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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5052-5054 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of the specific heat in the temperature range 2–300 K are presented for La2−xSrxCuO4 at selected values of doping: x=0.01, 0.025, 0.05, 0.1, and 0.2. Peaks are found in correspondence to the onset of long-range magnetic order, in good agreement with nuclear-quadrupole-resonance and muon-spin-resonance results. A contribution due to the excitation spectrum of the holes introduced by Sr substitution is observed for x=0.025 and 0.05. These results are compared with the predictions of a simple model.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 61 (1979), S. 375-387 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effect of charge exchange reactions: carbon ions with neutral hydrogen and carbon ions with neutral helium, on carbon ionization equations is analysed. Both, optically thin and optically thick, photoionization models for the line emission region of QSOs are considered. From the computed line intensities it is suggested that the charge exchange mechanism should be included in future models.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1743-1753 
    ISSN: 0392-6737
    Keywords: Superconducting materials (excluding high-T c cuprates) ; Nuclear magnetic resonance and relaxation ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary An overview on some works recently carried out by means of pulsed NMR-NQR experiments is given. The choice of the arguments is aimed at providing a flash on the topics and phenomena most tipically studied with the afore-mentioned approach: from the antiferromagnets (AF) precursors of high-temperature superconductors upon charge and spin doping (such as CuO-doped Li, La2CuO4-doped Sr and Zn) to the doping regime leading to superconductivity in LASCO and YBCO with the related issues involving the comparison with the Fermi-liquid behaviour, the possible opening of a pseudo-spin-gap aboveT c and the anisotropy and field effect ratios belowT c, the latter also in relation to thes-wave ord-wave orbital coupling. Finally, the topic of the motions of the flux lines in YBCO is addressed, in particular by discussing some experiments based on spin-echo dephasing due to thermal excitations and in the presence of d.c. currents and pulsed magnetic fields.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 2 (1983), S. 1019-1032 
    ISSN: 0392-6737
    Keywords: Nuclear magnetic resonance and relaxations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si è spesso assunto che la relazione tra mobilità e risposta NMR dell'acqua nei sistemi biologici (ossia eterogenei dinamicamente in quanto composti da fasi liquide e fasi solide) sia esprimibile mediante le equazioni di rilassamento di Bloembergen-Purcell-Pound (BPP). Però l'uso della teoria BPP richiede la presenza di un sistema tridimensionale, infinito ed isotropo. In questo lavoro si mostra che la mera presenza di superfici solide può far comparire andamenti «alla solido» nella risposta NMR di un liquido la cui dinamica microscopica non è mutata dall'interazione con le superfici. Alcuni di questi effetti «topologici» delle superfici si possono ricondurre alle anomalie della bassa dimensionalità che, da alcuni anni, sono investigate attivamente. L'ordine di grandezza degli effetti «topologici» è stimato per geometrie semplici ed un lavoro, a questo collegato, effettua un confronto tra teoria ed esperimento.
    Abstract: Резюме Предполагается, что существует простое соотношение мечду динамикой воды в гетерогенных системах и ЯМР откликом. Это соотношение обычно выражается с помощью уравнений Бломбергена-Пурселя-Паунда для релаксации и фазовой модели. Однако, использование теории Бломбергена-Пурселя-Паунда предполагает, что движения происходят в изотропном, бесконечном и трехмерном пространстве. Показывается, что наличие твердых поверхностей является причиной появления твердоподобных особенностей в ЯМР отклике жидкости, даже в том случае, если поверхности непосредственно не влияют на динамику. Некоторые из этих «топологических» или «непрямых» поверхностных эффектов являются аналогичными эффектам низкой размерности. Оценивается порядок величин этих эффектов для простых геометрий. В следующей статье проводится сравнение полученных результатов с экспериментом.
    Notes: Summary A simple relationship has been thought to exist between the dynamics of water in heterogeneous (liquid-solid) systems and the NMR response. This relationship is usually expressed by the Bloembergen-Purcell-Pound (BPP) equations for relaxation and the phase model. However, a requirement for the use of the BPP theory is that motions take place in an isotropic, infinite and three-dimensional space. It is shown that the mere presence of solid surfaces causes the appearance of solidlike features in the NMR response of the liquid even if its dynamics is directly affected by the surfaces. Some of these «topological» or «indirect» surface effects are of the same kind as the low-dimensionality effects. Their order of magnitude is estimated for simple geometries and by treating the liquid motion in a hydrodynamic approximation. Comparison with the experiment is carried on in a companion paper.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 2 (1983), S. 1033-1049 
    ISSN: 0392-6737
    Keywords: Nuclear magnetic resonance and relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Qui si presenta una ricerca sperimentale sulla risposta NMR dell'acqua nel gastrocnemio di rana. I dati sono discussi sulla base dei modelli di «spazio ristretto», sv-. luppati in un lavoro precedente, i quali suppongono l'esistenza di una sola fase d'acquai Alcune caratteristiche della risposta NMR si possono facilmente spiegare con questi modelli, mentre altre mostrano l'esistenza di piú di una «fase» di acqua. Un lavoro di reinterpretazione di dati NMR è stato fatto esaminando lavori condotti su sistemi biologici e modello. Se ne trae il suggerimento che è spesso piú conveniente interpretali dati in termini di una sola specie acquosa, con mobilità media minore di quella della H2O libera, piuttosto che in termini di molte fasi, la caratterizzazione delle quali è piú che mai incerta.
    Abstract: Резюме Предлагаются экстенсивные исследования ЯМР отклика воды в мускульной ткани. Наши данные сравниваются с результатами, полученными в предыдущей работе, в которой развита «клеточная модель», предполагающая существование одной фазы воды. С помощью этих «клеточных моделей» легко объясняются некоторые особенности ЯМР отклика. Однако, другие особенности указывают на существование других фаз воды. Проводится анализ ЯМР данных для биологических и модельных систем, изученных в литературе. Мы предполагаем, что в большинстве случаев наиболее подходящей является интерпретация ЯМР данных в терминах одной фазы воды со средней подвижностью, соответствующей подвижности свободной воды, а не в термиаах несклльких фаз.
    Notes: Summary An extensive investigation of water NMR response in the muscular tissue (frog gastrocnemius) is presented. Our data are compared with the predictions of the «cage models» (discussed in a companion paper), which envisions a single water phase subjected to topological constraints. Several features of the NMR response are easily accounted for by the cage models. Instead, other features give clear evidence for the existence of different phases of water. We performed also an analysis of NMR data for biological and model systems studied in the literature. We suggest that, in most cases, it is more appropriate to interpret NMR data in terms of a single water phase with an average mobility somewhat reduced with respect to that of free water, rather than in terms of several ill-characterized phases.
    Type of Medium: Electronic Resource
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