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Harinderjit Gill - One of the best experts on this subject based on the ideXlab platform.
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In vitro influence of Stem surface finish and mantle conformity on pressure generation in cemented hip arthroplasty
Acta Orthopaedica, 2009Co-Authors: Gavin E Bartlett, Harinderjit Gill, David W. Murray, David J BeardAbstract:Background and purpose Under physiological loads, debonded cemented femoral Stems have been shown to move within their cement mantle and generate a fluid pump that may facilitate peri-prosthetic osteolysis by pressurizing fluid and circulating wear debris. The long-term physiological loading of rough and polished tapered Stems in vitro has shown differences in performance, with greater interface pressures generated by the rough Stems. In this study we investigated the individual effects of Stem surface finish, degree of mantle wear, and mode of loading on the Stem pump mechanism. Method Rough and polished Stems were loaded under different regimes in artificially worn cement mantles that permitted either 2 or 5 degrees of rotational Stem Movement, and the interface pressures were compared. Results The pressures generated by the rough and polished Stems were similar in either type of mantle. The pattern of pressure generation in the 2-degree mantles was similar to the pressures generated by rough Stems after long-term loading, but the high posterior wall pressures fell and the tip pressures increased in the 5-degree mantles. The torsional loads were principal drivers of pressure generation in all areas of the interface other than the implant tip, where axial loading predominated. Interpretation Femoral Stems with rotational instability under cyclic torsional loads generate elevated interface fluid pressures and flows independently of Stem surface finish. The rough surface finish is only important in creating this instability in tapered Stems.
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MANTLE CONFORMITY EFFECTS PRESSURE GENERATION AT THE Stem/CEMENT INTERFACE IN HIP ARTHROPLASTY
2006Co-Authors: Gavin E Bartlett, David W. Murray, Harinderjit GillAbstract:Hypothesis Stem surface finish & cement mantle conformity influences pressure at the Stem/cement interface, under physiological load. Method We developed a scaled mechanical analogue of a cemented Exeter femoral Stem with a temperature and pressure controlled fluid environment. The Stem was subjected to physiological torsional & axial loads using a material testing machine with two perpendicularly mounted actuators. Rough (Ra=2.2μm), matt (Ra=1.16μm) & polished (Ra=0.02μm) Stems were tested in both conforming & artificially created, asymmetrically worn, cement mantles. Pressure was recorded at five sites along the interface. Results Pressure was generated in both conforming and worn mantles. Peak pressures recorded in worn mantles were nearly four times greater than in conforming; peak Stem tip pressures, worn: 12000Pa, versus conforming: 4680Pa. The axial load was the main determinant of pressure generation in the conforming mantle. Torsional loads generated a rise in interface pressure in both mantle types but the resultant Stem toggle seen in the worn mantle had a significant positive effect on pressure. Pressure fluctuations generated in the conforming mantle had the greatest range at the tip. Peak pressures within the worn mantle were more uniform, but marginally greater on the posterior wall. Surface finish influenced pressure; surface roughness had a positive association with pressure within conforming mantles & the reverse effect in worn mantles. Conclusion Asymmetrical wear leads to increased pressure generation at the Stem/cement interface under physiological loads, with the torsional load playing a key part in pressure generation. Well fixed, debonded Stems also generate limited pressure fluctuations at their mantle interface. This is principally due to axial load. Mantle shape dictates the influence of surface finish on pressure; surface roughness increases pressure within conforming mantles, but reduces pressure when the mantle is worn. This may be a confounding effect of worn mantle shape, restricting non-polished Stem Movement.
Gavin E Bartlett - One of the best experts on this subject based on the ideXlab platform.
