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Visagie IJH, de Waal DJ, Makgai SL, Bekker A. Contributions to the class of beta-generated distributions. COMMUN STAT-THEOR M 2021. [DOI: 10.1080/03610926.2021.1923748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- I. J. H. Visagie
- Subject Group Statistics, North-West University, Potchefstroom, South Africa
| | - D. J. de Waal
- Department of Statistics, University of Pretoria, Pretoria, South Africa
- Department of Mathematical Statistics and Actuarial Science, University of the Free State, Bloemfontein, South Africa
| | - S. L. Makgai
- Department of Statistics, University of Pretoria, Pretoria, South Africa
| | - A. Bekker
- Department of Statistics, University of Pretoria, Pretoria, South Africa
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Bekker A, Ferreira JT, Arashi M, Rowland BW. Computational methods applied to a skewed generalized normal family. COMMUN STAT-SIMUL C 2018. [DOI: 10.1080/03610918.2018.1530785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- A. Bekker
- Department of Statistics, University of Pretoria, Pretoria, South Africa
| | - J. T. Ferreira
- Department of Statistics, University of Pretoria, Pretoria, South Africa
| | - M. Arashi
- Department of Statistics, School of Mathematical Sciences, Shahrood University of Technology, Shahrood, Iran
| | - B. W. Rowland
- Department of Statistics, University of Pretoria, Pretoria, South Africa
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Swart D, Bekker A, Bienert J. Electric vehicle sound stimuli data and enhancements. Data Brief 2018; 21:1337-1346. [PMID: 30456255 PMCID: PMC6230979 DOI: 10.1016/j.dib.2018.10.074] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Revised: 10/15/2018] [Accepted: 10/22/2018] [Indexed: 11/24/2022] Open
Abstract
Data for six electric vehicle WOT interior sound measurements and eight enhanced sound signatures are presented. The measurement of electric vehicle interior sound signature data and the enhancement of these stimuli are documented in this data article. The procedures and equipment that were used to record the data, as well as the transposition, harmony and order addition, frequency filtering and modulation enhancement techniques that were applied to these stimuli are explained in detail. The transient frequency content of the 12 sound stimuli is presented in acoustic spectrograms along with the audio files in.mp3 format.
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de Waal R, Bekker A, Heyns P. Data for indirect load case estimation of ice-induced moments from shaft line torque measurements. Data Brief 2018; 19:1222-1236. [PMID: 30229002 PMCID: PMC6140293 DOI: 10.1016/j.dib.2018.05.115] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 05/15/2018] [Accepted: 05/20/2018] [Indexed: 11/27/2022] Open
Abstract
During ice navigation, blade measurements of ice-induced moments on ship propellers, are challenged by the harsh operating environment. To overcome this problem, shaft line measurements are performed inboard, and the required propeller loads are subsequently estimated using a dynamic model and the solution of an inverse problem. The inverse problem is mathematically ill-posed and requires the determination of the ice-induced moment on the propeller blades from shaft line measurements. Full-scale torsional response data is presented as calculated from indirect strain measurements on the shaft line of a polar supply and research vessel. The vessel operated on a 68-day voyage between Cape Town and Antarctica and spent almost 11 days in sea ice with observed concentrations above 90% and a maximum thickness of 3 m. Data for five ice-induced load cases are presented, including the shaft torque from indirect measurements and the estimated ice-induced moment, which is obtained by solving an ill-posed inverse problem. The ice-induced moments on the propeller are obtained by approximating the drive-train as a viscously damped, elastic lumped mass model. The ice-induced moment is then determined through existing approaches to solving the ill-conditioned inverse problem. The lumped mass model is presented along with algorithms to solve the inverse problem, including truncated singular value decomposition, truncated generalized singular value decomposition and Tikhonov׳s method. The resulting time series data for the inversely calculated ice-induced moments is published to provide industry with load cases for ice-going propulsion design.
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Affiliation(s)
- R.J.O. de Waal
- Sound and Vibration Research Group, Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Stellenbosch, South Africa
| | - A. Bekker
- Sound and Vibration Research Group, Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Stellenbosch, South Africa
| | - P.S. Heyns
- Centre for Asset Integrity Management, University of Pretoria, Pretoria, South Africa
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Bindeman IN, Zakharov DO, Palandri J, Greber ND, Dauphas N, Retallack GJ, Hofmann A, Lackey JS, Bekker A. Rapid emergence of subaerial landmasses and onset of a modern hydrologic cycle 2.5 billion years ago. Nature 2018; 557:545-548. [DOI: 10.1038/s41586-018-0131-1] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Accepted: 03/07/2018] [Indexed: 11/10/2022]
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Omer H, Bekker A. Human responses to wave slamming vibration on a polar supply and research vessel. Appl Ergon 2018; 67:71-82. [PMID: 29122202 DOI: 10.1016/j.apergo.2017.09.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 08/09/2017] [Accepted: 09/13/2017] [Indexed: 06/07/2023]
Abstract
A polar supply and research vessel is pre-disposed to wave slamming which has caused complaints among crew and researchers regarding interference with sleep, equipment use and research activities. The present work undertook to survey passenger claims of sleep interference, disturbed motor tasks and equipment damage as a result of wave slamming during normal operations of this vessel. The hypothesis was investigated that whole-body vibration metrics from ISO 2631-1 are potentially suitable for the prediction of human slamming complaints. Full-scale acceleration measurements were performed and wave slamming events were subsequently identified from the human weighted acceleration time histories. A daily diary survey was also conducted to gather the human response. The vibration caused by wave slamming was found to be strongly correlated with sleep disturbances and activity interference. Sleep and equipment use were found to be the most affected parameters by slamming. Daily vibration dose values were determined by accumulating the vibration as a result of slamming over 24 h periods. This metric accounted for increased magnitudes and frequency of slamming incidents and proved to be the best metric to represent human responses to slamming vibration. The greatest percentage of activities affected by slamming related to sleep regardless of daily cumulative VDV magnitude. More than 50% of the recorded responses related to sleep when the daily cumulative VDV ranged between 8.0 m/s1.75-10.0 m/s1.75. The peak vertical vibration levels recorded on the vessel reach magnitudes which are associated with sleep disturbance in environments where acoustic noise is present.
