Assessment of biodegradable magnesium alloys for enhanced mechanical and biocompatible properties

Biomaterials have been used for more than a century in the human body to improve body functions and replace damaged tissues. Currently approved and commonly used metallic biomaterials such as, stainless steel, titanium, cobalt chromium and other alloys have been found to have adverse effects leading in some cases, to mechanical failure and rejection of the implant. The physical or chemical nature of the degradation products of some implants initiates an adverse foreign body reaction in the tissue. Some metallic implants remain as permanent fixtures, whereas others such as plates, screws and pins used to secure serious fractures are removed by a second surgical procedure after the tissue has healed sufficiently. However, repeat surgical procedures increase the cost of health care and the possibility of patient morbidity. This study focuses on the development of magnesium based biodegradable alloys/metal matrix composites (MMCs) for orthopedic and cardiovascular applications. The Mg alloys/MMCs possessed good mechanical properties and biocompatible properties. Nine different compositions of Mg alloys/MMCs were manufactured and surface treated. Their degradation behavior, ion leaching, wettability, morphology, cytotoxicity and mechanical properties were determined. Alloying with Zn, Ca, HA and Gd and surface treatment resulted in improved mechanical properties, corrosion resistance, reduced cytotoxicity, lower pH and hydrogen evolution. Anodization resulted in the formation of a distinct oxide layer (thickness 5-10 μm) as compared with that produced on mechanically polished samples (~20-50 nm) under ambient conditions. It is envisaged that the findings of this research will introduce a new class of Mg based biodegradable alloys/MMCs and the emergence of innovative cardiovascular and orthopedic implant devices.^

An investigation of how foreign language departments at American colleges and universities view American Sign Language

Corwin and Wilcox (1985) sent surveys to more than 100 American colleges and universities to determine the policies on the matter of accepting American Sign Language (ASL) as a foreign language. Their results indicated that 81% of those surveyed rejected ASL as a foreign/modern language equivalent. The most frequently stated opposition to ASL was that it lacked a culture. Some of the other objections to ASL were: ASL is not foreign; there is no written form and therefore no original body of literature; it is a derivative of English; and it is indigenous to the United States and hence not foreign. Based on the work of Corwin and Wilcox this study sent surveys to 222 American colleges and universities. Noting an expanding cognizance and social awareness of ASL and deafness (as seen in the increasing number of movies, plays, television programs, the Americans with Disabilities Act, and related news stories), this study sought to find out if ASL was now considered an acceptable foreign language equivalent. The hypothesis of this study was that change has occurred since the 1985 study: that a significant percent of post secondary schools accepting ASL as a foreign/modern language equivalent has increased. The 165 colleges and universities that responded to this author's survey confirmed there has been a significant shift towards the acceptance of ASL. Only 50% of the respondents objected to ASL as a foreign language equivalent, a significant decrease from the 1985 findings. Of those who objected to granting ASL foreign language credit, the reasons were similar to those of the Corwin and Wilcox study, except that the belief in an absence of a Deaf culture dropped from the top reason listed, to the fifth. That ASL is not foreign was listed as the most frequent objection in this study. One important change which may account for increased acceptance of ASL, is that 16 states (compared to 10 in 1985) now have policies stating that ASL is acceptable as a foreign language equivalent. Two-year colleges, in this study, were more likely to accept ASL than were four-year colleges and universities. Neither two- nor four-year colleges and universities are likely to include ASL in their foreign language departments, and most schools that have foreign language entrance requirements are unlikely to accept ASL. In colleges and universities where ASL was already offered in some department within the system, there was a significantly higher likelihood that foreign language credit was given for ASL. Respondents from states with laws governing the inclusion of ASL did not usually know their state had a policy. Most respondents, 84%, indicated their knowledge on the topic of ASL was fair to poor. ^

High energy three -body breakup of three -nucleon systems

The main goal of this dissertation was to study two- and three-nucleon Short Range Correlations (SRCs) in high energy three-body breakup of 3He nucleus in 3He(e, e'NN) N reaction. SRCs are characterized by quantum fluctuations in nuclei during which constituent nucleons partially overlap with each other. ^ A theoretical framework is developed within the Generalized Eikonal Approximation (GEA) which upgrades existing medium-energy methods that are inapplicable for high momentum and energy transfer reactions. High momentum and energy transfer is required to provide sufficient resolution for probing SRCs. GEA is a covariant theory which is formulated through the effective Feynman diagrammatic rules. It allows self-consistent calculation of single and double re-scatterings amplitudes which are present in three-body breakup processes. The calculations were carried out in detail and the analytical result for the differential cross section of 3He(e, e'NN)N reaction was derived in a form applicable for programming and numerical calculations. The corresponding computer code has been developed and the results of computation were compared to the published experimental data, showing satisfactory agreement for a wide range of values of missing momenta. ^ In addition to the high energy approximation this study exploited the exclusive nature of the process under investigation to gain more information about the SRCs. The description of the exclusive 3He( e, e'NN)N reaction has been done using the formalism of the nuclear decay function, which is a practically unexplored quantity and is related to the conventional spectral function through the integration of the phase space of the recoil nucleons. Detailed investigation showed that the decay function clearly exhibits the main features of two- and three-nucleon correlations. Four highly practical types of SRCs in 3He nucleus were discussed in great detail for different orders of the final state re-interactions using the decay function as an unique identifying tool. ^ The overall conclusion in this dissertation suggests that the investigation of the decay function opens up a completely new venue in studies of short range nuclear properties. ^

High energy three-body breakup of three-nucleon systems

The main goal of this dissertation was to study two- and three-nucleon Short Range Correlations (SRCs) in high energy three-body breakup of 3He nucleus in 3He(e, e'NN)N reaction. SRCs are characterized by quantum fluctuations in nuclei during which constituent nucleons partially overlap with each other. A theoretical framework is developed within the Generalized Eikonal Approximation (GEA) which upgrades existing medium-energy methods that are inapplicable for high momentum and energy transfer reactions. High momentum and energy transfer is required to provide sufficient resolution for probing SRCs. GEA is a covariant theory which is formulated through the effective Feynman diagrammatic rules. It allows self-consistent calculation of single and double re-scatterings amplitudes which are present in three-body breakup processes. The calculations were carried out in detail and the analytical result for the differential cross section of 3He(e, e'NN)Nreaction was derived in a form applicable for programming and numerical calculations. The corresponding computer code has been developed and the results of computation were compared to the published experimental data, showing satisfactory agreement for a wide range of values of missing momenta. In addition to the high energy approximation this study exploited the exclusive nature of the process under investigation to gain more information about the SRCs. The description of the exclusive 3He(e, e'NN)N reaction has been done using the formalism of the nuclear decay function, which is a practically unexplored quantity and is related to the conventional spectral function through the integration of the phase space of the recoil nucleons. Detailed investigation showed that the decay function clearly exhibits the main features of two- and three-nucleon correlations. Four highly practical types of SRCs in 3He nucleus were discussed in great detail for different orders of the final state re-interactions using the decay function as an unique identifying tool. The overall conclusion in this dissertation suggests that the investigation of the decay function opens up a completely new venue in studies of short range nuclear properties.