Defect Growth Characterization in Modern Rail Steel

This thesis investigates the fatigue characterization of modern head-hardened rails, with a specific focus on detail (i.e. transverse) fracture. This study provides necessary information to determine a safe and economically viable rail inspection interval.Safe inspection interval has previously been established for legacy, i.e. non-head-hardened rails. The head hardening process, which evolved over the past several decades, has been designed to improve rail wear resistance by increasing hardness. Unfortunately, increasing hardness, which is related to strength, typically results in reduction of toughness and fatigue life. This means that while improved wear resistance can extend the wear life of the rail, its fatigue life can simultaneously be reduced. Consequently, the safe inspection interval for legacy rails is not necessarily valid for modern rails. Thorough material characterization of modern rails in reference to legacy rails is necessary to establish the applicability of the legacy rail inspection interval to head hardened rails.Three modern rails (i.e. ArcelorMittal’s AHH, HH, and SS – standard, control-cooled rail) and two unused legacy rails produced in 1977 and 1984, were investigated here. The SS rail, the legacy rails and existing data were used as a reference. As expected, the two modern head hardened rails (i.e. AHH and HH) are significantly harder and stronger than the control rail (i.e. SS) and the two legacy rails. Uniform pearlitic microstructure was observed in all rails, with hardness and strength variation caused primarily by pearlite spacing, which is controlled by the cooling rate and the alloy content. Despite the strength variation, toughness test results are fairly uniform across all rails, with some spatial variation inside the rail heads. Similarly, no significant differences in fatigue crack growth rates between modern and legacy rails have been observed (especially between AHH and legacy rails). These results indicate that the head hardening process designed to improve wear resistance, does not have a significant negative impact on fatigue life of rails. It is important to note that improving wear resistance of modern rails, without sacrificing fatigue properties in reference to legacy rails is a significant enhancement in rail manufacturing technology. However, it can result in fatigue becoming the limiting factor for the overall life of the rail, which places higher emphasis on rail inspection and characterization of fatigue and fracture properties.Residual stresses due to heat treatment and roller straightening were also investigated in the AHH and HH rails by means of neutron diffraction measurements supplemented by advanced numerical analysis. The results show that the largest stress component (~350MPa) is the longitudinal stress, which is also the most consequential for fatigue growth of transverse defects. Given long beam time required to penetrate the rail material, full 3D distribution of residual stresses is difficult to obtain. Additionally, interpretation of the residual stress state measured with smaller specimens, such as plane stress slices and half-rail samples cut along the longitudinal, vertical symmetry plane, is very challenging due to significant level of interaction between different stress components. This means that extracting a rail specimen by cutting, not only relives the stress component normal to the cut plane, but it also affects the remaining stress components. Considering the importance of the longitudinal residual stresses for transverse crack growth rates, their magnitude and distribution, as well as the effect of rail-wheel contact, require further investigation

Supermodular ordering of Poisson and binomial random vectors by tree-based correlations

We construct a dependence structure for binomial, Poisson and Gaussian random vectors, based on partially ordered binary trees and sums of independent random variables. Using this construction, we characterize the supermodular ordering of such random vectors via the componentwise ordering of their covariance matrices. For this, we apply Möbius inversion techniques on partially ordered trees, which allow us to connect the Lévy measures of Poisson random vectors on the discrete d-dimensional hypercube to their covariance matrices.We construct a dependence structure for binomial, Poisson and Gaussian random vectors, based on partially ordered binary trees and sums of independent random variables. Using this construction, we characterize the supermodular ordering of such random vectors via the componentwise ordering of their covariance matrices. For this, we apply Möbius inversion techniques on partially ordered trees, which allow us to connect the Lévy measures of Poisson random vectors on the discrete d-dimensional hypercube to their covariance matrices

The epidemiology and economic impact of varicella-related hospitalizations in Turkey from 2008 to 2010: A nationwide survey during the pre-vaccine era (VARICOMP study)

