ts. We have determined the crystal structures of the following reaction intermediates: two structures of EF-Tu:GDP:EF-Ts (2.2 and 1.8Å resolution), EF-Tu:PO4:EF-Ts (1.9Å resolution), EF-Tu:GDPNP:EF-Ts (2.2Å resolution) and EF-Tu:GDPNP:pulvomycin:Mg(2+):EF-Ts (3.5Å resolution). These structures provide snapshots throughout the entire exchange reaction and suggest a mechanism for the release of EF-Tu in its GTP conformation. An inferred sequence of events during the exchange reaction is presented.

  8. Theoretical and experimental study of charge transfer through DNA: impact of mercury mediated T-Hg-T base pair.

    PubMed

    Kratochvílová, Irena; Golan, Martin; Vala, Martin; Špérová, Miroslava; Weiter, Martin; Páv, Ondřej; Šebera, Jakub; Rosenberg, Ivan; Sychrovský, Vladimír; Tanaka, Yoshiyuki; Bickelhaupt, F Matthias

    2014-05-22

    DNA-Hg complexes may play an important role in sensing DNA defects or in detecting the presence of Hg in the environment. A fundamental way of characterizing DNA-Hg complexes is to study the way the electric charge is transferred through the molecular chain. The main goal of this contribution was to investigate the impact of a mercury metal cation that links two thymine bases in a DNA T-T mismatched base pair (T-Hg-T) on charge transfer through the DNA molecule. We compared the charge transfer efficiencies in standard DNA, DNA with mismatched T-T base pairs, and DNA with a T-Hg(II)-T base pair. For this purpose, we measured the temperature dependence of steady-state fluorescence and UV-vis of the DNA molecules. The experimental results were confronted with the results obtained employing theoretical DFT methods. Generally, the efficiency of charge transfer was driven by mercury changing the spatial overlap of bases.

  9. Attenuating HIV Tat/TAR-mediated protein expression by exploring the side chain length of positively charged residues.

    PubMed

    Wu, Cheng-Hsun; Chen, Yi-Ping; Liu, Shing-Lung; Chien, Fan-Ching; Mou, Chung-Yuan; Cheng, Richard P

    2015-12-07

    RNA is a drug target involved in diverse cellular functions and viral processes. Molecules that inhibit the HIV TAR RNA-Tat protein interaction may attenuate Tat/TAR-dependent protein expression and potentially serve as anti-HIV therapeutics. By incorporating positively charged residues with mixed side chain lengths, we designed peptides that bind TAR RNA with enhanced intracellular activity. Tat-derived peptides that were individually substituted with positively charged residues with varying side chain lengths were evaluated for TAR RNA binding. Positively charged residues with different side chain lengths were incorporated at each Arg and Lys position in the Tat-derived peptide to enhance TAR RNA binding. The resulting peptides showed enhanced TAR RNA binding affinity, cellular uptake, nuclear localization, proteolytic resistance, and inhibition of intracellular Tat/TAR-dependent protein expression compared to the parent Tat-derived peptide with no cytotoxicity. Apparently, the enhanced inhibition of protein expression by these peptides was not determined by RNA binding affinity, but by proteolytic resistance. Despite the high TAR binding affinity, a higher binding specificity would be necessary for practical purposes. Importantly, altering the positively charged residue side chain length should be a viable strategy to generate potentially useful RNA-targeting bioactive molecules.

  10. Arf6 Guanine Nucleotide Exchange Factor Cytohesin-2 Binds to CCDC120 and Is Transported Along Neurites to Mediate Neurite Growth*

    PubMed Central

    Torii, Tomohiro; Miyamoto, Yuki; Tago, Kenji; Sango, Kazunori; Nakamura, Kazuaki; Sanbe, Atsushi; Tanoue, Akito; Yamauchi, Junji

    2014-01-01

    The mechanism of neurite growth is complicated, involving continuous cytoskeletal rearrangement and vesicular trafficking. Cytohesin-2 is a guanine nucleotide exchange factor for Arf6, an Arf family molecular switch protein, controlling cell morphological changes such as neuritogenesis. Here, we show that cytohesin-2 binds to a protein with a previously unknown function, CCDC120, which contains three coiled-coil domains, and is transported along neurites in differentiating N1E-115 cells. Transfection of the small interfering RNA (siRNA) specific for CCDC120 into cells inhibits neurite growth and Arf6 activation. When neurites start to extend, vesicles containing CCDC120 and cytohesin-2 are transported in an anterograde manner rather than a retrograde one. As neurites continue extension, anterograde vesicle transport decreases. CCDC120 knockdown inhibits cytohesin-2 localization into vesicles containing CCDC120 and diffuses cytohesin-2 in cytoplasmic regions, illustrating that CCDC120 determines cytohesin-2 localization in growing neurites. Reintroduction of the wild type CCDC120 construct into cells transfected with CCDC120 siRNA reverses blunted neurite growth and Arf6 activity, whereas the cytohesin-2-binding CC1 region-deficient CCDC120 construct does not. Thus, cytohesin-2 is transported along neurites by vesicles containing CCDC120, and it mediates neurite growth. These results suggest a mechanism by which guanine nucleotide exchange factor for Arf6 is transported to mediate neurite growth. PMID:25326380

  11. Mechanistic Studies of Charge Injection from Metallic Electrodes into Organic Semiconductors Mediated by Ionic Functionalities: Final Report

    SciTech Connect

    Nguyen, Thuc-Quyen; Bazan, Guillermo; Mikhailovsky, Alexander

    2014-04-15

    Metal-organic semiconductor interfaces are important because of their ubiquitous role in determining the performance of modern electronics such as organic light emitting diodes (OLEDs), fuel cells, batteries, field effect transistors (FETs), and organic solar cells. Interfaces between metal electrodes required for external wiring to the device and underlying organic structures directly affect the charge carrier injection/collection efficiency in organic-based electronic devices primarily due to the mismatch between energy levels in the metal and organic semiconductor. Environmentally stable and cost-effective electrode materials, such as aluminum and gold typically exhibit high potential barriers for charge carriers injection into organic devices leading to increased operational voltages in OLEDs and FETs and reduced charge extraction in photovoltaic devices. This leads to increased power consumption by the device, reduced overall efficiency, and decreased operational lifetime. These factors represent a significant obstacle for development of next generation of cheap and energy-efficient components based on organic semiconductors. It has been noticed that introduction of organic materials with conjugated backbone and ionic pendant groups known as conjugated poly- and oligoelectrolytes (CPEs and COEs), enables one to reduce the potential barriers at the metal-organic interface and achieve more efficient operation of a device, however exact mechanisms of the phenomenon have not been understood. The goal of this project was to delineate the function of organic semiconductors with ionic groups as electron injection layers. The research incorporated a multidisciplinary approach that encompassed the creation of new materials, novel processing techniques, examination of fundamental electronic properties and the incorporation of the resulting knowledgebase into development of novel organic electronic devices with increased efficiency, environmental stability, and reduced

  12. Uncovering the microscopic mechanism of strand exchange during RecA mediated homologous recombination using all-atom molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Shankla, Manish; Yoo, Jejoong; Aksimentiev, Aleksei

    2012-02-01

    Homologous recombination (HR) is a key step during the repair process of double-stranded DNA (dsDNA) breakage. RecA is a protein that mediates HR in bacteria. RecA monomers polymerize on a single-stranded DNA (ssDNA) separated from the broken dsDNA to form a helical filament, thus allowing strand exchange to occur. Recent crystal structures depict each RecA monomer in contact with three contiguous nucleotides called DNA triplets. Surprisingly, the conformation of each triplet is similar to that of a triplet in B-form DNA. However, in the filament the neighboring triplets are separated by loops of the RecA proteins. Single molecule experiments demonstrated that strand exchange propagation occurs in 3 base-pair increments. However, the temporal resolution of the experiments was insufficient to determine the exact molecular mechanism of the triplet propagation. Using all-atom molecular dynamics simulations, we investigated the effect of both the RecA protein and the conformation of the bound ssDNA fragment on the stability of the duplex DNA intermediate formed during the strand-exchange process. Specifically, we report simulations of force-induced unzipping of duplex DNA in the presence and absence of the RecA filament that explored the effect of the triplet ladder conformation.

  13. Modeling salt-mediated electrostatics of macromolecules: the discrete surface charge optimization algorithm and its application to the nucleosome.

    PubMed

    Beard, D A; Schlick, T

    2001-01-01

    Much progress has been achieved on quantitative assessment of electrostatic interactions on the all-atom level by molecular mechanics and dynamics, as well as on the macroscopic level by models of continuum solvation. Bridging of the two representations-an area of active research-is necessary for studying integrated functions of large systems of biological importance. Following perspectives of both discrete (N-body) interaction and continuum solvation, we present a new algorithm, DiSCO (Discrete Surface Charge Optimization), for economically describing the electrostatic field predicted by Poisson-Boltzmann theory using a discrete set of Debye-Hückel charges distributed on a virtual surface enclosing the macromolecule. The procedure in DiSCO relies on the linear behavior of the Poisson-Boltzmann equation in the far zone; thus contributions from a number of molecules may be superimposed, and the electrostatic potential, or equivalently the electrostatic field, may be quickly and efficiently approximated by the summation of contributions from the set of charges. The desired accuracy of this approximation is achieved by minimizing the difference between the Poisson-Boltzmann electrostatic field and that produced by the linearized Debye-Hückel approximation using our truncated Newton optimization package. DiSCO is applied here to describe the salt-dependent electrostatic environment of the nucleosome core particle in terms of several hundred surface charges. This representation forms the basis for modeling-by dynamic simulations (or Monte Carlo)-the folding of chromatin. DiSCO can be applied more generally to many macromolecular systems whose size and complexity warrant a model resolution between the all-atom and macroscopic levels.

  14. Na-H Exchanger Isoform-2 (NHE2) Mediates Butyrate-dependent Na+ Absorption in Dextran Sulfate Sodium (DSS)-induced Colitis*

    PubMed Central

    Rajendran, Vazhaikkurichi M.; Nanda Kumar, Navalpur S.; Tse, Chung M.; Binder, Henry J.