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Affiliation(s)
- H Omer
- Sound and Vibration Research Group, Department of Mechanical and Mechatronic Engineering, Stellenbosch University, South Africa
| | - A Bekker
- Sound and Vibration Research Group, Department of Mechanical and Mechatronic Engineering, Stellenbosch University, South Africa.
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McIlleron H, Hundt H, Smythe W, Bekker A, Winckler J, van der Laan L, Smith P, Zar HJ, Hesseling AC, Maartens G, Wiesner L, van Rie A. Bioavailability of two licensed paediatric rifampicin suspensions: implications for quality control programmes. Int J Tuberc Lung Dis 2018; 20:915-9. [PMID: 27287644 DOI: 10.5588/ijtld.15.0833] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
SETTING To assess the revised World Health Organization-recommended dose of 10-20 mg/kg rifampicin (RMP), we studied the steady state pharmacokinetics of RMP in South African children who received standard treatment for drug-susceptible tuberculosis (TB). OBJECTIVE To determine the formulation effect on the pharmacokinetics of RMP. DESIGN RMP plasma concentrations were characterised in 146 children (median age 1.4 years, range 0.2-10.2). The morning dose on the day of the pharmacokinetic evaluation was administered as one of two RMP single-drug oral suspensions. RESULTS While one formulation achieved 2 h concentrations in the range of those observed in adults (median 6.54 mg/l, interquartile range [IQR] 4.47-8.84), the other attained a median bioavailability of only 25% of this, with a median 2 h concentration of 1.59 mg/l (IQR 0.89-2.38). CONCLUSION RMP is a key drug for the treatment of TB. It is critical that the quality of RMP suspensions used to treat childhood TB is ensured.
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Affiliation(s)
- H McIlleron
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - H Hundt
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - W Smythe
- Division of Clinical Pharmacology, Department of Medicine, Clinical Research Centre, Health Sciences Faculty, University of Cape Town, Cape Town, South Africa
| | - A Bekker
- Desmond Tutu TB Centre, Department of Paediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - J Winckler
- Department of Paediatrics and Child Health, and Medical Research Council Unit on Child and Adolescent Health, University of Cape Town, Cape Town, South Africa
| | - L van der Laan
- Desmond Tutu TB Centre, Department of Paediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - P Smith
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - H J Zar
- Department of Paediatrics and Child Health, and Medical Research Council Unit on Child and Adolescent Health, University of Cape Town, Cape Town, South Africa; Red Cross War Memorial Children's Hospital, Cape Town, South Africa
| | - A C Hesseling
- Desmond Tutu TB Centre, Department of Paediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - G Maartens
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - L Wiesner
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - A van Rie
- Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA; International Health Unit, Epidemiology and Social Medicine, Faculty of Medicine, University of Antwerp, Antwerp, Belgium
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Affiliation(s)
- A. Bekker
- Department of Statistics, University of Pretoria, Pretoria, South Africa
| | - M. Arashi
- Department of Statistics, University of Pretoria, Pretoria, South Africa
- Department of Statistics, School of Mathematical Sciences, Shahrood University of Technology, Shahrood, Iran
| | - J. T. Ferreira
- Department of Statistics, University of Pretoria, Pretoria, South Africa
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Dramowski A, Aucamp M, Bekker A, Mehtar S. Infectious disease exposures and outbreaks at a South African neonatal unit with review of neonatal outbreak epidemiology in Africa. Int J Infect Dis 2017; 57:79-85. [PMID: 28161461 DOI: 10.1016/j.ijid.2017.01.026] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Revised: 01/17/2017] [Accepted: 01/23/2017] [Indexed: 01/15/2023] Open
Abstract
BACKGROUND Hospitalized neonates are vulnerable to infection, with pathogen exposures occurring in utero, intrapartum, and postnatally. African neonatal units are at high risk of outbreaks owing to overcrowding, understaffing, and shared equipment. METHODS Neonatal outbreaks attended by the paediatric infectious diseases and infection prevention (IP) teams at Tygerberg Children's Hospital, Cape Town (May 1, 2008 to April 30, 2016) are described, pathogens, outbreak size, mortality, source, and outbreak control measures. Neonatal outbreaks reported from Africa (January 1, 1996 to January 1, 2016) were reviewed to contextualize the authors' experience within the published literature from the region. RESULTS Thirteen outbreaks affecting 148 babies (11 deaths; 7% mortality) over an 8-year period were documented, with pathogens including rotavirus, influenza virus, measles virus, and multidrug-resistant bacteria (Serratia marcescens, Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci). Although the infection source was seldom identified, most outbreaks were associated with breaches in IP practices. Stringent transmission-based precautions, staff/parent education, and changes to clinical practices contained the outbreaks. From the African neonatal literature, 20 outbreaks affecting 524 babies (177 deaths; 34% mortality) were identified; 50% of outbreaks were caused by extended-spectrum β-lactamase-producing Klebsiella pneumoniae. CONCLUSIONS Outbreaks in hospitalized African neonates are frequent but under-reported, with high mortality and a predominance of Gram-negative bacteria. Breaches in IP practice are commonly implicated, with the outbreak source confirmed in less than 50% of cases. Programmes to improve IP practice and address antimicrobial resistance in African neonatal units are urgently required.
