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  • 1
    Electronic Resource
    Electronic Resource
    An intense lithium ion beam source using vacuum baking and discharge cleaning techniques (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3418-3425 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a high-purity, intense, lithium ion beam source which operates at 500 kV and 120 A/cm2 with pulse widths of 125 ns full width half maximum. The beams were generated using a lithium chloride anode in planar magnetically insulated geometry. We have found that the combination of vacuum baking of the anode at 250 °C followed by the application of 100 W of pure argon, steady-state, glow discharge cleaning reduced the impurity concentration in the beam to approximately 10% (components other than chlorine or lithium were considered impurities). Although the impurities were low, the concentration of chlorine in the 1+ and 2+ charge states was significant (∼25%). The remaining 65% of the beam consisted of Li+ ions. Without the special cleaning process, over half the beam particles were impurities. It was determined that these impurities entered the beam at the anode surface but came originally from material in the vacuum chamber. After the cleaning process, recontamination was observed to occur in approximately 6 min. This long recontamination time, which was much greater than the expected monolayer formation time, was attributed to the elevated temperature of the anode. We also compared the electrical characteristics of the beams produced by LiCl anodes to those generated by a standard polyethylene proton source. In contrast to the polyethylene anode, the LiCl source exhibited a higher impedance, produced beams of lower ion current efficiency and had longer turn on times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349260
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence for spatially indirect recombination in Ga0.52In0.48P (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2780-2787 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In previous work we have identified a near-gap photoluminescence in Ga0.52In0.48P which exhibits a strong dependence of emission energy on excitation intensity ("moving emission'') and correlated its presence and strength to conditions of growth. In this work we extend our investigations to the rise and decay lifetimes associated with the moving and nonmoving components of the emission. The two processes proceed simultaneously at the same energy. For the moving emission, the time constants scale approximately linearly with excitation intensity. Decaying luminescence can, in most cases, be well fitted with one or two exponentials with time constants as long as milliseconds. The rising luminescence is typically slower and in some cases has a nonmonotonic first time derivative. These results are discussed in terms of existing models of the microstructure of ordered Ga0.52In0.48P.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349364
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  • 3
    Electronic Resource
    Electronic Resource
    First-order optimization of multiple magnetic lens systems for transport and focusing of annular ion beams (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5179-5185 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A standard matrix method for tracing rays through an ion optical system is extended to include a recently discovered [W. Z. Liu and F. D. Bechetti, Rev. Sci. Instrum. 60, 1228 (1989)] defocusing solenoidal lens. The results of the matrix approach are shown to correspond with results obtained by numerical integration of particle trajectories through real coil configurations. First-order radial miss distances due to radial divergence of the beam, chromatic aberration of the lens system, and physical extent of the source are compared for one and two lens systems using the matrix formulation. It is demonstrated that a two lens system in a focusing-defocusing arrangement can simultaneously correct to first order for chromatic aberration and beam divergence, producing a better focus for thin annular beams with significant energy spread and divergence. A new calculation of the focal length for the negative solenoidal lens is also included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350225
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  • 4
    Electronic Resource
    Electronic Resource
    The thermal conductivity of isotopically enriched polycrystalline diamond films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 8122-8125 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal conductivity of a chemically vapor deposited (CVD) diamond film containing 0.07% 13C was measured as a function of temperature by ac and dc techniques and compared to CVD diamond with a natural isotopic abundance of 1.07% 13C. Unlike the single-crystal case where a large isotope enhancement effect has been reported, no increase in the thermal conductivity was observed in isotopically enriched CVD diamond films. The absence of an isotope effect in CVD diamond films indicates that a phonon scattering mechanism other than isotope scattering dominates in CVD diamond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347463
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  • 5
    Electronic Resource
    Electronic Resource
    Modeling of two-junction, series-connected tandem solar cells using top-cell thickness as an adjustable parameter (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1890-1895 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretical efficiencies are calculated for two-junction, series-connected solar cells using air mass 1.5 global and direct irradiance spectra. For band-gap combinations previously limited by a low bottom-cell current, thinning of the top cell is shown to result in significant increases in the theoretical efficiencies. The increases are primarily due to increased short-circuit currents, since current matching is achievable. Smaller gains are also seen in the open-circuit voltages of the thinner cells when a low surface-recombination velocity is assumed. Thus, a number of material combinations which previously could only be used in four-terminal configurations can now be considered for series-connected two-junction solar cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347177
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  • 6
    Electronic Resource
    Electronic Resource