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In vitro influence of Stem surface finish and mantle conformity on pressure generation in cemented hip arthroplasty
Acta Orthopaedica, 2009Co-Authors: Gavin E Bartlett, Harinderjit Gill, David W. Murray, David J BeardAbstract:Background and purpose Under physiological loads, debonded cemented femoral Stems have been shown to move within their cement mantle and generate a fluid pump that may facilitate peri-prosthetic osteolysis by pressurizing fluid and circulating wear debris. The long-term physiological loading of rough and polished tapered Stems in vitro has shown differences in performance, with greater interface pressures generated by the rough Stems. In this study we investigated the individual effects of Stem surface finish, degree of mantle wear, and mode of loading on the Stem pump mechanism. Method Rough and polished Stems were loaded under different regimes in artificially worn cement mantles that permitted either 2 or 5 degrees of rotational Stem Movement, and the interface pressures were compared. Results The pressures generated by the rough and polished Stems were similar in either type of mantle. The pattern of pressure generation in the 2-degree mantles was similar to the pressures generated by rough Stems after long-term loading, but the high posterior wall pressures fell and the tip pressures increased in the 5-degree mantles. The torsional loads were principal drivers of pressure generation in all areas of the interface other than the implant tip, where axial loading predominated. Interpretation Femoral Stems with rotational instability under cyclic torsional loads generate elevated interface fluid pressures and flows independently of Stem surface finish. The rough surface finish is only important in creating this instability in tapered Stems.
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MANTLE CONFORMITY EFFECTS PRESSURE GENERATION AT THE Stem/CEMENT INTERFACE IN HIP ARTHROPLASTY
2006Co-Authors: Gavin E Bartlett, David W. Murray, Harinderjit GillAbstract:Hypothesis Stem surface finish & cement mantle conformity influences pressure at the Stem/cement interface, under physiological load. Method We developed a scaled mechanical analogue of a cemented Exeter femoral Stem with a temperature and pressure controlled fluid environment. The Stem was subjected to physiological torsional & axial loads using a material testing machine with two perpendicularly mounted actuators. Rough (Ra=2.2μm), matt (Ra=1.16μm) & polished (Ra=0.02μm) Stems were tested in both conforming & artificially created, asymmetrically worn, cement mantles. Pressure was recorded at five sites along the interface. Results Pressure was generated in both conforming and worn mantles. Peak pressures recorded in worn mantles were nearly four times greater than in conforming; peak Stem tip pressures, worn: 12000Pa, versus conforming: 4680Pa. The axial load was the main determinant of pressure generation in the conforming mantle. Torsional loads generated a rise in interface pressure in both mantle types but the resultant Stem toggle seen in the worn mantle had a significant positive effect on pressure. Pressure fluctuations generated in the conforming mantle had the greatest range at the tip. Peak pressures within the worn mantle were more uniform, but marginally greater on the posterior wall. Surface finish influenced pressure; surface roughness had a positive association with pressure within conforming mantles & the reverse effect in worn mantles. Conclusion Asymmetrical wear leads to increased pressure generation at the Stem/cement interface under physiological loads, with the torsional load playing a key part in pressure generation. Well fixed, debonded Stems also generate limited pressure fluctuations at their mantle interface. This is principally due to axial load. Mantle shape dictates the influence of surface finish on pressure; surface roughness increases pressure within conforming mantles, but reduces pressure when the mantle is worn. This may be a confounding effect of worn mantle shape, restricting non-polished Stem Movement.
Majd Zouda - One of the best experts on this subject based on the ideXlab platform.
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Issues of power and control in Stem education: a reading through the postmodern condition
Cultural Studies of Science Education, 2018Co-Authors: Majd ZoudaAbstract:Stem, or the integration of science, technology, engineering and mathematics, has rapidly become a dominant discourse in political, economic and educational spheres. In the U.S., the Stem Movement has been boosted by global economic-based competition and associated fears, in terms of Stem graduates, when compared with other nations. However, many critiques question the nature and goals of this competition, as well as, the possibilities to improve Stem talents through the current dominant conceptualizations and practices of Stem education. In addition, the apparent lack of significant and coherent embracement of (and sometimes silence about) socioscientific and socio-political issues and perspectives renders Stem education incapable of preparing learners for active citizenships. Building on these critiques, I argue that these problems are possible consequences of Stem as a construct of power. My arguments are based on Lyotard’s conceptions of knowledge in postmodern society (as reported in The postmodern condition: A report on knowledge, University Press, Manchester, 1984 ), which I use to analyze some aspects of the Stem educational Movement. Throughout the paper, I explore the construction of Stem education within competitive frames that place prime value on high performativity. There seem to be two characteristics of current Stem education that support performativity; these are an increased focus on technological and engineering designs, and a tendency for interdisciplinary education. At the same time, the eagerness for performativity and competition seems to drag Stem education into selectiveness, thereby jeopardizing its possible benefits. Recommendations are also discussed.
