Virtual testing and design of barrier coating systems

The development of coating systems for high temperatures has two central challenges: (i) the selection of materials and layer architectures that are resistant to cracking and chemical attack, and (ii) the identification of active failure mechanisms and their dependency on the system’s intrinsic properties. This talk will describe two modeling frameworks that are tailored to meet these challenges. In the first framework, an automated system for analyzing delamination and mud-cracking in complex multilayers; this enables system developers to consider a broad range of materials and architectures and in turn rapidly identify promising material systems. The impact of CMAS penetration on coating reliability will be briefly discussed to illustrate potential applications of the framework. In the second framework, distributed cohesive zone models are used to develop a virtual testing framework: the framework is capable of predicting a broad range of cracking modes without a priori assumptions regarding the evolution of damage. The simulation framework exploits highly parallel computing approaches that enable simulations covering a broad range of parameter space; this enables the construction of “durability regime maps”, which indicate likely failure mechanisms as a function of material properties. Simulations will be presented illustrating the transition between crack penetration, kinking and delamination; the results demonstrate that crack kinking can occur even in the absence of a putative kink crack, and that in certain situations, cohesive strength plays a critical role in governing brittle failure modes (i.e. the relative toughness of the constituents alone is insufficient). The implications of these simulations for developing tough, CMAS resistant coatings will be discussed, with a particular focus on the role of microstructure in ceramic coatings

Virtual simulation and design of barrier coatings for ceramic composites

The development of environmental barrier coating systems for ceramic composites has two central challenges: (i) the selection of materials and layer architectures that are resistant to cracking, volatilization, and chemical attack, and (ii) the identification of active failure mechanisms and their dependency on the system’s intrinsic properties. This talk will describe two modeling frameworks that are tailored to these two objectives. In the first framework, an automated approach for analyzing delamination and mud-cracking in complex multilayers enables developers to consider a broad range of materials and architectures and in turn rapidly identify promising material systems. The opportunities created by this framework will be demonstrated by illustrating the likely failure modes of environmental barrier coatings comprising multiple layers of rare earth silicates on silicon carbide substrates. These map illustrate combinations of material properties (e.g. coating thickness and thermal expansion coefficients) that avoid penetrating mud cracks and delamination cracks. Maps will also be presented that quantify the likelihood of crack kinking, i.e. the transition of a penetrating crack to a delamination crack that leads to coating failure. In the second framework, distributed cohesive zone models are used to develop a virtual testing framework: the framework is capable of predicting a broad range of cracking modes without a priori assumptions regarding the failure mode and without phenomenological criteria for the evolution of damage. In this framework, cracks emerge from defects in the structure according to classical brittle fracture theory. The simulation framework exploits highly parallel computing approaches that enable simulations covering a broad range of parameter space; this enables the construction of “durability regime maps”, which indicate likely failure mechanisms as a function of material properties. This framework has been used to identify whether or not interface cracks will travel along an interface or kink into the coating (leading to spallation), as a function of interface toughness, film toughness, mixed mode loading, and interface waviness. The results shed new light on the physics of crack kinking, which plays a fundamental role in coating durability. Further, the results provide insights regarding the role of interface waviness between coatings and substrates, such as would occur with a coated woven textile composite

A Study to Determine if the Major Virginia School Systems are Teaching Middle School Technology Using Modular or Traditional Laboratory Arrangements

The goals of this research project were to: 1. Determine if the major Virginia school systems are teaching middle school technology education using modular or traditional laboratory arrangements; 2. Determine which major Virginia middle schools are teaching technology education using modular or traditional laboratory arrangements

‘Resolved to fight the ideology of genocide and all of its manifestations’: the Rwandan Patriotic Front, violence and ethnic marginalisation in post-genocide Rwanda and Eastern Congo

Using ethnographic data and James Scott’s (1990) concepts of public and hidden transcripts, this thesis examines fow the Rwandan Patriotic Front (RPF) government's public transcript has been institutionalised through the use of 'genocide ideology' laws. It is concerned with understanding how the RPF’s use of ‘genocide ideology’ is a mechanism to facilitate a continuum of violence, which I argue has led to ‘ethnic’ marginalisation. ‘Genocide ideology’ is a legally abstract term that refers to discourses that contest – consciously or unconsciously - the government narrative regarding the 1994 genocide. As focusing strictly om the public transcript does not tell the whole storry about power relations between the RPF government and Hutu, it also explores hidden transcript. This is necessary as the Rwandan government employs the category of ‘genocide ideology’ to silence dissent and to justify arbitrary arrest. For example, since taking power, the RPF government has strived to eliminate the Hutu/Tutsi identities, replacing the divisive identities with ‘Rwandan.’ Those who use Hutu/Tutsi identities outside the context of the genocide are considered génocidaire sympathisers and legally guilty of ‘genocide ideology’. I argue that within the public RPF transcript on the genocide, the victim/perpetrator dichotomy has become intertwined with Tutsi/Hutu identities, creating a hierarchy of victimhood. I concluded by arguing that the violence, fear and marginalisation experienced by participants through the government’s use of the public transcript in conjunction with ‘genocide ideology’ laws is causing resentment, which could lead to further conflict

