Indentation of Multi-Layered Materials Using Spherical Indentation

In the field of indentation there is a subset of study that examines indentation of thin films on substrate materials. Early work in this area primarily focused on the properties of the film, neglecting the substrate. However, there are a great many instances where understanding the substrate may be as important if not more important than understanding the film properties. The primary focus of this research and associated thesis is to extend the level of knowledge of the moderately deep spherical indentation of film-substrate systems, investigating both film and substrate. By choosing to use a spherical indenter the effects of damaging the test material at these moderate depths is reduced. It also allows for the incorporation of the innovative technique of invoking the non-self-similarity characteristics of this type of indenter. This thesis is focused on this phenomenon and furthers the present knowledge that exists today of thin film-substrate elastic indentation. The beginning of this thesis reviews the historical path that indentation has followed from the early work of Hertz to present day research in thin film on substrate materials. The next section focuses on thin films on substrates under spherical indentation in a fully elastic condition, investigating both film and substrate. A forward analysis incorporating Dimensional Analysis will be performed that will determine two relationships that can be used to solve for material properties of both film and substrate. Moderate indentation depths are chosen that will allow for the addition of the substrate effect while directly avoiding problems related to shallow indentation. A full numerical reverse analysis is performed using simulations that will check the applicability and accuracy of the relationships developed from the forward analysis. In the reverse analysis, different input values are used providing for a unique and unbiased review of the work performed. The next section will extend this research into the area of fully elastic film affixed on substrate systems with the film under an applied equi-biaxial steady-state stress. A forward analysis is performed incorporating dimensional analysis to help reduce the number of variables. A set of relationships are established that are then tested by an independent numerical reverse analysis using a full set of discreet and arbitrary input values. Finally a general examination of multi-layered systems is performed. This is done by first examining a specific problem that exists in industry today, water filtration, then extending this to a general relationship as a proof-of-principal investigation of a multi-layered system. Throughout this work an independent and rigorous error analyses is performed in order to identify potential instabilities in the proposed solutions. Finally an examination and proposal is made of how this work can be used to further extend specific areas of both research and commercial applications of indention of materials to moderate depth, incorporating the substrate effect

High temperature reliability of power module substrates

The thermal cycling reliability of candidate copper and aluminium power substrates has been assessed for use at temperatures exceeding 300°C peak using a combination of thermal cycling, nanoindentation and finite element modelling to understand the relative stresses and evolution of the mechanical properties. The results include the relative cycling lifetimes up to 350°C, demonstrating almost an order of magnitude higher lifetime for active metal brazed Al / AlN substrates over Cu / Si3N4, but four times more severe roughening and cracking of the Ni-P plating's on the Al / AlN (DBA) substrates. The nonlinear finite element modelling illustrated that the yield strength of the metal and the thickness of the ceramic are the main stress controlling factors, but comparisons with the cycling lifetime results demonstrated that the fracture toughness (resistance) of the ceramic is the over-riding controlling factor for the overall passive thermal cycling lifetimes. In order to achieve the highest substrate lifetime for the highly stressed high temperature thermal cycled applications, the optimum solution appears to be annealed copper, brazed on to a thicker than normal or higher fracture toughness Si3N4 ceramic

Giardia: a pathogen or commensal for children in high-prevalence settings?

Giardia is a common intestinal parasite worldwide, and infection can be associated with clear and sometimes persistent symptomatology. However, in children in high prevalence settings, it is not associated with or is perhaps even protective against acute diarrhea, and the association with long-term outcomes has been difficult to discern

Differences in both prevalence and titre of specific immunoglobulin E among children with asthma in affluent and poor communities within a large town in Ghana.

Background Reports from several African countries have noted an increasing prevalence of asthma in areas of extensive urbanization. Objective To investigate the relevance of allergen-specific sensitization and body mass index (BMI) to asthma/wheezing and exercise-induced bronchospasm (EIB) among children from affluent and poorer communities within a large town in Ghana. Methods Children with physician-diagnosed asthma and/or current wheezing aged 9-16 years (n=99; cases) from three schools with differing socio-economic backgrounds [urban affluent (UA), urban poor (UP) or suburban/rural (SR)] were recruited from a cross-sectional study (n=1848) in Kumasi, Ghana, and matched according to age, sex and area of residence with non-asthmatic/non-wheezy controls. We assayed sera for IgE antibodies to mite, cat, dog, cockroach, Ascaris and galactose-α-1,3-galactose. Results Children from the UA school had the lowest total serum IgE. However, cases from the UA school had a higher prevalence and mean titre of sIgE to mite (71.4%, 21.2IU/mL) when compared with controls (14.3%, 0.8IU/mL) or cases from UP (30%, 0.8IU/mL) and SR community (47.8%, 1.6IU/mL). While similar findings were observed with EIB in the whole population, among cases there was no difference in IgE antibody prevalence or titre between children with or without EIB. BMI was higher among UA children with and without asthma; in UP and SR communities, children with EIB (n=14) had a significantly higher BMI compared with children with asthma/wheezing without EIB (n=38) (18.2 vs. 16.4, respectively, P<0.01). Conclusions and Clinical Relevance In the relatively affluent school, asthma/wheezing and EIB were associated with high titre IgE antibodies to mite, decreased total IgE, and increased BMI. This contrasted with children in the urban poor school and suggests that changes relevant to a Western model of childhood asthma can occur within a short geographical distance within a large city in Africa. © 2011 Blackwell Publishing Ltd

Oh Dem Golden Slippers / words by James A. Bland

https://egrove.olemiss.edu/sharris_d/1049/thumbnail.jp

Ecologic and geographic distribution of filovirus disease

Centers for Disease Control and Prevention http://www.cdc.gov/ncidod/EID/vol10no1/03-0125.htmWe used ecologic niche modeling of outbreaks and sporadic cases of filovirus-associated hemorrhagic fever (HF) to provide a large-scale perspective on the geographic and ecologic distributions of Ebola and Marburg viruses. We predicted that filovirus would occur across the Afrotropics: Ebola HF in the humid rain forests of central and western Africa, and Marburg HF in the drier and more open areas of central and eastern Africa. Most of the predicted geographic extent of Ebola HF appear to have been observed; Marburg HF has the potential to occur farther south and east. Ecologic conditions appropriate for Ebola HF are also present in Southeast Asia and the Philippines, where Ebola Reston is hypothesized to be distributed. This first large-scale ecologic analysis provides a framework for a more informed search for taxa that could constitute the natural reservoir for this virus family

Status of Birds Newly Recorded in Arkansas Since 1985

In 1994 we published an annotated list of 14 bird species that were newly discovered in Arkansas since the publication in 1986 of the monograph Arkansas Birds, Their Distribution and Abundance. We now add 22 more new species found in Arkansas since the 1994 publication, and update the status of the original 14. Adding these 36 species to the number included in Arkansas Birds totals 402 bird species currently reported in Arkansas