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Deconstructing Stem: A Reading Through The Postmodern Condition
2016Co-Authors: Majd ZoudaAbstract:Since the beginning of the new millennium, educational research and policy making have increasingly involved integration of science, technology, engineering and mathematics (i.e. Stem). Integration of the four disciplines is argued to provide students with contextualized learning experiences that resemble real-life work in Stem fields, along with solutions to interdisciplinary problems that human face. In the U.S., the Stem Movement has been boosted by global economic-based competition and associated fears, in terms of Stem graduates, when compared with other nations. However, many critiques question the nature and goals of this competition, as well as, the possibilities to improve Stem talents through the current conceptualizations and practices of Stem education. Through Lyotard’s (1984) conceptions of knowledge in the postmodern society, this paper analyzes some aspects of the Stem educational Movement. It explores the construction of Stem discourse within competitive frames that place prime value on high performativity. There seem to be two characteristics of current Stem education that support performativity; these are an increased focus on technological and engineering designs, and a tendency for interdisciplinary education/curriculum integration. At the same time, the eagerness for performativity and competition seems to drag Stem education into selectiveness, thereby jeopardizing its possible benefits. Recommendations for educators are finally discussed.
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2016Co-Authors: Majd ZoudaAbstract:Since the beginning of the new millennium, educational research and policy making have increasingly involved integration of science, technology, engineering and mathematics (i.e. Stem). Integration of the four disciplines is argued to provide students with contextualized learning experiences that resemble real-life work in Stem fields, along with solutions to interdisciplinary problems that human face. In the U.S., the Stem Movement has been boosted by global economic-based competition and associated fears, in terms of Stem graduates, when compared with other nations. However, many critiques question the nature and goals of this competition, as well as, the possibilities to improve Stem talents through the current conceptualizations and practices of Stem education. Through Lyotard’s (1984) conceptions of knowledge in the postmodern society, this paper analyzes some aspects of the Stem educational Movement. It explores the construction of Stem discourse within competitive frames that place prime value on high performativity. There seem to be two characteristics of current Stem education that support performativity; these are an increased focus on technological and engineering designs, and a tendency for interdisciplinary education/curriculum integration. At the same time, the eagerness for performativity and competition seems to drag Stem education into selectiveness, thereby jeopardizing its possible benefits. Recommendations for educators are finally discussed.
Christophe Plomion - One of the best experts on this subject based on the ideXlab platform.
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(Not) Keeping the Stem straight: a proteomic analysis of maritime pine seedlings undergoing phototropism and gravitropism
BMC Plant Biology, 2010Co-Authors: Raul Herrera, Thierry Fourcaud, Catherine Krier, Celine Lalanne, Elhadji Maodo Ba, Alexia Stokes, Franck Salin, Stéphane Claverol, Christophe PlomionAbstract:Background Plants are subjected to continuous stimuli from the environment and have evolved an ability to respond through various growth and development processes. Phototropism and gravitropism responses enable the plant to reorient with regard to light and gravity. Results We quantified the speed of maritime pine seedlings to reorient with regard to light and gravity over 22 days. Seedlings were inclined at 15, 30 and 45 degrees with vertical plants as controls. A lateral light source illuminated the plants and Stem Movement over time was recorded. Depending on the initial angle of Stem lean, the apical response to the lateral light source differed. In control and 15° inclined plants, the apex turned directly towards the light source after only 2 h. In plants inclined at 30° and 45°, the apex first reoriented in the vertical plane after 2 h, then turned towards the light source after 24 h. Two-dimensional gel electrophoresis coupled with mass spectrometry was then used to describe the molecular response of Stem bending involved in photo- and gravi-tropism after 22 hr and 8 days of treatment. A total of 486 spots were quantitatively analyzed using image analysis software. Significant changes were determined in the protein accumulation of 68 protein spots. Early response gravitropic associated proteins were identified, which are known to function in energy related and primary metabolism. A group of thirty eight proteins were found to be involved in primary metabolism and energy related metabolic pathways. Degradation of Rubisco was implicated in some protein shifts. Conclusions Our study demonstrates a rapid gravitropic response in apices of maritime pine seedlings inclined >30°. Little or no response was observed at the Stem bases of the same plants. The primary gravitropic response is concomitant with a modification of the proteome, consisting of an over accumulation of energy and metabolism associated proteins, which may allow the Stem to reorient rapidly after bending.
