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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9642-9647 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational overtone excitation followed by laser-induced fluorescence (LIF) interrogation determines state-to-state rotational and vibrational relaxation rates of highly energetic acetylene molecules by argon. We initially excite a single rotational state of the vibration 3ν3 (three quanta of C–H stretch, Evib=9640 cm−1) and detect the state (3ν3, Jf=20) in rotational relaxation measurements or the state (ν1+ν2+ν3+2ν4, l=0, Jf=4) in vibrational relaxation measurements. The data, which we acquire under single-collision conditions, show that argon rotationally relaxes acetylene almost half as efficiently as acetylene itself but is relatively inefficient in vibrational relaxation. © 1994 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6079-6085 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron stimulated desorption (ESD) of fragment ions in the energy range between 0 and 18 eV from SF6 adsorbed on rare-gas films (Kr, Xe) is reported. The ESD results are compared with previous experiments on dissociative electron attachment (DA) to gas-phase SF6. At energies characteristic for the respective rare-gas substrate strong resonant enhancements in the ESD yield of F− are observed. This enhancement is explained by the appearance of an "electron–exciton complex" in the rare-gas film (the analogue to the anionic Feshbach resonances in single atoms) which couples to the first dipole allowed excitation of the SF6 molecule. After electron and energy transfer, the highly excited SF6*− ion dissociates at the surface resulting in the desorption of F− fragments. At low electron energies (in the range from 0 to 0.6 eV) charging of the rare-gas film covered with SF6 is observed. From these experiments a charging cross section of 2.1(±1.8)×10−15 cm2 is derived. © 1998 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3472-3478 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the first photoacoustic absorption spectra of higher C–H stretching overtones in formaldehyde up to the visible spectral region. The analysis of the coarse rotational structure on the basis of asymmetric rotor simulations provides band centers up to the fifth overtone (vCH=6). A two dimensional normal coordinate model for the C–H stretching degrees of freedom explains the observed polyad structure of the spectrum using ab initio (MP2/6-311G**) potential energy and electric dipole functions. The observed intensity distribution reflects the increasing local mode character of higher overtone wave functions within the normal coordinate subspace. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 729-731 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that doping of the transport layers can strikingly improve the properties of organic light emitting diodes (OLEDs). The electroluminescence onset voltage of diodes containing an vanadyl–phthalocyanine (VOPc) hole transport layer intentionally doped with tetrafluorotetracyano-quinodimethan (F4-TCNQ) is reduced by up to an order of magnitude compared to OLED with undoped VOPc. The improved properties of our devices can be explained by the improved conductivity and better injection for a doped transport layer. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3202-3204 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the doping of vanadyl–phthalocyanine by a fluorinated form of tetracyano-quinodimethane as an example of controlled doping of thin organic dye films by cosublimation of matrix and dopant. The electrical parameters of the films derived from conductivity and Seebeck measurements show that the results largely follow standard models used to describe the doping of crystalline semiconductors; e.g., a smooth shift of the Fermi level towards the valence states with increasing doping is observed. Other effects, like the superlinear increase of conductivity with the molar doping ratio, need the inclusion of additional effects like percolation. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 661-664 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a Monte Carlo study of hole transport in AlxGa1−xAs, In1−xAlxAs, and GaAsxSb1−x. The effects of alloy scattering are significant in all three cases, but mobilities are still high enough to be advantageous in particular device applications. We separately calculate the Hall r factors by a Boltzmann transport method and show that these factors are vitally important when attempting to compare Monte Carlo drift mobilities with experimental Hall data. © 1995 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3578-3584 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The extent of relaxation and orientation of linearly graded InxAl1-xAs (x=0.05–0.25) buffers grown on GaAs were examined using a novel x-ray diffraction reciprocal-space mapping technique (kmap). Samples were grown at temperatures ranging from 370 to 550 °C. The fractional relaxation of the buffers grown between 470 and 550 °C was essentially identical (77%) and symmetric in orthogonal 〈110〉 directions. These buffers are believed to be in equilibrium indicating that the incomplete relaxation is not a kinetic effect. The extent of relaxation was less than that expected for equilibrium relaxation in the absence of dislocation–dislocation interactions indicating that such interactions must be considered to accurately predict the extent of relaxation. The saturation of the relaxation as a function of temperature indicates that at the grading rate used (8% In/μm or 0.69% strain/μm), we are not working in a growth regime where the relaxation is nucleation limited. In addition, all the buffers are slightly tilted with respect to the GaAs substrate about [11¯0] toward the [110] direction suggesting either a bias in the dislocation types in the boule-grown GaAs, or a bias in the way in which α and β dislocations interact with unintentional substrate miscuts. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1721-1728 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New high-pressure shock-wave data have been obtained for W and Mo. These data have been combined with previous data sets for these materials to extend the range of linear us–up fits for the Hugoniot to 480 GPa for Mo and 680 GPa for W. The shock-wave data, supplemented by the necessary thermodynamic information, have been used to generate several isotherms (100, 200,...1000 K). Tables of pressure versus relative volume up to 380 GPa suitable for comparison with statically obtained data are given.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6447-6449 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe14Nd2C (Φ) shows structural and intrinsic magnetic properties comparable to Fe14Nd2B. The phase Fe14Nd2C is found in long-time-annealed samples only ((approximately-greater-than)20 d at 850 °C) because of nucleation difficulties and slow growth kinetics. Compared to the Fe-Nd-B system the phase relations in the Fe-Nd-C system are unfavorable to produce sintered or even as-cast magnet materials, as manifested in the phase diagram presented. Fe14Nd2C is in equilibrium with either ferromagnetic and/or very corrosive phases, therefore the pure Fe-Nd-C material is useless. This situation can be changed by the addition of several elements to the Fe-Nd-C material: boron (even in small amounts of ≈0.05 mass %) accelerates the formation of Φ and reduces annealing times from weeks to hours; Cu added in the correct amount leads to new phase relations between Φ and NdxCuy intermetallic compounds. These intermetallics are nonmagnetic and low melting. Starting from as-cast material using the knowledge about the influences of substituants on phase relations and kinetics, a heat treatment can be chosen that leads directly to an isotropic, magnetically hard material with a rather small grain size ((approximately-less-than)20 μm) and coercivities up to 1 T. The magnetization is comparable to isotropic Fe-Nd-B materials.
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  • 10
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent results are presented from two-dimensional LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasmas Phys. Controlled Thermonucl. Fusion 2, 51 (1975)] calculations of the indirectly driven hohlraum and ignition capsules proposed for the National Ignition Facility (NIF). The calculations concentrate on two capsule designs, the baseline design that has a bromine-doped plastic ablator, and the beryllium design that has a copper-doped beryllium ablator. Both capsules have a cryogenic fuel layer. Primary emphasis in these calculations is placed upon robustness studies detailing various sensitivities. Because of computer modeling limitations these studies fall into two categories: those performed with integrated modeling where the capsule, hohlraum, and laser rays all are modeled simultaneously with the laser power levels as the only energy input; and those performed in a capsule-only mode where an externally imposed radiative flux is applied to the exterior of the capsule, and only the capsule performance is modeled. Integrated modeling calculations address sensitivities to, e.g., the laser pointing; among other things, capsule-only calculations address yield degradation due to the growth of hydrodynamic instabilities seeded by initial surface roughnesses on the capsules. Limitations of the calculational models and directions for future research are discussed. The results of the robustness studies performed to date enhance the authors' confidence that the NIF can achieve ignition and produce 10–15 MJ of capsule yield with one or more capsule designs. © 1996 American Institute of Physics.
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