Fatigue cracking in gamma titanium aluminide

Fatigue crack initiation and growth were examined in cast and HIP'ed \textgamma-TiAl 4522XD. It was found that fatigue crack growth rates were higher at 750\celsius than 400\celsius, but that $\Delta K_\mathrm{th}$ was also higher. Temperature excursions between $400$ and 750\celsius during fatigue crack growth resulted in retardation of the crack growth rate, both on heating and cooling; however heating from 400 to 750\celsius at a $\Delta K$ that would then be below threshold did not result in complete crack arrest. It was also found that for notches $0.6$~mm in length and smaller, initiation from the microstructure could instead be observed at stresses similar to the material failure stress; a microstructural initiation site exists. Secondary cracking around borides could also be observed. A change from trans- to mixed trans-, inter- and intra-lamellar cracking could be observed where the estimated size of the crack tip plastic zone exceeded the colony size. Changes in fracture surface morphology could not be related to the temperature of fatigue crack growth, although this could be observed from the oxide scale colouration. Compressive pre-loading of a crack results in retardation of the crack, which could also be observed from the oxide

Environmentally assisted fatigue crack nucleation in Ti-6Al-2Sn-4Zr-6Mo

An unexplained feature was observed at the fatigue crack origin of a number of alpha/beta titanium specimens tested at 450 °C in the low cycle fatigue regime. The origin was discoloured blue but this was not a result of temper colouration; this feature sometimes resulted in large reductions in fatigue lives. A number of specimens were examined to determine the cause and formation mechanism of these “blue spots.” This feature was associated with elevated oxygen and chloride levels and the presence of sodium. A mechanism based on hot-salt stress-corrosion cracking is proposed and the implications for service components are discussed

AgCl-induced hot salt stress corrosion cracking in a titanium alloy

The mechanism of AgCl-induced stress corrosion cracking of Ti-6246 was examined at 500 MPa and 380 °C for 24 h exposures. SEM and STEM-EDX examination of a FIB-sectioned blister and crack showed that metallic Ag was formed and migrated along the crack. TEM analysis also revealed the presence of SnO2 and Al2O3 corrosion products mixed into TiO2. The fracture surface has a transgranular nature with a brittle appearance in the primary α phase. Long, straight and non-interacting dislocations were observed in a brittle appearance fractured primary α grain, with basal and pyramidal traces. This is consistent with a dislocation emission view of the cracking mechanism

Modeling the Impact of Tuberculosis Control Strategies in Highly Endemic Overcrowded Prisons

International audienceBACKGROUND: Tuberculosis (TB) in prisons is a major health problem in countries of high and intermediate TB endemicity such as Brazil. For operational reasons, TB control strategies in prisons cannot be compared through population based intervention studies. METHODOLOGY/PRINCIPAL FINDINGS: A mathematical model is proposed to simulate the TB dynamics in prison and evaluate the potential impact on active TB prevalence of several intervention strategies. The TB dynamics with the ongoing program was simulated over a 10 year period in a Rio de Janeiro prison (TB prevalence 4.6 %). Then, a simulation of the DOTS strategy reaching the objective of 70 % of bacteriologically-positive cases detected and 85 % of detected cases cured was performed; this strategy reduced only to 2.8% the average predicted TB prevalence after 5 years. Adding TB detection at entry point to DOTS strategy had no major effect on the predicted active TB prevalence. But, adding further a yearly X-ray mass screening of inmates reduced the predicted active TB prevalence below 1%. Furthermore, according to this model, after applying this strategy during 2 years (three annual screenings), the TB burden would be reduced and the active TB prevalence could be kept at a low level by associating X-ray screening at entry point and DOTS. CONCLUSIONS/SIGNIFICANCE: We have shown that X-ray mass screenings should be considered to control TB in highly endemic prison. Prisons with different levels of TB prevalence could be examined thanks to this model which provides a rational tool for public health deciders

Prevalence and predictors of tuberculin skin positivity in Hellenic Army recruits

BACKGROUND: Tuberculosis (TB) remains one of the leading causes of death among infectious diseases worldwide. Despite its low incidence rates in countries of Western Europe and North America, the resurgence of TB in Eastern Europe and the increased immigration from high-incidence countries imply that extreme vigilance is required in order to detect early, treat, and isolate all new cases. In this study, we analyzed the prevalence and predictors of tuberculin skin testing positivity in Hellenic Army recruits. METHODS: The study population consisted of 953 Greek military recruits enlisted inthe Army during the period from November 2005 toFebruary 2006. Tuberculin skin testing was performed on all study subjects upon enrollment, according to the routine procedures. A tuberculin skin test reaction size >15 mm was considered positive for all study participants. Epidemiological data regarding age, repatriation status, geographic area of residence, smoking habits, and parental occupation were collected by means of personal interviews. In addition, body weight, height, and body mass index were measured. RESULTS: The mean age of the studied subjects (± SD) was 23.5 (± 6.4) years. The overall prevalence of tuberculin positivity was 3.9% (37/953), and bivariable analysis showed that it was associated with lower weight (p = 0.047) and repatriation status (p < 0.001). Tuberculin skin testing was positive in 2.6% of natives (24/900) and 24.5% of repatriates (13/53). A backward, stepwise multivariable logistic regression model showed that only repatriation status was independently associated with tuberculin positivity (p < 0.001; odds ratio [OR]: 14.1; 95% confidence interval [CI]: 6.5–30.3). CONCLUSION: While the incidence of tuberculosis in the native Greek population is low, and comparable to other Western European countries, the extremely high tuberculin positivity in repatriated persons underscores the importance of actively screening for TB in order to promptly identify, isolate, and treat cases of active and latent infection

