Search Results - (Author, Cooperation:J. Neri)

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  1. 1
    Staff View
    Publication Date:
    2012-09-08
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    DNA/*genetics ; *DNA Footprinting ; DNA Methylation ; DNA-Binding Proteins/metabolism ; Deoxyribonuclease I/metabolism ; *Encyclopedias as Topic ; Genome, Human/*genetics ; Genomic Imprinting ; Genomics ; Humans ; *Molecular Sequence Annotation ; Polymorphism, Single Nucleotide/genetics ; Regulatory Sequences, Nucleic Acid/*genetics ; Transcription Factors/*metabolism ; Transcription Initiation Site
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Ottinger, P. F. ; Rose, D. V. ; Neri, J. M. ; Olson, C. L.

    [S.l.] : American Institute of Physics (AIP)
    Published 1992
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Light-ion inertial confinement fusion requires beam transport over distances of a few meters for isolation of the diode hardware from the target explosion and for power compression by time-of-flight bunching. This paper evaluates ballistic transport of light-ion beams focused by a solenoidal lens. The ion beam is produced by an annular magnetically insulated diode and is extracted parallel to the axis by appropriate shaping of the anode surface. The beam propagates from the diode to the solenoidal lens in a field-free drift region. The lens alters the ion trajectories such that the beam ballistically focuses onto a target while propagating in a second field-free region between the lens and the target. Ion orbits are studied to determine the transport efficiency ηt (i.e., the fraction of the beam emitted from the diode which hits the target) under various conditions relevant to light-ion inertial confinement fusion. Analytic results are given for a sharp boundary, finite thickness solenoidal lens configuration, and numerical results are presented for a more realistic lens configuration. From the analytic results, it is found that ηt can be in the range of 75%–100% for parameter values that appear to be achievable. Numerical results show that using a more realistic magnetic-field profile for the lens yields similar values of ηt for small radius diodes but significantly reduced values of ηt for large radius diodes. This reduction results from the radial gradient in the focusing field at larger radius.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.351867

    Articles: DFG German National Licenses
  3. 3
    Ottinger, P. F. ; Rose, D.V. ; Mosher, D. ; Neri, J. M.

    [S.l.] : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Ion inertial confinement fusion requires beam transport over distances of a few meters for isolation of the diode hardware from the target explosion and for power compression by time-of-flight bunching. This paper evaluates light ion beam transport in a wall-stabilized z-discharge channel, where the discharge azimuthal magnetic field radially confines the ion beam. The ion beam is focused onto the entrance aperture of the transport channel by shaping the diode to achieve beam convergence in a field-free drift region separating the diode from the transport section. Ion orbits are studied to determine the injection efficiency (i.e., the fraction of the beam emitted from the diode which is transported) under various conditions. Ions that are focused onto the channel entrance at too large of an angle for confinement hit the wall and are lost. For a multimodular scheme (10–30 beams), individual transport channels are packed around the target with the exit apertures at some standoff distance from it. The fraction of the beam that is lost in this field-free standoff region is also evaluated under various conditions. The standoff efficiency is then combined with the injection efficiency to give the dependence of the total transport efficiency ηt on diode, focusing, transport and standoff parameters. It is found that ηt can be in the range of 75%–100% for parameter values that appear to be achievable.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.350239

    Articles: DFG German National Licenses
  4. 4
    Watrous, J. J. ; Mosher, D. ; Neri, J. M. ; Ottinger, P. F. ; Olson, C. L. ; Crow, J. T. ; Peterson, R. R.

    [S.l.] : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Light ion inertial confinement fusion requires beam transport over distances of a few meters for isolation of the diode hardware from the target explosion and for power compression by time-of-flight bunching. This paper evaluates a wire-guided transport system that uses the azimuthal magnetic field, produced by a current driven through a thin wire, to radially confine the ion beam. Ion orbits are studied to determine the injection efficiency (i.e., the fraction of the beam which is transported) under various conditions. Some ions hit the wire because of too small angular momentum at injection; others hit the wire or are lost to large radius during transport because of chaotic orbit behavior induced by a small number of return-current wires close to the beam envelope. For a multimodular scheme (10–30 beams), individual transport system are packed around the target at some standoff distance. The fraction of the beam which is lost in this field-free standoff region is also evaluated under various conditions. The standoff efficiency is then combined with the injection efficiency to give the dependence of the total transport efficiency, ηt, on diode, focusing, transport, and standoff parameters. It is found that ηt can be as large as about 60% for parameter values which appear to be achievable.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.347344

    Articles: DFG German National Licenses
  5. 5
    Ottinger, P. F. ; Young, F. C. ; Stephanakis, S. J. ; Rose, D. V. ; Neri, J. M. ; Weber, B. V. ; Myers, M. C. ; Hinshelwood, D. D. ; Mosher, D.

