Critical currents in vicinal YBa2_2Cu3_3O7−δ_{7-\delta} films

Most measurements of critical current densities in YBa$_2$Cu$_3$O$_{7-\delta}$ thin films to date have been performed on films where the \textit{c}-axis is grown normal to the film surface. With such films, the analysis of the dependence of $j_c$ on the magnetic field angle is complex. The effects of extrinsic contributions to the angular field dependence of $j_c$, such as the measurement geometry and disposition of pinning centres, are convoluted with those intrinsically due to the anisotropy of the material. As a consequence of this, it is difficult to distinguish between proposed FLL structure models on the basis of angular critical current density measurements on \textit{c}-axis films. Films grown on mis-cut (vicinal) substrates have a reduced measurement symmetry and thus provide a greater insight into the critical current anisotropy. In this paper previous descriptions of the magnetic field angle dependence of $j_c$ in YBa$_2$Cu$_3$O$_{7-\delta}$ are reviewed. Measurements on YBa$_2$Cu$_3$O$_{7-\delta}$ thin films grown on a range of vicinal substrates are presented and the results interpreted in terms of the structure and dimensionality of the FLL in YBa$_2$Cu$_3$O$_{7-\delta}$. There is strong evidence for a transition in the structure of the flux line lattice depending on magnetic field magnitude, orientation and temperature. As a consequence, a simple scaling law can not, by itself, describe the observed critical current anisotropy in YBa$_2$Cu$_3$O$_{7-\delta}$. The experimentally obtained $j_c(\theta)$ behaviour of YBCO is successfully described in terms of a kinked vortex structure for fields applied near parallel to the \textit{a-b} planes.Comment: 10 pages, 12 figures, Submitted to PR

Assessment of flatness and symmetry of megavoltage x-ray beam with an electronic portal imaging device (EPID)

Copyright © 2002 ACPSEM. All rights reserved. The document attached has been archived with permission from the publisher.The input/output characteristics of the Wellhofer BIS 710 electronic portal imaging device (EPID) have been investigated to establish its efficacy for periodic quality assurance (QA) applications. Calibration curves have been determined for the energy fluence incident on the detector versus the pixel values. The effect of the charge coupled device (CCD) camera sampling time and beam parameters (such as beam field size, dose rate, photon energy) on the calibration have been investigated for a region of interest (ROI) around the central beam axis. The results demonstrate that the pixel output is a linear function of the incident exposure, as expected for a video-based electronic portal imaging system. The field size effects of the BIS 710 are similar to that of an ion chamber for smaller field sizes up to 10 x 10 cm2. However, for larger field sizes the pixel value increases more rapidly. Furthermore, the system is slightly sensitive to dose rate and is also energy dependent. The BIS 710 has been used in the current study to develop a QA procedure for measurements of flatness and symmetry of a linac x-ray beam. As a two-dimensional image of the radiation field is obtained from a single exposure of the BIS 710, a technique has been developed to calculate flatness and symmetry from a defined radiation area. The flatness and symmetry values obtained are different from those calculated conventionally from major axes only (inplane, crossplane). This demonstrates that the technique can pick up the "cold" and "hot" spots in the analysed area, providing thus more information about the radiation beam. When calibrated against the water tank measurements, the BIS 710 can be used as a secondary device to monitor the x-ray beam flatness and symmetry.G. Liu, T. van Doorn and E. Beza

Re-theorising the core: a ‘globalized’ business elite in Santiago, Chile

World systems theory continues to be a widely adopted approach in theorisations of the contemporary world economy. An important epistemological component to world systems theory is the metaphor of core-periphery. Recent work within the approach has sought to transcend earlier criticisms of regional conceptions of cores, peripheries and semi-peripheries by an increasing sensitivity to local differences and an increasing emphasis on Wallerstein's original idea of core-periphery as process, operating at all scales in the contemporary world system. However, this paper argues that the core-periphery metaphor currently used by world systems theorists is founded around a restrictively narrow spatial epistemology. Such a narrow epistemology implements the core-periphery metaphor only as something which produces territorial outcomes in the physical world. This paper contends that recent work within the social services, concerned with the globalization debate and issues of spatial epistemology, should inform world systems theory in producing a reformulated spatial understanding of the core-periphery metaphor, embodying a wider conception of space to include abstract social spaces. This argument is developed in the notion that the world economy must also be understood as having a ‘social core’: a transnational diasporic business elite exercising decision-making power over the capitalist world system. The contention is grounded in the presentation of research into a case study of such a ‘globalized’ business elite in the capital city of Chile, Santiago

