Towards a better understanding of the development of the strength in Asymmetrical Friction Connections (AFC)

In the current design practice, the strength of Asymmetric Friction Connections (AFCs) is calculated considering the friction force developed at both sliding interfaces using the bolt tension reduced by the moment – shear - axial interaction (MPV) effect. However, available models do not consider the friction induced by the bolt assembly force, termed assembly effect, or the bolt inclination effect, which is the increase in the AFC strength due to the horizontal component of the bolt tension produced when the bolt inclines. This paper proposes a model for quantifying the strength of AFCs considering the assembly, MPV, and inclination effects for the cases: i). Before the slotted plate breakaway, ii). Bolts inclining up to the angle defined by the bole hole oversize and termed bolt elastic inclination, iii) Bolts inclination angles larger than the angle defined by the bole hole oversize and produced by bolt flexural yielding and termed bolt yielding inclination. The proposed model is validated from the testing of an AFC scaled prototype, and from the quasi – static testing of 18 AFCs in real scale and assembled with Bisalloy 500 shims, and 2 M16 Grade 8.8 bolts with bolt grip lengths between 52.5mm and 172.5mm. It is shown that before breakaway the hysteresis loop is linear, and the peak strength depends only on the assembly effect. For the bolt elastic inclination, the hysteresis loop shape is bilinear, and the peak strength depends on the combined action of the assembly, MPV, and inclination effects. For the bolt yielding inclination, the hysteresis loop is square and pinched and the average strength across the plateau of the hysteresis loop depends on the MPV and inclination effects. For the three cases considered, the proposed model predicts the AFC strength with accuracies of 76% – 120%. The proposed model shows the horizontal component of the bolt tension from the bolt inclination effect was 6% - 28% of the AFC strength for the bolt elastic inclination, and 38% - 53% of the AFC strength for the bolt yielding inclination

Shake table test a structure retrofitted using 2-4 Direction Displacement Dependent (D3) viscous dampers

Many seismic codes are modified to represent increased hazard or performance expectations of structures. According to the new code, many structures require retrofit to meet these increase performance expectations. Fluid viscous dampers can add energy dissipation without requiring major structural modification. However, their addition can lead to substantial increases in the maximum base shear and column axial forces in non-linear structures. In practice, these increases in demand would likely require strengthening of the columns and the foundations, thus increasing cost and reducing the ease and potential impact of this approach. In contrast, the 2-4 configuration of a passive Direction and Displacement Dependent (D3) damper provides damping in only quadrants 2 and 4 of the force-displacement response plot, thus substantially reducing peak base shear loads compared to a conventional viscous damper. The paper looks at the seismic performance of a 1/2 scale, two storey steel frame building that is retrofitted with the passive 2-4 D3 damper subjected to uni-directional shake table testing. Performance in mitigating structural response and foundation demand are assessed by evaluating base shear, maximum drift and acceleration. The overall results show that simultaneous reductions in displacement, base-shear and acceleration demand are only available with the 2–4 D3 viscous device. This device is entirely passive, and provides unique retrofit opportunity that does not require strengthening of the columns and the foundations

Stable relocation of the radial head without annular ligament reconstruction using the Ilizarov technique to treat neglected Monteggia fracture: two case reports

<p>Abstract</p> <p>Introduction</p> <p>A Monteggia facture dislocation is not an uncommon injury, and the diagnosis can often be missed. Long-term follow-up of untreated Monteggia fracture dislocations reveals development of premature arthritis, pain, instability, and loss of pronation and supination. Methods involving annular ligament reconstruction require post-operative immobilization and use of transcapitellar pinning for maintenance of reduction, and thus a delay in rehabilitation. The literature reports satisfactory results with methods that involve ulnar osteotomy and open reduction of the radial head without annular ligament reconstruction. We used the Ilizarov method in two cases with neglected Monteggia fracture dislocations to stably reduce the radial head without open reduction and annular ligament reconstruction.</p> <p>Case presentation</p> <p>We report two cases of neglected Monteggia fracture dislocation, in two Kashmiri boys aged four and six years. Using ulnar osteotomy with distraction osteogenesis, we were able to relocate the radial head gradually and maintain the reduction without a requirement for open reduction and annular ligament reconstruction.</p> <p>Conclusion</p> <p>Distraction lengthening and hyperangulation in different planes by use of the Ilizarov technique effectively reduces the radial head without open reduction and annular ligament reconstruction.</p