    [S.l.] : American Institute of Physics (AIP)
    Published 2000
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Ion beam self-pinched transport (SPT) experiments have been carried out using a 1.1-MeV, 100-kA proton beam. A Rutherford scattering diagnostic and a LiF nuclear activation diagnostic measured the number of protons within a 5 cm radius at 50 cm into the transport region that was filled with low-pressure helium. Time-integrated signals from both diagnostics indicate self-pinching of the ion beam in a helium pressure window between 35 and 80 mTorr. Signals from these two diagnostics are consistent with ballistic transport at pressures above and below this SPT pressure window. Interferometric measurements of electron densities during beam injection into vacuum are consistent with ballistic transport with co-moving electrons. Interferometric measurements for beam injection into helium show that the electron density increases quadratically with pressure through the SPT window and roughly linearly with pressure above the SPT window. The ionization fraction of the helium plateaus at about 1.5% for pressures above 80 mTorr. In the SPT window, the electron density is 3 to 20 times the beam density. Numerical simulations of these beam transport experiments produce results that are in qualitative agreement with the experimental measurements. © 2000 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.873803

    Articles: DFG German National Licenses
  6. 6
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The interaction of intense proton beams with low-pressure (0.25 to 4 Torr) background gases is studied to evaluate beam-current neutralization during transport. Electrons to neutralize the beam are provided by beam-induced ionization of the gas. In experiments with 1 MeV, 1 kA/cm2 protons, net currents outside the beam envelope and electron densities within the beam envelope are measured for helium, neon, argon, and air. Net-current fractions are 2% to 8% and ionization fractions are 0.6% to 5% for 5 to 7 kA beams. Simulations of the experiments for helium and argon suggest that fast electrons play an important role in generating a significant fraction of the return current in a halo outside the beam. As a result, net currents inside the beam may be larger than inferred from magnetic-field measurements outside the beam. Ions at the head of the beam are observed to lose more energy than expected from collisional energy losses in the background gas.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.870673

    Articles: DFG German National Licenses
  7. 7
    Oliver, B. V. ; Ottinger, P. F. ; Rose, D. V. ; Hinshelwood, D. D. ; Neri, J. M. ; Young, F. C.

    [S.l.] : American Institute of Physics (AIP)
    Published 1999
    Staff View
    ISSN:
    1089-7674
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Electron density measurements from previous ion-beam-induced gas ionization experiments [F. C. Young et al., Phys. Plasmas 1, 1700 (1994)] are re-analyzed and compared with a recent theoretical model [B. V. Oliver et al., Phys. Plasmas 3, 3267 (1996)]. Ionization is produced by a 1 MeV, 3.5 kA, 55 ns pulse-duration, proton beam, injected into He, Ne, or Ar gas in the 1 Torr pressure regime. Theoretical and numerical analysis indicates that, after an initial electron population is produced by ion beam impact, ionization is dominated by the background plasma electrons and is proportional to the beam stopping power. The predicted electron density agrees with the measured electron densities within the factor of 2 uncertainty in the measurement. However, in the case of Ar, the theoretically predicted electron densities are systematically greater than the measured values. The assumptions of a Maxwellian distribution for the background electrons and neglect of beam energy loss to discrete excitation and inner shell ionization in the model equations are considered as explanations for the discrepancy. © 1999 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.873203

    Articles: DFG German National Licenses
  8. 8
    Young, F. C. ; Boller, J. R. ; Stephanakis, S. J. ; Jones, T. G. ; Neri, J. M.

    [S.l.] : American Institute of Physics (AIP)
    Published 1999
    Staff View
    ISSN:
    1089-7623
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Electrical Engineering, Measurement and Control Technology
    Notes:
    A simple technique has been developed to image intense pulsed proton beams with radiachromic film and to measure their spatial distribution. The optical density (OD) of 50 μm thick film, sufficient to stop 1.5 MeV protons, is measured to infer the incident beam fluence. The OD increases nearly linearly with fluence up to 0.25 cal/cm2. This film is used to measure the uniformity of large-area beams as well as the detector in a multiple-pinhole camera to determine the source uniformity and divergence of applied-magnetic field and pinched-beam ion diodes. © 1999 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1149298

    Articles: DFG German National Licenses
  9. 9
    Neri, J. W. ; Silveira, C. A. B. ; Rodrigues, N. A. S. ; Schwab, C. ; Riva, R. ; Destro, M. G. ; Mirage, A.

