The authors compared the longevity of all baseball players alive at the time of their induction i... more The authors compared the longevity of all baseball players alive at the time of their induction into the Baseball Hall of Fame with age-matched controls who were likewise alive at the time of the Hall of Famer's induction, and also matched them for career length, player position, and body-mass index, to assess if fame in sports is associated with increased longevity. Median post-induction survival for Hall of Famers was 5 years shorter than for noninducted players (18 vs. 23 years, respectively). In a second analysis, significantly more Hall of Famers died of cardiovascular or stroke causes than other players for whom cause of death was known. Baseball fame may have a hitherto unrecognized price.
Purpose To compare the antecedent gynecological characteristics, indications for, and complicatio... more Purpose To compare the antecedent gynecological characteristics, indications for, and complications associated with, the different laparoscopic approaches to hysterectomy, in women with benign gynecological conditions. Methods A retrospective cohort study of 957 patients who underwent laparoscopic supracervical (LSH), total (TLH), and assisted vaginal (LAVH) hysterectomies between January 2003 and December 2009. Results Among 957 LH, 799 (83.5%) were LSH, 62 (6.4%) TLH, and 96 (10.1%) LAVH. Demographic characteristics were not different among the groups. Antecedent gynecologic conditions that were associated with the type of laparoscopic hysterectomy (LH) performed were: postmenopausal bleeding [LAVH vs. LSH, odds ratio (OR) 2.20; 95% confidence interval (CI) 1.04-4.65], previous pelvic surgery (TLH vs. LSH, OR 1.92; CI 1.05-3.52), previous cesarean delivery (LAVH vs. LSH, OR 0.39; CI 0.21-0.76), and prior hysteroscopy (LAVH vs. LSH, OR 0.29; CI 0.16-0.50). Preoperative diagnoses that were associated with the choice of LH were: menometrorrhagia (LAVH vs. LSH, OR 0.23; CI 0.14-0.38; TLH vs. LSH, OR 0.50; CI 0.26-0.98), uterine fibroids (LAVH vs. LSH, OR 0.25; CI 0.15-0.41), endometrial hyperplasia (TLH vs. LSH, OR 5.5; CI 2.04-14.84), and cervical dysplasia (TLH vs. LSH, OR 17.1; CI 6.83-42.79; LAVH vs. LSH, OR 8.05; CI 3.05-22.06). Estimated blood loss, operating time, and length of hospital stay were significantly reduced with LSH. Conclusion Antecedent gynecological history and the indications for surgery were associated with the type of LH performed in our institution. LSH was the most common approach and was associated with significantly less morbidity.
We studied 1991 Gulf War (GW)-related environmental exposures and adverse birth outcomes in Iraqi... more We studied 1991 Gulf War (GW)-related environmental exposures and adverse birth outcomes in Iraqis. A random cross-sectional sample of 307 Iraqi families that immigrated to the United States responded to a structured interview covering socioeconomics, lifestyle, environmental exposures, and birth outcome. Data per each family was collected either from the man or the woman in the respective family. The respondents were divided into those that resided in Iraq during and following the GW (post-GW, n=185) and those that had left before (pre-GW, n=122). The primary outcome was lifetime prevalence of adverse birth outcomes, ie, congenital anomalies, stillbirth, low birth weight, and preterm delivery and its relationship to GW exposures. Mean number of adverse birth outcomes increased from 3.43 (SD=2.11) in the pre-GW to 4.63 (SD=2.63) in the post-GW group (P<.001). Mean chemical (Ch) and nonchemical (NCh) environmental exposure scores increased from pre-GW scores of 0.38 units (SD=1.76...
Objective-To determine the effects of 10 mg and 20 mg/day of escitalopram on objectivelyrecorded ... more Objective-To determine the effects of 10 mg and 20 mg/day of escitalopram on objectivelyrecorded hot flashes and on the rectal temperature threshold for sweating. Method-Two studies were performed: 16 women received 10 mg/day and 26 women received 20 mg/day escitalopram for eight weeks. They were randomly assigned in equal numbers to receive active drug or placebo in double-blind fashion. Hot flash frequency was measured with an ambulatory recorder during the first three weeks and during the eighth week of the study. The rectal temperature threshold for sweating was measured during the first and eighth weeks of the study using published methods. Results-In the first study, there were no significant effects whatsoever for any measure. In the second study, the escitalopram group showed an average decline in hot flash frequency of 14.4%, whereas, the placebo group showed an average increase of 6.7% (P < .05). However, there were no significant effects across time for either group. There were no significant effects whatsoever for rectal temperature sweating thresholds. Conclusions-Escitalopram at 10 mg or 20 mg/day is not effective in the treatment of menopausal hot flashes.