    2015-01-01

    Diarrhea associated with ulcerative colitis (UC) occurs primarily as a result of reduced Na+ absorption. Although colonic Na+ absorption is mediated by both epithelial Na+ channels (ENaC) and Na-H exchangers (NHE), inhibition of NHE-mediated Na+ absorption is the primary cause of diarrhea in UC. As there are conflicting observations reported on NHE expression in human UC, the present study was initiated to identify whether NHE isoforms (NHE2 and NHE3) expression is altered and how Na+ absorption is regulated in DSS-induced inflammation in rat colon, a model that has been used to study UC. Western blot analyses indicate that neither NHE2 nor NHE3 expression is altered in apical membranes of inflamed colon. Na+ fluxes measured in vitro under voltage clamp conditions in controls demonstrate that both HCO3−-dependent and butyrate-dependent Na+ absorption are inhibited by S3226 (NHE3-inhibitor), but not by HOE694 (NHE2-inhibitor) in normal animals. In contrast, in DSS-induced inflammation, butyrate-, but not HCO3−-dependent Na+ absorption is present and is inhibited by HOE694, but not by S3226. These observations indicate that in normal colon NHE3 mediates both HCO3−-dependent and butyrate-dependent Na+ absorption, whereas DSS-induced inflammation activates NHE2, which mediates butyrate-dependent (but not HCO3−-dependent) Na+ absorption. In in vivo loop studies HCO3−-Ringer and butyrate-Ringer exhibit similar rates of water absorption in normal rats, whereas in DSS-induced inflammation luminal butyrate-Ringer reversed water secretion observed with HCO3−-Ringer to fluid absorption. Lumen butyrate-Ringer incubation activated NHE3-mediated Na+ absorption in DSS-induced colitis. These observations suggest that the butyrate activation of NHE2 would be a potential target to control UC-associated diarrhea. PMID:26350456

  15. Soft X-ray study of solar wind charge exchange from the Earth's magnetosphere : Suzaku observations and a future X-ray imaging mission concept

    NASA Astrophysics Data System (ADS)

    Ezoe, Y.; Ishisaki, Y.; Ohashi, T.; Ishikawa, K.; Miyoshi, Y.; Fujimoto, R.; Terada, N.; Kasahara, S.; Fujimoto, M.; Mitsuda, K.; Nishijo, K.; Noda, A.

    2013-12-01

    Soft X-ray observations of solar wind charge exchange (SWCX) emission from the Earth's magnetosphere using the Japanese X-ray astronomy satellite Suzaku are shown, together with our X-ray imaging mission concept to characterize the solar wind interaction with the magnetosphere. In recent years, the SWCX emission from the Earth's magnetosphere, originally discovered as unexplained noise during the soft X-ray all sky survey (Snowden et al. 1994), is receiving increased attention on studying geospace. The SWCX is a reaction between neutrals in exosphere and highly charged ions in the magnetosphere originated from solar wind. Robertson et al. (2005) modeled the SWCX emission as seen from an observation point 50 Re from Earth. In the resulting X-ray intensities, the magnetopause, bow shock and cusp were clearly visible. High sensitivity soft X-ray observation with CCDs onboard recent X-ray astronomy satellites enables us to resolve SWCX emission lines and investigate time correlation with solar wind as observed with ACE and WIND more accurately. Suzaku is the 5th Japanese X-ray astronomy satellite launched in 2005. The line of sight direction through cusp is observable, while constraints on Earth limb avoidance angle of other satellites often limits observable regions. Suzaku firstly detected the SWCX emission while pointing in the direction of the north ecliptic pole (Fujimoto et al. 2007). Using the Tsyganenko 1996 magnetic field model, the distance to the nearest SWCX region was estimated as 2-8 Re, implying that the line of sight direction can be through magnetospheric cusp. Ezoe et al. (2010) reported SWCX events toward the sub-solar side of the magnetosheath. These cusp and sub-solar side magnetosheath regions are predicted to show high SWCX fluxes by Robertson et al. (2005). On the other hand, Ishikawa et al. (2013) discovered a similarly strong SWCX event when the line of sight direction did not transverse these two regions. Motivated by these detections

  16. Bacterial Diversity in Ships' Ballast Water, Ballast-Water Exchange, and Implications for Ship-Mediated Dispersal of Microorganisms.

    PubMed

    Lymperopoulou, Despoina S; Dobbs, Fred C

    2017-02-21

    Using next-generation DNA sequencing of the 16S rRNA gene, we analyzed the composition and diversity of bacterial assemblages in ballast water from tanks of 17 commercial ships arriving to Hampton Roads, Virginia (USA) following voyages in the North Atlantic Ocean. Amplicon sequencing analysis showed the heterogeneous assemblages were (1) dominated by Alpha- and Gammaproteobacteria, Bacteroidetes, and unclassified Bacteria; (2) temporally distinct (June vs August/September); and (3) highly fidelitous among replicate samples. Whether tanks were exchanged at sea or not, their bacterial assemblages differed from those of local, coastal water. Compositional data suggested at-sea exchange did not fully flush coastal Bacteria from all tanks; there were several instances of a genetic geographic signal. Quantitative PCR yielded no Escherichia coli and few instances of Vibrio species. Salinity, but not ballast-water age or temperature, contributed significantly to bacterial diversity. Whether anthropogenic mixing of marine Bacteria restructures their biogeography remains to be tested.

  17. Sulfate secretion and chloride absorption are mediated by the anion exchanger DRA (Slc26a3) in the mouse cecum.

    PubMed

    Whittamore, Jonathan M; Freel, Robert W; Hatch, Marguerite

    2013-07-15

    Inorganic sulfate (SO₄²⁻) is essential for a multitude of physiological processes. The specific molecular pathway has been identified for uptake from the small intestine but is virtually unknown for the large bowel, although there is evidence for absorption involving Na⁺-independent anion exchange. A leading candidate is the apical chloride/bicarbonate (Cl⁻/HCO₃⁻) exchanger DRA (down-regulated in adenoma; Slc26a3), primarily linked to the Cl⁻ transporting defect in congenital chloride diarrhea. The present study set out to characterize transepithelial ³⁵SO₄²⁻ and ³⁶Cl⁻ fluxes across the isolated, short-circuited cecum from wild-type (WT) and knockout (KO) mice and subsequently to define the contribution of DRA. The cecum demonstrated simultaneous net SO₄²⁻ secretion (-8.39 ± 0.88 nmol·cm⁻²·h⁻¹) and Cl⁻ absorption (10.85 ± 1.41 μmol·cm⁻²·h⁻¹). In DRA-KO mice, SO₄²⁻ secretion was reversed to net absorption via a 60% reduction in serosal to mucosal SO₄²⁻ flux. Similarly, net Cl⁻ absorption was abolished and replaced by secretion, indicating that DRA represents a major pathway for transcellular SO₄²⁻ secretion and Cl⁻ absorption. Further experiments including the application of DIDS (500 μM), bumetanide (100 μM), and substitutions of extracellular Cl⁻ or HCO₃⁻/CO₂ helped to identify specific ion dependencies and driving forces and suggested that additional anion exchangers were operating at both apical and basolateral membranes supporting SO₄²⁻ transport. In conclusion, DRA contributes to SO₄²⁻ secretion via DIDS-sensitive HCO₃⁻/SO₄²⁻ exchange, in addition to being the principal DIDS-resistant Cl⁻/HCO₃⁻ exchanger. With DRA linked to the pathogenesis of other gastrointestinal diseases extending its functional characterization offers a more complete picture of its role in the intestine.

  18. The Negotiation Model in Asynchronous Computer-Mediated Communication (CMC): Negotiation in Task-Based Email Exchanges

    ERIC Educational Resources Information Center

    Kitade, Keiko

    2006-01-01

    Based on recent studies, computer-mediated communication (CMC) has been considered a tool to aid in language learning on account of its distinctive interactional features. However, most studies have referred to "synchronous" CMC and neglected to investigate how "asynchronous" CMC contributes to language learning. Asynchronous CMC possesses…

  19. Seeing through the Screen: Is Evaluative Feedback Communicated More Effectively in Face-to-Face or Computer-Mediated Exchanges?

    ERIC Educational Resources Information Center

    Hebert, Brenda G.; Vorauer, Jacquie D.

    2003-01-01

    Describes a study of college students that examined how the use of computer mediated communication affected the transmission of performance and interpersonal appraisal information. Examined whether interpersonal judgments obtained through face-to-face communication resulted in greater positivity, but compromised accuracy, relative to…

  20. Fast and efficient charge transport across a lipid bilayer is electronically mediated by C{sub 70} fullerene aggregates

    SciTech Connect

    Niu, S.; Mauzerall, D.

    1996-06-19

    Fullerene anions, made by photoreduction in a lipid bilayer, produce the largest trans-membrane steady state photocurrents yet observed, nearly 6.0 {mu}A/cm{sup 2}. Since these photocurrents are not light saturated, their maximum value is considerably larger. Dithionite was used as electron donor for its ability to reduce photoexcited fullerenes at the donor interface on a time scale faster than 15 ns. Both photovoltage and photocurrent increase 15-fold on adding the acceptor ferricyanide trans to the donor. There are two components to the transit time of negative charge across the bilayer, <100 ns and 6 {mu}s, in the 100 mM dithionite 0.6 mM C{sub 70} 5 mM ferricyanide system, where stands for the water-bilayer interface. This is strong evidence that the conduction is electronic and not diffusive-ionic. The plot of the ratio of photovoltage for the dithionite C{sub 70} system to that of the dithionite C{sub 70} ferricyanide system versus concentration of C{sub 70} in the lipid-forming solution is highly monlinear. This suggests that aggregates of the fullerene are responsible for the fast negative charge transport. The action spectrum of the photocurrent further supports the existence of photoactive C{sub 70} aggregates in the lipid bilayer. These aggregates may form the conductive path for electrons across the lipid bilayer. 23 refs., 5 figs., 1 tab.