Abnormal spatial diffusion of Ca2+ in F508del-CFTR airway epithelial cells

<p>Abstract</p> <p>Background</p> <p>In airway epithelial cells, calcium mobilization can be elicited by selective autocrine and/or paracrine activation of apical or basolateral membrane heterotrimeric G protein-coupled receptors linked to phospholipase C (PLC) stimulation, which generates inositol 1,4,5-trisphosphate (IP₃) and 1,2-diacylglycerol (DAG) and induces Ca²⁺release from endoplasmic reticulum (ER) stores.</p> <p>Methods</p> <p>In the present study, we monitored the cytosolic Ca²⁺transients using the UV light photolysis technique to uncage caged Ca²⁺or caged IP₃into the cytosol of loaded airway epithelial cells of cystic fibrosis (CF) and non-CF origin. We compared in these cells the types of Ca²⁺receptors present in the ER, and measured their Ca²⁺dependent activity before and after correction of F508del-CFTR abnormal trafficking either by low temperature or by the pharmacological corrector miglustat (N-butyldeoxynojirimycin).</p> <p>Results</p> <p>We showed reduction of the inositol 1,4,5-trisphosphate receptors (IP₃R) dependent-Ca²⁺response following both correcting treatments compared to uncorrected cells in such a way that Ca²⁺responses (CF+treatment <it>vs </it>wild-type cells) were normalized. This normalization of the Ca²⁺rate does not affect the activity of Ca²⁺-dependent chloride channel in miglustat-treated CF cells. Using two inhibitors of IP₃R1, we observed a decrease of the implication of IP₃R1 in the Ca²⁺response in CF corrected cells. We observed a similar Ca²⁺mobilization between CF-KM4 cells and CFTR-cDNA transfected CF cells (CF-KM4-reverted). When we restored the F508del-CFTR trafficking in CFTR-reverted cells, the specific IP₃R activity was also reduced to a similar level as in non CF cells. At the structural level, the ER morphology of CF cells was highly condensed around the nucleus while in non CF cells or corrected CF cells the ER was extended at the totality of cell.</p> <p>Conclusion</p> <p>These results suggest reversal of the IP₃R dysfunction in F508del-CFTR epithelial cells by correction of the abnormal trafficking of F508del-CFTR in cystic fibrosis cells. Moreover, using CFTR cDNA-transfected CF cells, we demonstrated that abnormal increase of IP₃R Ca²⁺release in CF human epithelial cells could be the consequence of F508del-CFTR retention in ER compartment.</p

Knowledge of pressure ulcer prevention: a cross-sectional and comparative study among nurses

BACKGROUND: Pressure ulcers are a common, painful and costly condition. Results of a 1991 study into the knowledge among Dutch hospital nurses on the usefulness of measures to prevent pressure ulcers showed moderate knowledge. Results were confirmed by subsequent studies. In recent years, Dutch guidelines have been updated and the attention given to pressure ulcer care has been increased. This was expected to improve pressure ulcer care and to increase nurses' knowledge. The aims of the current study were to investigate (1) how much nurses employed in Dutch hospitals know about the usefulness of 28 preventive measures considered in the most recent national pressure ulcer guideline; (2) whether differences in knowledge exist between nurses working in hospitals that audit pressure ulcers and those employed in hospitals that do not; and (3) to study whether knowledge among Dutch hospital nurses regarding the usefulness of preventive measures had changed between 1991 and 2003. METHODS: A cross-sectional study design among nurses employed in Dutch hospitals in 2003 was used to investigate their knowledge and differences in knowledge between nurses employed in different types of institution. A comparative design was used to assess whether knowledge differed between this population and that of Dutch hospital nurses in 1991. The nurses' knowledge was assessed by a written questionnaire. Data of 522 respondents meeting the inclusion criteria were analyzed and compared with the results of the 351 nurses included in the 1991 study. RESULTS: Knowledge in 2003 was slightly better than that in 1991. The nurses were moderately aware of the usefulness of preventive measures. Nurses employed in organizations that monitored pressure ulcers did not display greater knowledge than those employed in organizations that did not do so. CONCLUSION: Knowledge among Dutch hospital nurses about the usefulness of measures to prevent pressure ulcers seems to be moderate. Being employed in an institution that monitors pressure ulcer care hardly affects the knowledge level. Knowledge about prevention has improved little since 1991

The rate of cellular hydrogen peroxide removal shows dependency on GSH: Mathematical insight into in vivo H2O2 and GPx concentrations

Although its concentration is generally not known, glutathione peroxidase-1 (GPx-1) is a key enzyme in the removal of hydrogen peroxide (H2O2) in biological systems. Extrapolating from kinetic results obtained in vitro using dilute, homogenous buffered solutions, it is generally accepted that the rate of elimination of H2O2 in vivo by GPx is independent of glutathione concentration (GSH). To examine this doctrine, a mathematical analysis of a kinetic model for the removal of H2O2 by GPx was undertaken to determine how the reaction species (H2O2, GSH, and GPx-1) influence the rate of removal of H2O2. Using both the traditional kinetic rate law approximation (classical model) and the generalized kinetic expression, the results show that the rate of removal of H2O2 increases with initial GPxr, as expected, but is a function of both GPxr and GSH when the initial GPxr is less than H2O2. This simulation is supported by the biological observations of Li et al.. Using genetically altered human glioma cells in in vitro cell culture and in an in vivo tumour model, they inferred that the rate of removal of H2O2 was a direct function of GPx activity × GSH (effective GPx activity). The predicted cellular average GPxr and H2O2 for their study are approximately GPxr ≤ 1 μm and H2O2 ≈ 5 μm based on available rate constants and an estimation of GSH. It was also found that results from the accepted kinetic rate law approximation significantly deviated from those obtained from the more generalized model in many cases that may be of physiological importance