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  • Articles: DFG German National Licenses  (15)
  • 2000-2004  (13)
  • 1935-1939  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Collisional effects on spectral line shape from the Doppler to the collisional regime: A rigorous test of a unified model (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 158-166 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The paper presents high resolution Raman investigations of the Q(1) line of H2 in Ar mixture from low density (Doppler regime) to high density (collisional regime) analyzed with a unique line shape profile. Measurements are performed by stimulated Raman gain spectroscopy between 300 and 1000 K in a wide density range (from 0.2 to 11 amagat). All the observed spectral features are accurately described by a unified model recently proposed by two of the authors. This model accounts for a velocity-memory process, not restricted to the usual hard and soft limits. It also includes correlation between velocity- and phase-changing collisions. An exhaustive analysis of various possible mechanisms on the line shape is achieved. These mechanisms are the Dicke narrowing, the radiator speed dependence of the collisional broadening and shifting parameters, the collisionally induced speed-class exchange and the nonimpact effect. The present test shows the high consistency of the unified model, since it allows one to get a remarkable agreement with all the data by using a unique set of parameters. This model should be useful for optical diagnostics at moderate density, as required for combusting media or atmospheric work. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480570
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  • 2
    Electronic Resource
    Electronic Resource
    Speed-dependent line profile: A test of a unified model from the Doppler to the collisional regime for molecule–molecule collisions (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4951-4956 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A speed-dependent line profile combining soft and hard fully correlated Dicke-narrowing collisions was recently successfully tested on Ar-broadened H2 spectra in a wide density and temperature range. A further test for mixtures of H2 in nitrogen molecules (instead of Ar atoms) is presented. This test is also based on high resolution Raman investigation of the isotropic Q(1) line of H2 from low to high density at various temperatures. The same consistency of the speed-dependent line profile as for H2–Ar is obtained for H2–N2 through a remarkable agreement with all the data by using a unique set of four parameters (the collisional width and shift, the kinetic frequency, and a characteristic velocity memory parameter). The present study is a preliminary step for the hydrogen CARS thermometry in H2–air flames at high pressure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287824
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  • 3
    Electronic Resource
    Electronic Resource
    Expression of IFNγ, coexpression of TNFα and matrix metalloproteinases and apoptosis of T lymphocytes and macrophages in granuloma annulare (2000)
    Springer
    Archives of dermatological research 292 (2000), S. 384-390 
    Details
    ISSN: 1432-069X
    Keywords: Key words Granuloma annulare ; Cytokine ; Apoptosis ; Lymphocytes ; Macrophages
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Granuloma annulare, a prototype noninfectious granulomatous dermatitis, is morphologically characterized by a necrobiotic core surrounded by a cellular infiltrate. Because of many morphological similarities to tuberculosis, granuloma annulare has been suggested to represent a delayed-type hypersensitivity (Th1) reaction in the course of which inflammatory cells elicit matrix degradation. In the present study we (1) investigated the expression of interferon-Á as the most important Th1-associated cytokine, (2) sought in situ evidence for the coexpression of the proinflammatory cytokine tumor necrosis factor-· and cytokine-regulated matrix metalloproteinases 2 (gelatinase A) and 9 (gelatinase B), and (3) sought to determine whether shrunken cells seen within necrobiotic areas of granuloma annulare are apoptotic cells. In situ hybridization combined with immunofluorescence showed that large numbers of infiltrating CD3+ lymphocytes express interferon-Á. Application of catalyzed signal amplification in immunodetection revealed that the vast majority of CD3+ lymphocytes and CD68+ macrophages contained tumor necrosis factor-·. Immunohistochemistry demonstrated that macrophages producing tumor necrosis factor-· coexpress matrix metalloproteinases 2 and 9. In situ end-labeling combined with immunofluorescence detected few apoptotic T cells in perivascular regions and numerous apoptotic macrophages within necrobiotic areas. These results suggest that in granuloma annulare interferon-Á+ Th-1 lymphocytes may cause a delayed-type hypersensitivity reaction whereby macrophages are differentiated to aggressive effector cells expressing tumor necrosis factor-α and matrix metalloproteinases. In parallel, activation-induced apoptosis in lymphocytes and macrophages may serve to restrict the destructive potential of the inflammatory cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004030000150
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of charge-density-wave depinning on the low frequency shear compliance of NbSe3 (2001)
    Springer
    The European physical journal 24 (2001), S. 425-429 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 71.45.Lr Charge-density-wave systems – 72.15.Nj Collective modes (e.g., in one-dimensional conductors) – 62.30.+d Mechanical and elastic waves; vibrations – 62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We report on measurements of the voltage dependence of the complex shear compliance of two crystals of the charge-density-wave (CDW) conductor NbSe3, for torsional frequencies between 1 Hz and 71 Hz. For both samples, there is a frequency independent, ∼1% increase of the magnitude of the compliance when the voltage exceeds the threshold for CDW depinning, but the internal friction has a striking sample dependence which we do not understand. For one sample, there is a frequency independent decrease in internal friction with CDW depinning, suggesting that the elastic changes are not relaxational and might reflect changes in the screening of the crystal strain by the CDW. For the second sample, the sign and magnitude of the change in internal friction is strongly frequency dependent, which we associate with a change in screening due to the finite electron diffusion time. The second sample also exhibits a frequency dependent peak in internal friction near threshold that may reflect relaxation of the CDW phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s10051-001-8694-1