  1. Identification of microdomains involved in association of "Arabidopsis" Ca(2+)/H(+) exchangers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In planta, high capacity tonoplast Ca2+/H+ antiport is mediated in part by a family of CAtion Exchangers (CAX). Each CAX can be divided into two weakly homologous halves (N- and C-) at the negatively charged loop between transmembrane (TM) 6 and TM7. Some CAX halves (N+C) co-expressed in yeast cells...

  2. Charge ulse studies of transport phenomena in bilayer membranes. II. Detailed theory of steady-state behavior and application to valinomycin-mediated potassium transport.

    PubMed

    Feldberg, S W; Nakadomari, H

    1977-02-24

    The charge-pulse technique is applied to a study of valinomycin-mediated potassium transport across glycerol monooleate (GMO) bilayers. The theory, based on the Läuger-Stark model, is developed for the steady-state domain. The voltage dependences of the surface complexation reactions are also considered. The analysis of the data yields the folowing values for the rate constants: (see article). With the exception of this last ratio, all the values agree well with previously published data. The implication of the exponential term, 0.045, is that the plane of reaction for the surface complexation actually occurs a small distance within the membrane dielectric. If one presumes that the reaction plane is about half way between the plane of adsorbed complex and the membrane-water interface, one deduces that the complex "feels" only about 80% of the applied voltage across the membrane.

  3. Acidosis-mediated regulation of the NHE1 isoform of the Na⁺/H⁺ exchanger in renal cells.

    PubMed

    Odunewu, Ayodeji; Fliegel, Larry

    2013-08-01

    The mammalian Na⁺/H⁺ exchanger isoform 1 (NHE1) is a ubiquitous plasma membrane protein that regulates intracellular pH by removing a proton in exchange for extracellular sodium. Renal tissues are subject to metabolic and respiratory acidosis, and acidosis has been shown to acutely activate NHE1 activity in other cell types. We examined if NHE1 is activated by acute acidosis in HEK293 and Madin-Darby canine kidney (MDCK) cells. Acute sustained intracellular acidosis (SIA) activated NHE1 in both cell types. We expressed wild-type and mutant NHE1 cDNAs in MDCK cells. All the cDNAs had a L163F/G174S mutation, which conferred a 100-fold resistance to EMD87580, an NHE1-specific inhibitor. We assayed exogenous NHE1 activity while inhibiting endogenous activity with EMD87580 and while inhibiting the NHE3 isoform of the Na⁺/H⁺ exchanger using the isoform-specific inhibitor S3226. We examined the activation and phosphorylation of the wild-type and mutant NHE1 proteins in response to SIA. In MDCK cells we demonstrated that the amino acids Ser⁷⁷¹, Ser⁷⁷⁶, Thr⁷⁷⁹, and Ser⁷⁸⁵ are important for NHE1 phosphorylation and activation after acute SIA. SIA activated ERK-dependent pathways in MDCK cells, and this was blocked by treatment with the MEK inhibitor U0126. Treatment with U0126 also blocked activation of NHE1 by SIA. These results suggest that acute acidosis activates NHE1 in mammalian kidney cells and that in MDCK cells this activation occurs through an ERK-dependent pathway affecting phosphorylation of a distinct set of amino acids in the cytosolic regulatory tail of NHE1.

  4. Deposition temperature mediated tunable tilt angle magnetization in Co-Pt/Ni81Fe19 exchange springs

    NASA Astrophysics Data System (ADS)

    Saravanan, P.; Hsu, Jen-Hwa; Tsai, C. L.; Lee, C.-M.

    2015-05-01

    In this study, we investigate the effect of deposition temperature of Co-Pt fixed layer, Td,CoPt (150, 250 and 350 °C) on the tilt angle magnetization (θM) of Ni81Fe19-layer grown at room temperature (RT) and at different thicknesses (tNiFe=0, 1.0, 2.5 and 4.0 nm) in Co-Pt(Td,CoPt)/NiFe(tNiFe) exchange springs. The magnetic studies demonstrated a strong perpendicular magnetic anisotropy (PMA) for the equi-compositional ordered Co-Pt layer grown on glass substrate using the film sequence: Ta(20 nm)/Pt(20 nm)/CoPt(5 nm), regardless of Td,CoPt. The PMA can be retained with the addition of a 4-nm NiFe layer on the top when Td,CoPt≥250 °C. In contrast, relatively a thin layer of Ni-Fe (2.5 nm) can destroy the perpendicular exchange-spring behavior if the Co-Pt layer is deposited at RT. Using 3-D micromagnetic simulation, the interfacial exchange coupling strength (Aij) between the Co-Pt and NiFe-layers was estimated and the Aij value is found to increase rapidly when Td,CoPt is increased from RT to 300 °C. Besides, the magnetization tilted angle (θM) of NiFe can be easily tuned from completely out-of-plane to almost 60° when tNiFe=4.0 nm. Through this study, it is demonstrated that the θM of NiFe-layer can be tuned by not only altering the tNiFe; but also by varying the Td,CoPt.

  5. The development of pedagogical content knowledge in science teachers: New opportunities through technology-mediated reflection and peer-exchange

    NASA Astrophysics Data System (ADS)

    Madeira, M. Cheryl-Ann

    This design-based research study investigates the development of pedagogical content knowledge among nine teacher-participants (N = 9) in three design phases. PCK is a particular type of teacher knowledge that addresses not only the teacher's understanding of the content to be instructed, but also ways of how to teach that content effectively. This knowledge has been well documented over several decades, and is seen as central to teacher expertise. However, its actual development has been difficult for researchers to investigate. This study offers a detailed perspective on how teachers developed PCK with their engagement in lesson planning and enactment of a project-based technology-enhanced lesson. The study includes two specific interventions designed to enhance teachers' development of PCK: (1) scaffolded reflection that occurs throughout the practices; and (2) peer-exchange of lesson plans, enactment ideas, and completed reflections. The findings demonstrate that teachers improve their planning and enactment of project-based technology-enhanced lessons with scaffolded reflection and peer exchange. Positive correlations were seen between teachers' engagement in the reflections and the quality of their lesson planning. Teachers who participated more deeply in the scaffolded reflections were able to understand how their lesson plans and enactment patterns fostered student understanding of relevant science concepts. Positive correlations were also seen between community influence and teacher lesson plans and enactment. Additionally, positive correlations were confirmed between teachers' level of participation in the peer exchange activities and the quality of their lesson planning and enactments. Teachers who contributed more deeply within the online and face-to-face peer community meetings benefited from the different perspectives of their peers about student learning and the best ways to succeed with project-based instruction. This study allowed some insight into

  6. Mesoporous gold sponges: electric charge-assisted seed mediated synthesis and application as surface-enhanced Raman scattering substrates

    PubMed Central

    Yi, Zao; Luo, Jiangshan; Tan, Xiulan; Yi, Yong; Yao, Weitang; Kang, Xiaoli; Ye, Xin; Zhu, Wenkun; Duan, Tao; Yi, Yougen; Tang, Yongjian

    2015-01-01

    Mesoporous gold sponges were prepared using 4-dimethylaminopyridine (DMAP)-stabilized Au seeds. This is a general process, which involves a simple template-free method, room temperature reduction of HAuCl4·4H2O with hydroxylamine. The formation process of mesoporous gold sponges could be accounted for the electrostatic interaction (the small Au nanoparticles (~3 nm) and the positively charged DMAP-stabilized Au seeds) and Ostwald ripening process. The mesoporous gold sponges had appeared to undergo electrostatic adsorption initially, sequentially linear aggregation, welding and Ostwald ripening, then, they randomly cross link into self-supporting, three-dimensional networks with time. The mesoporous gold sponges exhibit higher surface area than the literature. In addition, application of the spongelike networks as an active material for surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol (4-ATP) molecules as a probe. PMID:26538365

  7. Surface-state-mediated charge-transfer dynamics in CdTe/CdSe core-shell quantum dots.

    PubMed

    Rawalekar, Sachin; Kaniyankandy, Sreejith; Verma, Sandeep; Ghosh, Hirendra N

    2011-06-20

    Herein, we report the synthesis of aqueous CdTe/CdSe type-II core-shell quantum dots (QDs) in which 3-mercaptopropionic acid is used as the capping agent. The CdTe QDs and CdTe/CdSe core-shell QDs are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), steady-state absorption, and emission spectroscopy. A red shift in the steady-state absorption and emission bands is observed with increasing CdSe shell thickness over CdTe QDs. The XRD pattern indicates that the peaks are shifted to higher angles after growth of the CdSe shell on the CdTe QDs. HR-TEM images of both CdTe and CdTe/CdSe QDs indicate that the particles are spherical, with a good shape homogeneity, and that the particle size increases by about 2 nm after shell formation. In the time-resolved emission studies, we observe that the average emission lifetime (τ(av)) increases to 23.5 ns for CdTe/CdSe (for the thickest shell) as compared to CdTe QDs (τ(av) =12 ns). The twofold increment in the average emission lifetime indicates an efficient charge separation in type-II CdTe/CdSe core-shell QDs. Transient absorption studies suggest that both the carrier cooling and the charge-transfer dynamics are affected by the presence of traps in the CdTe QDs and CdTe/CdSe core-shell QDs. Carrier quenching experiments indicate that hole traps strongly affect the carrier cooling dynamics in CdTe/CdSe core-shell QDs.

