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P Becker

Publications and source records attributed to P Becker.

At least 19 recordsLinked to original sources
PubMed2006

Optical detection and ionization of donors in specific electronic and nuclear spin States.

We resolve the remarkably sharp bound exciton transitions of highly enriched 28Si using a single-frequency laser and photoluminescence excitation spectroscopy, as well as photocurrent spectroscopy. Well-resolved doublets in the spectrum of the 31P donor reflect the hyperfine coupling of the electronic and nuclear donor spins. The optical detection of the nuclear spin state, and selective pumping and ionization of donors in specific electronic and nuclear spin states, suggests a number of new possibilities which could be useful for the realization of silicon-based quantum computers.

Journal Article↗
PubMed2006

Prevalence of exercise-induced bronchospasm in Thokoza schoolchildren.

BACKGROUND: Asthma is a common childhood illness, with a prevalence of 1 in 10 children. Exercise-induced bronchospasm (EIB) is a common feature of asthma and is found more often in children than in adults. OBJECTIVE: To determine the prevalence and potential impact of various factors on the prevalence of EIB in Thokoza schoolchildren. METHODS: Data were collected on respiratory health and the home environment of children living in Thokoza, Gauteng. A total of 475 9- and 10-year-old children performed the free-running asthma screening test (FRAST). An abnormal response to FRAST was defined as a reduction in the post-exercise peak flow of more than 15% of the pre-exercise value, at 3- and 10- minute intervals. All children who had a fall in post-exercise flow rate (PEFR) of more than 15% on 2 occasions after FRAST were classified as having EIB. RESULTS: Using the above criteria to diagnose EIB, an overall prevalence rate of 7.26% (95% confidence interval (CI): 4.5 - 10.3%) was recorded. A less rigorous definition of EIB is a fall in PEFR of more than 10% on 2 occasions after FRAST, and if this was used then the prevalence of EIB was 15.69% (95% CI: 10.6 - 20.8%). Difficulty breathing and a tight chest were the most prevalent respiratory symptoms in children with EIB (odds ratio (OR): 1.79, 95% CI: 0.49 - 6.49 and OR 1.69, 95% CI: 0.72 - 3.99, respectively). The use of gas and electricity as domestic fuels was the strongest risk factor associated with EIB, as shown by logistical regression analysis using an adjusted OR in a reduced model (OR 2.44, 95% CI: 0.71 - 8.44 and OR 2.33, 95% CI: 0.59 - 9.24, respectively). CONCLUSION: The prevalence of EIB reported in this study is higher than that reported in studies from other African countries, with the exception of a study from Kenya. Findings of the present study suggest that there may be a trend towards increasing prevalence of EIB in South African urban areas.

Asthma, Exercise-Induced↗
PubMed2006

Thrombo-embolic and bleeding complications in patients with mechanical valve replacements--a prospective observational study.

