GaAs planar doped barrier diodes for millimetre-wave detector applications

Epitaxially grown GaAs planar doped barrier diodes have been designed and fabricated into coplanar structures specifically for millimetre-wave zero-bias detector applications. Results at 35 GHz and 94 GHz show that the tangential sensitivity, voltage sensitivity and dynamic range of these devices can significantly exceed those of any comparable Schottky diode detector. This is the first report of such a result.<>     

Bandwidth performance of 16-element thinned phased array withtapped delay-line filter

The bandwidth performance of a thinned phased adaptive array with and without a delay-line processor are compared. Five- and nine-jammer scenarios are considered for two EHF bands, 0.125 and 2.0 GHz. The null-depth which was used as the measure of performance was computed over the nulling band for three different delay-line configurations. The simulation results give some insight into the way in which delay-line compensation provides improved performance as the interference bandwidth increases     

Feature-based detection of the K-complex wave in the humanelectroencephalogram using neural networks

The main difficulties in reliable automated detection of the K-complex wave in EEG are its close similarity to other waves and the lack of specific characterization criteria. We present a feature-based detection approach using neural networks that provides good agreement with visual K-complex recognition: a sensitivity of 90% is obtained with about 8% false positives. The respective contribution of the features and that of the neural network is demonstrated by comparing the results to those obtained with i) raw EEG data presented to neural networks, and ii) features presented to Fisher's linear discriminant.     

Oriented Multiwalled Organic–Co(OH)2 Nanotubes for Energy Storage

In energy storage materials, large surface areas and oriented structures are key architecture design features for improving performance through enhanced electrolyte access and efficient electron conduction pathways. Layered hydroxides provide a tunable materials platform with opportunities for achieving such nanostructures via bottom‐up syntheses. These nanostructures, however, can degrade in the presence of the alkaline electrolytes required for their redox‐based energy storage. A layered Co(OH)₂–organic hybrid material that forms a hierarchical structure consisting of micrometer‐long, 30 nm diameter tubes with concentric curved layers of Co(OH)₂ and 1‐pyrenebutyric acid is reported. The nanotubular structure offers high surface area as well as macroscopic orientation perpendicular to the substrate for efficient electron transfer. Using a comparison with flat films of the same composition, it is demonstrated that the superior performance of the nanotubular films is the result of a large accessible surface area for redox activity. It is found that the organic molecules used to template nanotubular growth also impart stability to the hybrid when present in the alkaline environments necessary for redox function.     

Reduction of edge reflections in the TLM model

The author points out that in the transmission-line-matrix (TLM) method, spurious reflection is encountered at the edge of the mesh. By transforming the infinite region exterior to a finite region and discretizing it by a second mesh, the magnitude of reflection is much reduced. Numerical results are presented together with an application     

The treatment of thin wires in the FDTD method using a weighted residuals approach

In this contribution, the problem of accurately representing thin wires within the finite-difference time-domain (FDTD) mesh is addressed by means of a method based on the weighted residual (WR) interpretation of the FDTD algorithm. Results for wire dipoles and wire transmission lines, obtained using the proposed method, are presented and compared to those obtained using existing techniques. It is shown that the proposed method yields results which are more accurate and are less dependent on the choice of cell size than other approaches and, in addition, lends itself well to being extended for more complicated structures. Details of the calculation of the update equations are given.     

Observation of Mode Patterns for High Purity Mode Operation in the Submillimeter Wave Gyrotron FU VA

Operation tests of a cavity designed for high purity mode operation of the submillimeter wave gyrotron FU VA has been carried out successfully. The observed emission patterns of several cavity modes appear very pure and are compared with calculated results. High purity mode operation has the advantage of making the conversion to Gaussian-like beams more efficient.     

Si(hhm) surfaces: Templates for developing nanostructures

Semiconductors - The fabrication of ordered low-dimensional structures on clean and metal-atom-decorated stepped Si(557) and Si(556) surfaces is discussed. The formation conditions and atomic...     

The effect of gamma-irradiation on the bandgap width of ZnSe

Exposure to gamma-radiation from a ⁶⁰Co source affects the exciton photoluminescence (PL) spectra of single crystal zinc selenide measured at 4.2 K. As the radiation dose increases, the exciton PL maximum first shifts toward higher energies, but then returns to the initial position (in the range of sufficiently high doses). It is concluded that this behavior is due to variations of the semiconductor bandgap width related to the radiation-stimulated solid-state recrystallization and the accumulation of radiation-induced point defects during exposure.     

Prediction of the Period of Initiation of Macrocracks in Notched Specimens

We propose an experimental–numerical procedure for the prediction the number of cycles N _i to the initiation of a fatigue crack near stress concentrators in specimens of complex shape. This procedure is based on direct measurements of the opening displacements of the concentrator and the numerical evaluation of the total range of local strains * or its elastic component near the tip of the notch. The applicability of this procedure to the prediction of N _i is experimentally checked for specimens in the form of strips cut out from rolled sheets of V95pchT2 alloy with stress concentrators of different geometries.