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Affiliation(s)
- A Dramowski
- Department of Paediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, PO Box 241, Cape Town 8000, South Africa.
| | - M Aucamp
- Academic Unit for Infection Prevention and Control, Division of Community Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - A Bekker
- Department of Paediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, PO Box 241, Cape Town 8000, South Africa
| | - S Mehtar
- Academic Unit for Infection Prevention and Control, Division of Community Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
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Affiliation(s)
- J. Kleyn
- Department of Statistics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa
| | - M. Arashi
- Department of Statistics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa
- Department of Statistics, School of Mathematical Sciences, Shahrood University of Technology, Shahrood, Iran
| | - A. Bekker
- Department of Statistics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa
| | - S. Millard
- Department of Statistics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa
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Mostert PJ, Bekker A, Roux JJJ. A Bayesian analysis for censored Rayleigh model using a generalised hypergeometric prior. sasj 2016. [DOI: 10.37920/sasj.2016.50.2.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Based on a type II censored sample, Bayesian estimation for the scale parameter of the Rayleigh model is carried out under the assumption of the squared error loss function. A generalised hypergeometric distribution with its versatile shape of tails is introduced as a prior, and beta special cases are examined. A simulation study is carried out to investigate the sensitivity of four special cases of this beta prior family in terms of bias, frequentist coverage and mean square error and to determine their effect on robustness. Prediction bounds are derived for the lifetime of unused components using this beta prior family. A data set is used to illustrate and support some of the findings.
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Kline R, Wong E, Haile M, Didehvar S, Farber S, Sacks A, Pirraglia E, de Leon MJ, Bekker A. Peri-Operative Inflammatory Cytokines in Plasma of the Elderly Correlate in Prospective Study with Postoperative Changes in Cognitive Test Scores. ACTA ACUST UNITED AC 2016; 4:313-321. [PMID: 28317003 DOI: 10.19070/2332-2780-1600065] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Increasingly, postoperative cognitive dysfunction (POCD) is recognized as a complication after surgery in the elderly; but it's etiology remains unclear. Here we examine changes in cytokine levels during both the pre-operative and postoperative period, comparing them with long term variation in cognitive test scores. Forty-one patients aged 65 and older undergoing major surgery with general anesthesia were recruited after written consent in this IRB approved study. Thirty went on to complete this prospective, non-interven-tional and non-randomized study. Plasma levels of cytokines Il-6, Il-8, Il-10, and TNF were determined using ELISA with MILLIPLEX Multi-Analyte Profiling (Billerica, MA). All subjects had neurocognitive tests pre-operatively and 6 months post-surgery, including Paragraph Recall Immediate and Delayed, Digit Span Forward (DSF) and Backward (DSB), and Trail Making A and B. Spearman's Rho and repeated measure rank analysis were used to examine the dependence of z score changes in cognitive tests (baseline versus 6 months) as a function of 3 cytokine time points (presurgical, post anesthesia care unit (PACU), and post-operative day one (POD1)). A greater increase in PACU inflammatory burden correlated with a greater decline in performance on the DSB (IL6, IL8; r>-0.560; p<= 0.008). DSF changes correlated slightly better with pre-surgical cytokines, declining more with higher cytokines (IL6, r= -0.551, p=0.002; IL8, -0.468, 0.009). TNF, examining all 3 values, changed only slightly postoperatively, but still correlated with a decline in DSB (p=0.014). Thus, cognitive performance, over 6 months post surgery, declines with elevated perioperative inflammation. Specific cytokines at specific perioperative times may impact specific cognitive functions, serving as diagnostics as well as contributing causation.