BACKGROUND AND OBJECTIVES: Long-term anticoagulation therapy is essential to prevent thrombo-embolic events in patients with mechanical valve replacements. In order to offer indigent patients mechanical heart valve replacement surgery, dedicated anticoagulation clinics are necessary for follow-up. This study assessed the safety and efficacy of lifelong oral anticoagulation therapy in Johannesburg General Hospital mechanical heart valve replacement recipients. The incidence of bleeding and thrombo-embolic complications was documented in three groups of patients with mechanical valve replacements. The groups included patients with aortic valve replacements (AVRs), mitral valve replacements (MVRs) and double (aortic and mitral) valve replacements (DVRs). MATERIALS AND METHODS: A prospective observational study was conducted over a 4-month period. Data on 306 patients attending the Johannesburg General Hospital anticoagulation clinic between 2000 and 2005 were analysed. Of the total patients selected, 205 were assigned to the mechanical valve replacement group (which included 63 patients with AVRs, 93 with MVRs and 49 with DVRs); a control group of 101 nonmechanical valve replacement patients were also included. At each visit the level of anticoagulation was assessed from the international normalised ratio (INR) values, and the presence of bleeding and/or thrombo-embolic complications was documented. RESULTS: There were a total of 51 bleeding and thrombo-embolic complications in the study population. Patients with DVRs had a higher proportion of combined complications (30.61%) than patients with single valve replacements (14.29% in the AVR group and 18.05% in the MVR group) and patients in the control group (12.87%). There were 38 bleeding complications, 30 minor and 8 major. Twelve thrombo-embolic events were documented. Individually, there was no significant difference in thrombo-embolic and bleeding complications between the subgroups. Eighty-two per cent of patients in the mechanical valve replacement group were within the therapeutic range for anticoagulant control (INR 2.5-3.5) v. 54% in the control group (INR 2.0-3.0). Anticoagulant control was of a high quality and was not a contributing factor to the incidence of bleeding and/ or thrombo-embolic complications. CONCLUSION: The finding of a low incidence of bleeding and thrombo-embolic complications in patients with mechanical valve replacements supports the continued placement of mechanical valves in our setting and use of oral anticoagulation therapy at an INR of 2.5-3.5. However the increased risk of both bleeding and thrombo-embolic complications in the DVR group is cause for great concern and warrants further investigation.

Administration, Oral↗
PubMed2005

Temporomandibular joint morphology following post-traumatic ankylosis in 26 patients.

This study evaluated the joint morphology on coronal computed tomography of ankylosed temporomandibular joints in 26 patients. All patients developed ankylosis following blunt trauma. Post-ankylosis joint morphology was assessed to determine if the precursor condylar fracture could be identified and this was compared to the condylar fracture prevalence to determine if any condylar fractures have an increased risk factor for ankylosis. Mean age at presentation was 20.9+/-14.41 years (range 6-58) and mean age at injury was 13.84+/-13.81 years (range 3-53). Thirty-seven joints were ankylosed in 26 patients (11 bilateral, 15 unilateral) with 27 joints in 19 patients showing vestiges of a medially dislocated condylar fracture (72.9% of joints). The prevalence of MDCF at our unit over a period of 6 months was 16.8% (16 of 95 condylar fractures). This suggests that a medially dislocated condylar fracture is more likely to ankylose than other condylar fractures. A hypothesis is proposed to explain this increased risk.

Adolescent↗
PubMed2004

Attention and working memory in resident anaesthetists after night duty: group and individual effects.

AIMS: To investigate the effects of a single period of night duty on measures of attention and working memory in a group of residents (registrars) in anaesthesiology. Emphasis was placed on individual deficits using a reference point of the equivalent effect of a blood alcohol concentration (BAC) >0.05% determined by other researchers. METHODS: There were 33 subjects aged 26-42 years. Night duty was performed on a weekly basis. Baseline assessments were conducted at either 08 15 or 08 55 preceding night duty and repeated 24-25 hours later, just after the completion of duty. Questionnaires included items regarding duration of sleep and the Stanford Sleepiness Scale. A battery of four reaction time (RT) tasks of increasing difficulty, lasting approximately 35 minutes, was administered on a personal computer. These ranged from simple RT to progressively more complex RT tasks incorporating working memory. A significant change was regarded as >15% deterioration in respect of speed or accuracy. RESULTS: The mean duration of sleep preceding night duty was 7.04 hours and 1.66 hours during the period of night duty. Intergroup comparisons revealed significant prolongation in mean response speed in the first three tests. Mean accuracy was significantly reduced only in respect of the two more complex tests. A >15% deterioration in response speed occurred in up to 30% of subjects on a single task, rising to 52% (17/33) overall. Deterioration occurred in a patchy distribution in most subjects, involving no more than one or two of the four tasks. As regards accuracy, the prevalence of deterioration increased with task complexity. CONCLUSIONS: Results are in general agreement with previous group analyses. A new dimension was added by the analysis of a broad spectrum of individual response to sleep deprivation. The effects of sleep loss in residents cannot be overlooked, even in a relatively benign work schedule.

