341 research outputs found
Optical nonlinearity and light-induced structural transformations in gallium nanoparticles
We report that gallium nanoparticles, prepared by light-assisted self-assembly, show a nonlinear response to low-power optical excitation. Reversible reflectivity changes of several percent are induced as the result of light-induced structural transformations in the meta
Electrical and Mechanical Properties of new Recyclable Power Cable Insulation Materials based upon Polyethylene Blends
Chemically crosslinked polyethylene (XLPE) has been used as electrical insulation for power cables since the 1970s due to its favourable combination of electrical and mechanical properties. However, as the electrical engineering community has become increasingly aware of the life cycle environmental impacts, XLPE has come under scrutiny for its lack of recyclability and the high process energies used in its manufacture. Although technologies are being developed to facilitate the re-use of XLPE at the end of its initial service life, the use of this material is inferior to fully recyclable and low process energy alternatives. In this investigation, we concentrated on the use of binary blends of linear and branched polyethylene (LPE / BPE) as potential replacement materials for XLPE, since such systems have the potential to combine comparable mechanical properties and enhanced breakdown strength with good recyclability. We compare the thin film AC ramp breakdown behaviour of blends as a function of temperature up to 97 oC. These consist of the same BPE in virgin and crosslinked states and in a blend with 20wt% LPE. These data are augmented with dynamic mechanical analysis. In concert, these data indicate that with appropriate morphological control the blended thermoplastic material exhibits superior properties to XLPE under conventional operating conditions and may even be suitable for higher temperature operation than XLPE. The paper will discuss the importance of polymer blending and blend physical properties in the context of the process requirements and the implications for cable manufacture and on cable electrical and environmental performance in comparison with XLPE
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Evaluation of the onset of space charge and electroluminescence as a marker for cross linked polyethylene ageing
The aim of the âARTEMISâ project is to investigate the ageing mechanisms for cross-linked polyethylene under thermo-electrical stress and to identify ageing markers, which can be used to carry out diagnostic procedures. A carefully selected set of techniques which can give cross-correlated information on space charge phenomenology and material degradation were used to investigate specimens peeled from reference and aged cables. The paper shows that ageing induces a change in the density and depth of trapping levels, and an increase in the number and size of mesovoids. Interpretation of these results is discussed in terms of physico-chemical modifications, which can affect trap distribution and microstructure
Thermoplastic cable insulation comprising a blend of isotactic polypropylene and a propylene-ethylene copolymer
There is much interest in the development of replacement materials for crosslinked polyethylene (XLPE) that are both recyclable (i.e. thermoplastic) and capable of high temperature operation. Thermally, polypropylene is the ideal choice, although its stiffness and low electrical breakdown strength make for a challenging materials design problem. We report here on the compositional optimization of a propylene homopolymer/propylene-ethylene copolymer blend in terms of its dynamic mechanical properties and thin film electrical breakdown strength. The extrusion of a trial mini-cable using the optimized blend is also discussed, which is shown to exhibit a significantly improved electrical performance, as gauged by its DC breakdown strength, than an XLPE-insulated reference
Two new species of Cyperus (Cyperaceae) from Brazil
Abstract Two new species of Cyperus L. (Cyperaceae), both from Brazil, are described and compared to near relatives. Cyperus hooperae is described from two collections from the Chapada do Veadeiros in the State of GoiĂĄs; it is most similar to C. refractus of the southeastern U.S. Cyperus thomasii is described from a single collection from the municipality of Caruaru in Pernambuco; it is most similar to C. granatensis of Colombia. Following IUCN standards, both are considered threatened
Ultra-fast propagation of Schr\"odinger waves in absorbing media
We identify the characteristic times of the evolution of a quantum wave
generated by a point source with a sharp onset in an absorbing medium. The
"traversal'' or "B\"uttiker-Landauer'' time (which grows linearly with the
distance to the source) for the Hermitian, non-absorbing case is substituted by
three different characteristic quantities. One of them describes the arrival of
a maximum of the density calculated with respect to position, but the maximum
with respect to time for a given position becomes independent of the distance
to the source and is given by the particle's ``survival time'' in the medium.
This later effect, unlike the Hartman effect, occurs for injection frequencies
under or above the cut-off, and for arbitrarily large distances. A possible
physical realization is proposed by illuminating a two-level atom with a
detuned laser
Rapid And Durable Responses With The Syk/Jak Inhibitor Cerdulatinib In A Phase 2 Study In Relapsed/Refractory Follicular LymphomaâAlone Or In Combination With Rituximab
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149541/1/hon30_2629.pd
Magnetic Anisotropy in the Molecular Complex V15
We apply degenerate perturbation theory to investigate the effects of
magnetic anisotropy in the magnetic molecule V15. Magnetic anisotropy is
introduced via Dzyaloshinskii-Moriya (DM) interaction in the full Hilbert space
of the system. Our model provides an explanation for the rounding of
transitions in the magnetization as a function of applied field at low
temperature, from which an estimate for the DM interaction is found. We find
that the calculated energy differences of the lowest energy states are
consistent with the available data. Our model also offers a novel explanation
for the hysteretic nature of the time-dependent magnetization data.Comment: Final versio
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