    [S.l.] : American Institute of Physics (AIP)
    Published 1998
    Staff View
    ISSN:
    1089-7623
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Electrical Engineering, Measurement and Control Technology
    Notes:
    Uranium photoionization was observed in the afterglow of pulsed hollow cathode lamps illuminated by a dye laser tuned near the electronic transition around 591.5 nm (5L60−16 900 cm−1 7M7). The photoionization signal was used to monitor the time evolution of the ground state uranium vapor density in the cathode hole. Lifetimes over 1 ms were measured for the uranium vapor; that makes this device attractive for multistep photoionization spectroscopy. The obtained results lead to the conclusion that these long times are due to cluster formation in the afterglow. © 1998 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1148763

    Articles: DFG German National Licenses
  10. 10
    Jones, T. G. ; Noonan, W. A. ; Neri, J. M. ; Ottinger, P. F.

    [S.l.] : American Institute of Physics (AIP)
    Published 1999
    Staff View
    ISSN:
    1089-7623
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Electrical Engineering, Measurement and Control Technology
    Notes:
    A novel, spatially resolved diagnostic is being developed to measure magnetic fields associated with intense ion beam propagation through a low-pressure gas, as is envisioned for ion-driven inertial confinement fusion. The diagnostic technique uses laser-induced fluorescence spectroscopy, and can be varied to measure either small or large fields. Small fields, as expected in ballistic beam transport, produce Zeeman shifts, ΔλZ, much smaller than the transition linewidth Δλ. High sensitivity to measure these sub-Doppler shifts is achieved by a variation on the Babcock technique.〈citeref RID="R1" STYLE="SUPERIOR"〉1 Large fields, as expected in self-pinched beam transport, produce ΔλZ larger than Δλ. These ΔλZ will be resolved using a Fabry–Pérot interferometer, in a novel technique similar to that for small fields. Results from benchtop experiments using calibrated B fields for the small-field technique will be presented. Available results from a proof-of-principle experiment for the large-field technique will also be presented.© 1999 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1149449

    Articles: DFG German National Licenses
  11. 11
    Grossmann, J. M. ; Kulsrud, R. ; Neri, J. M. ; Ottinger, P. F.

    [S.l.] : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    During the conduction phase of the plasma erosion opening switch (PEOS), magnetic field has been observed experimentally to penetrate completely through plasmas up to 30 cm long. Current channels in the main body of the plasma have been observed that are more than 10 cm (or more than about 60 collisionless skin depths) wide. In addition, the maximum current carried by the switch before opening (the conduction current) seems to scale roughly linearly with plasma density n and switch length l. Collisionless pic code simulations of the plasma switch show current conducted in skin-depth-like channels, with the conduction current scaling close to l 2/5 and n1/4. In this paper, the effect of collisions on the behavior of the PEOS is investigated and is shown to bring the pic simulations and experimental results in closer agreement. In collisional simulations, current channels as wide as those in experiments are observed, and the conduction current scales linearly with l and as n1/2 in the anode-dominated case. In the cathode-dominated case, linear scaling with both length and density can be inferred from the cathode penetration distance versus time.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.342050

    Articles: DFG German National Licenses
  12. 12
    Grossmann, J. M. ; Ottinger, P. F. ; Neri, J. M. ; Drobot, A. T.

    [S.l.] : American Institute of Physics (AIP)
    Published 1986
    Staff View
    ISSN:
    1089-7666
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Current conduction through a low density (∼1012 cm−3) collisionless plasma injected between two coaxial conducting cylinders is simulated using a 2 (1)/(2) -D, electromagnetic particle-in-cell code. Plasma is injected through the anode towards the cathode with flow velocity, VF, and is assumed to be azimuthally symmetric. Current is driven through the plasma so that the 100 kA level is reached in (approximately-equal-to)5 nsec. The opening process, when current is diverted to a load, is also treated. Electrons are found to carry current in a narrow current channel across the plasma by E×B drift. A large electric field is established by charge separation in the plasma in order to provide the drift. The motion of the anode end of the current channel controls the time of opening and is found to be independent of VF and to depend strongly on density and length.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.865513

    Articles: DFG German National Licenses
  13. 13
    Neri, J. M. ; Ottinger, P. F. ; Rose, D. V. ; Goodrich, P. J. ; Hinshelwood, D. D. ; Mosher, D. ; Stephanakis, S. J. ; Young, F. C.