Adult↗
PubMed2003

Detection of peritoneal adhesions using ultrasound examination for the evaluation of an innovative intraperitoneal mesh.

BACKGROUND: In this multicenter study, we evaluated the efficiency of a specific ultrasound examination in detecting postoperative bowel adhesions and assessed the adhesion rate associated with the intraperitoneal use of Parietex composite mesh (polyester mesh covered on the visceral side by a hydrophilic resorbable film). METHODS: Eighty patients (36 male, 44 female; average age, 58.2 years [ranges 30-80]) were included in a study carried out at eight centers. The main inclusion criterion was the surgical treatment of incisional and umbilical hernias using an intraperitoneal mesh. The results of a preoperative ultrasound examination were compared to a macroscopic perioperative exploration. In addition, in 76 of the 80 patients, a postoperative ultrasound examination was repeated at 2 and 12 months. RESULTS: The ultrasound findings for peritoneal adhesion detection were as follows: sensitivity, 77%; specificity, 74%; positive predictive value, 65%; negative predictive value, 84%; accuracy, 75%. Postoperative adhesions after 1 year were detected in 14% of patients. CONCLUSIONS: Although these patients had undergone repeated surgery and treated to be (obese) body mass index (mean, 28), the ultrasound exam had a high accuracy rate; when it was negative, there were no adhesions in 84% of cases. The use of a hydrophilic composite mesh is associated with a low rate of adhesions (14%).

Adult↗
PubMed2002

Family history study of the restless legs syndrome.

BACKGROUND: Although there is a relatively high rate of occurrence of sporadic cases of restless legs syndrome (RLS), the systematic study of family history of RLS in populations of RLS patients has been very limited. The objective of the present study was to determine the risk of RLS for first- and second-degree relatives of a population of primary RLS patients not selected for the number of affected relatives in their families and to obtain an estimate of the degree of genetic involvement in RLS. METHODS: Consecutively consenting patients from two different sites who met the criteria for RLS completed a worksheet that asked them to indicate their current age, the date of their earliest RLS symptoms, and the names and RLS status of all of their first- and second-degree relatives. Controls with no clinical history of RLS also completed the worksheet. RESULTS: First- and second-degree relatives of patients with RLS had a significantly greater risk of RLS than the first- (P<0.001) and second-degree relatives (P<0.003) of controls. The risk of RLS was found to be greater for first-degree relatives of early-onset, rather than late-onset, RLS probands (P<0.001). CONCLUSIONS: This study provides a complete systematic examination of the risk of RLS among relatives of RLS probands and controls using the same assessment methodology. Although the results are consistent with a genetic etiology for RLS, they do not support the presence of one simple, Mendelian-inherited major gene in most RLS families.

Journal Article↗
PubMed2001

Early bursting strength of human colon anastomoses--an in vitro study comparing current anastomotic techniques.

An experimental in vitro study involving ten hand-sutured, ten biofragmentable anastomotic ring (BAR) and ten stapled anastomoses was conducted to compare current anastomotic techniques on the basis of early bursting pressure. The 30 fresh human colon segments used in the study were harvested from patients who had undergone elective oncologic resection. Following the construction of in vitro anastomoses, the pressure required to burst these specimens was measured. The results showed no significant differences among the three techniques. Since hand-sutured anastomoses proved to be as effective and reliable as the other methods and can offer the advantage of cost savings, they should remain standard procedure in colorectal surgery.

Adult↗
PubMed2001

Humoral immune response to autologous blood transfusion in hip surgery: whole blood versus packed red cells and plasma.

