Contact finite element stress analysis of porous ingrowth acetabular cup implantation, ingrowth, and loosening

Two-dimensional linear and contact finite element analyses were conducted of total hip arthroplasty using metal-backed, porous ingrowth acetabular components. The stress transmission characteristics from the component to the surrounding bone were given special attention. Resultant loads of 20 and 40 degrees medial of vertical were studied, and the influence of adding a metal flange to the rim of the cup was evaluated. The results indicated that when a conventional metal-backed component (without a flange) is initially implanted and subjected to normal loading, these components may experience distraction between the component and the surrounding bone at inferior sites. Compressive stresses in the superior dome cancellous bone, however, will be substantial. If complete porous ingrowth is achieved, the superior dome compressive stresses will be reduced and substantial shear stresses created. In addition, high local bone stresses were found at the component rim. If bone ingrowth is achieved only in specific locations, stress transmission will be dictated by those locations and may differ markedly from the case of complete bone ingrowth. In the event that no porous ingrowth is achieved and a fibrous layer forms around the component, the interface stresses will be similar to those calculated for the natural hip. The addition of a flange to the rim of the cup will reduce the magnitude of the radial stresses transmitted to the cancellous bone superiorly and medially by directly transferring some of the load to the lateral wall of the pelvis. The flange will also help to relieve the high local stresses that are found at the component rim.     

Laser Peening Process and Its Impact on Materials Properties in Comparison with Shot Peening and Ultrasonic Impact Peening

The laser shock peening (LSP) process using a Q-switched pulsed laser beam for surface modification has been reviewed. The development of the LSP technique and its numerous advantages over the conventional shot peening (SP) such as better surface finish, higher depths of residual stress and uniform distribution of intensity were discussed. Similar comparison with ultrasonic impact peening (UIP)/ultrasonic shot peening (USP) was incorporated, when possible. The generation of shock waves, processing parameters, and characterization of LSP treated specimens were described. Special attention was given to the influence of LSP process parameters on residual stress profiles, material properties and structures. Based on the studies so far, more fundamental understanding is still needed when selecting optimized LSP processing parameters and substrate conditions. A summary of the parametric studies of LSP on different materials has been presented. Furthermore, enhancements in the surface micro and nanohardness, elastic modulus, tensile yield strength and refinement of microstructure which translates to increased fatigue life, fretting fatigue life, stress corrosion cracking (SCC) and corrosion resistance were addressed. However, research gaps related to the inconsistencies in the literature were identified. Current status, developments and challenges of the LSP technique were discussed.     

Examining the Unique Stresses and Rewards of HIV/AIDS Work

Abstract

The article reports on findings from an exploratory study, a survey of 25 HIV/AIDS workers. The survey instrument included all items from the five main dimensions of stresses and rewards in the AIDS Impact Scale, in addition to a series of open-ended questions. The findings suggested the need for careful review of the items to ensure they adequately capture current day stresses and rewards of HIV/AIDS work and the possible need for an additional dimension that captures the stresses and rewards of working with multi-problem vulnerable clients and their families.     

Gene characteristics,immune and stress responses of PmPrx1 in black tiger shrimp (Penaeus monodon): Insights from exposure to pathogenic bacteria and toxic environmental stressors

Peroxiredoxins (Prxs) are ubiquitous, multifunctional and evolutionarily conserved enzymes that can protect cells from oxidative damage caused by ROS and play a vital role in immune responses. Here, a full-length Prx1 cDNA sequence (PmPrx1) was isolated from Penaeus monodon. The PmPrx1 cDNA was 951 base pairs (bp), encoding 198 amino acid polypeptides. The results of qRT-PCR showed that the PmPrx1 mRNA was ubiquitously expressed in all tissues tested and had a comparatively high expression level in immune-associated tissues (gill, hepatopancreas). To explore the immune and anti-stress roles of PmPrx1, the gills and hepatopancreas were chosen as target tissues in Penaeus monodon and were challenged with bacteria (Vibrio harveyi and Streptococcus agalactiae) and toxic environmental stresses. To further clarify the immune function of PmPrx1 after bacterial challenge, the recombinant PmPrx1 protein was acquired using a prokaryotic expression method. The antioxidant activity of the recombinant PmPrx1 was assessed by the catalyzing hydrogen peroxide assay method, and the results showed obvious antioxidant activity in a dose-dependent and temperature-dependent manner. The antimicrobial activity of purified PmPrx1 protein was evaluated and further studied in vitro relying on a bacterial growth inhibition test which was conducted in both liquid and solid cultures. Furthermore, E. coli transferred with pRSET-PmPrx1 was dramatically protected in response to metal toxicity and H₂O₂ oxidative stress. In summary, this study provides useful information about the role of the Prx1 gene in defense against a variety of toxic factors in shrimps that help to further clarify the functional mechanism of Prx.     

