Search Results - (Author, Cooperation:S. G. Hansen)

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  1. 1
    Staff View
    Publication Date:
    2011-05-13
    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:
    AIDS Vaccines/immunology ; Animals ; CD4-Positive T-Lymphocytes/immunology ; CD8-Positive T-Lymphocytes/immunology ; Cytomegalovirus/genetics ; DNA, Viral/analysis ; Genetic Vectors/genetics ; Immunity, Mucosal/immunology ; Immunologic Memory/*immunology ; Macaca mulatta/blood/immunology/virology ; Male ; RNA, Viral/analysis ; SAIDS Vaccines/genetics/*immunology ; Simian Acquired Immunodeficiency Syndrome/blood/*immunology/*prevention & ; control/virology ; Simian Immunodeficiency Virus/growth & development/*immunology/isolation & ; purification/*pathogenicity ; T-Lymphocytes/*immunology ; Time Factors ; Vaccines, DNA/genetics/immunology ; Viral Load ; Virus Replication
    Published by:
    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Staff View
    Publication Date:
    2013-09-13
    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:
    Animals ; Cytomegalovirus/genetics/immunology ; Female ; Macaca mulatta ; Male ; Molecular Sequence Data ; SAIDS Vaccines/*immunology ; Simian Acquired Immunodeficiency Syndrome/*prevention & control/virology ; Simian Immunodeficiency Virus/*immunology ; Time Factors ; Vaccines, Attenuated/immunology ; Viral Load ; Virus Replication/physiology
    Published by:
    Latest Papers from Table of Contents or Articles in Press
  3. 3
    Staff View
    Publication Date:
    2016-01-23
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Animals ; Antigen Presentation ; Antigenic Variation ; CD8-Positive T-Lymphocytes/*immunology ; Cytomegalovirus/genetics/*immunology ; Epitopes, T-Lymphocyte/chemistry/*immunology ; Genetic Vectors/genetics/immunology ; Histocompatibility Antigens Class I/chemistry/*immunology ; Host-Pathogen Interactions/immunology ; Immune Evasion ; Killer Cells, Natural/immunology ; Macaca mulatta ; Protein Structure, Secondary ; Simian Immunodeficiency Virus/*immunology ; Vaccination
    Published by:
    Latest Papers from Table of Contents or Articles in Press
  4. 4
    Staff View
    Publication Date:
    2013-05-25
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Animals ; CD8-Positive T-Lymphocytes/*immunology ; Cytokines/immunology ; Cytomegalovirus/genetics/*immunology ; Epitopes, T-Lymphocyte/*immunology ; Female ; Genetic Vectors/genetics/*immunology ; Histocompatibility Antigens Class II/immunology ; Humans ; Macaca mulatta ; Male ; Membrane Glycoproteins/genetics ; SAIDS Vaccines/administration & dosage/*immunology ; Viral Envelope Proteins/genetics
    Published by:
    Latest Papers from Table of Contents or Articles in Press
  5. 5
    Hansen, S. G. ; Luckman, G. ; Nieman, George C. ; Colson, Steven D.

    [S.l.] : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Laser-induced fluorescence of CF2 is used to monitor heterogeneous processes in ≈300 mTorr CF4/O2 plasmas. CF2 is rapidly removed at fluorinated copper and silver surfaces in 13.56-MHz rf discharges as judged by a distinct dip in its spatial distribution. These metals, when employed as etch masks, are known to accelerate plasma etching of silicon, and the present results suggest catalytic dehalogenation of CF2 is involved in this process. In contrast, aluminum and silicon dioxide exhibit negligible reactivity with CF2, which suggests that aluminum masks will not appreciably accelerate silicon etching and that ground state CF2 does not efficiently etch silicon dioxide. Measurement of CF2 decay in a pulsed discharge coupled with direct laser sputtering of metal into the gas phase indicates the interaction between CF2 and the active metals is purely heterogeneous. Aluminum does, however, exhibit homogeneous reactivity with CF2. Redistribution of active metal by plasma sputtering readily occurs; silicon etch rates may also be enhanced by the metal's presence on the silicon surface. Polymers contribute CF2 to the plasma as they etch. The observation of an induction period suggests fluorination of the polymer surface is the first step in its degradation. Polymeric etch masks can therefore depress the silicon etch rate by removal of F atoms, the primary etchants.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  6. 6
    Hansen, S. G.