BACKGROUND AND OBJECTIVES: The immune response to the transfused autologous buffy coat content in whole blood has, to date, not been studied in detail. SUBJECTS AND METHODS: Patients undergoing hip arthroplasty were studied according to whether they received autologous whole blood (WB) (n = 30), autologous fresh-frozen plasma and buffy coat-poor red cells (RC) (n = 40), or no transfusion (NT) (n = 27). Plasma levels of tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and complement SC5b-9 were analysed by enzyme-linked immunosorbent assay (ELISA) 7 days after surgery. RESULTS: There were no significant between-group differences regarding the time course of TNF-alpha, IL-6 and complement SC5b-9 plasma level changes, the infection rate, or the length of hospital stay. CONCLUSION: In comparison to the impact of surgery on cytokine and complement levels, the transfusion of autologous buffy coat is not relevant.

Adult↗
PubMed2001

Estimation of conduit taper for the hydraulic resistance model of West et al.

The model of West, Brown and Enquist (1999) showed that total hydraulic resistance in trees can be independent of path length, provided that vascular conduits taper sufficiently. The original model defined the coefficient of taper, a bar, in terms of conduit radius and segment number, but segments can be difficult to distinguish in old stems. Adhering strictly to the definitions and assumptions of West et al., we derived several equations for the estimation of a bar based on measurements of tracheary radius and flow path length. However, an additional parameter, b, was introduced to permit different models of variation in the length of segments along the flow path besides the volume-filling model of West et al., including a fixed-length model and intermediate versions. One of the new equations was fitted to previously published data for two tree species to illustrate the estimation of conduit taper from path-length relations, which proved quite sensitive to variation in b. Sampling protocols for improving such analyses are suggested.

Mathematics↗
PubMed2001

Stem cell engraftment strategies.

The donor stem cell phenotype and host microenvironment determine the outcome of a stem cell transplant. In a series of transplant studies in syngeneic male to female or congenic Ly5.1/Ly5.2 models in which hosts have received no or minimal irradiation (100 cGy), evidence overwhelmingly supports the concept that syngeneic engraftment is determined by stem cell competition. These approaches can be extended to H-2 mismatched allogeneic mouse combination when antigen pre-exposure and CD40-CD40 ligand antibody blockage are employed. A human trial in patients with resistant neoplasia infusing pheresed blood with 10(8) CD3 cells/kg showed that tumor responses and complete chimerism occur with very low levels of CD34+ cells/kg and that the extent of previous treatment is a critical factor in determining chimerism. A major feature of transplants is the phenotype of the donor stem cell. This phenotype shows dramatic reversible plasticity involving differentiation, adhesion protein expression, and engraftment with cytokine-induced cell-cycle transit. Homing is probably also plastic. Marked fluctuations in engraftment capacity are also seen at different points in marrow circadian rhythm.

Adolescent↗
PubMed2001

Detection of differential gene expression in biofilm-forming versus planktonic populations of Staphylococcus aureus using micro-representational-difference analysis.

Microbial proliferation and biofilm formation on biologic or inert substrates are characteristics of invasive Staphylococcus aureus infections and is associated with phenotypic alterations such as reduced antimicrobial susceptibility. To identify genes which are typically expressed in biofilms, a micro-representational-difference analysis (micro-RDA) was adapted for gram-positive bacteria and used with cDNA derived from populations of S. aureus DSM 20231 growing in a biofilm or plankonically. In comparison to previously described cDNA RDA protocols, micro-RDA has the advantages that only minimal quantities of total RNA are needed and, most importantly, that total RNA can be used since the large amount of rRNA in total RNA does not interfere with the micro-RDA procedure. Using a series of spiked controls with various amounts of MS2 RNA in a background of total RNA from S. aureus, the equivalent of five copies of MS2 per cell were detectable after three rounds of subtractive enrichment. Five genes were identified as being differentially expressed in biofilm versus planktonic cultures. These genes revealed homology to a threonyl-tRNA synthetase, a phosphoglycerate mutase, a triosephosphate isomerase, an alcohol dehydrogenase I, and a ClpC ATPase. Differential levels of expression were subsequently confirmed by standard Northern blotting. In conclusion, micro-RDA is a sensitive and specific method to detect transcripts differentially expressed as a function of different S. aureus growth conditions.