  8. High-yield cell-free synthesis of human EGFR by IRES-mediated protein translation in a continuous exchange cell-free reaction format

    PubMed Central

    Quast, Robert B.; Sonnabend, Andrei; Stech, Marlitt; Wüstenhagen, Doreen A.; Kubick, Stefan

    2016-01-01

    Cell-free protein synthesis systems derived from eukaryotic sources often provide comparatively low amounts of several μg per ml of de novo synthesized membrane protein. In order to overcome this, we herein demonstrate the high-yield cell-free synthesis of the human EGFR in a microsome-containing system derived from cultured Sf21 cells. Yields were increased more than 100-fold to more than 285 μg/ml by combination of IRES-mediated protein translation with a continuous exchange cell-free reaction format that allowed for prolonged reaction lifetimes exceeding 24 hours. In addition, an orthogonal cell-free translation system is presented that enabled the site-directed incorporation of p-Azido-L-phenylalanine by amber suppression. Functionality of cell-free synthesized receptor molecules is demonstrated by investigation of autophosphorylation activity in the absence of ligand and interaction with the cell-free synthesized adapter molecule Grb2. PMID:27456041

  9. La Displacement Driven Double-Exchange Like Mediation in Titanium dxy Ferromagnetism at the LaAlO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Odkhuu, Dorj; Rhim, Sonny H.; Shin, Dongbin; Park, Noejung

    2016-04-01

    The epitaxial atomistic interfaces of two insulating oxides, LaAlO3 (LAO)/SrTiO3 (STO), have attracted great interest owing to rich emergent phenomena such as interface metallicity, thickness dependent insulator-metal transition, superconductivity, ferromagnetism, and even their coexistence. However, the physics origin of ferromagnetic ordering in the n-type LAO/STO interface is in debate. Here, we propose that the polar distortion of La atom can ignite the ferromagnetism at the interface even without oxygen vacancy. The induced hybridization between La dz2 and O px,y states can mediate double-exchange like interaction between Ti dxy electrons. We further suggest that the structural and electrical modification of the outermost surface of LAO or switching the polarization direction of ferroelectric overlayers on LAO/STO can promote such La displacement.

  10. Co-metal-organic-frameworks with pure uniform crystal morphology prepared via Co2 + exchange-mediated transformation from Zn-metallogels for luminol catalysed chemiluminescence

    NASA Astrophysics Data System (ADS)

    Tang, Xue Qian; Xiao, Bo Wen; Li, Chun Mei; Wang, Dong Mei; Huang, Cheng Zhi; Li, Yuan Fang

    2017-03-01

    Cation exchange-mediated transformation from Zn-metallogels (MOGs), which was a mild facile strategy relative to the demanding hydrothermal method, was employed to develop Co2 + metal-organic frameworks (Co-MOFs) at room temperature. The obtained Co-MOFs was of uniform octahedral morphology and possessed high activity to catalyze luminol chemiluminescence without extra oxidants. By adding cysteine, the CL emission of luminol-Co-MOFs system was further enhanced. Based on this phenomenon, Co-MOFs was utilized to build a practical sensing platform for cysteine determination. Under the optimized conditions, the relative CL intensity (ΔI) was proportional to the concentration of cysteine in the range of 2-10 μM, and the detection limit was 0.49 μM (3S/N). Moreover, the established method was applied to the determination of cysteine in commercially available pharmaceutical injections.

  11. Exchange of groundwater and surface-water mediated by permafrost response to seasonal and long term air temperature variation

    USGS Publications Warehouse

    Ge, S.; McKenzie, J.; Voss, C.; Wu, Q.

    2011-01-01

    Permafrost dynamics impact hydrologic cycle processes by promoting or impeding groundwater and surface water exchange. Under seasonal and decadal air temperature variations, permafrost temperature changes control the exchanges between groundwater and surface water. A coupled heat transport and groundwater flow model, SUTRA, was modified to simulate groundwater flow and heat transport in the subsurface containing permafrost. The northern central Tibet Plateau was used as an example of model application. Modeling results show that in a yearly cycle, groundwater flow occurs in the active layer from May to October. Maximum groundwater discharge to the surface lags the maximum subsurface temperature by two months. Under an increasing air temperature scenario of 3C per 100 years, over the initial 40-year period, the active layer thickness can increase by three-fold. Annual groundwater discharge to the surface can experience a similar three-fold increase in the same period. An implication of these modeling results is that with increased warming there will be more groundwater flow in the active layer and therefore increased groundwater discharge to rivers. However, this finding only holds if sufficient upgradient water is available to replenish the increased discharge. Otherwise, there will be an overall lowering of the water table in the recharge portion of the catchment. Copyright 2011 by the American Geophysical Union.

  12. Exchange of Groundwater and Surface-Water Mediated by Permafrost Response to Seasonal and Long Term Air Temperature Variation

    USGS Publications Warehouse

    Ge, Shemin; McKenzie, Jeffrey; Voss, Clifford; Wu, Qingbai

    2011-01-01

    Permafrost dynamics impact hydrologic cycle processes by promoting or impeding groundwater and surface water exchange. Under seasonal and decadal air temperature variations, permafrost temperature changes control the exchanges between groundwater and surface water. A coupled heat transport and groundwater flow model, SUTRA, was modified to simulate groundwater flow and heat transport in the subsurface containing permafrost. The northern central Tibet Plateau was used as an example of model application. Modeling results show that in a yearly cycle, groundwater flow occurs in the active layer from May to October. Maximum groundwater discharge to the surface lags the maximum subsurface temperature by two months. Under an increasing air temperature scenario of 3?C per 100 years, over the initial 40-year period, the active layer thickness can increase by three-fold. Annual groundwater discharge to the surface can experience a similar three-fold increase in the same period. An implication of these modeling results is that with increased warming there will be more groundwater flow in the active layer and therefore increased groundwater discharge to rivers. However, this finding only holds if sufficient upgradient water is available to replenish the increased discharge. Otherwise, there will be an overall lowering of the water table in the recharge portion of the catchment.

  13. Identification and Characterization of K(+)-Dependent Na(+)-Ca(2+) Exchange Transport in Pigmented MEB4 Cells Mediated by NCKX4.

    PubMed

    Szerencsei, Robert T; Ginger, Rebecca S; Green, Martin R; Schnetkamp, Paul P M

    2016-05-17

    The SLC24 gene family encodes K(+)-dependent Na(+)-Ca(2+) exchangers or NCKX proteins. The NCKX4 and NCKX5 isoforms have been shown to be important for pigmentation, and single nucleotide polymorphism (SNP) in both alleles of the SLC24a5 gene is the major genetic determinant for light skin in Caucasians. NCKX4 is thought to operate in the surface membrane of cells, whereas NCKX5 is thought to be located in intracellular membranes. However, no functional data have yet been reported to describe either NCKX4 or NCKX5 activity in pigmented cells. In this study, we used the B16 and MEB4 mouse pigmented cell lines to investigate NCKX-mediated Ca(2+) fluxes using (45)Ca uptake experiments and measurements of changes in intracellular free Ca(2+) with the fluorescent Ca(2+)-indicating dye Fluo-4. We used siRNA-mediated knockdown to selectively reduce either NCKX4 or NCKX5 expression. The results show that both B16 and MEB4 cells contain roughly equal amounts of NCKX4 and NCKX5 transcript, but surface membrane NCKX activity is restricted to NCKX4. Intracellular NCKX4 activity was also observed, but we could not unambiguously detect any NCKX5 activity. We were able to demonstrate that NCKX5 is a functional K(+)-dependent Na(+)-Ca(2+) exchanger located in internal membranes after transfection of NCKX5 cDNA in HEK293 cells. We conclude that pigment cells express robust, functional NCKX4 activity, but that the role of NCKX5 remains enigmatic ten years after the discovery of its link to pigmentation.

  14. Ligand Exchange-Mediated Activation and Stabilization of a Re-Based Olefin Metathesis Catalyst by Chlorinated Alumina.

    PubMed

    Gallo, Alessandro; Fong, Anthony; Szeto, Kai C; Rieb, Julia; Delevoye, Laurent; Gauvin, Régis M; Taoufik, Mostafa; Peters, Baron; Scott, Susannah L

    2016-10-05

    Extensive chlorination of γ-Al2O3 results in the formation of highly Lewis acidic surface domains depleted in surface hydroxyl groups. Adsorption of methyltrioxorhenium (MTO) onto these chlorinated domains serves to activate it as a low temperature, heterogeneous olefin metathesis catalyst and confers both high activity and high stability. Characterization of the catalyst reveals that the immobilized MTO undergoes partial ligand exchange with the surface, whereby some Re sites acquire a chloride ligand from the modified alumina while donating an oxo ligand to the support. More specifically, Re LIII-edge EXAFS and DFT calculations support facile ligand exchange between MTO and Cl-Al2O3 to generate [CH3ReO2Cl(+)] fragments that interact with a bridging oxygen of the support via a Lewis acid-base interaction. According to IR and solid-state NMR, the methyl group remains intact, and does not evolve spontaneously to a stable methylene tautomer. Nevertheless, the chloride-promoted metathesis catalyst is far more active and productive than MTO/γ-Al2O3, easily achieving a TON of 100 000 for propene metathesis in a flow reactor at 10 °C (compared to TON < 5000 for the nonchlorinated catalyst). Increased activity is a consequence of both a larger fraction of active sites and a higher intrinsic activity for the new sites. Increased stability is tentatively attributed to a stronger interaction between MTO and chlorinated surface regions, as well as extensive depletion of the Brønsted acidic surface hydroxyl population. The reformulated catalyst represents a major advance for Re-based metathesis catalysts, whose widespread use has thus far been severely hampered by their instability.

  15. Role of the guanine nucleotide exchange factor in Akt2-mediated plasma membrane translocation of GLUT4 in insulin-stimulated skeletal muscle.