    [S.l.] : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Slow moving material (velocity ≈3×104 cm/s) ejected from polycarbonate and poly(α-methylstyrene) targets by ultraviolet laser photoablation is probed using time-of-flight mass spectroscopy. The product distribution seen from polycarbonate, using resonant-two-photon ionization with 248- or 266-nm light, consists of aromatic species smaller than the monomer. Mass spectra are similar for 355-, 266-, and 193-nm ablation, and the products differ structurally from the starting material; both observations suggest that slow moving species are ejected by a thermal mechanism at all three wavelengths. 248-nm ablation of polycarbonate near the ablation threshold, gives a different product distribution and it is argued that a cooler thermal regime is being sampled or, that photochemical effects are important. The dominant product seen in 266-, 248-, and 193-nm ablation of poly(α-methylstyrene) is the monomer in each case. Subtle differences present in the resulting mass spectra may be due to photochemical effects, but major similarities suggest that slow movers are ejected by a photothermal mechanism.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  7. 7
    Hansen, S. G. ; Luckman, G. ; Nieman, George C. ; Colson, Steven D.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The temporal profiles of metastable F(4 P3/2) and Ar(1s5) and emitting F(4D05/2 ) and Ar(2p2) in a sharp-edged, pulsed CF4/O2/Ar (87.5/10.4/2.1) discharge are discussed. All four states are so short lived that there is no net accumulation during the discharge pulse and the profiles merely reflect the formation rate. For Ar, electron impact on the ground state leads to both excited states. Their similar profiles mirror the electron excitation function. For excited F, two channels are open: electron impact on CF4, and electron impact on ground-state F which accumulates during the discharge pulse. The fact that metastable F is rapidly quenched in the gas phase indicates that it is not a major etchant of silicon or silicon nitride as was recently suggested in the literature.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  8. 8
    Hansen, S. G. ; Luckman, G. ; Colson, Steven D.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The temporal population profiles of F*, CF, and CF2 in a sharp-edged, pulsed (500 μs), fluorocarbon discharge are examined. F* population rises and falls with the discharge current suggesting that electron impact of the parent fluorocarbon is the primary source of emitting fluorine atoms. Ground-state CF and CF2, monitored by laser-induced fluorescence, show noticeably slower formation and decay, but a simple kinetic model assuming that each arises from direct electron impact of the parent gas fits the data. It is shown that CF can be conveniently monitored by exciting the B˜(v'=2)−X˜(v‘=0) transition with a 193 nm ArF excimer laser.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  9. 9
    Hansen, S. G. ; Robitaille, T. E.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Films were produced by pulsed laser evaporation of various solid polymer targets in vacuum. Smooth films and relatively low deposition power thresholds (〈107 W/cm2 peak) were observed for strongly absorbed ultraviolet wavelengths. Poorly absorbed wavelengths gave powdery deposits. For many polymers the evaporation process did not significantly alter the chemical structure, but the molecular weight was reduced.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  10. 10
    Hansen, S. G. ; Robitaille, T. E.

    [S.l.] : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    By measuring the rapid change in reflectivity of a substrate during film growth induced by pulsed laser evaporation, the time-of-arrival profiles of material emanating from polycarbonate and selenium targets were determined. Results for both targets are reasonably well described by Maxwell–Boltzmann velocity distributions. Selenium evaporation appears to be atomic while for polycarbonate a range of masses are involved. The high velocity of the material leaving polycarbonate strongly suggests that small polymers are not transported directly. The mechanism for polymer film formation must involve repolymerization on the substrate of species not weighing more than a few hundred amu. For both polycarbonate and selenium the time-of-arrival profiles were affected very little by changing the excitation wavelength from 248 to 1064 nm.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  11. 11
    Hansen, S. G. ; Robitaille, T. E.