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Affiliation(s)
- R Kline
- Department of Anesthesiology, Perioperative Care and Pain Medicine, The New York University School of Medicine, USA.; New York University School of Medicine, Center for Cognitive Neurology
| | - E Wong
- Department of Anesthesiology, Perioperative Care and Pain Medicine, The New York University School of Medicine, USA.; New York University School of Medicine, Center for Cognitive Neurology
| | - M Haile
- Department of Anesthesiology, Perioperative Care and Pain Medicine, The New York University School of Medicine, USA.; New York University School of Medicine, Center for Cognitive Neurology
| | - S Didehvar
- Department of Anesthesiology, Perioperative Care and Pain Medicine, The New York University School of Medicine, USA
| | - S Farber
- Department of Anesthesiology, Perioperative Care and Pain Medicine, The New York University School of Medicine, USA
| | - A Sacks
- Department Neuropsychology, Weill Cornell Medical College
| | - E Pirraglia
- Department of Anesthesiology, Perioperative Care and Pain Medicine1& Psychiatry of The New York University School of Medicine, USA.; New York University School of Medicine, Center for Cognitive Neurology and Center for Brain Health
| | - M J de Leon
- Department of Anesthesiology, Perioperative Care and Pain Medicine1& Psychiatry of The New York University School of Medicine, USA.; New York University School of Medicine, Center for Cognitive Neurology and Center for Brain Health
| | - A Bekker
- Department of Anesthesiology Rutgers NJMS
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Bekker A, Schaaf HS, Draper HR, van der Laan L, Murray S, Wiesner L, Donald PR, McIlleron HM, Hesseling AC. Pharmacokinetics of Rifampin, Isoniazid, Pyrazinamide, and Ethambutol in Infants Dosed According to Revised WHO-Recommended Treatment Guidelines. Antimicrob Agents Chemother 2016; 60:2171-9. [PMID: 26810651 PMCID: PMC4808214 DOI: 10.1128/aac.02600-15] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 01/17/2016] [Indexed: 11/20/2022] Open
Abstract
There are limited pharmacokinetic data for use of the first-line antituberculosis drugs during infancy (<12 months of age), when drug disposition may differ. Intensive pharmacokinetic sampling was performed in infants routinely receiving antituberculosis treatment, including rifampin, isoniazid, pyrazinamide, and ethambutol, using World Health Organization-recommended doses. Regulatory-approved single-drug formulations, including two rifampin suspensions, were used on the sampling day. Assays were conducted using liquid chromatography-mass spectrometry; pharmacokinetic parameters were generated using noncompartmental analysis. Thirty-nine infants were studied; 14 (36%) had culture-confirmed tuberculosis. Fifteen (38%) were premature (<37 weeks gestation); 5 (13%) were HIV infected. The mean corrected age and weight were 6.6 months and 6.45 kg, respectively. The mean maximum plasma concentrations (Cmax) for rifampin, isoniazid, pyrazinamide, and ethambutol were 2.9, 7.9, 41.9, and 1.3 μg/ml, respectively (current recommended adult target concentrations: 8 to 24, 3 to 6, 20 to 50, and 2 to 6 μg/ml, respectively), and the mean areas under the concentration-time curves from 0 to 8 h (AUC0-8) were 12.1, 24.7, 239.4, and 5.1 μg · h/ml, respectively. After adjusting for age and weight, rifampin exposures for the two formulations used differed inCmax(geometric mean ratio [GMR],2.55; 95% confidence interval [CI], 1.47 to 4.41;P= 0.001) and AUC0-8(GMR, 2.52; 95% CI, 1.34 to 4.73;P= 0.005). HIV status was associated with lower pyrazinamideCmax(GMR, 0.85; 95% CI, 0.75 to 0.96;P= 0.013) and AUC0-8(GMR, 0.79; 95% CI, 0.69 to 0.90;P< 0.001) values. No other important differences were observed due to age, weight, prematurity, ethnicity, or gender. In summary, isoniazid and pyrazinamide concentrations in infants compared well with proposed adult target concentrations; ethambutol concentrations were lower but similar to previously reported pediatric studies. The low rifampin exposures require further investigation. (This study has been registered at ClinicalTrials.gov under registration no. NCT01637558.).
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Affiliation(s)
- A Bekker
- Desmond Tutu TB Center, Department of Pediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - H S Schaaf
- Desmond Tutu TB Center, Department of Pediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - H R Draper
- Desmond Tutu TB Center, Department of Pediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - L van der Laan
- Desmond Tutu TB Center, Department of Pediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - S Murray
- Department of Clinical Research, Global Alliance for TB Drug Development, New York, New York, USA
| | - L Wiesner
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - P R Donald
- Desmond Tutu TB Center, Department of Pediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
| | - H M McIlleron
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - A C Hesseling
- Desmond Tutu TB Center, Department of Pediatrics and Child Health, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
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Bekker A, Steyn L, Charimba G, Jooste P, Hugo C. Comparison of the growth kinetics and proteolytic activities of Chryseobacterium species and Pseudomonas fluorescens. Can J Microbiol 2015; 61:977-82. [DOI: 10.1139/cjm-2015-0236] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effect of temperature on the growth kinetics and proteolytic activity of Chryseobacterium joostei and Chryseobacterium bovis was determined during this study. The results were compared with the activities of Pseudomonas fluorescens, which is regarded to be a major food spoilage psychrotolerant microorganism. For the growth studies, cultures were incubated in nutrient broth in a temperature gradient incubator (from 9 to 50 °C) and separately at 4 °C, and the optical density was measured at different time intervals. Growth temperature profiles for each organism were constructed. For determination of proteolytic activity, the cultures were incubated in fat-free ultra-high temperature processed milk in the temperature gradient incubator for 72 h (temperature range as above). Cell-free extracts were used to determine the proteolytic activity using the azocasein method. Results of the growth studies showed that C. joostei had the ability to grow over a wider temperature range than C. bovis and P. fluorescens without being affected by changes in the temperature. For the proteolytic activity, C. joostei had significantly (p < 0.001) higher activity per milligram of protein at 15.5 °C, followed by C. bovis and P. fluorescens. The results showed that C. joostei potentially has an even greater spoilage capacity in milk on the basis of growth rate and proteolytic activity than did P. fluorescens.