David W. Murray - One of the best experts on this subject based on the ideXlab platform.
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In vitro influence of Stem surface finish and mantle conformity on pressure generation in cemented hip arthroplasty
Acta Orthopaedica, 2009Co-Authors: Gavin E Bartlett, Harinderjit Gill, David W. Murray, David J BeardAbstract:Background and purpose Under physiological loads, debonded cemented femoral Stems have been shown to move within their cement mantle and generate a fluid pump that may facilitate peri-prosthetic osteolysis by pressurizing fluid and circulating wear debris. The long-term physiological loading of rough and polished tapered Stems in vitro has shown differences in performance, with greater interface pressures generated by the rough Stems. In this study we investigated the individual effects of Stem surface finish, degree of mantle wear, and mode of loading on the Stem pump mechanism. Method Rough and polished Stems were loaded under different regimes in artificially worn cement mantles that permitted either 2 or 5 degrees of rotational Stem Movement, and the interface pressures were compared. Results The pressures generated by the rough and polished Stems were similar in either type of mantle. The pattern of pressure generation in the 2-degree mantles was similar to the pressures generated by rough Stems after long-term loading, but the high posterior wall pressures fell and the tip pressures increased in the 5-degree mantles. The torsional loads were principal drivers of pressure generation in all areas of the interface other than the implant tip, where axial loading predominated. Interpretation Femoral Stems with rotational instability under cyclic torsional loads generate elevated interface fluid pressures and flows independently of Stem surface finish. The rough surface finish is only important in creating this instability in tapered Stems.
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MANTLE CONFORMITY EFFECTS PRESSURE GENERATION AT THE Stem/CEMENT INTERFACE IN HIP ARTHROPLASTY
2006Co-Authors: Gavin E Bartlett, David W. Murray, Harinderjit GillAbstract:Hypothesis Stem surface finish & cement mantle conformity influences pressure at the Stem/cement interface, under physiological load. Method We developed a scaled mechanical analogue of a cemented Exeter femoral Stem with a temperature and pressure controlled fluid environment. The Stem was subjected to physiological torsional & axial loads using a material testing machine with two perpendicularly mounted actuators. Rough (Ra=2.2μm), matt (Ra=1.16μm) & polished (Ra=0.02μm) Stems were tested in both conforming & artificially created, asymmetrically worn, cement mantles. Pressure was recorded at five sites along the interface. Results Pressure was generated in both conforming and worn mantles. Peak pressures recorded in worn mantles were nearly four times greater than in conforming; peak Stem tip pressures, worn: 12000Pa, versus conforming: 4680Pa. The axial load was the main determinant of pressure generation in the conforming mantle. Torsional loads generated a rise in interface pressure in both mantle types but the resultant Stem toggle seen in the worn mantle had a significant positive effect on pressure. Pressure fluctuations generated in the conforming mantle had the greatest range at the tip. Peak pressures within the worn mantle were more uniform, but marginally greater on the posterior wall. Surface finish influenced pressure; surface roughness had a positive association with pressure within conforming mantles & the reverse effect in worn mantles. Conclusion Asymmetrical wear leads to increased pressure generation at the Stem/cement interface under physiological loads, with the torsional load playing a key part in pressure generation. Well fixed, debonded Stems also generate limited pressure fluctuations at their mantle interface. This is principally due to axial load. Mantle shape dictates the influence of surface finish on pressure; surface roughness increases pressure within conforming mantles, but reduces pressure when the mantle is worn. This may be a confounding effect of worn mantle shape, restricting non-polished Stem Movement.