Normal state properties of high angle grain boundaries in (Y,Ca)Ba2Cu3O7-delta

By lithographically fabricating an optimised Wheatstone bridge geometry, we have been able to make accurate measurements of the resistance of grain boundaries in Y1-xCaxBa2Cu3O7-d between the superconducting transition temperature, Tc, and room temperature. Below Tc the normal state properties were assessed by applying sufficiently high currents. The behaviour of the grain boundary resistance versus temperature and of the conductance versus voltage are discussed in the framework charge transport through a tunnel barrier. The influence of misorientation angle, oxygen content, and calcium doping on the normal state properties is related to changes of the height and shape of the grain boundary potential barrier.Comment: 17 pages, 1 table, 5 figures, submitted to PR

Mobile π−\pi-kinks and half-integer zero-field-like steps in highly discrete alternating 0−π0-\pi Josephson junction arrays

The dynamics of a one-dimensional, highly discrete, linear array of alternating $0-$ and $\pi-$ Josephson junctions is studied numerically, under constant bias current at zero magnetic field. The calculated current - voltage characteristics exhibit half-integer and integer zero-field-like steps for even and odd total number of junctions, respectively. Inspection of the instantaneous phases reveals that, in the former case, single $\pi-$kink excitations (discrete semi-fluxons) are supported, whose propagation in the array gives rise to the $1/2-$step, while in the latter case, a pair of $\pi-$kink -- $\pi-$antikink appears, whose propagation gives rise to the $1-$step. When additional $2\pi-$kinks are inserted in the array, they are subjected to fractionalization, transforming themselves into two closely spaced $\pi-$kinks. As they propagate in the array along with the single $\pi-$kink or the $\pi-$kink - $\pi-$antikink pair, they give rise to higher half-integer or integer zero-field-like steps, respectively.Comment: 7 pages, 8 figures, submitted to Supercond. Sci. Techno

Korte mededeling

Leucojum aestivum L. In het verspreidingskaartje van het genus Leucojum (Gorteria 2, no. 12, p. 152) is het areaal van L. aestivum gearceerd aangegeven. Niet gearceerd zijn de Balearen en Sardinië, waar L. aestivum L. var. pulchellum (Salisb.) Fiori voorkomt. Deze gebieden zijn binnen het areaal van het genus Leucojum wit gelaten, omdat niet met zekerheid kon worden vastgesteld, dat L. pulchellum Salisb. inderdaad moet worden beschouwd als een variëteit van L. aestivum. Mocht dit zo zijn, dan heeft het gearceerde deel van het verspreidingskaartje betrekking op L. aestivum L. var. aestivum

Arenaria serpyllifolia L. var. macrocarpa Lloyd in Nederland niet eerder herkend

The first attention to Arenaria serpyllifolia var. macrocarpa in the Netherlands is paid in 1980, as the editors of Atlas Florae Europaeae asked for data of this neglected taxon. Dr. F.H. Perring (Oundle, Great-Britain) kindly controled the determinations of specimens of 'macrocarpa' in the collections of the Rijksherbarium (Leiden). The taxon only occurs in the coastal area of the Netherlands (fig. i). The differences of the infraspecific taxa of Arenaria serpyllifolia are given (table i). Awaiting 'closer study to clear up the taxonomical delimination and the range of this coastal ecotype' (Jalas & Suominen, 1983), the taxon has been considered subsp. serpyllifolia var. macrocarpa. closely related to var. serpyllifolia

Boekaankondigingen

* Anonymus, Veldbiologische waarnemingen op het landgoed Schothorst bij Hoogland in 1985 en 1986, Centrum voor Natuur en Milieu van de Gemeente Amersfoort, Schothorsterlaan 3a, 3828 NT Hoogland, 1987, 25 pag. * Anonymus, Naar een groenere binnenstad, groenplan voor de binnenstad van Den Haag, Dienst Groenvoorzieningen en Milieueducatie, Den Haag, 1987, 48 pag