    PubMed

    Takenaka, Nobuyuki; Yasuda, Naoto; Nihata, Yuma; Hosooka, Tetsuya; Noguchi, Tetsuya; Aiba, Atsu; Satoh, Takaya

    2014-11-01

    The small GTPase Rac1 plays a key role in insulin-promoted glucose uptake mediated by the GLUT4 glucose transporter in skeletal muscle. Our recent studies have demonstrated that the serine/threonine protein kinase Akt2 is critically involved in insulin-dependent Rac1 activation. The purpose of this study is to clarify the role of the guanine nucleotide exchange factor FLJ00068 in Akt2-mediated Rac1 activation and GLUT4 translocation in mouse skeletal muscle and cultured myocytes. Constitutively activated FLJ00068 induced GLUT4 translocation in a Rac1-dependent and Akt2-independent manner in L6 myocytes. On the other hand, knockdown of FLJ00068 significantly reduced constitutively activated Akt2-triggered GLUT4 translocation. Furthermore, Rac1 activation and GLUT4 translocation induced by constitutively activated phosphoinositide 3-kinase were inhibited by knockdown of FLJ00068. In mouse gastrocnemius muscle, constitutively activated FLJ00068 actually induced GLUT4 translocation to the sarcolemma. GLUT4 translocation by constitutively activated FLJ00068 was totally abolished in rac1 knockout mouse gastrocnemius muscle. Additionally, we were successful in detecting the activation of Rac1 following the expression of constitutively activated FLJ00068 in gastrocnemius muscle by immunofluorescence microscopy using an activation-specific probe. Collectively, these results strongly support the notion that FLJ00068 regulates Rac1 downstream of Akt2, leading to the stimulation of glucose uptake in skeletal muscle.

  16. Direct evaluation of a kinetic model for RecA-mediated DNA-strand exchange: the importance of nucleic acid dynamics and entropy during homologous genetic recombination.

    PubMed

    Xiao, Jie; Lee, Andrew M; Singleton, Scott F

    2006-08-01

    The Escherichia coli RecA protein is the prototype of a class of proteins that play central roles in genomic repair and recombination in all organisms. The unresolved mechanistic strategy by which RecA aligns a single strand of DNA with a duplex DNA and mediates a DNA strand switch is central to understanding homologous recombination. We explored the mechanism of RecA-mediated DNA-strand exchange using oligonucleotide substrates with the intrinsic fluorophore 6-methylisoxanthopterin. Pre-steady-state spectrofluorometric analysis elucidated the earliest transient intermediates formed during recombination and delineated the mechanistic strategy by which RecA facilitates this process. The structural features of the first detectable intermediate and the energetic characteristics of its formation were consistent with interactions between a few bases of the single-stranded DNA and the minor groove of a locally melted or stretched duplex DNA. Further analysis revealed RecA to be an unusual enzyme in that entropic rather than enthalpic contributions dominate its catalytic function, and no unambiguously active role for the protein was detected in the earliest molecular events of recombination. The data best support the conclusion that the mechanistic strategy of RecA likely relies on intrinsic DNA dynamics.

  17. Pollen-mediated gene flow and seed exchange in small-scale Zambian maize farming, implications for biosafety assessment

    NASA Astrophysics Data System (ADS)

    Bøhn, Thomas; Aheto, Denis W.; Mwangala, Felix S.; Fischer, Klara; Bones, Inger Louise; Simoloka, Christopher; Mbeule, Ireen; Schmidt, Gunther; Breckling, Broder

    2016-10-01

    Gene flow in agricultural crops is important for risk assessment of genetically modified (GM) crops, particularly in countries with a large informal agricultural sector of subsistence cultivation. We present a pollen flow model for maize (Zea mays), a major staple crop in Africa. We use spatial properties of fields (size, position) in three small-scale maize farming communities in Zambia and estimate rates of cross-fertilisation between fields sown with different maize varieties (e.g. conventional and transgene). As an additional factor contributing to gene flow, we present data on seed saving and sharing among farmers that live in the same communities. Our results show that: i) maize fields were small and located in immediate vicinity of neighboring fields; ii) a majority of farmers saved and shared seed; iii) modeled rates of pollen-mediated gene flow showed extensive mixing of germplasm between fields and farms and iv) as a result, segregation of GM and non-GM varieties is not likely to be an option in these systems. We conclude that the overall genetic composition of maize, in this and similar agricultural contexts, will be strongly influenced both by self-organised ecological factors (pollen flow), and by socially mediated intervention (seed recycling and sharing).

  18. Pollen-mediated gene flow and seed exchange in small-scale Zambian maize farming, implications for biosafety assessment

    PubMed Central

    Bøhn, Thomas; Aheto, Denis W.; Mwangala, Felix S.; Fischer, Klara; Bones, Inger Louise; Simoloka, Christopher; Mbeule, Ireen; Schmidt, Gunther; Breckling, Broder

    2016-01-01

    Gene flow in agricultural crops is important for risk assessment of genetically modified (GM) crops, particularly in countries with a large informal agricultural sector of subsistence cultivation. We present a pollen flow model for maize (Zea mays), a major staple crop in Africa. We use spatial properties of fields (size, position) in three small-scale maize farming communities in Zambia and estimate rates of cross-fertilisation between fields sown with different maize varieties (e.g. conventional and transgene). As an additional factor contributing to gene flow, we present data on seed saving and sharing among farmers that live in the same communities. Our results show that: i) maize fields were small and located in immediate vicinity of neighboring fields; ii) a majority of farmers saved and shared seed; iii) modeled rates of pollen-mediated gene flow showed extensive mixing of germplasm between fields and farms and iv) as a result, segregation of GM and non-GM varieties is not likely to be an option in these systems. We conclude that the overall genetic composition of maize, in this and similar agricultural contexts, will be strongly influenced both by self-organised ecological factors (pollen flow), and by socially mediated intervention (seed recycling and sharing). PMID:27694819

  19. Release of GTP Exchange Factor Mediated Down-Regulation of Abscisic Acid Signal Transduction through ABA-Induced Rapid Degradation of RopGEFs.

    PubMed

    Li, Zixing; Waadt, Rainer; Schroeder, Julian I

    2016-05-01

    The phytohormone abscisic acid (ABA) is critical to plant development and stress responses. Abiotic stress triggers an ABA signal transduction cascade, which is comprised of the core components PYL/RCAR ABA receptors, PP2C-type protein phosphatases, and protein kinases. Small GTPases of the ROP/RAC family act as negative regulators of ABA signal transduction. However, the mechanisms by which ABA controls the behavior of ROP/RACs have remained unclear. Here, we show that an Arabidopsis guanine nucleotide exchange factor protein RopGEF1 is rapidly sequestered to intracellular particles in response to ABA. GFP-RopGEF1 is sequestered via the endosome-prevacuolar compartment pathway and is degraded. RopGEF1 directly interacts with several clade A PP2C protein phosphatases, including ABI1. Interestingly, RopGEF1 undergoes constitutive degradation in pp2c quadruple abi1/abi2/hab1/pp2ca mutant plants, revealing that active PP2C protein phosphatases protect and stabilize RopGEF1 from ABA-mediated degradation. Interestingly, ABA-mediated degradation of RopGEF1 also plays an important role in ABA-mediated inhibition of lateral root growth. The presented findings point to a PP2C-RopGEF-ROP/RAC control loop model that is proposed to aid in shutting off ABA signal transduction, to counteract leaky ABA signal transduction caused by "monomeric" PYL/RCAR ABA receptors in the absence of stress, and facilitate signaling in response to ABA.

  20. Measurement of mitochondrial Ca2+ transport mediated by three transport proteins: VDAC1, the Na+/Ca2+ exchanger, and the Ca2+ uniporter.

    PubMed

    Ben-Hail, Danya; Palty, Raz; Shoshan-Barmatz, Varda

    2014-02-01

    Ca(2+) is a ubiquitous cellular signal, with changes in intracellular Ca(2+) concentration not only stimulating a number of intercellular events but also triggering cell death pathways, including apoptosis. Mitochondrial Ca(2+) uptake and release play pivotal roles in cellular physiology by regulating intracellular Ca(2+) signaling, energy metabolism and cell death. Ca(2+) transport across the inner and outer mitochondrial membranes is mediated by several proteins, including channels, antiporters, and a uniporter. In this article, we present the background to several methods now established for assaying mitochondrial Ca(2+) transport activity across both mitochondrial membranes. The first of these is Ca(2+) transport mediated by the outer mitochondrial protein, the voltage-dependent anion-selective channel protein 1 (VDAC1, also known as porin 1), both as a purified protein reconstituted into a planar lipid bilayer (PLB) or into liposomes and as a mitochondrial membrane-embedded protein. The second method involves isolated mitochondria for assaying the activity of an inner mitochondrial membrane transport protein, the mitochondrial Ca(2+) uniporter (MCU) that transports Ca(2+) and is powered by the steep mitochondrial membrane potential. In the event of Ca(2+) overload, this leads to opening of the mitochondrial permeability transition pore (MPTP) and cell death. The third method describes how Na(+)-dependent mitochondrial Ca(2+) efflux mediated by mitochondrial NCLX, a member of the Na(+)/Ca(2+) exchanger superfamily, can be assayed in digitonin-permeabilized HEK-293 cells. The Ca(2+)-transport assays can be performed under various conditions and in combination with inhibitors, allowing detailed characterization of the transport activity of interest.

  1. Preparation of zwitterionically charged nanocrystals by surface TEMPO-mediated oxidation and partial deacetylation of α-chitin.

    PubMed

    Ifuku, Shinsuke; Hori, Taishi; Izawa, Hironori; Morimoto, Minoru; Saimoto, Hiroyuki

    2015-05-20

    Zwitterionic nanocrystals were prepared by TEMPO-mediated oxidation, partial deacetylation, and subsequent mechanical disintegration of α-chitin. The pH dependence of the morphology, transparency, and viscosity of the nanocrystals were evaluated. After those reactions, the carboxylate and amino group contents of the chitin derivative were 0.45 and 1.26 mmol/g, respectively. After mechanical treatment, the water dispersion consisted of nanocrystals approximately 250 nm long and 10nm thick. Under acidic and basic conditions, the water dispersions were highly transparent. On the other hand, under neutral conditions, the dispersion was turbid due to the ionic interaction between the cationic and anionic groups on the nanocrystal surface. Although the surface zwitterionic nanocrystals collected from acidic and basic dispersion were randomly oriented due to electrostatic repulsions, nanocrystals formed aggregates in neutral water due to the cationic and anionic interaction between them. Nanocrystals in neutral water had higher viscosity than those in acidic and basic water, since ionic interaction caused nanocrystal networks to form in water.

  2. A novel amiloride-sensitive h+ transport pathway mediates enhanced superoxide production in thick ascending limb of salt-sensitive rats, not na+/h+ exchange.

