Bidirectional Artificial Neural Networks for Mobile‐Phone Fraud Detection

We propose a system for mobile‐phone fraud detection based on a bidirectional artificial neural network (bi‐ANN). The key advantage of such a system is the ability to detect fraud not only by offline processing of call detail records (CDR), but also in real time. The core of the system is a bi‐ANN that predicts the behavior of individual mobile‐phone users. We determined that the bi‐ANN is capable of predicting complex time series (Call_Duration parameter) that are stored in the CDR.     

Evaluation of compatibility of thick-film PTC thermistors and LTCC structures

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive temperature coefficients of resistivity, i.e. PTC 5093 (Du Pont) fired either on “green” LTCC (low temperature cofired ceramics) substrates or buried within LTCC structures, were evaluated. The active phase (ruthenium oxide) in the PTC thermistors is not present in the dried films but is formed during firing due to the decomposition of the ruthenate phase. Because of interactions between a glassy LTCC material and thermistors electrical characteristic, i.e. sheet resistivities and noise indices of thermistors fired on the surface LTCC substrates, changed from values obtained on alumina substrates. The differences in the measured electrical parameters were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and Al₂O₃, was confirmed by microanalysis. In the case of buried thermistors, presumably due to the incompatibility of both materials, the structure de-laminated during firing. Cracks between the buried PTC films and the LTCC substrates as well as cracks in PTC films resulted in high sheet resistivities and high noise indices.     

Analysis of light scattering in amorphous Si:H solar cells by a one‐dimensional semi‐coherent optical model

A one‐dimensional semi‐coherent optical model for thin‐film solar cells is presented. The optical circumstances at flat interfaces are addressed and the situation at rough interfaces in the model is described for the case of direct (coherent) incident and scattered (incoherent) incident light. After the model has been experimentally verified, analysis of the light scattering process in hydrogenated amorphous silicon (a‐Si:H) p–i–n solar cells is carried out. The influence of the interface root‐mean‐square roughness and the effect of different angular distribution functions of diffused light on quantum efficiency and short‐circuit current are investigated by the optical model. Copyright © 2002 John Wiley & Sons, Ltd.