Effect of oscillation on elevating shear stresses

The effect of oscillation on elevating turbulent shear stresses through the Jellyfish and St. Vincent valves has been investigated. Laser Doppler anemometry was employed to determine the velocity and shear stress distributions at various locations downstream of the valves. Comparison between two valves revealed that at 0.5D downstream of the valves the magnitude of shear stresses in the Jellyfish valve were much higher than those of the St. Vincent valve at cardiac outputs of 4, 5.5 and 7 l min^?1. The cause of high shear stresses in close proximity to the Jellyfish valve could be attributed to the oscillation of the membrane which in turn generated a wake downstream of the valve (in the core of valve chamber) and produced a wide region of disturbance further downstream. This resulted in further pressure drag, and consequently higher pressure drops across the valve and higher shear stresses downstream of the valve.     

Substantial regional differences in the biomechanical behavior of molar treated with selective caries tissue removal technique: a finite element study

ObjectivesSelective caries removal (SCR) is recommended over non-selective removal for managing deep carious lesions to avoid pulp exposure and maintain pulp vitality. During SCR, residual carious dentin is left behind and sealed beneath the restoration. The biomechanical effects of such residual lesions on the restored tooth remain unclear and were assessed using finite element modeling (FEM).MethodsBased on μ-CT images of a healthy permanent human third molar, we developed five finite element models. Generic class I and II cavity restorations were modeled where residual lesions of variable sizes were either left or fully removed on occlusal and proximal surfaces. The cavities were restored with adhesive composite. All 3D-FE models were compared with a model of a healthy, non-treated molar. A vertical load of 100 N was applied onto the occlusal surface.ResultsRegardless of the lesion size, in molars with occlusal lesions higher mean stresses were predicted along the filling-lesion interface than in all other models. The smallest occlusal lesion (Ø₁ = 1 mm) resulted in the highest maximum stresses at the filling-lesion interface with large stress concentrations at the filling walls indicating failure risk. In conclusion, lesion site and extent are influencing parameters affecting the filling-lesion interactions and thus the biomechanical behavior of the tooth after SCR.SignificanceRetaining carious lesions around the pulpal floor affects the deformation and stress states in tooth-filling complexes. The higher stresses observed in molars with occlusal lesions may affect restoration stability and longevity. Suprisingly, more extended occlusal lesions may provide a more favorable tooth performance than less extended ones. In contrast, in molars with proximal lesions the residual lesion had only limited effect on the tooth’s biomechanical condition.     

High-Resolution Strain/Stress Measurements by Three-Axis Neutron Diffractometer

Resolution properties of the unconventional high-resolution neutron diffraction three-axis setup for strain/stress measurements of large bulk polycrystalline samples are presented. Contrary to the conventional two-axis setups, in this case, the strain measurement on a sample situated on the second axis is carried out by rocking the bent perfect crystal (BPC) analyzer situated on the third axis of the diffractometer. Thus, the so-called rocking curve provides the sample diffraction profile. The neutron signal coming from the analyzer is registered by a point detector. This new setup provides a considerably higher resolution (at least by a factor of 5), which however, requires a much longer measurement time. The high-resolution neutron diffraction setting can be effectively used, namely, for bulk gauge volumes up to several cubic centimeters, and for plastic deformation studies on the basis of the analysis of diffraction line profiles, thus providing average values of microstructure characteristics over the irradiated gauge volume.