Objective: To investigate the effects of decreasing androgen levels on insulin action, in view of... more Objective: To investigate the effects of decreasing androgen levels on insulin action, in view of the relationship between hyperandrogenism and impaired insulin action in women with polycystic ovary syndrome.
American Journal of Obstetrics and Gynecology, 2013
The purpose of this study was to determine whether nuclear magnetic resonanceebased metabolomic m... more The purpose of this study was to determine whether nuclear magnetic resonanceebased metabolomic markers in firsttrimester maternal serum can detect fetuses with trisomy 18. STUDY DESIGN: This was a study of pregnancies between 11 weeks and 13 weeks 6 days' gestation. We analyzed 30 cases of trisomy 18 and a total of 114 euploid cases. Nuclear magnetic resonanceebased metabolomic analysis was performed. A further analysis was performed that compared 30 cases with trisomy 18 and 30 trisomy 21 (T21) cases. RESULTS: Metabolomic markers were sensitive for trisomy 18 detection. A combination of 2-hydroxybutyrate, glycerol and maternal age had a 73.3% sensitivity and 96.6% specificity for trisomy 18 detection, with an area under the receiver operating curve: 0.92 (P < .001). Other metabolite markers, which include trimethylamine, were sensitive for distinguishing trisomy 18 from T21 cases. CONCLUSION: This is the first report of prenatal trisomy 18 detection that has been based on metabolomic analysis. Preliminary results suggest that such markers are sensitive not only for the detection of fetal trisomy 18 but also for distinguishing this aneuploidy from T21.
This paper examines the hypothesis that cocaine and BE assays of hair demonstrate a putative bias... more This paper examines the hypothesis that cocaine and BE assays of hair demonstrate a putative bias effect for darker color hair samples. Although such an effect has been reported in the literature, no one has examined this claim outside the bounds of simple significance of mean difference. In this paper a large number of black and brown hair samples are compared for cocaine and BE concentration values, and this comparison is evaluated for both significance and effect size. Two innovative measures are used to assess this relationship - a calculation of effect size using Cohen&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s d, and the use of an ROC curve to evaluate the potential for a dark color bias. The paper reports mixed results for significance, but consistent results for effect size. There does not appear to be any significant effect for cocaine. While BE demonstrates a significant mean difference, both the effect size and the ROC analysis show the effect to be trivial.
In a variety of decision settings when categorical information is the data in hand, the correspon... more In a variety of decision settings when categorical information is the data in hand, the correspondence between an indicator test and a true condition (i.e., an accepted "gold standard") is often assessed by the use of comparison or "truth" tables. The results from such a table can be considered an informational yield and allow a practitioner to assess the utility of the indicator test in various ways, such as specificity and sensitivity, false positive and negative rates, and the positive and negative predictive values. There are many reasons for the use of an indicator test. This article proposes a novel application of an informational measure in determining the utility of hair and urine specimens for clinical decision making. It does this for two commonly abused substances, cocaine and cannabinoids. It suggests that in clinical applications the ability to assess informational yield is an important factor in developing clinical strategies for treatment of addictive disorders.
Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine, 2007
The aim of this study was to compare gestational age at delivery and the performance of middle ce... more The aim of this study was to compare gestational age at delivery and the performance of middle cerebral artery (MCA), ductus venosus (DV), and umbilical artery Doppler parameters in the prediction of perinatal mortality and morbidity in intrauterine growth-restricted (IUGR) fetuses delivered at 32 weeks or earlier. The study population consisted of 41 patients with IUGR fetuses. Delivery occurred for maternal or fetal indications. Two-tailed chi(2) and Fisher exact tests, an independent t test, and logistic regression were used for the analysis. P < .05 was considered statistically significant. Gestational age at delivery ranged between 23.1 and 32 weeks (median, 27.6 weeks). There were 17 perinatal deaths. Ninety-four percent of the perinatal deaths occurred when the fetuses were delivered before 29 weeks. No fetus survived when delivered before 25 weeks. Two parameters predicted the perinatal mortality: gestational age at delivery (odds ratio, 0.52; 95% confidence interval, 0.3...
