Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Abstract. The paper presents an analysis of the development of the Tel Aviv metropolis using the concept of fractal. The fractal density of the whole urban ensemble and of its parts was estimated as a function of the time, from 1935 on. The central part and the northern tier is fractal at all times. Its fractal dimension increase with time. However, the whole ensemble can be said to be fractal only after 1985. There is a general tendency toward fractality in the sense that the fractal dimensions of the different parts converge toward the same value. Terms of use: Documents in EconStor may

The electrical and dielectric properties of compression‐molded segregated polyethylene‐carbon black mixtures are described in the frequency range between 10 and 8000 kHz as a function of frequency, temperature, and carbon black loading. The segregated systems investigated exhibit insulator‐conductor transitions in the range 0.25–0.65% (volume/volume) carbon black. The dielectric constant and the dissipation factor of the conductive samples are relatively very high in the frequency range studied. The dielectric constant increased sharply with the carbon black concentration, and then increased moderately beyond the insulator‐conductor transition. The dissipation factor‐concentration curves for different carbon blacks show maximum values in the vicinity of the critical concentration values. The dielectric properties of these systems are discussed in terms of interfacial Maxwell‐Wagner polarization effects.

PACS. 61.41.+e Polymers, elastomers, and plastics, 61.12.-q Neutron diffraction and scattering, 62.20.-x Mechanical properties of solids,

We present microrheology experiments on a series of polysiloxane-type liquid-crystal polymers with mesogen-graft amounts of 25%, 70% and 100%. The experiments, conducted as a function of sample thickness, show that the low-frequency response of all of these polymers shifts progressively from a liquid-type behavior for thick samples (>100 μm) to a purely elastic behavior for thin samples (<20 μm). This surprising change in behavior, which occurs in all phases including the isotropic phase, points to the fact that these polymers do not behave like melts but like gels below their gelation point. Comparison of the results obtained in the nematic and isotropic phases shows that the clusters are not sensitive to the orientational order. The absence of any rubbery plateau (in the case of thick samples) and the simultaneous presence of a low-frequency elastic plateau (in the case of thin samples) are indicative of the existence of temporary knots of a new type, associated with interaction between the mesogens. We also present a confined-geometry percolation model and a model consisting of an association in parallel of the elastic and viscous regions which make up the sample. This latter model offers an explanation of the whole set of results obtained, unlike the percolation model in confined geometry.