    Photoluminescence, photoluminescence excitation, and resonant Raman spectroscopy of disordered and ordered Ga0.52In0.48P (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5163-5172 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ordering in the CuPt structure is known to significantly reduce the band gap of Ga0.52In0.48P as well as induce a number of unusual details in its optical properties, including long, excitation-intensity-dependent lifetimes and an excitation-intensity-dependent emission energy. We report photoluminescence (PL), photoluminescence excitation (PLE), and resonant Raman measurements performed on ordered and disordered Ga0.52In0.48P. The dominant high energy emission process at low temperature in disordered Ga0.52In0.48P is established to be excitonic, but the exciton trapping energy is not unique. PLE from ordered Ga0.52In0.48P shows significant tailing of electronic states into the band gap and a "band edge'' which depends on detection energy. The dominant radiative process in ordered Ga0.52In0.48P is not excitonic. A large increase in the Stokes shift between the absorption edge (band gap) and PL emission peak occurs when the material orders. Hence, low temperature PL is determined to be a particularly poor measure of band gap. Resonant Raman scattering is used to study optical phonons and their coupling to electronic states. We find that the resonance enhancement at the band edge occurs via localized excitons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353792
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  • 7
    Electronic Resource
    Electronic Resource
    Selective resputtering of bismuth in sputtered Bi-Sr-Ca-Cu-O films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3867-3875 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present studies using a dc magnetron in an on-axis configuration to sputter Bi-Sr-Ca-Cu-O films from a composite target. These studies show that bismuth can be preferentially resputtered. The influence of ozone, molecular oxygen, and total pressure on the resputtering of bismuth is investigated and discussed. Ozone, in low concentrations, can dramatically affect the degree of resputtering. By comparing the effects of molecular oxygen and ozone, some insight is gained regarding the possible mechanisms of negative ion formation in the magnetron environment. Based on our results we suggest that molecular oxygen can bring about resputtering primarily by forming O+2, which collides with the target to produce energetic negative oxygen ions. In contrast, ozone may form negative ions by electron impact in the dark space above the target, giving rise to lower-energy negative ions, which can traverse the plasma unneutralized and can be stopped with an applied bias on the sample block. With no added oxidant, negative oxygen ions from the target oxygen may dominate the background resputtering. Similarity is found between our results and those for similar studies on Y-Ba-Cu-O by other workers. Bismuth in Bi-Sr-Ca-Cu-O behaves as barium in Y-Ba-Cu-O with regards to preferential resputtering; furthermore, the response of strontium, calcium, and copper to oxygen in sputtered Bi-Sr-Ca-Cu-O is similar to what is observed for copper in Y-Ba-Cu-O.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349193
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  • 8
    Electronic Resource
    Electronic Resource
    Progress toward a microsecond duration, repetitively pulsed, intense-ion beam for active spectroscopic measurements on ITER : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 332-335 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the design of an intense, pulsed, repetitive, neutral beam based on magnetically insulated diode technology for injection into ITER for spectroscopic measurements of thermalizing alpha particle and thermal helium density profiles, ion temperature, plasma rotation, and low Z impurity concentrations throughout the confinement region. The beam is being developed to enhance low signal-to-noise ratios expected with conventional steady-state ion beams because of severe beam attenuation and intense bremsstrahlung emission. A 5 GW (e.g., 100 keV, 50 kA) 1 μs duration beam would increase the charge exchange recombination signal by 103 compared to a conventional 5 MW beam. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147862
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  • 9
    Electronic Resource
    Electronic Resource
    A Possible Role for Taurine in Osmoregulation Within the Brain (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 51 (1988), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Intracranial microdialysis was used to measure changes in extracellular amino acids within the rat brain during local osmotic alteration of the extracellular micro-environment or during systemic water intoxication. Increased cellular hydration produced by either of these methods was accompanied by a marked increase in extracellular taurine levels without affecting the other amino acids measured. With local osmotic alteration, this increase was osmolarity dependent and reversible. The specificity, sensitivity, and reversibility of the increase in extracellular taurine strongly suggest a functional role in osmoregulation in the brain under normal as well as pathological conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1988.tb01807.x
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  • 10
    Electronic Resource
    Electronic Resource
    Transcription-Independent Activation of Ornithine Decarboxylase Activity by Heparin in Cloned Cerebral Endothelial Cells (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 60 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Heparin, a highly sulfated glycosaminoglycan, is known to be obligatory for long-term endothelial cell cultures; it potentiates the mitogenic activities of endothelial cell growth factors and prolongs the replicative life span of the cells. Here we have shown that besides its growth factor-supportive role, heparin exerts a specific action on cerebral capillary endothelial cells (cECs), unrelated to serum or growth factors, by increasing activity of ornithine decarboxylase (ODC; EC 4.1.1.17) in these cells. For our experiments we have used two different types of cloned cECs: type I cECs, grown in the presence of endothelial cell growth factor and heparin, and type II cECs, usually cultivated without growth factors. Heparin action on ODC activity was shown to be dose dependent within the range of 1–100 μg/ml. Increasing concentrations of or depletion of endothelial cell growth factor from type I cultures had no effect on ODC activity. The increase in enzyme activity was highest after 30 min to 1 h of heparin treatment. As evidenced by northern analysis, the heparin-mediated enhancement of ODC activity was not accompanied by changes of ODC mRNA levels. Studies of DNA replication revealed that in the absence of heparin-binding growth factors, heparin did not affect the proliferative activity of cloned cECs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb03316.x
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