PubMed ID: 22170238Varicella can cause complications that are potentially serious and require hospitalization. Our current understanding of the causes and incidence of varicella-related hospitalization in Turkey is limited and sufficiently accurate epidemiological and economical information is lacking. The aim of this study was to estimate the annual incidence of varicella-related hospitalizations, describe the complications, and estimate the annual mortality and cost of varicella in children. VARICOMP is a multi-center study that was performed to provide epidemiological and economic data on hospitalization for varicella in children between 0 and 15 years of age from October 2008 to September 2010 in Turkey. According to medical records from 27 health care centers in 14 cities (representing 49.3% of the childhood population in Turkey), 824 children (73% previously healthy) were hospitalized for varicella over the 2-year period. Most cases occurred in the spring and early summer months. Most cases were in children under 5 years of age, and 29.5% were in children under 1 year of age. The estimated incidence of varicella-related hospitalization was 5.29-6.89 per 100,000 in all children between 0-15 years of age in Turkey, 21.7 to 28 per 100,000 children under 1 year of age, 9.8-13.8 per 100,000 children under 5 years of age, 3.96-6.52 per 100,000 children between 5 and 10 years of age and 0.42 to 0.71 per 100,000 children between 10 and 15 years of age. Among the 824 children, 212 (25.7%) were hospitalized because of primary varicella infection. The most common complications in children were secondary bacterial infection (23%), neurological (19.1%), and respiratory (17.5%) complications. Secondary bacterial infections (p<0.001) and neurological complications (p<0.001) were significantly more common in previously healthy children, whereas hematological complications (p<0.001) were more commonly observed in children with underlying conditions. The median length of the hospital stay was 6 days, and it was longer in children with underlying conditions (<0.001). The median cost of hospitalization per patient was $338 and was significantly higher in children with underlying conditions (p<0.001). The estimated direct annual cost (not including the loss of parental work time and school absence) of varicella-related hospitalization in children under the age of 15 years in Turkey was$856,190 to $1,407,006. According to our estimates, 882 to 1,450 children are hospitalized for varicella each year, reflecting a population-wide occurrence of 466-768 varicella cases per 100,000 children. In conclusion, this study confirms that varicella-related hospitalizations are not uncommon in children, and two thirds of these children are otherwise healthy. The annual cost of hospitalization for varicella reflects only a small part of the overall cost of this disease, as only a very few cases require hospital admission. The incidence of this disease was higher in children <1 year of age, and there are no prevention strategies for these children other than population-wide vaccination. Universal vaccination is therefore the only realistic option for the prevention of severe complications and deaths. The surveillance of varicellaassociated complications is essential for monitoring of the impact of varicella immunization. © Springer-Verlag 2011

The epidemiology and economic impact of varicella-related hospitalizations in Turkey from 2008 to 2010: a nationwide survey during the pre-vaccine era (VARICOMP study)

Varicella can cause complications that are potentially serious and require hospitalization. Our current understanding of the causes and incidence of varicella-related hospitalization in Turkey is limited and sufficiently accurate epidemiological and economical information is lacking. The aim of this study was to estimate the annual incidence of varicella-related hospitalizations, describe the complications, and estimate the annual mortality and cost of varicella in children. VARICOMP is a multi-center study that was performed to provide epidemiological and economic data on hospitalization for varicella in children between 0 and 15 years of age from October 2008 to September 2010 in Turkey. According to medical records from 27 health care centers in 14 cities (representing 49.3% of the childhood population in Turkey), 824 children (73% previously healthy) were hospitalized for varicella over the 2-year period. Most cases occurred in the spring and early summer months. Most cases were in children under 5 years of age, and 29.5% were in children under 1 year of age. The estimated incidence of varicella-related hospitalization was 5.29-6.89 per 100,000 in all children between 0-15 years of age in Turkey, 21.7 to 28 per 100,000 children under 1 year of age, 9.8-13.8 per 100,000 children under 5 years of age, 3.96-6.52 per 100,000 children between 5 and 10 years of age and 0.42 to 0.71 per 100,000 children between 10 and 15 years of age. Among the 824 children, 212 (25.7%) were hospitalized because of primary varicella infection. The most common complications in children were secondary bacterial infection (23%), neurological (19.1%), and respiratory (17.5%) complications. Secondary bacterial infections (p < 0.001) and neurological complications (p < 0.001) were significantly more common in previously healthy children, whereas hematological complications (p < 0.001) were more commonly observed in children with underlying conditions. The median length of the hospital stay was 6 days, and it was longer in children with underlying conditions (< 0.001). The median cost of hospitalization per patient was $338 and was significantly higher in children with underlying conditions (p < 0.001). The estimated direct annual cost (not including the loss of parental work time and school absence) of varicella-related hospitalization in children under the age of 15 years in Turkey was$856,190 to $1,407,006. According to our estimates, 882 to 1,450 children are hospitalized for varicella each year, reflecting a population-wide occurrence of 466-768 varicella cases per 100,000 children. In conclusion, this study confirms that varicella-related hospitalizations are not uncommon in children, and two thirds of these children are otherwise healthy. The annual cost of hospitalization for varicella reflects only a small part of the overall cost of this disease, as only a very few cases require hospital admission. The incidence of this disease was higher in children < 1 year of age, and there are no prevention strategies for these children other than population-wide vaccination. Universal vaccination is therefore the only realistic option for the prevention of severe complications and deaths. The surveillance of varicella-associated complications is essential for monitoring of the impact of varicella immunization

