Applicability of the kp method to modeling of InAs/GaSb short-period superlattices

We investigate the long-standing controversy surrounding modeling of the electronic spectra of InAs/GaSb short-period superlattices (SPSLs). Most commonly, such modeling for semiconductor heterostructures is based on the kp method. However, this method has so far failed to predict the band structure for type-II InAs/GaSb SPSLs. Instead, it has systematically overestimated the energy gap between the electron and heavy-hole minibands, which led to the suggestion that the kp method is inadequate for these heterostructures. Our results show that the physical origin of the discrepancy between modeling and experimental results may be the graded and asymmetric InAs/GaSb interface profile. We have performed band-structure modeling within the kp method using a realistic interface profile based on experimental observations. Our calculations show good agreement with experimental data, both from our own measurements and from the published literature. © 2009 The American Physical Society

Magnetic array-templated method for fabrication of polymer nanoporous films

This paper describes the development of a novel method of producing nanoporous polymeric membranes in a cost-effective and reproducible manner. The novelty of the technique hinges on the exploitation of a new type of sacrificial material & structures - self-assembled arrays of magnetic nanoparticles. The arrays are obtained through application of an external magnetic field to a thin layer of colloidal solution of superparamagnetic nanoparticles in a polymerizable monomer; this is followed by photopolymerisation. The resulting columnar structures form the pore templates which when selectively etched away leave an array of nanopores spanning across the polymeric film. The morphological characterisation of the nanopores by scanning electron microscopy and ionic conductivity revealed a very unusual sponge-like pore morphology. The applications which would benefit from the specific pore morphology and arrayed manufacturing are discussed

Small-vocabulary speech recognition using a silent speech interface based on magnetic sensing

This paper reports on word recognition experiments using a silent speech interface based on magnetic sensing of articulator movements. A magnetic field was generated by permanent magnet pellets fixed to relevant speech articulators. Magnetic field sensors mounted on a wearable frame measured the fluctuations of the magnetic field during speech articulation. These sensor data were used in place of conventional acoustic features for the training of hidden Markov models. Both small vocabulary isolated word recognition and connected digit recognition experiments are presented. Their results demonstrate the ability of the system to capture phonetic detail at a level that is surprising for a device without any direct access to voicing information

Electrifying The Fleet : More sustainable propulsion options for the small-scale fishing fleet

Report for, and funded by, National Federation of Fisherman’s Organisations Future Fisheries Alliance (RSPB, MCS, and WWF) North Sea Wildlife Trusts looking at the future of propulsion for small-scale fishing vessels

Evaluation of a silent speech interface based on magnetic sensing

This paper reports on isolated word recognition experiments using a novel silent speech interface. The interface consist of magnetic pellets that are fixed to relevant speech articulators, and a set of magnetic field sensors that measure changes in the overall magnetic field created by these pellets during speech. The reported experiments demonstrate the effectiveness of this technique and show the suitability of the system, even at its early stages of development, for small vocabulary speech recognition

Stark shift in electroluminescence of individual InAs quantum dots

We have fabricated light-emitting-diode heterostructure devices, in which a layer of InAs self-assembled quantum dots is embedded, with an active area of submicron size. In the electroluminescence spectra of these devices, we observed isolated narrow peaks due to emission from individual dots. From the shift of the peaks in an electric field (the quantum confined Stark effect), we show that the ground and excited states in the dots have different spatial alignments of the electron and hole. (C) 2000 American Institute of Physics. [S0003-6951(00)02526-2]

Tuning of electronic coupling between self-assembled quantum dots

Semiconductor self-assembled quantum dots (SAQDs) normally have zero-dimensional properties, but become coupled and acquire higher-dimensional character if the distance between the dots is small. Using photoluminescence spectroscopy under high hydrostatic pressure, we have obtained clear evidence for electronic coupling due to quantum-mechanical tunneling in stacks of InGaAs/GaAs SAQDs. We demonstrate that application of pressure allows controllable tuning and suppression of the electronic coupling. The effect originates from a pressure-induced increase in the effective mass of Gamma-electrons and a related increase in the interdot-barrier height. (c) 2005 American Institute of Physics

Strained arrays of colloidal nanoparticles: Conductance and magnetoresistance enhancement

Colloidal nanoparticles are very popular as building blocks of functional arrays for electronic and optical applications. However, there is a problem in achieving electrical conductivity in such nanoarrays due to their molecular shells. These shells, which are inherent to colloidal particles, physically separate the nanoparticles in an array and act as very effective insulators. Post-assembly thinning of the shells is therefore required to enhance the array conductivity to a sensible value. Here, we introduce a conceptually new approach to the thinning, using compressive stress applied to the array by the supporting matrix. The stress arises from polymerization-induced shrinkage of the matrix as an integral step during device assembly. Using arrays of oleic-acid-covered magnetite nanoparticles in conjunction with an HDDA-polymer (HDDA: 1,6-hexanediol diacrylate) matrix, we have achieved a significant steady current in the array along with an unprecedented value of the magnetoresistance. Our results serve as a proof-of-concept for other colloidal nanoparticles

Speech synthesis parameter generation for the assistive silent speech interface MVOCA

In previous publications, a silent speech interface based on permanent-magnetic articulography (PMA) has been introduced and evaluated using standard automatic speech recognition techniques. However, word recognition is a task that is computationally expensive and introduces a significant time delay between speech articulation and generation of the acoustic signal. This paper investigates a direct synthesis approach where control parameters for parametric speech synthesis are generated directly from the sensor data of the silent speech interface, without an intermediate lexical representation. Users of such a device would not be tied to the limited vocabulary of a word-based recogniser and could therefore express themselves more freely. This paper presents a feasibility study that investigates whether it is possible to infer speech synthesis parameters from PMA sensor dat

Speech synthesis parameter generation for the assistive silent speech interface MVOCA

In previous publications, a silent speech interface based on permanent-magnetic articulography (PMA) has been introduced and evaluated using standard automatic speech recognition techniques. However, word recognition is a task that is computationally expensive and introduces a significant time delay between speech articulation and generation of the acoustic signal. This paper investigates a direct synthesis approach where control parameters for parametric speech synthesis are generated directly from the sensor data of the silent speech interface, without an intermediate lexical representation. Users of such a device would not be tied to the limited vocabulary of a word-based recogniser and could therefore express themselves more freely. This paper presents a feasibility study that investigates whether it is possible to infer speech synthesis parameters from PMA sensor dat