An algorithm for accurately estimating the harmonic magnitudes and phase shifts of periodic signals with asynchronous sampling

A digital sampling algorithm that uses two high-resolution integrating voltmeters in a master-slave configuration for accurately measuring the harmonic magnitudes and phase angles of two low-noise, low-frequency, arbitrary voltage signals is presented. It is shown that it is possible to measure up to 64 harmonic magnitudes of 60-Hz signals with an uncertainty of less than 13 /spl mu/V/V relative to the fundamental using commercial stable signal generators and high-resolution digital voltmeters. It is also possible to measure the phase shift between the fundamental components of two equally-synthesized 60-Hz signals with about 3.8% total harmonic distortion with an uncertainty of less than 2.5 /spl mu/rad. Even lower uncertainties can be obtained for low-distortion signals. The algorithm was applied to the measurement of the harmonics of periodic arbitrary signals generated by a commercial source. The differences between computed and measured values of harmonic magnitude suggest that stable digitally-synthesized signal generators can be used as calculable standards of harmonic distortion with an accuracy of less than 6 parts in 10/sup 5/ relative to the fundamental.     

An expert judgement approach to determining the physical vulnerability of roads to debris flow

The physical vulnerability of roads to debris flow may be expressed through fragility functions that relate flow volume to damage probabilities. Fragility relationships are essential components of quantitative risk assessments as they allow for the estimation of risk within a consequence-based framework. To the best of the authors’ knowledge, this is the first time that fragility curves have been produced in order to provide the conditional probability for a road to be in, or to exceed, a certain damage state for a given debris flow volume. Preliminary assessments were undertaken by means of a detailed questionnaire. A total of 47 returns were received from experts in 17 countries: 32 % academia, 51 % the commercial sector and 17 % governments. Fragility curves have been defined for three damage states (limited damage, serious damage and destroyed) for each of low-speed and high-speed roads in order to cover the typical characteristics of roads vulnerable to debris flow. The probability of any given damage state being reached or exceeded by a debris flow of a given volume (10–100,000 m³) was derived from the mean of the responses received. Inevitably there was a degree of scatter in the results, and the treatment of such variation, or ‘experimental errors’, was crucial to understanding the data and developing the fragility curves. Fragility curves are quantitative expressions of vulnerability. The method adopted is based upon qualitative, expert judgment of quantitative probabilities. In addition to an assessment of the probabilities of given damage states being exceeded, respondents to the questionnaire were polled as to their level of experience and confidence in their ability to provide a valid and coherent set of answers to the questions posed. The development of the fragility curves and their validation are described in the paper.     

Bayesian recursive estimation of linear dynamic system states from measurement information

The evaluation of uncertainty in dynamic measurements has recently become a demanding issue. A Bayesian approach is employed here to derive the equations required to recursively generate the solution to the problem of estimating (and predicting) the states of linear dynamic systems. It is shown that this approach allows a derivation of Kalman’s filtering algorithm which is more easily accessible to those involved with dynamic measurements. The complete time-varying Kalman filter is particularly useful when the linear dynamic system and/or signal statistics are time varying and also when optimum estimates are required from the very beginning.     

Colloidal gel from amphiphilic heteroarm polyelectrolyte stars in aqueous media

We report on the gelation capability of polystyrene/poly(2-vinyl pyridine) amphiphilic heteroarm polyelectrolyte stars in acidic salt-free aqueous media. The star polymers associate through hydrophobic interactions, by retraction of the stretched arms under no interdigitation conditions, in the dilute regime forming colloidal soft nanoparticles comprising about 6 stars, At concentrations significantly higher than the hydrodynamic overlap concentration (c > 40c^∗), the crowding of the colloidal nanoparticles drives a jamming transition, leading to a colloidal gel. The intermediate overlap regime (c^∗ < c < 40c^∗) is characterized by a significant compaction of the polyelectrolyte entities prior interdigitation and jamming.     