The epidemiology and economic impact of varicella-related hospitalizations in Turkey from 2008 to 2010: a nationwide survey during the pre-vaccine era (VARICOMP study)

Varicella can cause complications that are potentially serious and require hospitalization. Our current understanding of the causes and incidence of varicella-related hospitalization in Turkey is limited and sufficiently accurate epidemiological and economical information is lacking. The aim of this study was to estimate the annual incidence of varicella-related hospitalizations, describe the complications, and estimate the annual mortality and cost of varicella in children. VARICOMP is a multi-center study that was performed to provide epidemiological and economic data on hospitalization for varicella in children between 0 and 15 years of age from October 2008 to September 2010 in Turkey. According to medical records from 27 health care centers in 14 cities (representing 49.3% of the childhood population in Turkey), 824 children (73% previously healthy) were hospitalized for varicella over the 2-year period. Most cases occurred in the spring and early summer months. Most cases were in children under 5 years of age, and 29.5% were in children under 1 year of age. The estimated incidence of varicella-related hospitalization was 5.29-6.89 per 100,000 in all children between 0-15 years of age in Turkey, 21.7 to 28 per 100,000 children under 1 year of age, 9.8-13.8 per 100,000 children under 5 years of age, 3.96-6.52 per 100,000 children between 5 and 10 years of age and 0.42 to 0.71 per 100,000 children between 10 and 15 years of age. Among the 824 children, 212 (25.7%) were hospitalized because of primary varicella infection. The most common complications in children were secondary bacterial infection (23%), neurological (19.1%), and respiratory (17.5%) complications. Secondary bacterial infections (p < 0.001) and neurological complications (p < 0.001) were significantly more common in previously healthy children, whereas hematological complications (p < 0.001) were more commonly observed in children with underlying conditions. The median length of the hospital stay was 6 days, and it was longer in children with underlying conditions (< 0.001). The median cost of hospitalization per patient was $338 and was significantly higher in children with underlying conditions (p < 0.001). The estimated direct annual cost (not including the loss of parental work time and school absence) of varicella-related hospitalization in children under the age of 15 years in Turkey was$856,190 to $1,407,006. According to our estimates, 882 to 1,450 children are hospitalized for varicella each year, reflecting a population-wide occurrence of 466-768 varicella cases per 100,000 children. In conclusion, this study confirms that varicella-related hospitalizations are not uncommon in children, and two thirds of these children are otherwise healthy. The annual cost of hospitalization for varicella reflects only a small part of the overall cost of this disease, as only a very few cases require hospital admission. The incidence of this disease was higher in children < 1 year of age, and there are no prevention strategies for these children other than population-wide vaccination. Universal vaccination is therefore the only realistic option for the prevention of severe complications and deaths. The surveillance of varicella-associated complications is essential for monitoring of the impact of varicella immunization