Resolving the structure of TiBe12_{12}

There has been considerable controversy regarding the structure of TiBe$_{12}$, which is variously reported as hexagonal and tetragonal. Lattice dynamics simulations based on density functional theory show the tetragonal phase space group $I4/mmm$ to be more stable over all temperatures, while the hexagonal phase exhibits an imaginary phonon mode, which, if followed, would lead to the cell adopting the tetragonal structure. We then report the predicted ground state elastic constants and temperature dependence of the bulk modulus and thermal expansion for the tetragonal phase.Comment: In press at Acta Crystallographica B. Supplementary material appende

Hydrogen solubility in zirconium intermetallic second phase particles

The enthalpies of solution of H in Zr binary intermetallic compounds formed with Cu, Cr, Fe, Mo, Ni, Nb, Sn and V were calculated by means of density functional theory simulations and compared to that of H in {\alpha}-Zr. It is predicted that all Zr-rich phases (formed with Cu, Fe, Ni and Sn), and those phases formed with Nb and V, offer lower energy, more stable sites for H than {\alpha}-Zr. Conversely, Mo and Cr containing phases do not provide preferential solution sites for H. In all cases the most stable site for H are those that offer the highest coordination fraction of Zr atoms. Often these are four Zr tetrahedra but not always. Implications with respect to H-trapping properties of commonly observed ternary phases such as Zr(Cr,Fe)2, Zr2(Fe,Ni) and Zr(Nb,Fe)2 are also discussed.Comment: manuscript accepted for publication in Journal of Nuclear Materials (2013

Application of Lortie’s Apprenticeship of Observation Model: Evidence of Iowa Teaching Standards with Amish School Teachers

Classroom educators are held to standards of teaching and learning throughout their professional careers. The standards are the expectations laid out by the national and state levels to determine how and why teachers should teach the way they do to increase student achievement (NBPTS, 2016; State of Iowa Department of Education, 2019; CCSSO, 2013). The teaching standards in Iowa align with pedagogy, instruction, and professionalism (State of Iowa Department of Education, 2019). Some educators learn how to become teachers through their post-secondary education courses. Those teachers who are part of the Amish community do not follow a traditional path to becoming an educator within the Amish school system. Their preservice learning and teaching requirements are much different, which is the focus of this research, as they have no post-secondary formal education on how to be an educator. The intent of this qualitative study was to understand if Amish teachers, without any formal post-secondary education, were able to show evidence of the Iowa Teaching Standards within their teaching instruction. Classroom observations were conducted and evidence was collected that show which standards were being implemented. The secondary part of this study is to understand how these Amish teachers were able to know how to be teachers in the Amish classroom. Structured interviews were conducted of Amish teachers and explored how Amish teachers learned to be instructors of the classroom while determining if their responses align with Dan C. Lortie’s (1975) Apprenticeship of Observation Model

Developing the Intervention and Outcome Components of a Proposed Randomised Controlled trial (RCT) of a National Screening Programme for Open Angle Glaucoma (OAG) : Medical Research Council funded trial platform study (G0701759): Study protocol

Postprin

Skeletal Microdamage: Less About Biomechanics and More About Remodeling

The mechanical consequences of skeletal microdamage have been clearly documented using various experimental methods, yet recent experiments suggest that physiological levels of microdamage accumulation are not sufficient to compromise the bones’ biomechanical properties. While great advances have been made in our understanding of the biomechanical implications of microdamage, less is known concerning the physiological role of microdamage in bone remodeling. Microdamage has been shown to act as a signal for bone remodeling, likely through a disruption of the osteocyte-canalicular network. Interestingly, age-related increases in microdamage are not accompanied by increases in bone remodeling suggesting that the physiological mechanisms which link microdamage and remodeling are compromised with aging

The pathogenesis of bisphosphonate-related osteonecrosis of the jaw: so many hypotheses, so few data.

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) has generated great interest in the medical and research communities yet remains an enigma, given its unknown pathogenesis. The goal of this review is to summarize the various proposed hypotheses underlying BRONJ. Although a role of the oral mucosa has been proposed, the bone is likely the primary tissue of interest for BRONJ. The most popular BRONJ hypothesis-manifestation of necrotic bone resulting from bisphosphonate--induced remodeling suppression--is supported mostly by indirect evidence, although recent data have shown that bisphosphonates significantly reduce remodeling in the jaw. Remodeling suppression would be expected, and has been shown, to allow accumulation of nonviable osteocytes, whereas a more direct cytotoxic effect of bisphosphonates on osteocytes has also been proposed. Bisphosphonates have antiangiogenic effects, leading to speculation that this could contribute to the BRONJ pathogenesis. Compromised angiogenesis would most likely be involved in post-intervention healing, although other aspects of the vasculature (eg, blood flow) could contribute to BRONJ. Despite infection being present in many BRONJ patients, there is no clear evidence as to whether infection is a primary or secondary event in the pathophysiology. In addition to these main factors proposed in the pathogenesis, numerous cofactors associated with BRONJ (eg, diabetes, smoking, dental extraction, concurrent medications) could interact with bisphosphonates and affect remodeling, angiogenesis/blood flow, and/or infection. Because our lack of knowledge concerning BRONJ pathogenesis results from a lack of data, it is only through the initiation of hypothesis-driven studies that significant progress will be made to understand this serious and debilitating condition

Bisphosphonate effects on bone turnover, microdamage, and mechanical properties: what we think we know and what we know that we don't know

The bisphosphonates (BPs) have been useful tools in our understanding of the role that bone remodeling plays in skeletal health. The purpose of this paper is to outline what we know, and what is still unknown, about the role that BPs play in modulating bone turnover, how this affects microdamage accumulation, and ultimately what the effects of these changes elicited by BPs are to the structural and the material biomechanical properties of the skeleton. We know that BPs suppress remodeling site-specifically, probably do not have a direct effect on formation, and that the individual BPs vary with respect to speed of onset, duration of effect and magnitude of suppression. However, we do not know if these differences are meaningful in a clinical sense, how much remodeling is sufficient, the optimal duration of treatment, or how long it takes to restore remodeling to pre-treatment levels following withdrawal. We also know that suppression is intimately tied to microdamage accumulation, which is also site-specific, that BPs impair targeted repair of damage, and that they can reduce the energy absorption capacity of bone at the tissue level. However, the BPs are clearly effective at preventing fracture, and generally increase bone mineral density and whole bone strength, so we do not know whether these changes in damage accumulation and repair, or the mechanical effects at the tissue level, are clinically meaningful. The mechanical effects of BPs on the fatigue life of bone, or BP effects on bone subject to an impact, are entirely unknown. This paper reviews the literature on these topics, and identifies gaps in knowledge that can be addressed with further research