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  • 1
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Systematic measurements are made of ESR spectra with g ≈ 4.2 in YBa2Cu3O6+y compounds with various doping indices y. Temperature dependences of the spectrum intensity show that the ground states of the centers are singlet and the energies of the excited states M S = ±1 correspond to 8−11 K. In general, the intensity of the ESR spectra varies with time and depends on the sample preparation technology. The most probable models for the paramagnetic centers studied are considered to be chain fragments of copper ions of variable valence. General laws governing the energy structure of these centers are described.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0930-9225
    Keywords: Schlüsselwörter Mammaria – Arteria thoracica interna –¶Koronarer Bypass – Coronare Revaskularisation ; Key words Internal mammary artery – internal thoracic artery –¶coronary revascularization – coronary bypass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Internal mammary artery (IMA) bypass grafts have a satisfactorily long lasting blood supply to the myocardium. Their initial flow capacity can be insufficient with subsequent regional myocardial ischemia. This study represents a feasable surgical method to evaluate the effectiveness of the IMA graft function by temperature measurement of the heart during warm reperfusion after hypothermic cardioplegia. Twenty-five patients with multi-vessel coronary artery disease underwent coronary artery bypass grafting using the IMA as an arterial graft to the left anterior descending coronary artery and saphenous vein grafts to the remaining coronary arteries. Distal anastomoses were installed during cold intermittent blood-cardioplegic arrest. After unclamping the aorta and IMA graft, the temperatures in cardiac front and rear sides were measured during the first five minutes of warm reperfusion. A sufficient IMA graft function was expressed by a typical rise of temperature: The cardiac front and rear sides showed a parabolic and exponential course, respectively. The rewarming speed expressed as the first derivative of temperature over time led to a sharp and early peak for the front side, and a smaller and delayed peak for the rear side. An insufficient IMA graft function could be recognized by atypical temperature courses.
    Notes: Zusammenfassung Die Arteria thoracica interna (Mammaria) hat als Koronarbypass gute Langzeitergebnisse bezüglich der Myokardrevaskularisation. Eine regionale Myokardischämie kann nach Anastomosierung der Mammaria durch einen initial insuffizienten Fluß entstehen. Die vorliegende klinische Studie stellt ein einfaches Verfahren dar, mit dem die Effektivität der Mammaria-Funktion intraoperativ durch Temperaturmessung des Herzens während der warmen Reperfusion nach hypothermer Kardioplegie bestimmt werden kann. Fünfundzwanzig Patienten mit Koronarer Mehrgefäßerkrankung wurden revaskularisiert unter Verwendung der Mammaria auf den ramus interventricularis anterior (RIVA) und Vena saphena magna Bypässe auf die übrigen stenosierten Koronargefäße. Die distalen Anastomosen wurden in hypothermer Blutkardioplegie angelegt bevor die Klemmen der Aorta und der Mammaria gelöst wurden. Während der ersten fünf Minuten warmer Reperfusion wurde die Temperatur der kardialen Vorder- und Hinterwand gemessen. Ein charakteristischer Temperaturanstieg ließ eine gute Mammaria-Funktion erwarten: Die Vorderwand erwärmte sich nach einer parabolischen Funktion über die Zeit, wohingegen die Hinterwand sich nach einer exponentiellen Funktion über die Zeit erwärmte. Die Erwärmungsgeschwindigkeit als erste Ableitung der Temperatur über die Zeit zeigte einen steilen frühen Gipfel an der Vorderwand, während die Hinterwand einen schwachen und verzögert eintretenden Gipfel verzeichnete. Eine insuffiziente Mammaria-Funktion war an einem untypischen Temperaturverlauf zu erkennen.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9605
    Keywords: EPR ; LSCD ; isotope effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The electron paramegnetic resonance (EPR) of Mn2+ doped into La2−x Sr x CuO4 was used to probe the copper spin relaxation via the bottleneck effect for oxygen isotope (16O and 18O)–substituted samples. It was found that the EPR linewidth is larger for the 18O isotope samples than for the 16O samples. For x = 0.03, the linewidth for the 18O sample is larger than for 16O sample by a factor of 2. The isotope effect is pronounced at low temperatures and decreases with increasing Sr concentration. This effect is quantitatively explained by the Cu2+ S = 1/2 spin relaxation to the lattice via Dzyaloshinski terms coupled linearly to the local Q 4/Q 5 tilting modes of the CuO6 octahedra as proposed by Kochelaev et al. [1] The Q 4/Q 5 modes are coupled sterically to the Q 2 Jahn–Teller modes considered to be relevant for the (bi)-polaron formation and thus for the high-temperature superconductivity (HTSC).
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9605
    Keywords: phase diagram ; critical fluctuations ; isotope effect ; polarons ; magnetic torque
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Studies of the critical behavior of high-temperature superconductors (HTSC) show the importance of the strong doping dependence of the effective mass anisotropy γ for the generic (T, x) phase diagram of these materials. A possible microscopic model that can explain the doping dependence of γ is based on polaronic charge carriers. That lattice effects may play a role for high-temperature superconductivity is further supported by measurements of the oxygen-isotope effect on the in-plane penetration depth λ ab (0) in underdoped La2−x Sr x CuO4 single crystals that are reported in this paper. The oxygen-isotope effect on λ−2 ab (0) is found to be around −9% for the samples investigated. It arises mainly from the oxygen–mass dependence of the in-plane effective mass m* ab . The experimental facts presented in this paper suggest that lattice vibrations are important for the occurrence of high-temperature superconductivity.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 13 (2000), S. 895-897 
    ISSN: 1572-9605
    Keywords: EPR ; YBCO ; rare-earth ions ; impurities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The first observation of electron paramagnetic resonance (EPR) of Tb3+ doped into YBa2Cu3O6 is reported. EPR is used to determine the local symmetry of the rare-earth ion and to study the effect of suppression of high-T c superconductivity by doping. The distance between the lowest singlets of Tb3+ ion Δ ≅ 7.1 GHz ≡ 0.24 cm−1 and g-factor g ∥ ≃ 17.9 have been estimated from measurements. Both these parameters are in a good agreement with the corresponding calculated values. No evidence of Tb4+ ions was found.
    Type of Medium: Electronic Resource
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