The promise of ultrafast light field driven electronic nanocircuits has stimulated the developmen... more The promise of ultrafast light field driven electronic nanocircuits has stimulated the development of the new research field of attosecond nanophysics. An essential prerequisite for advancing this new area is the ability to characterize optical nearfields from light interaction with nanostructures with sub cycle resolution. Here, we experimentally demonstrate attosecond nearfield retrieval with a gold nanotip using streaking spectroscopy. By comparison of the results from gold nanotips to those obtained for a noble gas, the spectral response of the nanotip near field arising from laser excitation can be extracted. Monte Carlo MC trajectory simulations in near fields obtained with the macroscopic Maxwells equations elucidate the streaking mechanism on the nanoscale.
This paper presents the methodology for a new technique to measure the impedance of transmission ... more This paper presents the methodology for a new technique to measure the impedance of transmission lines and the associated earth fault return paths. The test procedure is detailed, and practical results are presented from tests on a utility network. The procedure is critically examined for comparison with existing theoretical studies and other empirical methods to calculate distance protection and fault location settings. The significance of the varied quality and accuracy of the results from these existing techniques arises from the particular importance of the accuracy of the residual compensation or k-factor setting in preventing over- or under-reach of the protection of transmission line systems. The simple practical method presented has highlighted the limitations and the cost of failure of existing techniques, with major implications for improving the protection of, fault finding and fault-location on the electricity transmission network. Related testing proposals are also pres...
Sweep Frequency Response Analysis (SFRA) has turned out to be a powerful and sensitive method to ... more Sweep Frequency Response Analysis (SFRA) has turned out to be a powerful and sensitive method to evaluate the mechanical integrity of core, windings and clamping structures within power transformers by measuring their electrical transfer functions over a wide frequency range. The contribution summarizes various aspects of the practical application of SFRA. After a short introduction of SFRA basics a survey of existing standards and guides on FRA is given. The different sources of reference data and their significance are discussed. Uncertainties are shown and tips for dealing with them are presented. The choice of test types is discussed for measurements without existing reference data. Information about the handling of test data is mentioned. Finally a summary of guidelines derived from a large number of successful measurements is given to put the reader in a position to achieve a good degree of repeatability, too.
This paper starts with a systematic benchmark test of the three commercialised dielectric diagnos... more This paper starts with a systematic benchmark test of the three commercialised dielectric diagnostic methods RVM (recovery voltage method), PDC (polarisation and depolarisation currents) and FDS (frequency domain spectroscopy), performed on a large transformer model. The water content as analysed by the specific software was compared under three parame-ters: insulation geometry, insulation temperature and oil conductivity. It was found, that for the RV method the interpretation scheme based on the central time constant is too simplistic. The other two methods PDC and FDS compensate much better for the mentioned parameters but nevertheless analyse a drier cellulose with increas-ing temperature and a wetter cellulose for increasing oil conductivity. Actually the moisture in cellulose re-mained constant at 1 % during all the tests. Starting from these weaknesses a more sophisticated software was developed. The new software called "Dirana" bases on a new data pool, measured at...
The transfer function (TF), also called frequency response, can be used as a diagnostic method to... more The transfer function (TF), also called frequency response, can be used as a diagnostic method to detect mechanical and electrical defects. The assessment of FRA (Frequency Response Analysis) results is done by a comparison between a recent and a previous measurement, which is called the reference measurement. An acknowledged problem with FRA is that up to now there is no international standardized procedure for comparison. Analyses are done by experts but run the risk of being judged with subjectivity. Thus, the need for an algorithm enabling quantitative determination of the identicalness of two FRA measurements within a certain frequency range is obvious. The article will present different algorithms to assess the FRA: expectation, standard deviation, correlation factor and analysis of resonance frequencies. The performance of these algorithms is verified using data sets obtained during measurements for the investigation of sensitivity of the FRA method to mechanical winding disp...
The frequency response analysis (FRA) is a well-established method used for assessment of the mec... more The frequency response analysis (FRA) is a well-established method used for assessment of the mechanical and electrical conditions of power transformer windings. The evaluation of the winding condition is done by comparison between an actual FRA and a reference FRA, which are carried out previously. A deviation between both FRA curves can indicate a change of the winding condition of the tested transformer. According to the standard of knowledge, the connections between measuring device and transformer terminals, as well as the grounding technique are of main importance for a good repeatability. Additionally, a power transformer is a large construction that needs long cables and grounding lines for the signal transmission. Against this background, it is clear, that the geometric arrangement of the measuring setup may not be the same as it was at the reference measurement and this change can have an influence on FRA results. Therefore, an excellent repeatability of the measurements i...
