Stress In Different Regions Research Articles

Biomechanical Analysis of Femoral Stem Features in Hinged Revision TKA with Valgus or Varus Deformity: A Comparative Finite Elements Study

Hinged total knee arthroplasty (TKA) is a valid option to treat patients during revision of an implant; however, in case of varus/valgus deformity, the force transmission from the femur to the tibia could be altered and therefore the performance of the implant could be detrimental. To be able to evaluate this, the goal of this study was to investigate, using a validated finite element analysis, the effect of varus/valgus load configurations in the bones when a hinged TKA is used. In detail, short and long stem lengths (50 mm, and 120 mm), were analyzed both under cemented or press-fit fixation under the following varus and valgus deformity: 5°, 10°, 20°, and 30°. The main outputs of the study were average bone stress in different regions of interest, together with tibio-femoral contact pressure and force. Results demonstrated that changes in the varus or valgus deformity degrees induce a change in the medio-lateral stress and force distribution, together with a change in the contact area. The effect of stem length and cement do not alter the tibio-femoral contact biomechanics but its effect is mainly localized in the distal femoral region, and it is negligible in the proximal regions.

Neuroprotective Effect of N-acetylcysteine Against Monocrotophos-Induced Oxidative Stress in Different Brain Regions of Rats.

Monocrotophos (MCP) is systemic organophosphate insecticide used against crop pests. It is reported to cause mammalian toxicity through both acute and chronic exposure. In the present study, we have shown the protective role of N-acetylcysteine (NAC) against MCP-induced oxidative stress in frontal cortex, corpus striatum and hippocampus brain regions of rats. Male Albino Wistar rats were divided into control, NAC-treated, MCP and NAC + MCP-treated groups. An oral dose of MCP (0.9mg/kg b.wt) and NAC (200mg/kg b.wt) was administered for 28days. Results showed an increase in lipid peroxidation (LPO) and protein oxidation followed by decreased antioxidant enzymes after 28days of MCP exposure. Histopathological analysis showed that monocrotophos exposure caused neurodegenerative changes as evident by neurons with dystrophic changes in the form of shrunken hyperchromatic nuclei in all the regions of the rat brain. N-acetylcysteine supplementation to MCP-treated rats showed a reduction in oxidative stress and ameliorated cellular alterations in all of the three regions. The results of the study indicate that N-acetylcysteine offers neuroprotection by improving antioxidant response and decreasing oxidative stress in different regions of the rat brain.

Fabrication analysis of flat vacuum enclosures for solar collectors sealed with Cerasolzer 217

Vacuum flat plate (VFP) solar thermal collectors exhibit excellent optical and thermal characteristics due to a combination of wide surface area and high vacuum thermal insulation offering a high performance and architecturally versatile collector with a variety of applications for industrial process heat and building integration. A vacuum flat plate solar collector consists of a solar absorber in a flat vacuum enclosure comprising glass or glass and metal covers sealed around the periphery with an array of support pillars to maintain the separation of the enclosure under atmospheric pressure. The edge seal must be both mechanically strong and hermetic to ensure the durability of the internal vacuum over collector lifetime. This presents several challenges for the fabrication of flat vacuum enclosures. In this study a novel sealing technique is presented using a tin-based alloy, Cerasolzer 217, to create the vacuum seal between two glass panes and an edge separating spacer. The sealing process is undertaken at temperatures ≤250 °C allowing the use of thermally tempered glass panes. The mechanical strength of the edge seal was investigated using a tensometer. It was demonstrated that the bond between glass and edge spacer was sufficiently strong to withstand induced stresses in the edge seal region. The edge seal was leak tested using a conventional Helium mass spectrometer leak detector and was shown to possess leak rates low enough to maintain an adequate vacuum pressure to supress conductive and convective heat transfer in the collector. A finite element method (FEM) is developed and validated against the experimental results and employed to predict the stresses in different regions of the enclosure. It was found that the mechanical strength limits of the seal and glass are higher than the stresses in the edge seal region and on the glass surface, respectively.

Influence of high-energy shot peening on the microstructure and mechanical properties of Ti–6Al–4V welded joints

In this study, Ti–6Al–4V welded joints were subjected to a high-energy shot peening (HESP) treatment. The structural characteristics of the Ti–6Al–4V welded joints were investigated by optical microscopy (OM) and x-ray diffraction (XRD). The Rockwell hardness and residual stress in different regions of the Ti–6Al–4V welded joints were assessed before and after treatment. Tension tests were then performed to investigate the effect of HESP on the welded samples. Experimental results showed that an Surface nanocrystallization (SNC) layer can be prepared on a Ti–6Al–4V welded joint via HESP. The average grain size of the SNC layer was approximately 30 nm after HESP. HESP also resulted in a higher surface hardness compared with that of the original sample. After treatment, surface compressive residual stresses formed in welded joints, and the residual peak stress of the weld zone was decreased from 650 MPa to −638 MPa. The surface hardness and surface residual stress were distributed more uniformly on the surface of the welded joint. After treatment, the tensile properties were improved.