    PubMed

    O'Connor, Paul M; Lu, Limin; Liang, Mingyu; Cowley, Allen W

    2009-08-01

    It has been reported previously that H(+) efflux via the Na(+)/H(+) exchange stimulates NAD(P)H oxidase-dependent superoxide (O(2)(.-)) production in medullary thick ascending limb. We have demonstrated recently that N-methyl-amiloride-sensitive O(2)(.-) production is enhanced in the thick ascending limb of Dahl salt-sensitive (SS) rats, suggesting that H(+) efflux through Na(+)/H(+) exchangers may promote renal oxidative stress and the development of hypertension in these animals. In the current study we demonstrate, using selective and potent inhibitors, that inhibition of Na(+)/H(+) exchange does not mediate the ability of N-methyl-amiloride to inhibit thick ascending limb O(2)(.-) production. To determine the mechanism of action of N-methyl-amiloride, we examined H(+) efflux and O(2)(.-) production in SS and SS.13(BN) thick ascending limbs of prehypertensive, 0.4% NaCl-fed rats. Tissue strips containing the medullary thick ascending limb were isolated from male SS and salt-resistant consomic SS.13(BN) rats, loaded with either dihydroethedium or 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester, and imaged in a heated tissue bath. In Na(+)-replete media, activation of Na(+)/H(+) exchange using an NH(4)Cl prepulse did not stimulate thick ascending limb O(2)(.-) production. In Na(+)-free media containing BaCl(2) in which Na(+)/H(+) activity was inhibited, an NH(4)Cl prepulse stimulated O(2)(.-) production in medullary thick ascending limb renal tubular segments. This response was enhanced in medullary thick ascending limb of SS rats (slope Deltaethidium/Deltadihydroethedium=0.029+/-0.004) compared with SS.13(BN) rats (slope=0.010+/-0.004; P<0.04) and could be inhibited by N-methyl-amiloride (slope=0.005+/-0.002 and 0.006+/-0.002 for SS and SS.13(BN), respectively). We concluded that only H(+) efflux through a specific, as-yet-unidentified, amiloride-sensitive H(+) channel promotes O(2)(.-) production in the medullary thick ascending limb

  3. Organochlorine pesticides (OCPs) in the Indus River catchment area, Pakistan: Status, soil-air exchange and black carbon mediated distribution.

    PubMed

    Bajwa, Anam; Ali, Usman; Mahmood, Adeel; Chaudhry, Muhammad Jamshed Iqbal; Syed, Jabir Hussain; Li, Jun; Zhang, Gan; Jones, Kevin C; Malik, Riffat Naseem

    2016-06-01

    Organochlorine pesticides (OCPs) were investigated in passive air and soil samples from the catchment area of the Indus River, Pakistan. ∑15OCPs ranged between 0.68 and 13.47 ng g(-1) in soil and 375.1-1975 pg m-(3) in air. HCHs and DDTs were more prevalent in soil and air compartments. Composition profile indicated that β-HCH and p,p'-DDE were the dominant of all metabolites among HCHs and DDTs respectively. Moreover, fBC and fTOC were assessed and evaluated their potential role in the distribution status of OCPs. The fTOC and fBC ranged between 0.77 and 2.43 and 0.04-0.30% respectively in soil. Regression analysis showed the strong influence of fBC than fTOC on the distribution of OCPs in the Indus River catchment area soil. Equilibrium status was observed for β-HCH, δ-HCH, p,p'-DDD, o,p'-DDT, TC, HCB and Heptachlor with ff ranged between 0.3 and 0.59 while assessing the soil-air exchange of OCPs.

  4. Macula densa Na(+)/H(+) exchange activities mediated by apical NHE2 and basolateral NHE4 isoforms.

    PubMed

    Peti-Peterdi, J; Chambrey, R; Bebok, Z; Biemesderfer, D; St John, P L; Abrahamson, D R; Warnock, D G; Bell, P D

    2000-03-01

    Functional and immunohistochemical studies were performed to localize and identify Na(+)/H(+) exchanger (NHE) isoforms in macula densa cells. By using the isolated perfused thick ascending limb with attached glomerulus preparation dissected from rabbit kidney, intracellular pH (pH(i)) was measured with fluorescence microscopy by using 2',7'-bis-(2-carboxyethyl)-5-(and -6) carboxyfluorescein. NHE activity was assayed by measuring the initial rate of Na(+)-dependent pH(i) recovery from an acid load imposed by prior lumen and bath Na(+) removal. Removal of Na(+) from the bath resulted in a significant, DIDS-insensitive, ethylisopropyl amiloride (EIPA)-inhibitable decrease in pH(i). This basolateral transporter showed very low affinity for EIPA and Hoechst 694 (IC(50) = 9.0 and 247 microM, respectively, consistent with NHE4). The recently reported apical NHE was more sensitive to inhibition by these drugs (IC(50) = 0.86 and 7.6 microM, respectively, consistent with NHE2). Increasing osmolality, a known activator of NHE4, greatly stimulated basolateral NHE. Immunohistochemical studies using antibodies against NHE1-4 peptides demonstrated expression of NHE2 along the apical and NHE4 along the basolateral, membrane, whereas NHE1 and NHE3 were not detected. These results suggest that macula densa cells functionally and immunologically express NHE2 at the apical membrane and NHE4 at the basolateral membrane. These two isoforms likely participate in Na(+) transport, pH(i), and cell volume regulation and may be involved in tubuloglomerular feedback signaling by these cells.

  5. Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for a dipole-coupled spin-1/2 pair

    NASA Astrophysics Data System (ADS)

    Chang, Zhiwei; Halle, Bertil

    2013-10-01

    In complex biological or colloidal samples, magnetic relaxation dispersion (MRD) experiments using the field-cycling technique can characterize molecular motions on time scales ranging from nanoseconds to microseconds, provided that a rigorous theory of nuclear spin relaxation is available. In gels, cross-linked proteins, and biological tissues, where an immobilized macromolecular component coexists with a mobile solvent phase, nuclear spins residing in solvent (or cosolvent) species relax predominantly via exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings. The physical or chemical exchange processes that dominate the MRD typically occur on a time scale of microseconds or longer, where the conventional perturbation theory of spin relaxation breaks down. There is thus a need for a more general relaxation theory. Such a theory, based on the stochastic Liouville equation (SLE) for the EMOR mechanism, is available for a single quadrupolar spin I = 1. Here, we present the corresponding theory for a dipole-coupled spin-1/2 pair. To our knowledge, this is the first treatment of dipolar MRD outside the motional-narrowing regime. Based on an analytical solution of the spatial part of the SLE, we show how the integral longitudinal relaxation rate can be computed efficiently. Both like and unlike spins, with selective or non-selective excitation, are treated. For the experimentally important dilute regime, where only a small fraction of the spin pairs are immobilized, we obtain simple analytical expressions for the auto-relaxation and cross-relaxation rates which generalize the well-known Solomon equations. These generalized results will be useful in biophysical studies, e.g., of intermittent protein dynamics. In addition, they represent a first step towards a rigorous theory of water 1H relaxation in biological tissues, which is a prerequisite for unravelling the molecular basis of soft

  6. Rapid and Efficient Generation of Recombinant Human Pluripotent Stem Cells by Recombinase-mediated Cassette Exchange in the AAVS1 Locus

    PubMed Central

    Pistoni, Mariaelena; Chen, Yemiao; Sambathkumar, Rangarajan; Helsen, Nicky; Vanhove, Jolien; Berckmans, Pieter; Cai, Qing; Vanuytsel, Kim; Raitano, Susanna; Verfaillie, Catherine M.

    2016-01-01

    Even with the revolution of gene-targeting technologies led by CRISPR-Cas9, genetic modification of human pluripotent stem cells (hPSCs) is still time consuming. Comparative studies that use recombinant lines with transgenes integrated into safe harbor loci could benefit from approaches that use site-specific targeted recombinases, like Cre or FLPe, which are more rapid and less prone to off-target effects. Such methods have been described, although they do not significantly outperform gene targeting in most aspects. Using Zinc-finger nucleases, we previously created a master cell line in the AAVS1 locus of hPSCs that contains a GFP-Hygromycin-tk expressing cassette, flanked by heterotypic FRT sequences. Here, we describe the procedures to perform FLPe recombinase-mediated cassette exchange (RMCE) using this line. The master cell line is transfected with a RMCE donor vector, which contains a promoterless Puromycin resistance, and with FLPe recombinase. Application of both a positive (Puromycin) and negative (FIAU) selection program leads to the selection of RMCE without random integrations. RMCE generates fully characterized pluripotent polyclonal transgenic lines in 15 d with 100% efficiency. Despite the recently described limitations of the AAVS1 locus, the ease of the system paves the way for hPSC transgenesis in isogenic settings, is necessary for comparative studies, and enables semi-high-throughput genetic screens for gain/loss of function analysis that would otherwise be highly time consuming. PMID:27911376

  7. The RhoA guanine nucleotide exchange factor, LARG, mediates ICAM-1-dependent mechanotransduction in endothelial cells to stimulate transendothelial migration.

    PubMed

    Lessey-Morillon, Elizabeth C; Osborne, Lukas D; Monaghan-Benson, Elizabeth; Guilluy, Christophe; O'Brien, E Timothy; Superfine, Richard; Burridge, Keith

    2014-04-01

    RhoA-mediated cytoskeletal rearrangements in endothelial cells (ECs) play an active role in leukocyte transendothelial cell migration (TEM), a normal physiological process in which leukocytes cross the endothelium to enter the underlying tissue. Although much has been learned about RhoA signaling pathways downstream from ICAM-1 in ECs, little is known about the consequences of the tractional forces that leukocytes generate on ECs as they migrate over the surface before TEM. We have found that after applying mechanical forces to ICAM-1 clusters, there is an increase in cellular stiffening and enhanced RhoA signaling compared with ICAM-1 clustering alone. We have identified that leukemia-associated Rho guanine nucleotide exchange factor (LARG), also known as Rho GEF 12 (ARHGEF12) acts downstream of clustered ICAM-1 to increase RhoA activity, and that this pathway is further enhanced by mechanical force on ICAM-1. Depletion of LARG decreases leukocyte crawling and inhibits TEM. To our knowledge, this is the first report of endothelial LARG regulating leukocyte behavior and EC stiffening in response to tractional forces generated by leukocytes.