The authors compared the longevity of all baseball players alive at the time of their induction i... more The authors compared the longevity of all baseball players alive at the time of their induction into the Baseball Hall of Fame with age-matched controls who were likewise alive at the time of the Hall of Famer's induction, and also matched them for career length, player position, and body-mass index, to assess if fame in sports is associated with increased longevity. Median post-induction survival for Hall of Famers was 5 years shorter than for noninducted players (18 vs. 23 years, respectively). In a second analysis, significantly more Hall of Famers died of cardiovascular or stroke causes than other players for whom cause of death was known. Baseball fame may have a hitherto unrecognized price.
Purpose To compare the antecedent gynecological characteristics, indications for, and complicatio... more Purpose To compare the antecedent gynecological characteristics, indications for, and complications associated with, the different laparoscopic approaches to hysterectomy, in women with benign gynecological conditions. Methods A retrospective cohort study of 957 patients who underwent laparoscopic supracervical (LSH), total (TLH), and assisted vaginal (LAVH) hysterectomies between January 2003 and December 2009. Results Among 957 LH, 799 (83.5%) were LSH, 62 (6.4%) TLH, and 96 (10.1%) LAVH. Demographic characteristics were not different among the groups. Antecedent gynecologic conditions that were associated with the type of laparoscopic hysterectomy (LH) performed were: postmenopausal bleeding [LAVH vs. LSH, odds ratio (OR) 2.20; 95% confidence interval (CI) 1.04-4.65], previous pelvic surgery (TLH vs. LSH, OR 1.92; CI 1.05-3.52), previous cesarean delivery (LAVH vs. LSH, OR 0.39; CI 0.21-0.76), and prior hysteroscopy (LAVH vs. LSH, OR 0.29; CI 0.16-0.50). Preoperative diagnoses that were associated with the choice of LH were: menometrorrhagia (LAVH vs. LSH, OR 0.23; CI 0.14-0.38; TLH vs. LSH, OR 0.50; CI 0.26-0.98), uterine fibroids (LAVH vs. LSH, OR 0.25; CI 0.15-0.41), endometrial hyperplasia (TLH vs. LSH, OR 5.5; CI 2.04-14.84), and cervical dysplasia (TLH vs. LSH, OR 17.1; CI 6.83-42.79; LAVH vs. LSH, OR 8.05; CI 3.05-22.06). Estimated blood loss, operating time, and length of hospital stay were significantly reduced with LSH. Conclusion Antecedent gynecological history and the indications for surgery were associated with the type of LH performed in our institution. LSH was the most common approach and was associated with significantly less morbidity.
We studied 1991 Gulf War (GW)-related environmental exposures and adverse birth outcomes in Iraqi... more We studied 1991 Gulf War (GW)-related environmental exposures and adverse birth outcomes in Iraqis. A random cross-sectional sample of 307 Iraqi families that immigrated to the United States responded to a structured interview covering socioeconomics, lifestyle, environmental exposures, and birth outcome. Data per each family was collected either from the man or the woman in the respective family. The respondents were divided into those that resided in Iraq during and following the GW (post-GW, n=185) and those that had left before (pre-GW, n=122). The primary outcome was lifetime prevalence of adverse birth outcomes, ie, congenital anomalies, stillbirth, low birth weight, and preterm delivery and its relationship to GW exposures. Mean number of adverse birth outcomes increased from 3.43 (SD=2.11) in the pre-GW to 4.63 (SD=2.63) in the post-GW group (P<.001). Mean chemical (Ch) and nonchemical (NCh) environmental exposure scores increased from pre-GW scores of 0.38 units (SD=1.76...
Objective-To determine the effects of 10 mg and 20 mg/day of escitalopram on objectivelyrecorded ... more Objective-To determine the effects of 10 mg and 20 mg/day of escitalopram on objectivelyrecorded hot flashes and on the rectal temperature threshold for sweating. Method-Two studies were performed: 16 women received 10 mg/day and 26 women received 20 mg/day escitalopram for eight weeks. They were randomly assigned in equal numbers to receive active drug or placebo in double-blind fashion. Hot flash frequency was measured with an ambulatory recorder during the first three weeks and during the eighth week of the study. The rectal temperature threshold for sweating was measured during the first and eighth weeks of the study using published methods. Results-In the first study, there were no significant effects whatsoever for any measure. In the second study, the escitalopram group showed an average decline in hot flash frequency of 14.4%, whereas, the placebo group showed an average increase of 6.7% (P < .05). However, there were no significant effects across time for either group. There were no significant effects whatsoever for rectal temperature sweating thresholds. Conclusions-Escitalopram at 10 mg or 20 mg/day is not effective in the treatment of menopausal hot flashes.
