Polarization characteristics of semipolar (112̄2) InGaN/GaN quantum well structures grown on relaxed InGaN buffer layers and comparison with experiment.

Partial strain relaxation effects on polarization ratio of semipolar (112̄2) InxGa1−xN/GaN quantum well (QW) structures grown on relaxed InGaN buffers were investigated using the multiband effective-mass theory. The absolute value of the polarization ratio gradually decreases with increasing In composition in InGaN buffer layer when the strain relaxation ratio (ε0y'y'−εy'y')/ε0y'y' along y'-axis is assumed to be linearly proportional to the difference of lattice constants between the well and the buffer layer. Also, it changes its sign for the QW structure grown on InGaN buffer layer with a relatively larger In composition (x > 0.07). These results are in good agreement with the experiment. This can be explained by the fact that, with increasing In composition in the InGaN subsrate, the spontaneous emission rate for the y'-polarization gradually increases while that for x'-polarization decreases due to the decrease in a matrix element at the band-edge (k‖ = 0).

Highly stretchable resistive pressure sensors using a conductive elastomeric composite on a micropyramid array.

A stretchable resistive pressure sensor is achieved by coating a compressible substrate with a highly stretchable electrode. The substrate contains an array of microscale pyramidal features, and the electrode comprises a polymer composite. When the pressure-induced geometrical change experienced by the electrode is maximized at 40% elongation, a sensitivity of 10.3 kPa(-1) is achieved.

Highly stretchable electric circuits from a composite material of silver nanoparticles and elastomeric fibres.

Conductive electrodes and electric circuits that can remain active and electrically stable under large mechanical deformations are highly desirable for applications such as flexible displays, field-effect transistors, energy-related devices, smart clothing and actuators. However, high conductivity and stretchability seem to be mutually exclusive parameters. The most promising solution to this problem has been to use one-dimensional nanostructures such as carbon nanotubes and metal nanowires coated on a stretchable fabric, metal stripes with a wavy geometry, composite elastomers embedding conductive fillers and interpenetrating networks of a liquid metal and rubber. At present, the conductivity values at large strains remain too low to satisfy requirements for practical applications. Moreover, the ability to make arbitrary patterns over large areas is also desirable. Here, we introduce a conductive composite mat of silver nanoparticles and rubber fibres that allows the formation of highly stretchable circuits through a fabrication process that is compatible with any substrate and scalable for large-area applications. A silver nanoparticle precursor is absorbed in electrospun poly (styrene-block-butadiene-block-styrene) (SBS) rubber fibres and then converted into silver nanoparticles directly in the fibre mat. Percolation of the silver nanoparticles inside the fibres leads to a high bulk conductivity, which is preserved at large deformations (σ ≈ 2,200 S cm(-1) at 100% strain for a 150-µm-thick mat). We design electric circuits directly on the electrospun fibre mat by nozzle printing, inkjet printing and spray printing of the precursor solution and fabricate a highly stretchable antenna, a strain sensor and a highly stretchable light-emitting diode as examples of applications.

Cost- and time-effective three-dimensional bone-shape reconstruction from X-ray images.

BACKGROUND: Three-dimensional (3D) bone shapes need to be created for visualization and pre-operative surgery planning. Conventionally such shape data is extracted from volumetric data sets, obtained by three-dimensional sensors, such as computerized tomography (CT) and magnetic resonance imaging (MRI). This conventional method is highly labor intensive and time consuming. METHODS: This paper presents a cost- and time-effective computational method for generating a 3D bone shape from multiple X-ray images. Starting with a predefined 3D template bone shape that is clinically normal and scaled to an average size, our method scales and deforms the template shape until the deformed shape gives an image similar to an input X-ray image when projected onto a two-dimensional (2D) plane. The hierarchical freeform deformation method is used to scale and deform the template bone. The problem of finding the 3D shape of the bond is reduced to a sequence of optimization problems. The objective of this optimization is to minimize the error between the input X-ray image and the projected image of the deformed template shape. The sequential quadratic programming (SQP) is used to solve this multi-dimentional optimization problem. RESULTS: The proposed X-ray image-based shape reconstruction is more computationally efficient, cost-effective and portable compared to the conventional CT- or MRI-based methods. Within a couple of minutes with a standard personal computer, the proposed method generates a 3D bone shape that is sufficiently accurate for many applications, such as (a) making a 3D physical mock-up for training and (b) importing into, and using in, a computer-aided planning system for orthopedic surgery, including bone distraction and open/closed wedge osteotomy. CONCLUSIONS: Because the proposed method requires only a small number of X-ray images and a minimum input from the user, the method can serve as a cost- and time-effective 3D bone shape reconstruction method for various medical applications.