Direct Segmentation of Algebraic Models for Reverse Engineering

In Reverse Engineering a physical object is digitally reconstructed from a set of boundary points. In the segmentation phase these points are grouped into subsets to facilitate consecutive steps as surface fitting. In this paper we present a segmentation method with subsequent classification of simple algebraic surfaces. Our method is direct in the sense that it operates directly on the point set in contrast to other approaches that are based on a triangulation of the data set. The segmentation process involves a fast algorithm for k-nearest neighbors search and an estimation of first and second order surface properties. The first order segmentation, that is based on normal vectors, provides an initial subdivision of the surface and detects sharp edges as well as flat or highly curved areas. One of the main features of our method is to proceed by alternating the steps of segmentation and normal vector estimation. The second order segmentation subdivides the surface according to principal curvatures and provides a sufficient foundation for the classification of simple algebraic surfaces. If the boundary of the original object contains such surfaces the segmentation is optimized based on the result of a surface fitting procedure.     

Concurrent analogue fault simulation,the equation formulation aspect

Fault simulation is an essential tool for developing test patterns for circuits. Because the potential number of faults in a circuit is potentially very large, computational efficiency is an important consideration. In the digital domain, concurrent fault simulation is well‐established as an efficient tool. For analogue circuits, fault simulation is often performed by repeated insertion of possible faults and resimulation of the circuit. Consequently, methods for efficient concurrent analogue fault simulation are attracting attention. A review of existing methods of concurrent analogue fault simulation shows that most are based on a similar fundamental perturbation of the original fault‐free circuit equations, although the methods differ in the procedure applied after the circuit equations are formulated. We develop here a comprehensive set of element stamps, describing faulty elements, enabling effective and routine equation formulation for faulty circuits. These may be used no matter what method of fault simulation is later applied. These stamps are used in a new technique for concurrent analogue fault simulation, based on modified nodal analysis. A significant improvement in efficiency, compared with other methods, is demonstrated. Copyright © 2004 John Wiley & Sons, Ltd.     

Analogue electronic circuit diagnosis based on ANNs

Feed-forward artificial neural networks (ANNs) have been applied to the diagnosis of nonlinear dynamic analogue electronic circuits. Using the simulation-before-test (SBT) approach, a fault dictionary was first created containing responses observed at all inputs and outputs of the circuit. The ANN was considered as an approximation algorithm to capture mapping enclosed within the fault dictionary and, in addition, as an algorithm for searching the fault dictionary in the diagnostic phase. In the example given DC and small signal frequency domain measurements were taken as these data are usually given in device’s data-sheets. A reduced set of data per fault (DC output values, the nominal gain and the 3 dB cut-off frequency, measured at one output terminal) was recorded. Soft (parametric) and catastrophic (shorts and opens) defects were introduced and diagnosed simultaneously and successfully. Large representative set of faults was considered, i.e., all possible catastrophic transistor faults and qualified representatives of soft transistor faults were diagnosed in an integrated circuit. The generalization property of the ANNs was exploited to handle noisy measurement signals.     

WebFlow – a visual programming paradigm for Web/Java based coarse grain distributed computing

We present here recent work at NPAC aimed at developing WebFlow – a general purpose Web-based visual interactive programming environment for coarse grain distributed computing. We follow the 3-tier architecture with the central control and integration WebVM layer in tier-2, interacting with the visual graph editor applets in tier-1 (front-end) and the legacy systems in tier-3. WebVM is given by a mesh of Java Web servers such as Jeeves from JavaSoft or Jigsaw from MIT/W3C. All system control structures are implemented as URL-addressable servlets which enable Web browser-based authoring, monitoring, publication, documentation and software distribution tools for distributed computing. We view WebFlow/WEbVM as a promising programming paradigm and co-ordination model for the exploding volume of Web/Java software, and we illustrate it in a set of ongoing application development activities. © 1997 John Wiley & Sons, Ltd.     

Computationally efficient large-change statistical analysis of linear electronic circuits

A new method is presented for efficient statistical analysis of linear electronic circuits, when small and large parameter tolerances are given. The statistically generated value of the parameter is considered as a faulted value, as it deviates from the nominal thus enabling the application of a simulation method which uses a new approach of concurrent fault simulation. This method adds new elements to the circuit, representing individual parameter increments, while keeping the topology of the original one. The equations for the original and several perturbed circuits are formulated and solved simultaneously. In this way, redundant computations are avoided in both the equation formulation and equation solving phases, which shorten the simulation time. A statistical frequency and time domain tolerance simulator of linear circuits was developed on the basis of this method with effective user-friendly interface. The method is especially suited for yield sensitivity to some selected circuit parameters estimation. Here simulation results of several benchmark circuits are presented. Efficiency analysis is also included.     

Frequency and time domain comparison of selective polynomial filters with corrected phase characteristics

Two solutions to the polynomial filter’s transfer function synthesis problem are considered for comparison in the frequency and time domain: the broad class of filters with a critical monotonic amplitude characteristic (CMAC) in the passband and filters which use Chebyshev (C) polynomials. To complete the synthesis procedure for linear phase applications, group delay correctors are considered, for which a convenient approximation procedure is proposed here. Comparisons of the original functions and the corrected ones are performed in the frequency and time domain. It is shown that when CMAC and C are compared as such, the latter is by no means preferable from the selectivity point of view, while the opposite stands when the comparison is based on passband amplitude distortions. When phase-corrected filtering functions are compared, based on circuit complexity and time domain performance, the CMAC are shown to be preferable.     

Computer Security Vulnerability as Concerns the Electricity Distribution Grid

The usual way of creating a cyber attack is through implementation of malware via the Internet. Among many types of malware, of special interest are those that enable eavesdropping on the activities within the computer, making it possible to define the software on which the computer is running. An adversary can benefit from this information in a way that is convenient for him or her. Here, we expose a new, entirely different way of eavesdropping and of monitoring the activities within the computer. It is based on measurement of the supply current taken from the electricity distribution grid. Because the computer, as many other electronic loads, is a nonlinear one, abundance of harmonics can be found in that current. Our discovery is the fact that the harmonic content is dependent on the type of activity within the computer, so, by proper analysis of the current waveform, one may recognize what is going on in it. We propose an artificial neural network-based method that unambiguously recognizes which software is running. We also propose a proper measurement procedure based on the technology we described in our earlier articles.