Marshall-Peierls sign rule in frustrated Heisenberg chains

We consider the frustrated antiferromagnetic s=1 Heisenberg quantum spin chain with regard to the Marshall-Peierls sign rule (MPSR). By using exact diagonalization data we investigate the breakdown of the MPSR in dependence on frustration and compare our findings with data for s=1/2. We calculate a critical value of frustration J_2(crit) where the MPSR is violated. The extrapolation of this value to the infinite chain limit holds J_2(crit) approx. 0.016, lower than in the case of s=1/2 (J_2(crit) approx. 0.027). This points to a stronger influence of frustration in the case of s=1. Nevertheless the calculation of the weight of the Ising-states violating the MPSR shows that the MPSR holds approximately even for quite large frustration and may be used for numerical techniques.Comment: 4 pages (Latex), 2 Postscript figures, to be published in acta physica polonica A (European Conference 'Physics of Magnetism 99'

'Backbone' of the Orient/East-Med Corridor: Vienna-Bratislava-Budapest-Belgrade Axis

Two corridors leading from northwestern to southeastern Europe - the Orient/East- Med and Rhine-Danube Corridors - are key areas for European spatial development. Moreover, sections of them are of special importance for central and southeast Europe. These sections include: 1) the primary axis of the Orient/East-Med Corridor leading from Vienna/Bratislava across Budapest and Sofia to Thessaloniki, 2) the Orient/ East-Med branch from Vienna/Bratislava across Budapest, Novi Sad, Belgrade and Skopje to Thessaloniki, and 3) the Danube river, from its source in Germany to the Black Sea. The area where these sections overlap includes the metropolitan areas of Vienna, Bratislava, Budapest and Belgrade and serves as a backbone for integrated infrastructure and spatial development along the Orient/East-Med Corridor, with many and varied connections to northern and southern Europe. Metropolitan nodes and infrastructural links along this backbone need to be further developed in a coordinated and strategic way. Current and future aspects of spatial development in the above-mentioned metropolitan cores - with a specific focus on Vienna - are briefly discussed in this contribution.Zwei Korridore, die von Nordwest- nach Südosteuropa führen - die Korridore Orient/ East-Med und Rhein-Donau - sind Schlüsselräume für die europäische Raumentwicklung. Darüber hinaus sind Teilabschnitte für Mittel- und Südosteuropa von besonderer Bedeutung. Zu diesen Abschnitten gehören: 1) die Hauptachse des Orient/East-Med Corridors, die von Wien/Bratislava über Budapest und Sofia nach Thessaloniki führt, 2) der Orient/East-Med-Zweig von Wien/Bratislava über Budapest, Novi Sad, Belgrad und Skopje nach Thessaloniki und 3) die Donau, von ihrer Quelle in Deutschland bis zum Schwarzen Meer. Überschneidungsbereiche dieser Abschnitte umfassen die Metropolregionen Wien, Bratislava, Budapest und Belgrad und sind Rückgrat für eine integrierte Infrastruktur und Raumentwicklung entlang des Orient/East-Med Corridors mit vielfältigen Verbindungen nach Nord- und Südeuropa. Metropolknoten und Infrastrukturverbindungen entlang dieser wichtigen Bereiche müssen koordiniert und strategisch weiterentwickelt werden. Aktuelle und zukünftige Aspekte der Raumentwicklung in den oben genannten Ballungszentren - mit besonderem Fokus auf Wien - werden in diesem Beitrag kurz diskutiert

The anisotropic quantum antiferromagnet on the Sierpinski gasket: Ground state and thermodynamics

We investigate an antiferromagnetic s=1/2 quantum spin system with anisotropic spin exchange on a fractal lattice, the Sierpinski gasket. We introduce a novel approximative numerical method, the configuration selective diagonalization (CSD) and apply this method to the Sierpinski gasket with N=42. Using this and other methods we calculate ground state energies, spin gap, spin-spin correlations and specific heat data and conclude that the s=1/2 quantum antiferromagnet on the Sierpinski gasket shows a disordered magnetic ground state with a very short correlation length of about 1 and an, albeit very small, spin gap. This conclusion holds for Heisenberg as well a for XY exchange.Comment: LaTeX: 16 pages, 9 figures, 1 tabl

The Triangle Metric: Fast Link Quality Estimation for Mobile Wireless Sensor Networks (Invited Paper)

ReSensesuppleCONE