Objective: To investigate the effects of decreasing androgen levels on insulin action, in view of... more Objective: To investigate the effects of decreasing androgen levels on insulin action, in view of the relationship between hyperandrogenism and impaired insulin action in women with polycystic ovary syndrome.
American Journal of Obstetrics and Gynecology, 2013
The purpose of this study was to determine whether nuclear magnetic resonanceebased metabolomic m... more The purpose of this study was to determine whether nuclear magnetic resonanceebased metabolomic markers in firsttrimester maternal serum can detect fetuses with trisomy 18. STUDY DESIGN: This was a study of pregnancies between 11 weeks and 13 weeks 6 days' gestation. We analyzed 30 cases of trisomy 18 and a total of 114 euploid cases. Nuclear magnetic resonanceebased metabolomic analysis was performed. A further analysis was performed that compared 30 cases with trisomy 18 and 30 trisomy 21 (T21) cases. RESULTS: Metabolomic markers were sensitive for trisomy 18 detection. A combination of 2-hydroxybutyrate, glycerol and maternal age had a 73.3% sensitivity and 96.6% specificity for trisomy 18 detection, with an area under the receiver operating curve: 0.92 (P < .001). Other metabolite markers, which include trimethylamine, were sensitive for distinguishing trisomy 18 from T21 cases. CONCLUSION: This is the first report of prenatal trisomy 18 detection that has been based on metabolomic analysis. Preliminary results suggest that such markers are sensitive not only for the detection of fetal trisomy 18 but also for distinguishing this aneuploidy from T21.
This paper examines the hypothesis that cocaine and BE assays of hair demonstrate a putative bias... more This paper examines the hypothesis that cocaine and BE assays of hair demonstrate a putative bias effect for darker color hair samples. Although such an effect has been reported in the literature, no one has examined this claim outside the bounds of simple significance of mean difference. In this paper a large number of black and brown hair samples are compared for cocaine and BE concentration values, and this comparison is evaluated for both significance and effect size. Two innovative measures are used to assess this relationship - a calculation of effect size using Cohen&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s d, and the use of an ROC curve to evaluate the potential for a dark color bias. The paper reports mixed results for significance, but consistent results for effect size. There does not appear to be any significant effect for cocaine. While BE demonstrates a significant mean difference, both the effect size and the ROC analysis show the effect to be trivial.
In a variety of decision settings when categorical information is the data in hand, the correspon... more In a variety of decision settings when categorical information is the data in hand, the correspondence between an indicator test and a true condition (i.e., an accepted "gold standard") is often assessed by the use of comparison or "truth" tables. The results from such a table can be considered an informational yield and allow a practitioner to assess the utility of the indicator test in various ways, such as specificity and sensitivity, false positive and negative rates, and the positive and negative predictive values. There are many reasons for the use of an indicator test. This article proposes a novel application of an informational measure in determining the utility of hair and urine specimens for clinical decision making. It does this for two commonly abused substances, cocaine and cannabinoids. It suggests that in clinical applications the ability to assess informational yield is an important factor in developing clinical strategies for treatment of addictive disorders.
Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine, 2007
The aim of this study was to compare gestational age at delivery and the performance of middle ce... more The aim of this study was to compare gestational age at delivery and the performance of middle cerebral artery (MCA), ductus venosus (DV), and umbilical artery Doppler parameters in the prediction of perinatal mortality and morbidity in intrauterine growth-restricted (IUGR) fetuses delivered at 32 weeks or earlier. The study population consisted of 41 patients with IUGR fetuses. Delivery occurred for maternal or fetal indications. Two-tailed chi(2) and Fisher exact tests, an independent t test, and logistic regression were used for the analysis. P < .05 was considered statistically significant. Gestational age at delivery ranged between 23.1 and 32 weeks (median, 27.6 weeks). There were 17 perinatal deaths. Ninety-four percent of the perinatal deaths occurred when the fetuses were delivered before 29 weeks. No fetus survived when delivered before 25 weeks. Two parameters predicted the perinatal mortality: gestational age at delivery (odds ratio, 0.52; 95% confidence interval, 0.3...