Has the DOTS Strategy Improved Case Finding or Treatment Success? An Empirical Assessment

Background: Nearly fifteen years after the start of WHO's DOTS strategy, tuberculosis remains a major global health problem. Given the lack of empirical evidence that DOTS reduces tuberculosis burden, considerable debate has arisen about its place in the future of global tuberculosis control efforts. An independent evaluation of DOTS, one of the most widely-implemented and longest-running interventions in global health, is a prerequisite for meaningful improvements to tuberculosis control efforts, including WHO's new Stop TB Strategy. We investigate the impact of the expansion of the DOTS strategy on tuberculosis case finding and treatment success, using only empirical data. Methods and Findings: We study the effect of DOTS using time-series cross-sectional methods. We first estimate the impact of DOTS expansion on case detection, using reported case notification data and controlling for other determinants of change in notifications, including HIV prevalence, GDP, and country-specific effects. We then estimate the effect of DOTS expansion on treatment success. DOTS programme variables had no statistically significant impact on case detection in a wide range of models and specifications. DOTS population coverage had a significant effect on overall treatment success rates, such that countries with full DOTS coverage benefit from at least an 18% increase in treatment success (95% CI: 5–31%). Conclusions: The DOTS technical package improved overall treatment success. By contrast, DOTS expansion had no effect on case detection. This finding is less optimistic than previous analyses. Better epidemiological and programme data would facilitate future monitoring and evaluation efforts

Screening for latent tuberculosis infection among undocumented immigrants in Swiss healthcare centres; a descriptive exploratory study

BACKGROUND: Migration is one of the major causes of tuberculosis in developed countries. Undocumented patients are usually not screened at the border and are not covered by a health insurance increasing their risk of developing the disease unnoticed. Urban health centres could help identify this population at risk. The objective of this study is to assess the prevalence of latent tuberculosis infection (LTBI) and adherence to preventive treatment in a population of undocumented immigrant patients. METHODS: All consecutive undocumented patients that visited two urban healthcare centres for vulnerable populations in Lausanne, Switzerland for the first time were offered tuberculosis screening with an interferon-gamma assay. Preventive treatment was offered if indicated. Adherence to treatment was evaluated monthly over a nine month period. RESULTS: Of the 161 participants, 131 (81.4%) agreed to screening and 125 had complete examinations. Twenty-four of the 125 patients (19.2%; CI95% 12.7;27.2) had positive interferon-gamma assay results, two of which had active tuberculosis. Only five patients with LTBI completed full preventive treatments. Five others initiated the treatment but did not follow through. CONCLUSION: Screening for tuberculosis infection in this hard-to-reach population is feasible in dedicated urban clinics, and the prevalence of LTBI is high in this vulnerable population. However, the low adherence to treatment is an important public health concern, and new strategies are needed to address this problem

In Vitro and In Vivo Efficacy of Monepantel (AAD 1566) against Laboratory Models of Human Intestinal Nematode Infections

Soil-transmitted helminthiases affect more than one billion people among the most vulnerable populations in developing countries. Currently, control of these infections primarily relies on chemotherapy. Only five drugs are available, all of which have been in use for decades. None of the drugs are efficacious using single doses against all soil-transmitted helminths (STH) species and show low efficacy observed against Trichuris trichiura. In addition, the limited availability of current drug treatments poses a precarious situation should drug resistance occur. Therefore, there is great interest to develop novel drugs against infections with STH. Monepantel, which belongs to a new class of veterinary anthelmintics, the amino-acetonitrile derivatives, might be a potential drug candidate in humans. It has been extensively tested against livestock nematodes, and was found highly efficacious and safe for animals. Here we describe the in vitro and in vivo effect of monepantel, on Ancylostoma ceylanicum, Necator americanus, Trichuris muris, Strongyloides ratti, and Ascaris suum, five parasite-rodent models of relevance to human STH. Since we observed that monepantel showed only high activity on one of the hookworm species and lacked activity on the other parasites tested we cannot recommend the drug as a development candidate for human soil-transmitted helminthiases