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[en] Although failure data are usually treated as being continuous, they may have been collected in a discrete manner, or in fact be discrete in nature. Reliability models with bathtub-shaped hazard rate are fundamental to the concepts of burn-in and maintenance, but how well do they incorporate discrete data? We explore discrete versions of the additive Weibull distribution, which has the twin virtues of mathematical tractability and the ability to produce bathtub-shaped hazard rate functions. We derive conditions on the parameters for the hazard rate function to be increasing, decreasing, or bathtub shaped. While discrete versions may have the same shaped hazard rate for the same parameter values, we find that when fitted to data the fitted hazard rate shapes can vary between versions. Our results are illustrated using several real-life data sets, and the implications of using continuous models for discrete data discussed.
[en] In a system subject to both repairable and catastrophic (i.e., nonrepairable) failures, 'mission success' can be defined as operating for a specified time without a catastrophic failure. We examine the effect of a burn-in process of duration τ on the mission time x, and also on the probability of mission success, by introducing several functions and surfaces on the (τ,x)-plane whose extrema represent suitable choices for the best burn-in time, and the best burn-in time for a desired mission time. The corresponding curvature functions and surfaces provide information about probabilities and expectations related to these burn-in and mission times. Theoretical considerations are illustrated with both parametric and, separating the failures by failure mode, nonparametric analyses of a data set, and graphical visualization of results.
[en] To investigate the short-term therapeutic effect of percutaneous vertebroplasty (PVP) for intravertebral cleft (IVC) and to analyze possible outcome predictors. After retrospective review of spot radiographs during PVP, 23 patients were included in this study. Age, sex, symptom duration, functional status, injected cement volume, and type of approach were evaluated using patients' medical and operative records. The following factors were analyzed on radiographs, MRI, dual bone densitometry, spot radiographs during PVP, and CT: anatomical location of the fracture, bone mineral density, morphology of the fracture, IVC morphology, presence of surrounding non-enhanced area and bone marrow edema, degeneration of adjacent discs, co-existing old compression fractures, patterns of cement opacification, pre-procedural kyphosis, and post-procedural kyphosis correction. Effectiveness was defined as a much-improved state or no pain after 1 week, 1 month, and 2 months. Statistical analyses were conducted to evaluate the relationship between those factors and therapeutic outcome using Fisher's exact test, Chi-squared test, and the Mann-Whitney U test. Percutaneous vertebroplasty of IVC was effective in 16 out of 23 (69.6%) patients after 1 week and 1 month and 15 out of 23 (65.2%) patients after 2 months. Post-procedural kyphosis correction ≥5 and poor functional status (full dependency) were more common in the ineffective group after 1 week and 2 months respectively (P = 0.047, P = 0.02). Kyphotic correction ≥5 was related to pre-procedural kyphosis ≥15 (P = 0.018). Functional status was related to subsequent fracture (P = 0.005). Other factors were not statistically significant (P > 0.05). Percutaneous vertebroplasty on osteoporotic vertebral compression fractures (VCF) with IVC was effective in only about 69.6% of patients after the first week and month and in 65.2% of patients after 2 months. Post-procedural kyphosis correction ≥5 was associated with poor outcomes after the first week. Two months after PVP, the functional status was more important because of the development of subsequent fractures. (orig.)
