1,720,994 research outputs found
Una concezione capitalistica della modernità: Ivan Kondrat'evič Babst sullo sviluppo della Russia (1852 - 1861)
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Electrical anisotropy in high-Tc granular superconductors in a magnetic field
Full text linkWe propose an analytical model devoted to explain the anisotropy of the electrical resistance observed below the critical temperature in granular high-Tc superconductors submitted to a magnetic field H. Reported experimental results obtained on a YBCO sample show that the superconducting transition occurs in two stages, with a steep drop of the resistance at Tc and a subsequent, smoother decrease. In this second stage, the resistance versus temperature curve is strongly dependent not only on the field intensity, but also on the angle between H and the macroscopic current density j. We start from the assumption that the resistance below Tc is mainly due to the weak links between grains. In the model, weak links are thought of as flat surface elements separating adjacent grains. We calculate the probability for a weak link to undergo the transition to the resistive state as a function of the angle it makes with the external magnetic field H and the macroscopic current density j. In doing this, an important role is given to the strong nonuniformity of the local magnetic field within the specimen, due to the effect of the screening supercurrents flowing on the surface of the grains. Finally, we calculate the electrical resistance of the sample in the two cases H⊥j and H∥j. The predictions of this simple model turn out to be in reasonable agreement with reported experimental results obtained on a YBCO granular specimen
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Barkhausen-like conductance noise in polycrystalline high-Tc superconductors immersed in a slowly varying magnetic field
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MAGNETORESISTIVE THICK-FILM SENSOR FOR LINEAR DISPLACEMENTS
No full textA new thick film material has been developed starting from Ni and Co powders in the ratio Ni:Co=3:1. The thermal treatment (in N,, up to 950 degrees C) of the metal films deposited on glazed alumina enables the in situ formation of the NiCo alloy. The films as created exhibit a high longitudinal (current I parallel to the field B) magnetoresistive response with Delta R/R approximate to 4% at 1.2 kGauss, and a negligible transverse one. The temperature coefficient of resistance (TCR) is approximate to 2700 ppm degrees C-1. These properties make the new material superior, from the point of view of magnetoresistive applications, to the Ni-based currently available thick film conductors. Contactless sensors for linear displacements have been created with the sensor's structure enclosing either Ni-based and Ni/Co-based meanders, having two magnetoresistive elements on each side of the substrate. This paper compares the magnetoresistive and thermoresistive properties of Ni and Ni/Co-based layers as well as the performances of the sensors in the range -20 to 120 degrees C
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