Space-time domain decomposition for advection-diffusion problems in mixed formulations

This paper is concerned with the numerical solution of porous-media flow and transport problems , i. e. heterogeneous, advection-diffusion problems. Its aim is to investigate numerical schemes for these problems in which different time steps can be used in different parts of the domain. Global-in-time, non-overlapping domain-decomposition methods are coupled with operator splitting making possible the different treatment of the advection and diffusion terms. Two domain-decomposition methods are considered: one uses the time-dependent Steklov--Poincar{\'e} operator and the other uses optimized Schwarz waveform relaxation (OSWR) based on Robin transmission conditions. For each method, a mixed formulation of an interface problem on the space-time interface is derived, and different time grids are employed to adapt to different time scales in the subdomains. A generalized Neumann-Neumann preconditioner is proposed for the first method. To illustrate the two methods numerical results for two-dimensional problems with strong heterogeneities are presented. These include both academic problems and more realistic prototypes for simulations for the underground storage of nuclear waste

Experiences With Surgical Treatment of Chronic Lower Limb Ulcers at a Tertiary Hospital in Northwestern Tanzania: A Prospective Review of 300 Cases.

Chronic lower limb ulcers constitute a major public health problem of great important all over the world and contribute significantly to high morbidity and long-term disabilities. There is paucity of information regarding chronic lower limb ulcers in our setting; therefore it was necessary to conduct this study to establish the patterns and outcome of chronic lower limb ulcers and to identify predictors of outcome in our local setting. This was a descriptive prospective study of patients with chronic lower limb ulcers conducted at Bugando Medical Centre between November 2010 and April 2012. Ethical approval to conduct the study was sought from relevant authorities. Statistical data analysis was done using SPSS version 17.0 and STATA version 11.0. A total of 300 patients were studied. Their ages ranged from 3 months to 85 years (median 32 years). The male to female ratio was 2:1. The median duration of illness was 44 days. Traumatic ulcer was the most frequent type of ulcer accounting for 60.3% of patients. The median duration of illness was 44 days. The leg was commonly affected in 33.7% of cases and the right side (48.7%) was frequently involved. Out of 300 patients, 212 (70.7%) had positive aerobic bacterial growth within 48 hours of incubation. Pseudomonas aeruginosa (25.5%) was the most frequent gram negative bacteria isolated, whereas gram positive bacteria commonly isolated was Staphylococcus aureus (13.7%). Twenty (6.7%) patients were HIV positive with a median CD4+ count of 350 cells/μl. Mycological investigation was not performed. Bony involvement was radiologically reported in 83.0% of cases. Histopathological examination performed in 56 patients revealed malignancy in 20 (35.7%) patients, of which malignant melanoma (45.0%) was the most common histopathological type. The vast majority of patients, 270 (90.0%) were treated surgically, and surgical debridement was the most common surgical procedure performed in 24.1% of cases. Limb amputation rate was 8.7%. Postoperative complication rate was 58.3% of which surgical site infection (77.5%) was the most common post-operative complications. The median length of hospital stay was 23 days. Mortality rate was 4.3%. Out of the two hundred and eighty-seven (95.7%) survivors, 253 (91.6%) were treated successfully and discharged well (healed). After discharge, only 35.5% of cases were available for follow up at the end of study period. Chronic lower limb ulcers remain a major public health problem in this part of Tanzania. The majority of patients in our environment present late when the disease is already in advanced stages. Early recognition and aggressive treatment of the acute phase of chronic lower limb ulcers at the peripheral hospitals and close follow-up are urgently needed to improve outcomes of these patients in our environment

Space-time Domain Decomposition and Mixed Formulation for solving reduced fracture models

International audienceIn this paper we are interested in the "fast path" fracture and we aim to use global-in-time, nonoverlapping domain decomposition methods to model flow and transport problems in a porous medium containing such a fracture. We consider a reduced model in which the fracture is treated as an interface between the two subdomains. Two domain decomposition methods are considered: one uses the time-dependent SteklovPoincaré operator and the other uses optimized Schwarz waveform relaxation (OSWR) based on Ventcell transmission conditions. For each method, a mixed formulation of an interface problem on the space-time interface is derived, and different time grids are employed to adapt to different time scales in the subdomains and in the fracture. Demonstrations of the well-posedness of the Ventcell subdomain problems is given for the mixed formulation. An analysis for the convergence factor of the OSWR algorithm is given in the case with fractures to compute the optimized parameters. Numerical results for two-dimensional problems with strong heterogeneities are presented to illustrate the performance of the two methods

Geriatric Injuries among Patients Attending a Regional Hospital in Shinyanga Tanzania