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Affiliation(s)
- A. Bekker
- Department of Microbial, Biochemical, and Food Biotechnology, University of the Free State, Bloemfontein, South Africa
| | - L. Steyn
- Department of Microbial, Biochemical, and Food Biotechnology, University of the Free State, Bloemfontein, South Africa
| | - G. Charimba
- Department of Microbial, Biochemical, and Food Biotechnology, University of the Free State, Bloemfontein, South Africa
| | - P. Jooste
- Department of Biotechnology and Food Technology, Tshwane University of Technology, Pretoria, South Africa
| | - C. Hugo
- Department of Microbial, Biochemical, and Food Biotechnology, University of the Free State, Bloemfontein, South Africa
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Arashi M, Bekker A, Loots MT, Roux JJJ. Integral Representation of Quaternion Elliptical Density and its Applications. COMMUN STAT-THEOR M 2015. [DOI: 10.1080/03610926.2012.753089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Coetsee J, Bekker A, Millard S. Preliminary test and Bayes Estimation of a Location Parameter Under Blinex Loss. COMMUN STAT-THEOR M 2014. [DOI: 10.1080/03610926.2012.707737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Morkel G, Bekker A, Marais BJ, Kirsten G, van Wyk J, Dramowski A. Bloodstream infections and antimicrobial resistance patterns in a South African neonatal intensive care unit. Paediatr Int Child Health 2014; 34:108-14. [PMID: 24621234 DOI: 10.1179/2046905513y.0000000082] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
BACKGROUND Bloodstream infections remain a leading cause of morbidity and mortality in neonatal intensive care units (NICU) worldwide. Commonly isolated NICU pathogens are increasingly resistant to standard antimicrobial treatment regimes. OBJECTIVES The primary aim of this study was to determine the burden of bloodstream infections (BSI) in an NICU in a low-to-middle-income country and to describe the spectrum of pathogens isolated together with their drug susceptibility patterns. METHODS This retrospective, descriptive study included NICU patients admitted to the Tygerberg Children's Hospital, Cape Town, between 1 January and 31 December 2008. All blood culture samples submitted to the reference laboratory were extracted and clinical data on patients were obtained by hospital record review. RESULTS There were 78 culture-confirmed episodes of BSI in 54/503 (11%) patients admitted; median gestational age was 31 weeks (IQR 29-37) and birth weight 1370 g (IQR 1040-2320). Common isolates included coagulase-negative Staphylococcus (22/78, 28%), Klebsiella spp. (17/78, 22%), Acinetobacter spp. (14/78, 18%), Candida spp. (9/78, 11·5%) and methicillin-resistant Staphylococcus aureus (5/78, 6%). There was a predominance of gram-negative organisms (38/78, 48·7%). All Staphylococcus aureus isolates were methicillin-resistant and 59% of Klebsiella pneumoniae isolates were extended spectrum β-lactamase (ESBL) producers. Acinetobacter baumanii isolates showed low susceptibility to the aminoglycosides, carbapenems and cephalosporins. Of 54 infants admitted to the NICU with BSI, 25 (46%) died; 9/25 deaths (36%) were attributable solely to infection. CONCLUSION Compared with overall mortality in the NICU, that attributable solely or partly to BSI was high. Many bacterial BSI isolates were resistant to current empiric antibiotic regimens. Regular microbiological and clinical surveillance of BSI in NICUs is required to inform appropriate antibiotic protocols and monitor the impact of infection prevention strategies.
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Bekker A, Slogrove AL, Schaaf HS, Du Preez K, Hesseling AC. Determinants of tuberculosis treatment completion among newborns in a high-burden setting. Int J Tuberc Lung Dis 2014; 18:335-40. [DOI: 10.5588/ijtld.13.0506] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Didehvar S, Viola-Blitz J, Haile M, Franco L, Kline R, Kurian M, Fielding G, Ren C, Bekker A. A Randomized, Double Blind Study to Evaluate the Efficacy of Palonosetron with Dexamethasone Versus Palonosetron Alone for Prevention of Post-Operative Nausea and Vomiting in Subjects Undergoing Bariatric Surgeries with High Emetogenic Risk. ACTA ACUST UNITED AC 2013. [DOI: 10.2174/1874321801307010030] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Introduction:
Postoperative (PONV) and postdischarge (PDNV) nausea and vomiting are common (60-70%) after bariatric surgery. Palonosetron (Pal), a novel 5-HT3 antagonist, is an effective antiemetic with a prolonged duration of action in the setting of PDNV. We hypothesized that combination therapy with Palonosetron (Pal) and dexamethasone (Dex) would improve treatment in comparison to Palonosetron alone in patients at high risk for PONV.
