Low-cost small-size tapered slot antenna for lower band UWB applications

A low-cost small-size tapered slot antenna (TSA) is investigated in view of ultra-wideband (UWB) applications. First, the bandwidth of the antenna is studied for the lower UWB band: 3.1-4.85 GHz. Secondly, the design is made as small as possible. Thirdly, the pulse distortion of a modulated Gaussian pulse in the lower UWB band, between 3.5 and 4.5 GHz, is investigated based on the measured S/sub 21/-parameter. The low distortion observed indicates that this TSA is suitable for applications in the lower UWB band.     

A variable bit rate video codec for asynchronous transfer modenetworks

The bandwidth flexibility offered by the asynchronous transfer mode (ATM) technique makes it possible to select picture quality and bandwidth over a wide range in a simple and straightforward manner. A prototype model of a video codec was developed that demonstrates the feasibility of both variable bit rate (VBR) coding and user-selectable picture quality. The VBR coding algorithm is discussed and it is shown how a stabilized quality is achieved and how this quality and associated bandwidth can be selected by the user. How error propagation is limited to reduce the visibility of cell losses is also discussed. Interfaces with the ATM network are analyzed, with emphasis on decoder synchronization and absorption of cell delay jitter. The VBR codec offers very good picture quality for videophony applications at an equivalent load of 5.9 Mb/s. Picture quality remains relatively constant, even for heavy motion     

Oxidation of solid gold in chloroform solutions of cetyltrimethylammonium bromide

Oxidation of solid gold was studied in chloroform solutions of cetyltrimethylammonium bromide (CTAB). We observed that, upon sonication, solid gold is oxidized and cetyltrimethylammonium tetrabromo aurate is formed. The Br⁻ ions act as a nucleophile that lowers the reduction potential of gold and molecular oxygen from the air acts as an oxidant. Addition of hydrazine to the sonicated solution leads to the formation of gold nanoparticles dispersed in chloroform.     

Image-based rendering for photo-realistic visualization

Digital models of objects have long stood synonymous for 3D models with fixed textures. More recently, image-based rendering has made its way to offer an effective alternative. Rather than producing a 3D model, views are created by interpolating between images taken from many different viewpoints. The advantages are that the resulting visualizations look very realistic and that a wider range of objects can be dealt with. One can go a step further and follow a similar strategy for the illumination direction: for every reference viewpoint, now take multiple images, each with a different illumination. Again, images for novel illumination directions follow from interpolation. But there is an obvious catch in that many, many images are needed, unless at least a crude 3D shape model and preferably also a model for the surface reflectance are used to support the interpolation from more sparsely taken images. Even then, the number of images needed remains appreciable. Hence, we present a dome to efficiently capture such images.

Fortunately, it is possible to generate this crude 3D model, as well as the surface reflectance characteristics' directly from the images. We describe methods to achieve this. Also, in order to make real-time visualization possible, all critical steps of the visualization pipeline are programmed on off-the-shelf graphics hardware. The dome provides an easy to use and structured acquisition procedure. Yet, the applicability of the algorithms is not limited to structured input. The images could, for example be taken with a hand-held camera.     

Chirality in surface nonlinear optics

The efficiency of second-harmonic generation from chiral surfaces and thin films is different for left- and right-hand circularly-polarized fundamental light. Such optical activity can occur in the electric-dipole approximation. However, to explain our results for chiral polymer films, magnetic contributions to the nonlinearity must be included. A technique that uses a quarter wave plate to continuously vary the polarization of the fundamental beam was used to determine the relative complex values of the components of the tensors that characterize the nonlinear interaction. The largest magnetic components were 20% of the largest electric components. Second-harmonic generation from achiral anisotropic surfaces can also lead to optical activity. This occurs if the orientation of the anisotropic sample makes an otherwise achiral experimental arrangement chiral. The effect occurs in the electric-dipole approximation and changes sign as the handedness of the setup is reversed.     

Nonlinear optical active poly(adamantyl methacrylate-methyl vinyl urethane)s functionalised with phenyltetraene-bridged chromophore

Nonlinear optical (NLO) poly(adamantyl methacrylate-methylvinylurethane)s were prepared by functionalisation of adamantyl methacrylate vinyl isocyanate precursor polymers. A modified pathway to obtain phenyltetraene-bridged chromophore was worked out. Poled films of the polymers show high and very stable NLO response even at elevated temperatures.     

On the use of evolutionary feature selection for improving fuzzy rough set based prototype selection

The k-nearest neighbors classifier is a widely used classification method that has proven to be very effective in supervised learning tasks. In this paper, a fuzzy rough set method for prototype selection, focused on optimizing the behavior of this classifier, is presented. The hybridization with an evolutionary feature selection method is considered to further improve its performance, obtaining a competent data reduction algorithm for the 1-nearest neighbors classifier. This hybridization is performed in the training phase, by using the solution of each preprocessing technique as the starting condition of the other one, within a cycle. The results of the experimental study, which have been contrasted through nonparametric statistical tests, show that the new hybrid approach obtains very promising results with respect to classification accuracy and reduction of the size of the training set.