The promise of ultrafast light field driven electronic nanocircuits has stimulated the developmen... more The promise of ultrafast light field driven electronic nanocircuits has stimulated the development of the new research field of attosecond nanophysics. An essential prerequisite for advancing this new area is the ability to characterize optical nearfields from light interaction with nanostructures with sub cycle resolution. Here, we experimentally demonstrate attosecond nearfield retrieval with a gold nanotip using streaking spectroscopy. By comparison of the results from gold nanotips to those obtained for a noble gas, the spectral response of the nanotip near field arising from laser excitation can be extracted. Monte Carlo MC trajectory simulations in near fields obtained with the macroscopic Maxwells equations elucidate the streaking mechanism on the nanoscale.
This paper presents the methodology for a new technique to measure the impedance of transmission ... more This paper presents the methodology for a new technique to measure the impedance of transmission lines and the associated earth fault return paths. The test procedure is detailed, and practical results are presented from tests on a utility network. The procedure is critically examined for comparison with existing theoretical studies and other empirical methods to calculate distance protection and fault location settings. The significance of the varied quality and accuracy of the results from these existing techniques arises from the particular importance of the accuracy of the residual compensation or k-factor setting in preventing over- or under-reach of the protection of transmission line systems. The simple practical method presented has highlighted the limitations and the cost of failure of existing techniques, with major implications for improving the protection of, fault finding and fault-location on the electricity transmission network. Related testing proposals are also pres...
Sweep Frequency Response Analysis (SFRA) has turned out to be a powerful and sensitive method to ... more Sweep Frequency Response Analysis (SFRA) has turned out to be a powerful and sensitive method to evaluate the mechanical integrity of core, windings and clamping structures within power transformers by measuring their electrical transfer functions over a wide frequency range. The contribution summarizes various aspects of the practical application of SFRA. After a short introduction of SFRA basics a survey of existing standards and guides on FRA is given. The different sources of reference data and their significance are discussed. Uncertainties are shown and tips for dealing with them are presented. The choice of test types is discussed for measurements without existing reference data. Information about the handling of test data is mentioned. Finally a summary of guidelines derived from a large number of successful measurements is given to put the reader in a position to achieve a good degree of repeatability, too.
This paper starts with a systematic benchmark test of the three commercialised dielectric diagnos... more This paper starts with a systematic benchmark test of the three commercialised dielectric diagnostic methods RVM (recovery voltage method), PDC (polarisation and depolarisation currents) and FDS (frequency domain spectroscopy), performed on a large transformer model. The water content as analysed by the specific software was compared under three parame-ters: insulation geometry, insulation temperature and oil conductivity. It was found, that for the RV method the interpretation scheme based on the central time constant is too simplistic. The other two methods PDC and FDS compensate much better for the mentioned parameters but nevertheless analyse a drier cellulose with increas-ing temperature and a wetter cellulose for increasing oil conductivity. Actually the moisture in cellulose re-mained constant at 1 % during all the tests. Starting from these weaknesses a more sophisticated software was developed. The new software called "Dirana" bases on a new data pool, measured at...
The transfer function (TF), also called frequency response, can be used as a diagnostic method to... more The transfer function (TF), also called frequency response, can be used as a diagnostic method to detect mechanical and electrical defects. The assessment of FRA (Frequency Response Analysis) results is done by a comparison between a recent and a previous measurement, which is called the reference measurement. An acknowledged problem with FRA is that up to now there is no international standardized procedure for comparison. Analyses are done by experts but run the risk of being judged with subjectivity. Thus, the need for an algorithm enabling quantitative determination of the identicalness of two FRA measurements within a certain frequency range is obvious. The article will present different algorithms to assess the FRA: expectation, standard deviation, correlation factor and analysis of resonance frequencies. The performance of these algorithms is verified using data sets obtained during measurements for the investigation of sensitivity of the FRA method to mechanical winding disp...
The frequency response analysis (FRA) is a well-established method used for assessment of the mec... more The frequency response analysis (FRA) is a well-established method used for assessment of the mechanical and electrical conditions of power transformer windings. The evaluation of the winding condition is done by comparison between an actual FRA and a reference FRA, which are carried out previously. A deviation between both FRA curves can indicate a change of the winding condition of the tested transformer. According to the standard of knowledge, the connections between measuring device and transformer terminals, as well as the grounding technique are of main importance for a good repeatability. Additionally, a power transformer is a large construction that needs long cables and grounding lines for the signal transmission. Against this background, it is clear, that the geometric arrangement of the measuring setup may not be the same as it was at the reference measurement and this change can have an influence on FRA results. Therefore, an excellent repeatability of the measurements i...
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Papers by Michael Kruger