Methods:
In this study, patients undergoing bariatric laparoscopic surgery under general anesthesia, a subgroup of a larger Phase IV clinical trial of patients who had laparoscopic surgery, were randomized to 8 mg Dex + 0.075mg Pal or saline + 0.075mg Pal. Data was collected postoperatively at 2, 6, 24 and 72 hrs. A Functional Living Index-Emesis (QOL-FLIE) test was administered at 96 hrs.
Results:
We enrolled 76 ASA 1-2 patients with at least 3 PONV risk factors. Both randomization groups had a low incidence of vomiting in the PACU (Pal, 0.0%; Pal + Dex, 5.4%) as well as at 72 hours (0.0% both groups). Complete response (no vomiting, no rescue medication) was not different between treatment groups at any time intervals. Cumulative success rates over the entire 72 hrs were 60.4% (Pal alone) vs. 60.0% (Pal + Dex). Nausea scores (4 point ordinal scale) were not different between groups for any time intervals. Cumulative success scores for nausea (score = “none”; 0-72 hrs) were 41.9% for the Pal group, and 55.2% for the Pal+ Dex group. The Pal + Dex group showed a trend toward greater satisfaction on the QOL-FLIE scores with the greatest differences in the “nausea domain”.
Discussion:
The combination therapy (Pal + Dex) did not significantly reduce the incidence of PONV or PDNV when compared with Pal alone although a trend was observed indicating the possible increased efficacy of multi-drug therapy. There was no change in comparative efficacy over 72 hrs, possibly due to the low incidence of PDNV in both groups.
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Jacobs R, Bekker A, Human SW. On the Bivariate Kummer-Beta Type IV Distribution. COMMUN STAT-THEOR M 2012. [DOI: 10.1080/03610926.2011.560737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Bekker A, Du Preez K, Schaaf HS, Cotton MF, Hesseling AC. High tuberculosis exposure among neonates in a high tuberculosis and human immunodeficiency virus burden setting. Int J Tuberc Lung Dis 2012; 16:1040-6. [PMID: 22691968 DOI: 10.5588/ijtld.11.0821] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Maternal and neonatal tuberculosis (TB) are under-recognised, particularly in settings with a high burden of human immunodeficiency virus (HIV) infection. DESIGN AND SETTING Retrospective audit of neonates routinely screened for TB in a South African hospital during 2009. Surveillance sources reviewed included routine clinical, laboratory and pharmacy records. RESULTS Among 70 neonates (60% HIV-exposed) screened for TB, the median gestational age was 35.5 weeks (IQR 33-38), and the median birth weight was 2000 g (IQR 1530-2484). The neonates were grouped according to a history of documented TB exposure: maternal TB in 41/70 (59%), suspected maternal TB in 9/70 (13%), other documented household TB exposure in 5/70 (7%), and no known TB exposure 15/70 (21%). Of the 50 neonates exposed to confirmed or suspected maternal TB, 36 (72%) were initiated on TB chemoprophylaxis, 5 (10%) received TB treatment and 9 (18%) received no intervention. Eight (8/50, 16%) were diagnosed with TB, all of whom were born to mothers with suspected or proven TB. CONCLUSIONS Maternal TB, primarily among HIV-infected women, was the main indication for TB screening of neonates. Routine TB screening of pregnant women and TB care in mothers and infants should be improved in settings with a high burden of TB and HIV.
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Affiliation(s)
- A Bekker
- Division of Neonatology, Department of Paediatrics and Child Health, Faculty of Health Science, Stellenbosch University, Cape Town, South Africa.
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Bekker A, Roux JJJ, Ehlers R, Arashi M. Bimatrix Variate Beta Type IV Distribution: Relation to Wilks's Statistic and Bimatrix Variate Kummer-Beta Type IV Distribution. COMMUN STAT-THEOR M 2011. [DOI: 10.1080/03610926.2010.508145] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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Bekker A, Hugo C, Albertyn J, Boucher CE, Bragg RR. Pathogenic Gram-positive cocci in South African rainbow trout, Oncorhynchus mykiss (Walbaum). J Fish Dis 2011; 34:483-487. [PMID: 21545442 DOI: 10.1111/j.1365-2761.2011.01259.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Affiliation(s)
- A Bekker
- Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, Bloemfontein, South Africa
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Dramowski A, Bekker A, Kirsten G, Marais BJ, Rabie H, Cotton MF. A case of congenital measles during the 2010 South African epidemic. Ann Trop Paediatr 2011; 31:185-188. [PMID: 21575327 DOI: 10.1179/1465328111y.0000000010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Congenital measles is a well recognised but uncommon transplacental infection in the post-vaccine era. A 4-day-old infant is described who presented with uncomplicated congenital measles during the 2010 South African measles outbreak. Clinicians working in regions affected by measles outbreaks should be mindful of waning vaccine-induced measles immunity where infections among pregnant women may result in a resurgence of congenital measles.
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Affiliation(s)
- A Dramowski
- Department of Paediatrics & Child Health, Tygerberg Children's Hospital, Stellenbosch University, Cape Town, South Africa.