Geophysical Investigations at Cairo’s Oldest,the Church of Abu Serga (St. Sergius), Cairo,Egypt

The results of an integrated geophysical survey at the archaeological site of Abu Serga church, Cairo, Egypt are presented and discussed. The aim was to investigate the ground conditions of the Church of Abu Serga (St. Sergius), the Cairo’s oldest, dated from 4th Century church, which is located at Qasr el-Shama in old Cairo in Egypt. In particular the objective is to study the subsurface geological structures at the location of the church, and to detect and possibly map any ancient remains concealed under the monument. The survey was conducted using two geophysical methods: the ground penetrating radar (GPR), which is a fully non-destructive method, and the electrical resistivity tomographies (ERTs). The usefulness of combining conventional geophysical mapping techniques and high resolution imaging methods in delineating shallow targets of archaeological interest at such complex archaeological sites, is studied. Ground penetrating radar time slices and 3D electrical tomography depth slices were used for the verification of specific anthropogenic anomalies, which were detected on the geophysical maps Processing of geophysical maps included filtering with the gradient and first derivative operators in the space domain and the upward continuation and Butterworth filters in the wave number domain. The integration of the geophysical measurements revealed that the present Crypt is not the original holy Crypt. The anomalous reflector is detected at depth of about 5 m below the sanctuary floor, in the form of buried ceiling of the original Crypt. The present Crypt is just a small low subterranean church belong to the 2nd century. High resistivity anomalies and distinct GPR signals were also observed deeper in the inner parts of the church. They are attributed to possible remains of ancient walls and surrounding tunnels, or other man-made structures concealed under the floor of the monument. The geophysical survey at Abu Serga church also demonstrates that the general features of the foundation soil are heterogeneous with abundance of fractures; the water table is very high at 1.8m below the sanctuary floors. The benefits of combined geophysical surveys in case of archaeological investigations at complex sites are highlighted.     

Fault tolerant and prioritized scheduling in OGSA‐based mobile Grids

Grids and mobile Grids can form the basis and the enabling technology for pervasive and utility computing due to their ability to being open, highly heterogeneous and scalable. In this paper we present a scheme for advancing quality of service (QoS) attributes, such as fault tolerance and prioritized scheduling, in OGSA‐based mobile Grids. The fault tolerance is achieved by producing and managing sufficient replicas of tasks submitted for execution on the mobile Grid resources. We design a simple and efficient prioritization scheme, which allows the scheduling of the tasks submitted by the Grid users as distinguished priorities that can be managed and exploited as a QoS parameter by the Grid infrastructure operator. The results that are presented show the efficiency of the proposed scheme in being simple and additionally enriching with reliability and QoS features the applications that are built on the concept of mobile Grids. Copyright © 2008 John Wiley & Sons, Ltd.     

Dynamic properties of cemented soils from Cyprus

The paper presents results from a laboratory investigation into the dynamic properties of natural cemented sandy and cohesive soils from Cyprus, as expressed by shear modulus and damping ratio. The influence of various soil parameters, such as strain level, confining stress, undrained shear strength, void ratio, plasticity index, cementation and organic matter content is discussed. The test results show that cementation increases the small-strain shear modulus, but does not affect the other dynamic properties, such as small-strain damping ratio and the variations of shear modulus and damping ratio with shear strain.     

An Orthogonal Design of Experiments for Accurately Estimating Harmonics of Periodic Signals at Low Frequencies

The lack of synchronization between the sampling rate and the signal frequency is the main source of leakage errors in the harmonic analysis of periodic signals performed by means of digital techniques. An algorithm for accurately measuring the harmonic parameters of low-frequency, arbitrary voltage signals without using synchronization circuits was published recently. It is shown that the algorithm is an alternative orthogonal design of experiments for the problem of fitting a linear trigonometric model to integrating digital voltmeter data. This was experimentally confirmed in recent comparison of the proposed method with a synchronous synthesizing and sampling system. The harmonic magnitudes as a percentage of the fundamental measured by both methods differ by less than one part in 10^{6}. The algorithm can be advantageously used in almost any kind of low-frequency ac applications where two arbitrary voltage signals measured by two voltmeters are to be compared for harmonic magnitude and phase shift.