Geriatric injuries pose a major challenge to surgeons and general practitioners in developing countries. The objective of this study was to determine the prevalence, injury characteristics and outcomes of geriatric injury among patients at Shinyanga Regional Hospital in Tanzania. Data was collected using a pre-tested, coded questionnaire and analyzed using SPSS computer system. A total of 94 geriatric trauma patients constituting 22.7% of all trauma admissions were studied. The male to female ratio was 1.4:1. Their mean age was 68.5 years (ranged 60-98 years). Premorbid illness was reported in 38.3% of patients. Most injuries were intentional in fifty-three (56.4%) patients. Assaults, falls and road traffic crashes were the mechanism of injuries in 52.1%, 19.1% and 11.7% of cases, respectively. The majority of cases of assault were females accounting for 64.6%. The majority of injuries (81.9%) occurred at home. Pre-hospital care was recorded in 5.3% of cases. The musculoskeletal (72.3%) and head (66.0%) regions were commonly affected. Soft tissue injuries (wounds) (89.4%) and fractures (52.2%) were the most common type of injuries. The majority of patients (90.4%) underwent surgical treatment of which wound debridement was the most common procedure performed in 91.8% of cases. Complication rate was 39.4%. The mean length of hospital stay was 28.6 days (ranged 1 – 124 days). The length of hospital stay was significantly longer in patients with co-morbidities, long bone fractures and those with complications (P<0.05). Mortality rate was 14.9% and it was significantly related to advanced age, presence of pre-morbid illness, high injury severity score, severe head injuries and the need for ventilatory support (P< 0.05). In conclusion, traumatic injuries in elderly constitute a major but preventable public health problem in Shinyanga region and contribute significantly to high morbidity and mortality. Urgent preventive measures focusing at the root causes of the injuries and early appropriate treatment is highly needed to reduce the occurrence, morbidity and mortality associated with these injurie

Space-Time Domain Decomposition Methods for Diffusion Problems in Mixed Formulations

This paper is concerned with global-in-time, nonoverlapping domain decomposition methods for the mixed formulation of the diffusion problem. Two approaches are considered: one uses the time-dependent Steklov-Poincar\'e operator and the other uses Optimized Schwarz Waveform Relaxation (OSWR) based on Robin transmission conditions. For each method, a mixed formulation of an interface problem on the space-time interfaces between subdomains is derived, and different time grids are employed to adapt to different time scales in the subdomains. Demonstrations of the well-posedness of the subdomain problems involved in each method and a convergence proof of the OSWR algorithm are given for the mixed formulation. Numerical results for 2D problems with strong heterogeneities are presented to illustrate the performance of the two methods

Ten-year experiences with Tetanus at a Tertiary hospital in Northwestern Tanzania: A retrospective review of 102 cases

<p>Abstract</p> <p>Background</p> <p>Tetanus is still a major health problem in developing countries and it is associated with a high morbidity and mortality rate. There is paucity of published data regarding the management of tetanus in Tanzania, especially the study area. This study was conducted to describe our own experiences with tetanus outlining the clinical characteristics and treatment outcome of tetanus patients in our environment and to identify predictors of outcome of these patients.</p> <p>Methods</p> <p>This was a ten-year period retrospective study of patients who presented with a clinical diagnosis of tetanus at Bugando Medical Centre between January 2001 and December 2010. Data was analyzed using SPSS computer software system.</p> <p>Results</p> <p>A total of 102 patients were studied. The male to female ratio was 11.8: 1. The majority of patients (74.5%) were aged < 40 years and 51.0% of them were farmers. Only 23.5% of patients had prior tetanus immunization. 53.5% of patients had a reasonably identifiable acute injury prior to the onset of tetanus and commonly involved the lower limbs (53.8%). The majority of patients (97.1%) had generalized tetanus. The mean incubation period and period of onset were 8.62 ± 4.34 and 3.8 ± 2.2 days respectively. Complication rate was 54.9%. The average overall duration of hospitalization was 34.12 ± 38.44 days (1-120 days). Mortality rate was 43.1%. According to multivariate logistic regression analysis, the age ≥ 40 years (P = 0.002), incubation period < 7 days (P = 0.014), tracheostomy (P = 0.004), severity of tetanus (P = 0.001) and need for ventilatory support (P = 0.013) were found to be significantly associated with higher mortality.</p> <p>Conclusion</p> <p>Tetanus remains a major public health problem in our centre and still carries unacceptably high morbidity and mortality despite the available advanced management facilities including ICU care. Young adult males are commonly affected. The incidence of tetanus can be reduced significantly by an effective immunization program and proper wound management of the patients. Early recognition, intense support and prompt treatment improves morbidity and mortality of patients diagnosed with tetanus.</p

The Effect of Early Versus Delayed Surgical Debridement on the Outcome of Open Long Bone Fractures at Bugando Medical Centre, Mwanza, Tanzania.