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Abstract
Disseminated cryptococcosis is an uncommon occurrence in immunocompetent populations and occurs mainly in immunocompromised patients. The first case of cryptococcus meningitis and skin lesions in a 4-year-old confirmed HIV negative boy who presented with fever, meningism and skin lesions is reported. On examination the child was confused, uncooperative, and had neck stiffness and raised skin lesions. A septic screen, including skin scraping, was performed; the child was treated with penicillin and ceftriaxone for suspected meningococcal meningitis. The cerebrospinal fluid (CSF) had normal protein, glucose and chloride levels; yeasts were observed on Gram stain from the CSF and skin scraping. The India ink stain and Cryptococcus neoformans latex agglutination test on the CSF were both positive. Bacterial culture of the skin biopsy, CSF and blood culture specimens was negative. The child was treated with amphotericin B based on preliminary results, and had a gradual recovery with no neurological sequelae. The child continued oral fluconazole.
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Bekker A, Holland HD, Wang PL, Rumble D, Stein HJ, Hannah JL, Coetzee LL, Beukes NJ. Dating the rise of atmospheric oxygen. Nature 2004; 427:117-20. [PMID: 14712267 DOI: 10.1038/nature02260] [Citation(s) in RCA: 371] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2003] [Accepted: 11/28/2003] [Indexed: 11/09/2022]
Abstract
Several lines of geological and geochemical evidence indicate that the level of atmospheric oxygen was extremely low before 2.45 billion years (Gyr) ago, and that it had reached considerable levels by 2.22 Gyr ago. Here we present evidence that the rise of atmospheric oxygen had occurred by 2.32 Gyr ago. We found that syngenetic pyrite is present in organic-rich shales of the 2.32-Gyr-old Rooihoogte and Timeball Hill formations, South Africa. The range of the isotopic composition of sulphur in this pyrite is large and shows no evidence of mass-independent fractionation, indicating that atmospheric oxygen was present at significant levels (that is, greater than 10(-5) times that of the present atmospheric level) during the deposition of these units. The presence of rounded pebbles of sideritic iron formation at the base of the Rooihoogte Formation and an extensive and thick ironstone layer consisting of haematitic pisolites and oölites in the upper Timeball Hill Formation indicate that atmospheric oxygen rose significantly, perhaps for the first time, during the deposition of the Rooihoogte and Timeball Hill formations. These units were deposited between what are probably the second and third of the three Palaeoproterozoic glacial events.
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Affiliation(s)
- A Bekker
- Department of Earth and Planetary Sciences, 20 Oxford Street, Harvard University, Cambridge, Massachusetts 02138, USA.
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Abstract
Intraoperative neurophysiologic monitoring requires information on the effects of anesthetic drugs because these drugs can directly alter evoked potentials, thus interfering with monitoring. We report on our evaluation of the effect of the recently introduced alpha2-adrenergic agonist, dexmedetomidine, on the somatosensory evoked potentials in two patients undergoing cervico-occipital fusion. Our results suggest that, although dexmedetomidine can affect the later cortical peaks of somatosensory evoked potentials (SSEPs), consistent and reproducible potentials can be recorded.
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Affiliation(s)
- M Bloom
- New York University Medical Center, Department of Anesthesiology, New York, New York 10016, USA
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Abstract
A new self-consistency condition in pulsed lasers with strong intracavity dispersion imposes dispersion modes with specific cavity-length dependent pulse rates, utilizing pulse-train self-imaging properties of a temporal Talbot effect. We give an experimental demonstration of such a laser operation, using a long fiber cavity. We also demonstrate temporal Talbot imaging of a train of short pulses that propagate along large distances of dispersive fibers.
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Fischer B, Rosen A, Bekker A, Fishman S. Experimental observation of localization in the spatial frequency domain of a kicked optical system. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 2000; 61:R4694-7. [PMID: 11031504 DOI: 10.1103/physreve.61.r4694] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/1999] [Revised: 10/27/1999] [Indexed: 04/15/2023]
Abstract
An experimental realization of an optical "kicked" system is presented. It exhibits localization analogous to that of the quantum "kicked-rotor." In the experiment, free space propagating light is periodically kicked by thin sinusoidal phase gratings, which produce high order diffractions and tend to increase the spatial frequency band. The wave property suppresses this diffusive spread. The localization is realized in a regime near anti-resonance of the system, which is also studied theoretically. The behavior in this regime is similar to that of electronic motion in incommensurate potentials. A crucial part of the experimental system is the grating in-phase positioning, which is done by using the Talbot effect.
