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A Georgakis

Publications and source records attributed to A Georgakis.

6 recordsLinked to original sources
PubMed2004

Marginal median SOM for document organization and retrieval.

The self-organizing map algorithm has been used successfully in document organization. We now propose using the same algorithm for document retrieval. Moreover, we test the performance of the self-organizing map by replacing the linear Least Mean Squares adaptation rule with the marginal median. We present two implementations of the latter variant of the self-organizing map by either quantifying the real valued feature vectors to integer valued ones or not. Experiments performed using both implementations demonstrate a superior performance against the self-organizing map based method in terms of the number of training iterations needed so that the mean square error (i.e. the average distortion) drops to the e(-1) = 36.788% of its initial value. Furthermore, the performance of a document organization and retrieval system employing the self-organizing map architecture and its variant is assessed using the average recall-precision curves evaluated on two corpora; the first comprises of manually selected web pages over the Internet having touristic content and the second one is the Reuters-21578, Distribution 1.0.

Algorithms↗
PubMed2003

Fatigue analysis of the surface EMG signal in isometric constant force contractions using the averaged instantaneous frequency.

The averaged instantaneous frequency (AIF) is proposed as an alternative method for the frequency analysis of surface electromyography (EMG) in the study of muscle fatigue during sustained, isometric muscle contractions. Results from performance analysis using experimental EMG signals demonstrate the low variability of the proposed frequency variable. Indeed, the AIF measure is shown to perform significantly better than the widely used mean and median frequency variables, in terms of robustness to the length of the analysis window.

Action Potentials↗
PubMed2002

Automatic algorithm for filtering kinematic signals with impacts in the Wigner representation.

An automatic filtering algorithm is proposed for the accurate estimation of the second derivatives of kinematic signals with impacts. The impacts considered here occur when a moving object hits a rigid surface. The algorithm performs time-frequency filtering in the Wigner representation, to deal efficiently with the non-stationarities caused by such impacts, and adjusts the parameters of its time-frequency filtering function so that the filtering process adapts to the individual characteristics of the signal in hand. Performance analysis and comparative evaluation with experimentally acquired kinematic impact signals demonstrated a higher accuracy, with performance advantages over two widely used conventional automatic methods: linear phase autoregressive model-based derivative assessment (LAMBDA) and generalised cross-validation using quintic splines (GCVQS). For high impacts, the average absolute relative error in estimating the peak acceleration was 5.7% with the proposed method, 17.2% with a Butterworth low-pass filter optimised to yield minimum overall acceleration RMS error (best-case result), 18.3% with the LAMBDA method, and 37.2% with the GCVQS method. For signals with low impacts, the average absolute relative error was 19.4%, 6.9%, 8.3% and 19.1%, respectively, in each case, which indicates that, for signals with a low-frequency content, there is no need for such time-frequency filtering.

Algorithms↗
PubMed1991

[Analysis of steroids. Part 40. Isolation and identification of unusual impurities in ethynodiol diacetate].

In the course of the estimation of the impurity profile of ethynodiol diacetate, in addition to common impurities such as norethisterone acetate, ethynodiol-3-acetate and alpha-ethynodiol diacetate, two unknown impurities were detected by analytical reversed phase HPLC (C-18 silica and 80% aq. methanol as the eluent) and isolated by normal phase preparative HPLC (silica and 98:2 mixture of hexane and 2-propanol as the eluent). The 1H- and 13C-NMR spectra of the isolated impurities revealed that their structures could be characterized as the E and Z isomers of an analogue of EDDA containing "trimerised acetyl" group at the 17-hydroxy group (structures 4 and 4a). These structures were in good agreement with the extended UV spectra of the impurities and the mass spectra with the m/z 438 peak which can be derived from 4 and 4a by the loss of ketene.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Improving participation in HIV clinical trials: impact of a brief intervention.

PURPOSE: To determine if a brief intervention that provides information about AIDS clinical trials to HIV-infected patients at the initiation of primary care increases the participation of women, persons of color, and injection drug users (IDUs) in clinical trials. METHOD: 196 outpatients beginning HIV primary care at a municipal hospital were followed from September 1994 to April 1996. During the intake assessment, each patient met briefly with a research assistant who described the purpose, role, and availability of clinical trials. Contacts for further information about trials were given to patients who expressed interest. At the end of the 20-month period, enrollment rates of all patients, including women, persons of color, and IDUs, into clinical trials were compared with previously published enrollment rates of patients at the same hospital but prior to the development of this brief intervention. RESULTS: The characteristics of the 196 HIV-infected patients were: 27% women; 47% IDUs; 14% gay/bisexual men; and 76% persons of color. Overall enrollment in AIDS clinical trials was 14.8% during the 20-month follow-up period. There was no significant difference in participation rates between males and females (p =.20), whites and persons of color (p =.71), and IDUs compared with non-IDUs (p =.90), whereas previously published data had shown significantly higher enrollment rates among males, whites, and non-IDUs. CONCLUSION: Providing all HIV-infected patients with information about the meaning, role, and availability of AIDS clinical trials at the initiation of HIV primary care reduces differences in participation rates by gender, race, and history of drug use.

Anti-HIV Agents↗