[en] Firearm injuries cause significant morbidity and mortality among its victims. The present study, carried out at a major tertiary care hospital of Peshawar, Pakistan was aimed at highlighting the extent and severity of firearm-related morbidity and resultant mortality despite expert medical care. All victims of firearm injury brought to the Lady Reading Hospital Peshawar Emergency Department and thereafter admitted to hospital wards during the period mid-2006 to mid- 2007 were included in the study prospectively regardless of age, gender or socio-economic status. Data relevant to the background of firearm use, type of firearm used, types and extents of injuries, clinical condition of the patients and final outcome were collected on performas and entered into SPSS 15.0 for analysis. Seventy-four cases of firearm injury were recorded during the study period, with a predominant male to female ratio (9.6:1). Most victims (79.7%) were in the age group of 15-35 years. Although there were more cases from Peshawar (28.4%), there was no major referral pattern noted. High velocity weapons were used in 95.9% of cases and homicide was the main motive for injury (60.8%). Injuries were sustained most frequently in the abdomen and pelvis (44.6%) and 67.6% of victims sustained internal injuries. There were only 5 (6.8%) deaths from firearm injuries. It is concluded, the young males of the population must be targeted for lifestyle adjustments such as training to refrain from anger or disputes (usually over petty things) and to prevent the easy access of firearms as a weapon to settle disputes. (author)
[en] Purpose: To assess the efficacy of the Wallstent endoprosthesis in malignant tracheobronchial obstruction. Methods: Seven patients with irresectable carcinoma of the bronchus were treated with nine Wallstent endoprostheses. The procedures were performed under endoscopic and fluoroscopic guidance. Wallstent endoprostheses ranging from 8<+>-<+>16 mm in diameter and 26<+>-<+>49 mm in length were deployed after balloon dilatation of the strictures. Results: All stents were successfully deployed in the desired positions. There was one procedural complication and one procedure-related death. Three patients showed significant improvement in respiratory status after stenting. At a mean follow-up of 5.1 months, there has been no stent migration, fracture, or collapse. One patient had proximal tumor overgrowth that was treated with additional stent insertion. One patient died after a bout of massive hemoptysis 3 months poststenting and it was difficult to tell whether this was related to the endoprosthesis. Conclusion: The use of the Wallstent endoprosthesis in malignant tracheobronchial obstruction is technically feasible
[en] Understanding flame spread behavior is crucial to Fire Safety Engineering. It is noted that the natural fiber exhibits different flame spread behavior than the one of the synthetic fiber. This different may influences the flame spread behavior over combined fabric. There is a research has been done to examined the flame spread behavior over kenaf/polyester fabric. It is seen that the flame spread shape is dependent on the thread angle dependency. However, the explanation of this phenomenon is not described in detail in that research. In this study, explanation about this phenomenon is given in detail. Results show that the flame spread shape is dependent on the position of synthetic thread. For thread angle, θ = 0°, the polyester thread is breaking when the flame approach to the thread and the kenaf thread tends to move to the breaking direction. This behavior produces flame to be ‘V’ shape. However, for thread angle, θ = 90°, the polyester thread melts while the kenaf thread decomposed and burned. At this angle, the distance between kenaf threads remains constant as flame approaches. (paper)
[en] To study the changes in physiological parameters i e PAO2, pulse and blood pressure changes during ECT under GA. Study Design: Quasi-experimental study. Place and Duration of Study: Department of Psychiatry and Department of Anaesthesiology, Combined Military Hospital Abbottabad from Sep 2009 to Feb 2010. Patients and Methods: A total of 50 patients with depression were given four separate ECT sessions each. All patients were anaesthetized using propofol 180-200 mg I/V and suxamethonium 50 mg i e 0.75-1 mg per kg I/V without atropine. They were stratified according to physiological changes including PAO2, pulse and blood pressure at 1, 2 and 5 min after ECT. Oxygen saturation was measured using a pulse oximeter, which measures saturations in the range of 65-100%. Results: Age range was 19-65 years; mean 46 years (SD+-13). Mean diastolic BP before ECT was 84.72 that decreased post ECT ie 78.02 and 77.46 and 74.44 at interval of 1, 2 and 5 minute respectively. Post-ECT pulse and PAO2 behaved similarly. Post ECT systolic BP decreased at 1 and 5 minutes. Pulse rate decreased after ECT. Conclusion: ECT under propofol is one of the most effective and safe modality of treatment for psychiatric patients under the supervision of qualified psychiatrists and anaesthesiologists and it gives more stable hemodynamic changes. (author)