Flux penetration and a.c. losses in type II superconductors : II. Experiments on Nb-50% Ti

The a.c. behaviour of Nb-50% Ti can be described in terms of the quasi-static Critical State Model. The critical current density jc as a function of position and magnetic induction as well as the Ben(Ba) and Bex(Ba) relations which described the surface screening currents have been determined experimentally with the help of trapezoidal a.c. fields. The results are in agreement with the calculated induced voltage waveforms presented in part I

Conductivity measurements with trapezoidal a.c. magnetic fields

The inductive response of normal metals to trapezoidal a.c. fields is studied theoretically as well as experimentally. A method is presented to determine the conductivity and its magnetic induction dependence from the decay of the induced voltage during periods of constant field. The correctness of the analysis is confirmed by the close agreement between the complete experimental and theoretical voltage waveforms

Deviations from the critical state model observed in niobium

The values of the critical current density of niobium slabs, measured with the help of trapezoidal ac magnetic fields are not in agreement with the critical state model. Extensions of this model are suggested to explain the observed deviation

Flux penetration and a.c. losses in type II superconductors: I. Model calculations

A numerical method is presented which allows the calculation of the a.c. response of type II superconductors under quasi-static conditions for arbitrary jc (B,x), Ben (Ba) and Bex (Ba) relations. Flux distributions, induced voltage waveforms, hysteresis loops and a.c. losses have been calculated. Deviations between experimental results and earlier calculations with respect to a minimum in the a.c. losses are explained by taking into account the finite thickness of the sample and realistic Ben (Ba) and Bex (Ba) relations

The response of metals in trapezoidal magnetic fields

The inductive response of metals to applied fields with trapezoidal time dependence is described for samples with cylindrical geometry and for slabs. The influence of coil effects and magnetoresistance is accounted for but mean free path and surface effects are ignored. Experimental data obtained for tin show a close agreement with the theoretical predictions

Non-isothermal flux penetration in type II superconductors

The development of thermal instabilities in a single niobium crystal has been studied experimentally under various external conditions. The observed flux jump behaviour cannot be explained in terms of existing theoretical models. A new model, taking account of surface currents only, is introduced. The results of model calculations agree well with the experimental results

Vervuld leven na de dood van God

We zijn volledig in de ban van productie en consumptie. Maar brengen persoonlijke prestaties en de bevrediging van begeerten werkelijk voldoening? Of zijn het de enige existentiële oriëntatiepunten die ons nog resten? De dood van God heeft de wereld en het leven van absolute betekenis beroofd. En hoewel de gevolgen daarvan nog altijd niet tot de mensen zijn doorgedrongen, behoren filosofen zich hierom te bekommeren. Want gaat er onder de oppervlakte van onze alledaagsheid geen akelige onbestemdheid schuil? Dit essay verkent de consequenties van de dood van God voor ons bestaan en zoekt daarop een antwoord. Het evalueert Heideggers gedachte van inter-esse en Sloterdijks antropotechnische oefenbegrip als mogelijke oplossingen, concludeert dat beiden afzonderlijk tekortschieten en ontwikkelt vervolgens een eigen antwoord op basis van hun vruchtbaarste ideeën. Wat daarmee wordt voorgelegd is de ge-waar-wording van een vervuld leven door existentiële oefeningen in inter-esse

The response of type H superconductors to trapezoidal magnetic fields

The inductive response of type II superconductors to applied fields with trapezoidal time dependence is described for samples with a slab geometry. An extension of the critical state model which accounts for the observed waveform of the voltage, induced in the pick-up coil, is given. Typical experiments on Nb-slabs with weak pinning and flux flow in fields with both small and large amplitudes are reported

Redistributing the Possible

This thesis shows how Michel Foucault’s critico-historical approach can be used to enable us to stop our ongoing production of economic, ecological and social crises. It argues that the true problem with these crises resides in the constraints on our perception of the ways in which it could be(come) possible for us to stop them. After that, it develops Foucault’s critico-historical approach into an instrument that enables us to displace these constraints