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  • 5
    Electronic Resource
    Electronic Resource
    Doping-dependent electronic structure of cuprates studied using angle-scanned photoemission (2000)
    Springer
    The European physical journal 18 (2000), S. 215-225 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 79.60.-i Photoemission and photoelectron spectra - 74.25.Jb Electronic structure - 71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Full k -maps of the electronic structure near the Fermi level of differently doped cuprates measured with angle-scanned photoelectron spectroscopy are presented. The valence band maximum of the antiferromagnetic insulator Sr2CuO2Cl2, which is taken as a representative of an undoped cuprate, and the Fermi surfaces of overdoped, optimally doped and underdoped Bi2Sr2CaCu2O8+δ high-temperature superconductors are mapped in the normal state. The results confirm the existence of large Luttinger Fermi surfaces at high doping with a Fermi surface volume proportional to (1+x), where x is the hole concentration. At very low doping, however, we find that this assumption based on Luttinger's theorem is not fulfilled. This implies a change in the topology of the Fermi surface. Furthermore the intensity of the shadow bands observed on the Fermi surface of Bi2Sr2CaCu2O8+δ as a function of the doping is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070051
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  • 6
    Electronic Resource
    Electronic Resource
    Hydrogen CARS thermometry in H2–N2 mixtures at high pressure and medium temperatures: influence of linewidths models (2000)
    Springer
    Applied physics 70 (2000), S. 447-454 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 33.20; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. In order to improve the accuracy of H2 CARS thermometry, H2 Q-branch CARS spectra have been recorded for various H2–N2 mixtures in a high-pressure cell at different pressures and temperatures (up to 40 bar and 875 K). Due to the low spectral resolution of broadband CARS experiments, the relevant spectral lineshape factor is the linewidth ratio Γ(Q(3))/Γ(Q(1)), since Q(1) and Q(3) are the most intense lines of the Q-branch spectrum in this temperature range. For the first time, the speed-inhomogeneous effects are accounted for in the simulation of the CARS profiles. The evaluated temperatures are in good agreement with reference values obtained by thermocouples. The specific role on the accuracy of H2 CARS thermometry of the speed inhomogeneity is carefully analyzed, in connection with the influence of the nitrogen concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003400050071
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  • 7
    Electronic Resource
    Electronic Resource
    Optical evidence for the proximity to a spin-density-wave metallic state in $\mathsf{Na_{0.7}CoO_2}$ (2004)
    Springer
    The European physical journal 40 (2004), S. 231-234 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present the optical properties of Na0.7CoO2 single crystals, measured over a broad spectral range as a function of temperature (T). The capability to cover the energy range from the far-infrared up to the ultraviolet allows us to perform reliable Kramers-Kronig transformation, in order to obtain the absorption spectrum (i.e., the complex optical conductivity). To the complex optical conductivity we apply the generalized Drude model, extracting the frequency dependence of the scattering rate ( $\Gamma$ ) and effective mass (m *) of the itinerant charge carriers. We find that $\Gamma(\omega)\sim \omega$ at low temperatures and for $\omega 〉 T$ . This suggests that Na0.7CoO2 is at the verge of a spin-density-wave metallic phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2004-00275-9
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  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopic and dc-transport investigations of the electronic properties of $\mathsf{TaSe_{3}}$ (2004)
    Springer
    The European physical journal 39 (2004), S. 433-440 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. TaSe3 belongs to a class of low-dimensional materials characterized by the interplay and competition between dimensionality crossover and broken symmetry ground states. A comprehensive study by dc-transport, optical, and angle-resolved photoemission (ARPES) experiments shows that the electronic properties of this compound are strongly anisotropic between the chain and the transverse crystallographic direction. Even though TaSe3 fails to undergo a charge-density-wave (CDW) phase transition, we found evidence for short range order CDW segments, which progressively disappear with decreasing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2004-00214-x
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  • 9
    Electronic Resource
    Electronic Resource
    Infrared spectroscopy of tetrahedral quantum spin systems Cu $\mathsf{_2}$ Te $\mathsf{_2}$ O $\mathsf{_5}$ X $\mathsf{_2}$ (X = Br and Cl) (2004)
    Springer
    The European physical journal 38 (2004), S. 65-70 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Cu2Te2O5X2, with X = Br and Cl, are spin-tetrahedral systems displaying magnetic ordering at low temperatures. We have performed optical reflectivity measurements over a broad spectral range as a function of temperature and magnetic field. We have identified the resonance frequencies of the infrared optically active phonon modes and estimated the value of the electronic gap in both tellurate compounds. No variation of the spectra has been observed while crossing the magnetic ordering transition temperature or by applying a magnetic field. The implications of these findings are discussed in relation to the nature of the phase transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2004-00100-7
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  • 10
    Electronic Resource
    Electronic Resource
    Gefäßchirurgie – Quo vadis? (2000)
    Springer
    Gefässchirurgie 5 (2000), S. 1-3 
    Details
    ISSN: 1434-3932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010569
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