  8. Spatio-temporal variations of plant mediated exchange - diurnal and seasonal changes of the function status of plant canopies measured by sun-induced fluorescence

    NASA Astrophysics Data System (ADS)

    Rascher, Uwe; Schickling, Anke; Crewell, Susanne; Schween, Jan; Geiß, Heiner

    2010-05-01

    Fluxes of plant mediated exchange processes are large and substantially influence patterns in atmospheric CO2 concentrations and water vapor. Plant canopies are not constant, but continuously adapt their physiology to the ever changing environmental conditions. Structural changes of plant canopies mainly occur on the time scale of weeks and seasons and are generally parametrized in regional and global carbon and water models. Changes of the physiological status of plant ecosystems, however, may occur within hours or a few days and are often not accounted for in models. Nevertheless, a reduction of photosynthesis because of e.g. stress may greatly reduce carbon and water exchange below the theoretical optimum. Such physiological changes are often are not correctly parametrized in spatially explicit and high resolution carbon and water models. For a better understanding of the diurnal and seasonal variations of soil-vegetation-atmosphere exchange processes, the structure and function of two main agricultural crops were monitored over two years in the frame of the collaborative research consortium Transregio TR32. Seasonal development of the two main crops of the region, winter wheat and sugar beet, has been characterized during diurnal courses using non invasive methods ranging from leaf to canopy level including gas exchange, PAM fluorometry and eddy correlation measurements. The day course of photosynthetic capacity varied between the two species by being constant during the day for winter wheat whereas sugar beet showed a constant decrease over the day. The highest photosynthetic electron transport rates appeared before solar noon. Additionally the region was scanned by an airborne high-resolution spectrometer that allowed the extraction of sun-induced fluorescence. Sun-induced fluorescence is currently evaluated to serve as a direct measure of photosynthetic efficiency from air- and spaceborne platforms. In this presentation we present the first conceptual view

  9. Surface charge fine tuning of reversed-phase/weak anion-exchange type mixed-mode stationary phases for milder elution conditions.

    PubMed

    Zimmermann, Aleksandra; Horak, Jeannie; Sánchez-Muñoz, Orlando L; Lämmerhofer, Michael

    2015-08-28

    A series of new mixed-mode reversed-phase/weak anion-exchange (RP/WAX) phases have been synthesized by immobilization of N-undecenyl-3-α-aminotropane onto thiol-modified silica gel by thiol-ene click chemistry and subsequent introduction of acidic thiol-endcapping functionalities of different type and surface densities. Click chemistry allowed to adjust a controlled surface concentration of the RP/WAX ligand in such a way that a sufficient quantity of residual thiols remained unmodified which have been capped by thiol click with either 3-butenoic acid or allylsulfonic acid as co-ligands. In another embodiment, performic acid oxidation of N-undecenyl-3-α-aminotropane-derivatized thiol-modified silica gave a RP/WAX phase with high density of sulfonic acid end-capping groups. ζ-Potential determinations confirmed the fine-tuned pI of these mixed-mode stationary phases which was shifted from 9.5 to 8.2, 7.8, and 6.5 with 3-butenoic acid and allylsulfonic acid end-capping as well as performic acid oxidation. For acidic solutes, the co-ionic endcapping leads to strongly reduced retention times and clearly allowed elution of these analytes under lower ionic strength thus milder elution conditions. In spite of the acidic endcapping, the new mixed-mode phases maintained their hydrophobic and anion-exchange selectivity as well as their multimodal nature featuring RP and HILIC elution domains at acetonitrile percentages below and above 50%, respectively. Column classification by principal component analysis of an extended retention map in comparison to a set of polar commercial and in-house synthesized stationary phases confirmed complementarity of the new mixed-mode phases with respect to HILIC, polar RP, amino and commercial mixed-mode phases.

  10. Exchange protein activated by cAMP (Epac) mediates cAMP-dependent but protein kinase A-insensitive modulation of vascular ATP-sensitive potassium channels.

    PubMed

    Purves, Gregor I; Kamishima, Tomoko; Davies, Lowri M; Quayle, John M; Dart, Caroline

    2009-07-15

    Exchange proteins directly activated by cyclic AMP (Epacs or cAMP-GEF) represent a family of novel cAMP-binding effector proteins. The identification of Epacs and the recent development of pharmacological tools that discriminate between cAMP-mediated pathways have revealed previously unrecognized roles for cAMP that are independent of its traditional target cAMP-dependent protein kinase (PKA). Here we show that Epac exists in a complex with vascular ATP-sensitive potassium (KATP) channel subunits and that cAMP-mediated activation of Epac modulates KATP channel activity via a Ca2+-dependent mechanism involving the activation of Ca2+-sensitive protein phosphatase 2B (PP-2B, calcineurin). Application of the Epac-specific cAMP analogue 8-pCPT-2'-O-Me-cAMP, at concentrations that activate Epac but not PKA, caused a 41.6 +/- 4.7% inhibition (mean +/- S.E.M.; n = 7) of pinacidil-evoked whole-cell KATP currents recorded in isolated rat aortic smooth muscle cells. Importantly, similar results were obtained when cAMP was elevated by addition of the adenylyl cyclase activator forskolin in the presence of the structurally distinct PKA inhibitors, Rp-cAMPS or KT5720. Activation of Epac by 8-pCPT-2'-O-Me-cAMP caused a transient 171.0 +/- 18.0 nM (n = 5) increase in intracellular Ca2+ in Fura-2-loaded aortic myocytes, which persisted in the absence of extracellular Ca2+. Inclusion of the Ca2+-specific chelator BAPTA in the pipette-filling solution or preincubation with the calcineurin inhibitors, cyclosporin A or ascomycin, significantly reduced the ability of 8-pCPT-2'-O-Me-cAMP to inhibit whole-cell KATP currents. These results highlight a previously undescribed cAMP-dependent regulatory mechanism that may be essential for understanding the physiological and pathophysiological roles ascribed to arterial KATP channels in the control of vascular tone and blood flow.

  11. Uncovering the Key Role of the Fermi Level of the Electron Mediator in a Z-Scheme Photocatalyst by Detecting the Charge Transfer Process of WO3-metal-gC3N4 (Metal = Cu, Ag, Au).

    PubMed

    Li, Houfen; Yu, Hongtao; Quan, Xie; Chen, Shuo; Zhang, Yaobin

    2016-01-27

    Z-scheme photocatalytic system shows superiority in degradation of refractory pollutants and water splitting due to the high redox capacities caused by its unique charge transfer behaviors. As a key component of Z-scheme system, the electron mediator plays an important role in charge carrier migration. According to the energy band theory, we believe the interfacial energy band bendings facilitate the electron transfer via Z-scheme mechanism when the Fermi level of electron mediator is between the Fermi levels of Photosystem II (PS II) and Photosystem I (PS I), whereas charge transfer is inhibited in other cases as energy band barriers would form at the semiconductor-metal interfaces. Here, this inference was verified by the increased hydroxyl radical generation and improved photocurrent on WO3-Cu-gC3N4 (with the desired Fermi level structure), which were not observed on either WO3-Ag-gC3N4 or WO3-Au-gC3N4. Finally, photocatalytic degradation rate of 4-nonylphenol on WO3-Cu-gC3N4 was proved to be as high as 11.6 times than that of WO3-gC3N4, further demonstrating the necessity of a suitable electron mediator in Z-scheme system. This study provides scientific basis for rational construction of Z-scheme photocatalytic system.

  12. The effect of exchange of bacteriopheophytin a with plant pheophytin a on charge separation in Y(M210)W mutant reaction centers of Rhodobacter sphaeroides at low temperature.

    PubMed

    Shkuropatov, Anatoli Ya; Neerken, Sieglinde; Permentier, Hjalmar P; de Wijn, Rik; Schmidt, Kristiane A; Shuvalov, Vladimir A; Aartsma, Thijs J; Gast, Peter; Hoff, Arnold J

    2003-03-06

    The bacteriopheophytin a molecules at the H(A) and H(B) binding sites of reaction centers (RCs) of the Y(M210)W mutant of Rhodobacter sphaeroides were chemically exchanged with plant pheophytin a. The Y(M210)W mutation slows down the formation of H(A)(-), presumably by raising the free energy level of the P(+)B(A)(-) state above that of P* due to increasing the oxidation potential of the primary electron donor P and lowering the reduction potential of the accessory bacteriochlorophyll B(A). Exchange of the bacteriopheophytins with pheophytin a on the contrary lowers the redox potential of H(A), inhibiting its reduction. A combination of the mutation and pigment exchange was therefore expected to make the A-side of the RC incapable of electron transfer and cause the excited state P* to deactivate directly to the ground state or through the B-side, or both. Time-resolved absorption difference spectroscopy at 10 K on the RCs that were modified in this way showed a lifetime of P* lengthened to about 500 ps as compared to about 200 ps measured in the original Y(M210)W RCs. We show that the decay of P* in the pheophytin-exchanged preparations is accompanied by both return to the ground state and formation of a new charge-separated state, the absorption difference spectrum of which is characterized by bleachings at 811 and 890 nm. This latter state was formed with a time constant of ca. 1.7 ns and a yield of about 30%, and lasted a few nanoseconds. On the basis of spectroscopic observations these bands at 811 and 890 nm are tentatively attributed to the presence of the P(+)B(B)(-) state, where B(B) is the accessory bacteriochlorophyll in the "inactive" B-branch of the cofactors. The B(B) molecules in Y(M210)W RCs are suggested to be spectrally heterogeneous, absorbing in the Q(y) region at 813 or 806 nm. The results are discussed in terms of perturbation of the free energy level of the P(+)B(B)(-) state and absorption properties of the B(B) bacteriochlorophyll in the

  13. Anion exchange membrane

    DOEpatents

    Verkade, John G; Wadhwa, Kuldeep; Kong, Xueqian; Schmidt-Rohr, Klaus

    2013-05-07

    An anion exchange membrane and fuel cell incorporating the anion exchange membrane are detailed in which proazaphosphatrane and azaphosphatrane cations are covalently bonded to a sulfonated fluoropolymer support along with anionic counterions. A positive charge is dispersed in the aforementioned cations which are buried in the support to reduce the cation-anion interactions and increase the mobility of hydroxide ions, for example, across the membrane. The anion exchange membrane has the ability to operate at high temperatures and in highly alkaline environments with high conductivity and low resistance.