Lineages and family resemblances: tracing the Italian DC vote after 1994

The Christian Democracy \u2013 Democrazia Cristiana (Dc) constituted the center of gravity in Italian post-war politics. The party collapsed after 1992, due to long-term changes in Italian society and the eruption of the Clean Hands investigation on political corruption. The Dc lost more than half of its vote in the 1994 elections: where did they go? Our answer highlights the effects of modernization and secularization as key causes in regional variations on the Dc vote and on the vote of the parties claiming a lineage from the Dc, either truly Dc-legacy parties (Ppi, Ccd, Cdu, Daisy, Udc), or new comers on the centre-right (Fi and Lega), or finally the last by-products of the party system transformation (Pd and PdL). Second we consider which parties could advocate the more direct lineage from the DC. Finally we analyse the differences in these dynamics as we move from national level to the geopolitical regional level

Votes and Votive Candles: Modernization, Secularization, Vatican II, and The Decline of Religious Voting in Italy: 1953-1992

In this article the traditional interpretation of the relationship between modernization, secularization and vote for religious parties are validated with respect to the Italian case. Such case is of particular relevance because of the centrality of the Catholic religion in the Italian society and politics, and of the domination of the religious party - the Christian Democracy (Democrazia Cristiana \u2013DC) - in the country\u2019s party system. This article analyses the impact on the DC vote of a series of indicators of modernization, and secularization, and of Church organization, over the entire period of the first republic(1953-1992). The uniqueness of this analysis rests on the exceptional detailed and historical data set employed, for the Italian comune (N= 6,140) across this time period. At the end, the analysis confirms the force of the modernization and secularizing factors in depressing the religious vote for the DC, and the countervailing effects , up to a certain point, of the Church organization

Religion, Rurality and Voting: Secularisation, Landownership and Italian Electoral Behaviour, 1953\u20132008

This paper analyses the impact of socioeconomic and religious factors in explaining the long-run electoral decay of the dominant party in Italy\u2019s so-called \u201cFirst Republic\u201d (the Catholic Dc), and the emergence of the regional autonomous Lega Nord-Northern League on the Dc\u2019s debris. On the basis of a unique data set collected by the authors this paper examines: a) the effects of modernization and secularization of the Dc electoral d\ue9nouement with particular reference to the change over time of the religious and rural constituencies, the two main DC reservoir of votes; b) the attraction of former Dc voters by the Lega Nord particularly in the old DC territorial bastion of support, characterized by high religiosity and concentration of direct cultivators. The research demonstrates the relevance and persistence of structures profondes such as religion and rural property in the electoral behaviour over a long span of time ranging from 1953 to 2008

Mu SR investigation of anisotropy and temperature dependence of magnetic penetration lengths in crystals of YBa₂Cu₃O_7-d

Pulsed mu SR measurements on an aligned mosaic of single crystals of YBCO are interpreted in terms of an anisotropic magnetic penetration length arising from currents flowing parallel and perpendicular to the CuO2 planes. At low temperatures a mean penetration depth ( lambda 1 lambda 3)1/2 of 502 nm is reduced from measurements in fields parallel to the ab plane. Relaxation rate measurements for fields at angles up to 24 degrees out of the plane exhibit a marked angular anisotropy. The observed anisotropy implies a ratio of effective masses perpendicular and parallel to the CuO2 planes of at least 30. The values obtained are compared with those obtained by other authors and techniques. A different temperature dependence of the relaxation rate is observed for fields parallel and at 24 degrees to the CuO2 planes.</p