    [S.l.] : American Institute of Physics (AIP)
    Published 1987
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The laser ablation properties of a (50%)-isopropyl methyl–(50%)-n-propyl methyl silane copolymer are examined. Both 193- and 248-nm-pulsed excimer laser radiation cleanly and completely remove this material in vacuum above certain energy thresholds (30 and 50 mJ/cm2, respectively). Under these conditions the ablation properties are quite similar to those reported for typical organic polymers. Below threshold, ablation is less efficient and becomes increasingly inefficient as irradiation continues due to spectral bleaching. In the presence of air, material removal is incomplete even for high-energy densities and long exposures. The ablation rate is shown to be independent of substrate material both above and below threshold.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  12. 12
    Nieman, George C. ; Colson, Steven D. ; Hansen, S. G. ; Luckman, G.

    [S.l.] : American Institute of Physics (AIP)
    Published 1990
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Emission from atomic copper and CuF is characterized in a pulsed dc discharge in CF4/O2/Ar with a copper electrode. Similar emission is seen from neat Ar discharges, provided that a F- (or H2O-) containing plasma has been operated first. Near the electrode surface emissions from CuF and lower-energy states of Cu are observed. In the bulk of the plasma, additional emission is seen from more energetic states of Cu at the end of the pulse. Lifetime and energy considerations suggest that much of the Cu emission seen in Ar plasmas may arise from collisions between argon metastables and some molecular species, such as CuF.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  13. 13
    Hansen, S. G.

    [S.l.] : American Institute of Physics (AIP)
    Published 1989
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Velocity distributions of molecular species ejected by ∼80 mJ/cm2, 266-nm laser ablation of polycarbonate, polyimide, poly(ethylene terephthalate), and poly(α-methylstyrene) are presented and discussed. Time-of-flight mass spectroscopy in conjunction with both 248- and 193-nm laser ionization was used to probe the escaping vapor. Up to three distinct waves of material pass through the ionization zone. The fastest wave (6–8×105 cm/s) appears to consist of highly degraded species such as C3; the arrival profiles are well fit by a velocity offset Maxwell–Boltzmann distribution with offsets typically 3–6×105 cm/s and transverse temperatures above 10 000 K. The second wave has a characteristic velocity of 1–2×105 cm/s, and, except with the poly(α-methylstyrene) target, the associated material is not cleanly ionized to parent ions under our typical conditions. It is hypothesized that this wave consists of hot, fairly heavy (up to a few hundred amu) radicals. The slow wave (2–5×104 cm/s) is composed of stable molecules which do not readily condense on the chamber walls. Its arrival profile is too broad to be described by a simple Maxwell–Boltzmann velocity distribution. A mechanism involving a thermal velocity distribution combined with laser-associated background vapor might explain the broad profiles. Problems related to the largely unknown and highly variable ionization cross sections of diverse organic molecules with 193- and 248-nm light are briefly discussed.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses
  14. 14
    Hansen, S. G.

    [S.l.] : American Institute of Physics (AIP)
    Published 1989
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The material ejected into vacuum by 266-nm pulsed laser ablation of poly(α-methylstyrene) (PαMS), polycarbonate, poly(ethylene terephthalate), polybenzimidazole, and polyimide is examined using time-of-flight mass spectroscopy with both 193- and 248-nm ionization. PαMS is well behaved in that the primary ejected species are based on the monomer, and intact units ranging up to trimer are observed. The other four polymers show two distinct waves of material passing through the ionization zone: a fast wave (105–106 cm/s) consisting of small bare or nearly bare carbon clusters and a much slower one composed of mainly aromatic fragments in the 128±50 amu range. These species are all smaller than the corresponding monomers and tend to be fairly similar regardless of target material although the spectrum arising from each polymer is unique. It is speculated that the difference in behavior between PαMS and the others relates to the known favorable, thermally induced "unzipping'' which occurs in PαMS; when this low energy decomposition channel is not open, the laser-induced temperature rise is greater, and more severe bond-breaking processes occur. This work supports our previous conclusion that polymer film formation by laser ablation proceeds by a fragmentation/repolymerization mechanism but does not generally identify the film-forming species. As part of establishing the range of molecules our ionization scheme is sensitive to, mass spectra of a number of different permanent organic vapors were taken using 193-, 248-, and 266-nm ionization. These results are also discussed.
    Type of Medium:
    Electronic Resource
    URL:
    Articles: DFG German National Licenses