  14. Charge exchange recombination spectroscopy measurements in the extreme ultraviolet region of central carbon concentrations during high power neutral beam heating in TFTR (Tokamak Fusion Test Reactor)

    SciTech Connect

    Stratton, B.C.; Fonck, R.J.; Ramsey, A.T.; Synakowski, E.J.; Grek, B.; Hill, K.W.; Johnson, D.W.; Mansfield, D.K.; Park, H.; Taylor, G.; Valanju, P.M. . Plasma Physics Lab.; Texas Univ., Austin, TX . Fusion Research Center)

    1989-09-01

    The carbon concentration in the central region of TFTR discharges with high power neutral beam heating has been measured by charge-extracted recombination spectroscopy (CXRS) of the C{sup +5} n = 3--4 transition in the extreme ultraviolet region. The carbon concentrations were deduced from absolute measurements of the line brightness using a calculation of the beam attenuation and the appropriate cascade-corrected line excitation rates. As a result of the high ion temperatures in most of the discharges, the contribution of beam halo neutrals to the line brightness was significant and therefore had to be included in the modeling of the data. Carbon concentrations have been measured in discharges with I{sub p} = 1.0-1.6 MA and beam power in the range of 2.6-30 MW, including a number of supershots. The results are in good agreement with carbon concentrations deduced from the visible bremsstrahlung Z{sub eff} and metallic impurity concentrations measured by x-ray pulse-height analysis, demonstrating the reliability of the atomic rates used in the beam attenuation and line excitation calculations. Carbon is the dominant impurity species in these discharges; the oxygen concentration measured via CXRS in a high beam power case was 0.0006 of n{sub e}, compard to 0.04 for carbon. Trends with I{sub p} and beam power in the carbon concentration and the inferred deuteron concentration are presented. The carbon concentration is independent of I{sub p} and decreases from 0.13 at 2.6 MW beam power to 0.04 at 30 MW, while the deuteron concentration increases from 0.25 to 0.75 over the same range of beam power. These changes are primarily the result of beam particle fueling, as the carbon density did not vary significantly with beam power. The time evolutions of the carbon and deuteron concentrations during two high power beam pulses, one which exhibited a carbon bloom and one which did not, are compared. 30 refs., 12 figs., 2 tabs.

  15. Ion exchange phenomena

    SciTech Connect

    Bourg, I.C.; Sposito, G.

    2011-05-01

    Ion exchange phenomena involve the population of readily exchangeable ions, the subset of adsorbed solutes that balance the intrinsic surface charge and can be readily replaced by major background electrolyte ions (Sposito, 2008). These phenomena have occupied a central place in soil chemistry research since Way (1850) first showed that potassium uptake by soils resulted in the release of an equal quantity of moles of charge of calcium and magnesium. Ion exchange phenomena are now routinely modeled in studies of soil formation (White et al., 2005), soil reclamation (Kopittke et al., 2006), soil fertilitization (Agbenin and Yakubu, 2006), colloidal dispersion/flocculation (Charlet and Tournassat, 2005), the mechanics of argillaceous media (Gajo and Loret, 2007), aquitard pore water chemistry (Tournassat et al., 2008), and groundwater (Timms and Hendry, 2007; McNab et al., 2009) and contaminant hydrology (Chatterjee et al., 2008; van Oploo et al., 2008; Serrano et al., 2009).

  16. The roles of electronic exchange and correlation in charge-transfer- to-solvent dynamics: Many-electron nonadiabatic mixed quantum/classical simulations of photoexcited sodium anions in the condensed phase.

    PubMed

    Glover, William J; Larsen, Ross E; Schwartz, Benjamin J

    2008-10-28

    The charge-transfer-to-solvent (CTTS) reactions of solvated atomic anions serve as ideal models for studying the dynamics of electron transfer: The fact that atomic anions have no internal degrees of freedom provides one of the most direct routes to understanding how the motions of solvent molecules influence charge transfer, and the relative simplicity of atomic electronic structure allows for direct contact between theory and experiment. To date, molecular dynamics simulations of the CTTS process have relied on a single-electron description of the atomic anion-only the electron involved in the charge transfer has been treated quantum mechanically, and the electronic structure of the atomic solute has been treated via pseudopotentials. In this paper, we examine the severity of approximating the electronic structure of CTTS anions with a one-electron model and address the role of electronic exchange and correlation in both CTTS electronic structure and dynamics. To do this, we perform many-electron mixed quantum/classical molecular dynamics simulations of the ground- and excited-state properties of the aqueous sodium anion (sodide). We treat both of the sodide valence electrons quantum mechanically and solve the Schrodinger equation using configuration interaction with singles and doubles (CISD), which provides an exact solution for two electrons. We find that our multielectron simulations give excellent general agreement with experimental results on the CTTS spectroscopy and dynamics of sodide in related solvents. We also compare the results of our multielectron simulations to those from one-electron simulations on the same system [C. J. Smallwood et al., J. Chem. Phys. 119, 11263 (2003)] and find substantial differences in the equilibrium CTTS properties and the nonadiabatic relaxation dynamics of one- and two-electron aqueous sodide. For example, the one-electron model substantially underpredicts the size of sodide, which in turn results in a dramatically

  17. High-charge-state ion sources

    SciTech Connect

    Clark, D.J.

    1983-06-01

    Sources of high charge state positive ions have uses in a variety of research fields. For heavy ion particle accelerators higher charge state particles give greater acceleration per gap and greater bending strength in a magnet. Thus higher energies can be obtained from circular accelerators of a given size, and linear accelerators can be designed with higher energy gain per length using higher charge state ions. In atomic physics the many atomic transitions in highly charged ions supplies a wealth of spectroscopy data. High charge state ion beams are also used for charge exchange and crossed beam experiments. High charge state ion sources are reviewed. (WHK)

  18. First Charge-Exchange Measurements with SHARAQ

    SciTech Connect

    Miki, K.; Sakai, H.

    2011-10-28

    The isovector spin monopole resonances (IVSMR) of the {beta}{sup +} type were observed for the first time in the {sup 208}Pb and {sup 90}Zr(t,{sup 3}He) reactions at 300 MeV/u. The experiment was performed at the RI Beam Factory (RIBF) at RIKEN by using the newly-constructed magnetic spectrometer SHARAQ. The double differential cross sections for the {sup 208}Pb and {sup 90}Zr(t,{sup 3}He) reactions were obtained at the excitation energy of 0{<=}E{sub x}{<=}70 MeV and the scattering angles of 0 deg. {<=}{theta}{<=}3 deg. The monopole component was identified by making a difference between the zero-degree and backward-angle spectra. The signatures of the IVSMR are observed at an excitation energy of 12 MeV(20 MeV) in {sup 208}Pb({sup 90}Zr)(t,{sup 3}He) reaction, which agrees fairly well with the theoretical predictions.

  19. Visible charge exchange spectroscopy at JET

    NASA Astrophysics Data System (ADS)

    von Hellermann, M. G.; Mandl, W.; Summers, H. P.; Weisen, H.; Boileau, A.; Morgan, P. D.; Morsi, H.; Koenig, R.; Stamp, M. F.; Wolf, R.

    1990-11-01

    Recent developments and results of the JET CXRS diagnostic are reported. The measurements of radial profiles of ion temperatures and densities are based on CXR spectra of fully stripped ions of either carbon or beryllium. Considerable effort has been expended in ensuring consistency between radial profiles of low Z impurity densities and those from other diagnostics. The contributions of the main light impurities are used to reconstruct radial profiles of Zeff which can be compared with Abel-inverted signals from visible bremsstrahlung or soft x-ray emission. Active Balmer-Alpha spectroscopy (ABAS) is being introduced as a diagnostic tool providing data on local magnetic fields, neutral beam densities, and dilution factors. The effects of collision-energy-dependent CXR cross sections on observed CXR spectra are calculated. Corrections for the values of deduced ion temperatures, toroidal velocities, and impurity densities are discussed for the case of plasmas with high ion temperatures and high toroidal rotation velocities. Some recent results of the JET 1989 operation illustrating the CXRS diagnostic potential are given.

  20. Visible charge exchange spectroscopy at JET (abstract)

    NASA Astrophysics Data System (ADS)

    von Hellermann, M. G.; Mandl, W.; Summers, H. P.; Weisen, H.; Boileau, A.; Morgan, P. D.; Morsi, H.; Koenig, R.; Stamp, M. F.; Wolf, R.

    1990-10-01

    Recent developments and results of the JET CXRS diagnostic are reported. The measurements of radial profiles of ion temperatures and densities are based on CXR spectra of fully stripped ions of either carbon or beryllium. Considerable effort has been expended in ensuring consistency between radial profiles of low Z impurity densities and those from other diagnostics. The contributions of the main light impurities are used to reconstruct radial profiles of Zeffwhich can be compared with Abel-inverted signals from visible bremsstrahlung or soft x-ray emission. Active Balmer-Alpha spectroscopy (ABAS) is being introduced as a diagnostic tool providing data on local magnetic fields, neutral beam densities, and dilution factors. The effects of collision-energy-dependent CXR cross sections on observed CXR spectra are calculated. Corrections for the values of deduced ion temperatures, toroidal velocities, and impurity densities are discussed for the case of plasmas with high ion temperatures and high toroidal rotation velocities. Some recent results of the JET 1989 operation illustrating the CXRS diagnostic potential are given.