Bioengineered Nisin A Derivatives with Enhanced Activity against Both Gram Positive and Gram Negative Pathogens

peer-reviewedNisin is a bacteriocin widely utilized in more than 50 countries as a safe and natural antibacterial food preservative. It is the most extensively studied bacteriocin, having undergone decades of bioengineering with a view to improving function and physicochemical properties. The discovery of novel nisin variants with enhanced activity against clinical and foodborne pathogens has recently been described. We screened a randomized bank of nisin A producers and identified a variant with a serine to glycine change at position 29 (S29G), with enhanced efficacy against S. aureus SA113. Using a site-saturation mutagenesis approach we generated three more derivatives (S29A, S29D and S29E) with enhanced activity against a range of Gram positive drug resistant clinical, veterinary and food pathogens. In addition, a number of the nisin S29 derivatives displayed superior antimicrobial activity to nisin A when assessed against a range of Gram negative food-associated pathogens, including E. coli, Salmonella enterica serovar Typhimurium and Cronobacter sakazakii. This is the first report of derivatives of nisin, or indeed any lantibiotic, with enhanced antimicrobial activity against both Gram positive and Gram negative bacteria.This work was supported by the Irish Government under the National Development Plan, through Science Foundation Ireland Investigator awards (10/IN.1/B3027) and (06/IN.1/B98) (http://www.sfi.ie)

Neutrophil gelatinase-associated lipocalin: its response to hypoxia and association with acute mountain sickness.

Acute Mountain Sickness (AMS) is a common clinical challenge at high altitude (HA). A point-of-care biochemical marker for AMS could have widespread utility. Neutrophil gelatinase-associated lipocalin (NGAL) rises in response to renal injury, inflammation and oxidative stress. We investigated whether NGAL rises with HA and if this rise was related to AMS, hypoxia or exercise. NGAL was assayed in a cohort (n = 22) undertaking 6 hours exercise at near sea-level (SL); a cohort (n = 14) during 3 hours of normobaric hypoxia (FiO2 11.6%) and on two trekking expeditions (n = 52) to over 5000 m. NGAL did not change with exercise at SL or following normobaric hypoxia. During the trekking expeditions NGAL levels (ng/ml, mean ± sd, range) rose significantly (P < 0.001) from 68 ± 14 (60-102) at 1300 m to 183 ± 107 (65-519); 143 ± 66 (60-315) and 150 ± 71 (60-357) at 3400 m, 4270 m and 5150 m respectively. At 5150 m there was a significant difference in NGAL between those with severe AMS (n = 7), mild AMS (n = 16) or no AMS (n = 23): 201 ± 34 versus 171 ± 19 versus 124 ± 12 respectively (P = 0.009 for severe versus no AMS; P = 0.026 for mild versus no AMS). In summary, NGAL rises in response to prolonged hypobaric hypoxia and demonstrates a relationship to the presence and severity of AMS

Barriers and Disparities in Emergency Medical Services 911 Calls for Stroke Symptoms in the United States Adult Population: 2009 BRFSS Survey

Introduction: This study examines barriers and disparities in the intentions of American citizens, when dealing with stroke symptoms, to call 911. This study hypothesizes that low socioeconomic populations are less likely to call 911 in response to stroke recognition. Methods: The study is a cross-sectional design analyzing data from the Centers for Disease Control’s 2009 Behavioral Risk Factor Surveillance Survey, collected through a telephone-based survey from 18 states and the District of Columbia. The study identified the 5 most evident stroke-warning symptoms based on those given by the American Stroke Association. We conducted appropriate weighting procedures to account for the complex survey design. Results: A total of 131,988 respondents answered the following question: “If you thought someone was having a heart attack or a stroke, what is the first thing you would do?” A majority of those who said they would call 911 were insured (85.1%), had good health (84.1%), had no stroke history (97.3%), had a primary care physician (PCP) (81.4%), and had no burden of medical costs (84.9%). Those less likely to call 911 were found in the following groups: 65 years or older, men, other race, unmarried, less than or equal to high school degree, less than $25,000 family income, uninsured, no PCP, burden of medical costs, fair/poor health, previous history of strokes, or interaction between burden of medical costs and less than$50,000 family income (p\u3c0.0001 by X2 tests). The only factors significantly associated with “would call 911” were age, sex, race/ethnicity, marital status, and previous history of strokes. Conclusion: Barriers and disparities exist among subpopulations of different socioeconomic statuses. This study suggests that some potential stroke victims could have limited access to EMS services. Greater effort targeting certain populations is needed to motivate citizens to call 911. [West J Emerg Med. 2014;15(2):251–259]