    New York, NY : American Institute of Physics (AIP)
    Published 1993
    Staff View
    ISSN:
    1089-7666
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A z-discharge plasma channel is used to confine and transport an intense proton beam. A pinch-reflex ion diode on the NRL Gamble II accelerator focuses a proton beam onto the entrance aperture of a 2.5 cm diam, 1.2 m long z-discharge transport system. The beam ions are charge and current neutralized in the discharge plasma, and execute betatronlike orbits in the magnetic field of the discharge. Ion beam diagnostics include shadowbox imaging and prompt-γ radiation measurements from LiF targets. Under appropriate conditions, 95% particle transport and 90% energy transport are observed, with the only energy loss attributed to classical stopping in the channel gas. The transverse phase-space distribution of the beam measured by the shadowbox is consistent with full charge and current neutralization of the transported beam.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.860851

    Articles: DFG German National Licenses
  14. 14
    Villela, T. ; Braga, J. ; D'Amico, F. ; Jayanthi, U. B. ; Neri, J. A.
    Springer
    Published 1994
    Staff View
    ISSN:
    1572-946X
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract We describe an imaging telescope for observations of celestial sources in the energy range between 30 keV and 1.8 MeV onboard stratospheric balloons. The detector is a 41 cm diameter, 5 cm thick NaI(Tl) crystal coupled to 19 photomultipliers in an Anger camera configuration. It is surrounded by a plastic scintillator 15 cm thick on the sides, 0.2 cm thick at the top and 20 cm thick at the bottom. The imaging device is based upon a 19 × 19 element square MURA (Modified Uniformly Redundant Array) coded mask mounted in an one-piece mask-antimask configuration. The detector's spatial resolution is about 10 mm at 100 keV. This is the first experiment to use such a mask pattern and configuration for astrophysical purposes. The expected 3σ sensitivity for an on-axis source observed for 104 s at a residual atmosphere of 3.5 g cm−2 is 1.44 × 10−5 photons cm−2 s−1 keV−1 at 100 keV and 1.00 × 10−6 photons cm−2 s−1 keV−1 at 1 MeV. The angular resolution is approximately 14 arcminutes over a 13°field of view. The instrument is mounted in an automatic platform with a capability for pointing and stabilization in both azimuth and elevation axis with 2 arcmin accuracy.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00982333

    Articles: DFG German National Licenses
  15. 15
    Roa-Neri, J. A. E. ; Jimenez, J. L.
    Springer
    Published 1994
    Staff View
    ISSN:
    1572-9524
    Keywords:
    radiation reaction ; Lagrange expansion ; Liénard-Wiechert fields ; extended charge ; Abraham-Lorentz equation
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract We make a thorough non-covariant analysis of the derivation of the equation of motion for a charged particle, including radiation reaction, by means of a simple model for the charge: a dumbbell. This model and our method to expand retarded quantities, based on complex-variable theory, allow us to avoid some of the usual approximations, so we can show several features of the radiation reaction problem.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF02189244

    Articles: DFG German National Licenses
  16. 16
    Braga, J. ; Villela, T. ; Jayanthi, U. B. ; D'Amico, F. ; Neri, J. A.
    Springer
    Published 1991
    Staff View
    ISSN:
    1572-9508
    Keywords:
    instrumentation ; X-rays ; detectors ; imaging telescopes
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract A new imaging balloon-borne telescope for hard X-rays in the energy range from 30 to 100 keV is described. The imaging capability is provided by the use of an extended URA-based coded-mask. With only one motor and suitable stop pins, we can rotate a carbon-fiber wheel with most of the mask elements attached to it by 180°, and a bar, which is also part of the mask pattern and is allowed to rotate freely over the wheel, by 90°; this combined rotation creates an antimask of the original mask, except for the central element. This is a novel and elegant manner of providing an antimask without additional weight and complex mechanical manipulations. We show that the use of antimasks is a very effective method of eliminating systematic variations in the background map over the position-sensitive detector area. The expected sensitivity of the instrument for the 30–100 keV range is of the order of 7 × 10-5 photons cm-2 s-1 keV-1, for an integration time of 104 seconds at a residual atmosphere of 3.5 g cm-2. This telescope will provide imaging observations of bright galactic hard X-ray sources with an angular resolution of ∼2° in a 10° by 10° FOV, which is defined by a collimator placed in front of the detector system. We are particularly interested in the galactic center region, where recent imaging results in X-rays have shown the presence of an interesting source field. Results of computer simulations of the imaging system are reported.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00576323

    Articles: DFG German National Licenses
  17. 17
    Roa-Neri, J. A. E. ; Nasser, L. ; Jiménez, J. L.
    Springer
    Published 1996
    Staff View
    ISSN:
    1572-9524
    Keywords:
    radiation reaction ; extended dual charge ; duality transformations ; Lagrange expansion ; Lienard-Wiechert fields
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract We offer a non-covariant derivation of the equation of motion for a dual charge, taking into account the radiation reaction, by means of a simple model of charge: a dumbbell. In the derivation we handle retarded quantities avoiding some of the usual approximations, in particular we do not restrict our calculations to first order inv/c nor overlook thet′ dependence ofR=|x−r(t′)|. The differences with the radiation reaction problem for pure electric or magnetic charges are exhibited.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF02190029

    Articles: DFG German National Licenses