Urgent surgical debridement of open long bone fractures is of paramount importance for prevention of subsequent infection. Due to limited information on the timing of this surgical procedure in Mwanza, Tanzania; the present study was conducted to evaluate the effect of early versus delayed surgical debridement on the outcome of open long bone fractures. A prospective cohort study involving 143 patients with open long bone fractures admitted at Bugando Medical Centre (BMC) between December 2014 and April 2015 was conducted. Patients were stratified into two main groups basing on whether they presented at BMC and operated early (within 6 h) or late (more than 6 h). Socio-demographic and clinical information were collected using structured questionnaire. Analysis was done using STATA software version 11. The male to female ratio was 1.6: 1, with most of the patients being in their third decade of life (30.8 %). Road traffic accident (RTA) was the most common cause of fractures (67.8 %). Majority of patients, 91 (63.6 %) had Gustillo-Anderson grade II and the timing of debridement was significantly associated with this grading (p-value = 0.05). Nine (6.3 %) patients developed surgical site infection (SSI) and the median length of hospital stay (LOS) (interquartile range) was 7 (5-10) days, ranging from 3 to 35 days. SSI was found more in the late group compared to the early group [7.5 % (6/80) versus 4.8 % (3/63) respectively, p-value = 0.503)] and LOS was also longer in the late group compared to the early group [7 (6-11.5) days and 6 (5-10) days respectively, p-value = 0.06]. Pseudomonas aeruginosa was the predominant bacteria causing SSI. Open long bone fracture injuries due to RTA are common at BMC. The risk of developing SSI in this setting is low and comparable to many other countries. Despite the fact that there was no statistical significant difference between early versus delayed debrided groups on SSI and LOS stays; the need for prompt surgical intervention in both groups should be an enduring focus to maintain these favorable outcomes

The Effect of Early Versus Delayed Surgical Debridement on the Outcome of Open Long Bone Fractures at Bugando Medical Centre, Mwanza, Tanzania.

Urgent surgical debridement of open long bone fractures is of paramount importance for prevention of subsequent infection. Due to limited information on the timing of this surgical procedure in Mwanza, Tanzania; the present study was conducted to evaluate the effect of early versus delayed surgical debridement on the outcome of open long bone fractures. A prospective cohort study involving 143 patients with open long bone fractures admitted at Bugando Medical Centre (BMC) between December 2014 and April 2015 was conducted. Patients were stratified into two main groups basing on whether they presented at BMC and operated early (within 6 h) or late (more than 6 h). Socio-demographic and clinical information were collected using structured questionnaire. Analysis was done using STATA software version 11. The male to female ratio was 1.6: 1, with most of the patients being in their third decade of life (30.8 %). Road traffic accident (RTA) was the most common cause of fractures (67.8 %). Majority of patients, 91 (63.6 %) had Gustillo-Anderson grade II and the timing of debridement was significantly associated with this grading (p-value = 0.05). Nine (6.3 %) patients developed surgical site infection (SSI) and the median length of hospital stay (LOS) (interquartile range) was 7 (5-10) days, ranging from 3 to 35 days. SSI was found more in the late group compared to the early group [7.5 % (6/80) versus 4.8 % (3/63) respectively, p-value = 0.503)] and LOS was also longer in the late group compared to the early group [7 (6-11.5) days and 6 (5-10) days respectively, p-value = 0.06]. Pseudomonas aeruginosa was the predominant bacteria causing SSI. Open long bone fracture injuries due to RTA are common at BMC. The risk of developing SSI in this setting is low and comparable to many other countries. Despite the fact that there was no statistical significant difference between early versus delayed debrided groups on SSI and LOS stays; the need for prompt surgical intervention in both groups should be an enduring focus to maintain these favorable outcomes

Evaluation of nephrotoxic effect of lead exposure among automobile repairers in Nnewi Metropolis

Background:Lead toxicity is one of the most common occupational hazards that affect several organs of the body, kidney inclusive. Auto repairers are exposed to lead in petrol, radiator, leaded battery, lead soldering wire, and spray paints, thus this study was designed to evaluate lead-induced nephrotoxic effect among automobile repairers.Methods:A total of 80 male subjects within the age range of 20 and 65 years were recruited for this study. 50 subjects were occupationally exposed automobile repairers, of which 15 were electricians, 21 mechanics and 14 panel beaters/spray painters, whereas 30 were non-exposed students and staff from Nnamdi Azikiwe University, Nnewi campus. Blood sample was collected from these individuals and their blood lead levels were determined alongside creatinine, urea, uric acid, sodium, potassium, chloride and bicarbonate.Results:The results showed that the mean levels of blood lead is significantly higher in automobile repairers than in control group (P 0.05). The evaluation of the renal function markers show that, there were significant increases in the mean serum concentration of creatinine, urea, and uric acid in the study group compare to the control subjects (P 0.05).Conclusion:Findings from this study show that blood lead level is high among automobile repairers above CDC recommended level for adults. This high blood lead level among automobile repairers may be responsible for raised levels of renal markers which may eventually lead to their renal damage.