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Affiliation(s)
- B Fischer
- Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa, Israel
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Bekker A, Roux J, Mosteit P. A generalization of the compound rayleigh distribution: using a bayesian method on cancer survival times. COMMUN STAT-THEOR M 2000. [DOI: 10.1080/03610920008832554] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Bekker A. Versternema struthionis in ostriches: is there an association with peritonitis? J S Afr Vet Assoc 1998; 69:118-9. [PMID: 10192083 DOI: 10.4102/jsava.v69i4.838] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
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Karhu JA, Bekker A, Kortelainen N. Paleoproterozoic positive carbon isotope excursion: Comparison of δ13C records in Fennoscandia and North America. Chin Sci Bull 1998. [DOI: 10.1007/bf02891469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Bekker A, Karhu JA, Beukes NJ. Carbon isotope study of early paleoproterozoic interglacial carbonates in North America and South Africa: Implications for the earliest stages of the carbon isotope excursion. Chin Sci Bull 1998. [DOI: 10.1007/bf02891361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Bekker A, Wolk S, Turndorf H, Kristol D, Ritter A. Computer simulation of cerebrovascular circulation: assessment of intracranial hemodynamics during induction of anesthesia. J Clin Monit Comput 1996; 12:433-44. [PMID: 8982908 DOI: 10.1007/bf02199704] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE The purpose of this project was to develop a computer model of cerebrovascular hemodynamics interacting with a pharmacokinetic drug model to examine the effects of various stimuli on cerebral blood flow and intracranial pressure during anesthesia. METHODS The mathematical model of intracranial hemodynamics is a seven-compartment, constant-volume system. A series of resistance relate blood and cerebrospinal fluid fluxes to pressure gradients between compartments. Arterial, venous, and tissue compliance are also included. Autoregulation is modeled by transmural pressure-dependent, arterial-arteriolar resistance. The effect of a drug (thiopental) on cerebrovascular circulation was simulated by a variable arteriolar-capillary resistance. Thiopental concentration was predicted by a three-compartment, pharmacokinetic model. The effect site compartment was included to account for a disequilibrium between drug plasma and biophase concentrations. The model was validated by comparing simulation results with available experimental observations. The simulation program is written in VisSim dynamic simulation language for an IBM-compatible PC. RESULTS The model developed was used to calculate the cerebral blood flow and intracranial pressure changes that occur during the induction phase of general anesthesia. Responses to laryngoscopy and intubation were predicted for simulated patients with elevated intracranial pressure and non-autoregulated cerebral circulation. Simulation shows that the induction dose of thiopental reduces intracranial pressure up to 15%. The duration of this effect is limited to less than 3 minutes by rapid redistribution of thiopental and cerebral autoregulation. Subsequent laryngoscopy causes acute intracranial hypertension, exceeding the initial intracranial pressure. Further simulation predicts that this untoward effect can be minimized by an additional dose of thiopental administered immediately prior to intubation. CONCLUSION The presented simulation allows comparison of various drug administration schedules to control intracranial pressure and preserve cerebral blood flow during induction of anesthesia. The model developed can be extended to analyze more complex intraoperative events by adding new submodels.
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Affiliation(s)
- A Bekker
- Department of Anesthesiology, New York University Medical Center, New York 10016, USA
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Abstract
We demonstrate a new fixing method with Sr(x)Ba(1-x)Nb(2)O(6) crystals. This is done by inducing ferroelectric domains in the crystal in real time, by a screening mechanism. Images or their holograms can be recorded in small separate locations in the crystal. This crystal pixelization permits the recording of many pictures and their individual readout and erasure.
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Wratten ML, van Ginkel G, van't Veld AA, Bekker A, van Faassen EE, Sevanian A. Structural and dynamic effects of oxidatively modified phospholipids in unsaturated lipid membranes. Biochemistry 1992; 31:10901-7. [PMID: 1329957 DOI: 10.1021/bi00159a034] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Phospholipid hydroperoxides and phospholipid alcohols are two of the major forms of oxidatively modified phospholipids produced during oxidant stress and lipid peroxidation. The process of lipid peroxidation is known to affect the physiological function of membranes. We, therefore, investigated the effects of lipid peroxidation products on the molecular interactions in membranes. Our study was specifically focused on the effects of lipid peroxidation products on static membrane structure (molecular orientational order) and on the reorientational dynamics of the probe molecules in lipid bilayers. The study was done by performing angle-resolved fluorescence depolarization measurements (AFD) on the fluorescent probe diphenylhexatriene (DPH) and by performing angle-resolved electron spin resonance (A-ESR) measurements on cholestane (CSL) nitroxide spin probes embedded in macroscopically oriented planar bilayers consisting of 2-10% 1-palmitoyl-2-(9/13-hydroperoxylinoleoyl)phosphatidylcholine (PLPC-OOH) or 1-palmitoyl-2-(9/13-hydroxylinoleoyl)phosphatidylcholine (PLPC-OH) in 1-palmitoyl-2-linoleoylphosphatidylcholine (PLPC) or dilinoleoylphosphatidylcholine (DLPC). Both probe molecules have rigid cylindrical geometries and report on the overall molecular order and dynamics. However, being more polar, the nitroxide spin probe CSL is preferentially located near the surface of the membrane, while the less polar fluorescent probe DPH reports preferentially near the central hydrophobic region of the lipid bilayers. The results show that the presence of relatively small amounts of oxidatively modified phospholipids within the PLPC or DLPC membranes causes pronounced structural effects as the molecular orientational order of the probe molecules is strongly decreased. In contrast, the effect on membrane reorientational dynamics is minimal.
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Affiliation(s)
- M L Wratten
- Department of Pathology, University of Southern California, Los Angeles 90033
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Bekker A, Von Hagen S, Yarmush J. A Macintosh Hypercard stack to simulate the pharmacokinetics of infusion of intravenous anesthetic drugs (NarSim). Comput Appl Biosci 1991; 7:531-2. [PMID: 1747786 DOI: 10.1093/bioinformatics/7.4.531] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- A Bekker
- Department of Anesthesiology, UMDNJ-New Jersey Medical School, Newark 07103
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Roux J, Bekker A. Characterizing priors by posterior expectations in multivariate analysis. Comput Stat Data Anal 1990. [DOI: 10.1016/0167-9473(90)90003-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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