Influence of Grain Size on the Superconductivity of?La1.85Sr0.15CuO4

We study the influence of varying grain size on superconductivity of bulk La_1.85Sr_0.15CuO₄ superconductor. The samples are synthesized by a sol-gel method. The grain size is varied by sintering the samples at various temperatures between 700?°C to 1050?°C. The samples are characterized by X-Ray Diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), resistivity and magnetization measurements. The electrical resistivity measurements revealed considerable lowering of the superconducting transition temperature ( $T_{\mathrm{c}}^{R=0}$ ) and broadening of the transition width (??T _c) with decreasing grain size though the onset of transition temperature ( $T_{\mathrm{c}}^{\mathrm{onset}}$ ) changes only marginally. The magnetic measurements carried out are consistent with each other and scale well with the grain size. Critical current density has been calculated from the magnetization hysteresis, assuming that supercurrents flow throughout the sample as a whole and within the individual grains as well. The observed results have been discussed on the basis of inter- and intra-granular boundary characteristics of high-temperature superconductors (HTSc). It is found that lowering of grain size deteriorates the superconducting properties in general.     

DC and AC susceptibility study of sol–gel synthesized Bi2Sr2CaCu2O8+δ superconductor

We study DC susceptibility along with amplitude and frequency dependence of AC susceptibility of sol–gel synthesized polycrystalline samples of Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) sintered at different temperatures. In particular, it is demonstrated that susceptibility techniques are an effective tool to characterize granular characteristics of high temperature superconductors. The results are discussed in the framework of Bean's critical state model whence the field and temperature dependence of critical current density is determined. Flux pinning force density is calculated and possibility of the pinning mechanisms prevalent in type II superconductors are investigated. Flux creep activation energy is determined in the light of vortex dynamics exhibited by frequency dependence of AC susceptibility. Since polycrystalline samples are granular in nature, we calculated grain volume fraction and separated the contribution of grain and matrix susceptibility from total measured AC susceptibility. We establish that increase in the sintering temperature not only changes the grain morphology but affects the superconducting properties significantly, validating the impact of grain boundaries on superconducting performance of studied Bi-2212 superconductor.     

Places to stay on the move: Software architectures for mobile user interfaces

Architectural design has an important effect on usability, most notably on temporal properties. This paper investigates software architecture options for mobile user interfaces, in particular those for collaborative systems. One of the new features of mobile systems, as compared with fixed networks, is the connection point to the physical network, the point of presence (PoP), which forms an additional location for code and data. This allows architectures that bring computation closer to the users, hence reducing feedback and feedthrough delays. A consequence of using PoPs is that code and data have to be mobile within the network, leading to potential security problems.     

Physigrams: modelling devices for natural interaction

This paper explores the formal specification of the physical behaviour of devices ‘unplugged’ from their digital effects. By doing this we seek to better understand the nature of physical interaction and the way this can be exploited to improve the design of hybrid devices with both physical and digital features. We use modified state transition networks of the physical behaviour, which we call physiograms, and link these to parallel diagrams of the digital state. These are used to describe a number of features of physical interaction exposed by previous work and relevant properties expressed using a formal semantics of the diagrams. As well as being an analytic tool, the physigrams have been used in a case study where product designers used and adapted them as part of the design process.