Search

Cathodic electrochromic materials realized by n-type doping of conducting polymers are scarce. Even with limited cases reported in the literature, long-term stability is an urgent problem to be sol...

Neutral perylene bisimides (PBI) are well-known n-type organic semiconductors, with number of challenging electronic properties in their neutral and reduced states. We report the characteristic electronic properties of PBI anionic films. We unexpectedly discovered that pristine PBI dianion film showed p-type character, while oxidized dianion film (dominant neutral state with few radical anions) showed normal n-type semiconductor character based on Seebeck effect measurements. Both kinds of films exhibit high electrical conductivity with a potential for thermoelectric applications. The mechanism of polarity reversal is proposed.

The deformation structure within individual grains of a deformed material is resolved by electron backscattering diffraction. The employed evaluation scheme for local orientation data is illustrated on cold-rolled aluminium. The orientation distribution of each grain is characterized by an averaged orientation spread and its anisotropy; the dependence of both parameters on grain size and grain orientation is discussed. The preferred rotation axis in each grain is determined and shows a dominant orientation spreading around the transversal direction. Characteristic features of the deformation structure (as alternating orientation differences or orientation gradients) are resolved from sign-carrying disorientation angles defined with respect to the preferred rotation axis in each grain. Five components of the dislocation density tensor – corresponding to part of the geometrically necessary dislocation content – are inferred from the local curvatures. The spatially inhomogeneous distribution of the dislocation density offers a new possibility for identifying dislocation boundaries.

The application of composites has been increasing dramatically in aerospace structures recently, for example, composites have contributed over 50 % of the structure mass of large transport airplanes. However, the further usage has been restricted because of the high material and manufacturing costs. Hence, it is essential to utilise cost estimation tools for accurate cost estimation in the early design stages, and then efficient decisions and design optimisations could be made to reduce the cost of composite products. A cost modelling system has been developed for aerospace CFRP composites, which can help designers and cost engineers to estimate the manufacturing cost in early development stages. The system consists of several modules: material selection, process planning, cost estimation, cost reporting and a user friendly interface. Moreover, the selection and planning modules are combined with databases, including material and process.

A type of planar magnetic metamaterial is proposed with a square winding microstructure as a superlens for magnetic resonance imaging (MRI) applications. A direct magnetic field mapping measurement demonstrates that the radio-frequency magnetic field passing through the superlens is increased by as high as 46.9% at the position of about 3 cm behind the superlens. The resonance frequency of the fabricated slabs is found to be in good agreement with the target frequency (63.6 MHz) for a 1.5 T MRI system. MRI experiments with the magnetic superlens show that the intensity of the image and the SNR (signal-to-noise ratio) are both enhanced, implying promising MRI applications of our planar magnetic superlens.

A novel surface plasmon sensor which is constructed with sub-wavelength metal slit arrays deposited on a buffer media layer is proposed. To obtain the maximum resonant transmission, the buffer layer is coated on a glass substrate and the refractive index of the buffer layer is selected close to that of the water environment. Based on rigorous coupled wave analysis, the numerical simulation shows that the resonant transmission is enhanced and the peak mediated by surface plasmon resonance is much sharper due to the buffer layer. Therefore, this surface plasmon sensor with a buffer layer provides an improved measurement precision in biosensing application.

A high channel-count comb filter based on multi-concatenated sampled chirped fiber Bragg gratings (MC-SCFBGs) is proposed and optimally designed by using several chirped gratings with different fundamental grating periods, instead of non-grating sections of SCFBGs. The numerical simulations of the reflection spectra show that the channel spacing and the channel bandwidth in MC-SCFBGs are smaller than those in multi-concatenated chirped fiber Bragg gratings (MC-CFBGs) and that the spectral bandwidth of MC-SCFBGs can be greatly broadened by increasing the cascade number of the grating sections in each sampling period.