Bacterial Proteins↗
PubMed2001

The novel transcription factor e(y)2 interacts with TAF(II)40 and potentiates transcription activation on chromatin templates.

Weak hypomorph mutations in the enhancer of yellow genes, e(y)1 and e(y)2, of Drosophila melanogaster were discovered during the search for genes involved in the organization of interaction between enhancers and promoters. Previously, the e(y)1 gene was cloned and found to encode TAF(II)40 protein. Here we cloned the e(y)2 gene and demonstrated that it encoded a new ubiquitous evolutionarily conserved transcription factor. The e(y)2 gene is located at 10C3 (36.67) region and is expressed at all stages of Drosophila development. It encodes a 101-amino-acid protein, e(y)2. Vertebrates, insects, protozoa, and plants have proteins which demonstrate a high degree of homology to e(y)2. The e(y)2 protein is localized exclusively to the nuclei and is associated with numerous sites along the entire length of the salivary gland polytene chromosomes. Both genetic and biochemical experiments demonstrate an interaction between e(y)2 and TAF(II)40, while immunoprecipitation studies demonstrate that the major complex, including both proteins, appears to be distinct from TFIID. Furthermore, we provide genetic evidence suggesting that the carboxy terminus of dTAF(II)40 is important for mediating this interaction. Finally, using an in vitro transcription system, we demonstrate that recombinant e(y)2 is able to enhance transactivation by GAL4-VP16 on chromatin but not on naked DNA templates, suggesting that this novel protein is involved in the regulation of transcription.

Amino Acid Sequence↗
PubMed2001

Prevention of construction falls by organizational intervention.

OBJECTIVES: Determine if a university based (third party) intervention can improve construction contractor organizational performance to increase use of fall prevention practices and technologies. SETTING: Falls are the leading cause of worker injury and death in the construction industry. Equipment and practices that can prevent falls are often not used appropriately in the dynamic construction work environment. METHODS: A contractual partnership between a university and construction contractors created management systems to ensure use of fall protection measures. Audits by university faculty provided accountability for implementing the fall prevention system. Evaluation was conducted by quasiexperimental methodology comparing changes in audit score from baseline to fifth quarter from baseline for intervention and control contractors. RESULTS: Audit scores improvement was greater for intervention than for control contractor group. CONCLUSION: A third party intervention can improve contractor fall prevention performance.

Accidental Falls↗
PubMed2001

Microtubule disassembly increases endothelial cell barrier dysfunction: role of MLC phosphorylation.

Endothelial cell (EC) barrier regulation is critically dependent on cytoskeletal components (microfilaments and microtubules). Because several edemagenic agents induce actomyosin-driven EC contraction tightly linked to myosin light chain (MLC) phosphorylation and microfilament reorganization, we examined the role of microtubule components in bovine EC barrier regulation. Nocodazole or vinblastine, inhibitors of microtubule polymerization, significantly decreased transendothelial electrical resistance in a dose-dependent manner, whereas pretreatment with the microtubule stabilizer paclitaxel significantly attenuated this effect. Decreases in transendothelial electrical resistance induced by microtubule disruption correlated with increases in lung permeability in isolated ferret lung preparations as well as with increases in EC stress fiber content and MLC phosphorylation. The increases in MLC phosphorylation were attributed to decreases in myosin-specific phosphatase activity without significant increases in MLC kinase activity and were attenuated by paclitaxel or by several strategies (C3 exotoxin, toxin B, Rho kinase inhibition) to inhibit Rho GTPase. Together, these results suggest that microtubule disruption initiates specific signaling pathways that cross talk with microfilament networks, resulting in Rho-mediated EC contractility and barrier dysfunction.

Actin Cytoskeleton↗