The effects of water stress on croplands in the Aral Sea basin

Water scarcity constitutes an important challenge faced by croplands in the Aral Sea basin (ASB). The croplands in the ASB are highly vulnerable to water stress and land degradation and experience high anthropogenic disturbances. This study investigated the spatiotemporal patterns of water stress and land degradation and detected the years with abrupt changes in the water stress index (WSI) by applying linear regression analysis and the breaks for additive seasonal and trend (BFAST) method. Furthermore, these analyses were combined with statistical data on water intake to explore the relationship between water stress and land degradation in the sub-basins. The results revealed that water stress was more serious in the downstream areas than in the upstream area. The downstream regions experienced increasing water stress, resulting in severe land degradation and cropland abandonment. The BFAST results indicated that abrupt changes in the WSI mainly occurred in 2005, 2008 and 2010. The correlations between water intake, water stress and land degradation in the lower reach were stronger than those in the upper reach. Subsequently, the water intake had a great influence on the cropping intensity and cotton yield in the downstream regions. Water stress in different regions was caused by different drivers. In the upstream areas, precipitation was the major driver of water stress in crops. In contrast, the water allocation in the middle and lower reaches was affected by anthropogenic disturbances and resulted in serious water deficits in the Amudarya River delta in 2000 and 2008. Because each country had a unique irrigation scheme and cropping pattern, obvious spatial differences in water stress and land degradation changes were detected between Tashauz and Karakalpakstan. This study can provide a decision-making reference for the implementation of sustainable development goals in the ASB.

Understanding of residual stresses in chain-die-formed dual-phase (DP) metallic components: predictive modelling and experimental validation

Residual stresses in metallic components greatly affect the geometrical accuracy of advanced high-strength steels (AHSS) products used for automotive industry. Chain-die forming is a promising method to fabricate AHSS products which can minimize the residual stress induced. This paper aims to understand the residual stress in chain-die-formed dual-phase (DP) steels through analytical and numerical modelling together with experimental validation. Analytical and numerical models were firstly employed to predict the stress development and associated residual stresses induced by chain-die forming in consideration of an as-received residual stress field and a comprehensive material-hardening model. The residual stresses in different regions of formed parts were practically measured using the neutron diffraction method to verify the developed models. Same as the mesh size of the examining points of finite element analysis (FEA) models, the averaged over the same sampling size is measured to guarantee the accuracy. It seems to be consistent with the simulation and experimental results in consideration of both factors. However, compared with as-received residual stress, the kinematic factor has a more dominating impact on the final residual stress. The results presented should contribute to the prediction of geometric errors and minimize product defects caused by the residual stresses in chain-die forming or equivalent sheet metal-forming industry.

Fourier Transform Infrared Spectroscopic Imaging-Derived Collagen Content and Maturity Correlates with Stress in the Aortic Wall of Abdominal Aortic Aneurysm Patients

Abdominal aortic aneurysm (AAA) is a degenerative disease of the aorta characterized by severe disruption of the structural integrity of the aortic wall and its major molecular constituents. From the early stages of disease, elastin in the aorta becomes highly degraded and is replaced by collagen. Questions persist as to the contribution of collagen content, quality and maturity to the potential for rupture. Here, using our recently developed Fourier transform infrared imaging spectroscopy (FT-IRIS) method, we quantified collagen content and maturity in the wall of AAA tissues in pairs of specimens with different wall stresses. CT scans of AAAs from 12 patients were used to create finite element models to estimate stress in different regions of tissue. Each patient underwent elective repair of the AAA, and two segments of the AAA tissues from anatomic regions more proximal or distal with different wall stresses were evaluated by histology and FT-IRIS after excision. For each patient, collagen content was generally greater in the tissue location with lower wall stress, which corresponded to the more distal anatomic regions. The wall stress/collagen ratio was greater in the higher stress region compared to the lower stress region (1.01±1.09 vs. 0.55±0.084, p=0.02). The higher stress region also corresponded to the location with reduced intraluminal thrombus thickness. Further, collagen maturity tended to decrease with increased collagen content (p=0.068, R=0.38). Together, these results suggest that an increase in less mature collagen content in AAA patients does not effectively compensate for the loss of elastin in the aortic wall, and results in a reduced capability to endure wall stresses.

Effect of ageing and oxidative stress on antioxidant enzyme activity in different regions of the rat kidney.

Oxidative stress has been implicated in ageing and the pathogenesis of chronic kidney disease. We examined levels of antioxidant enzymes glutathione peroxidase, glutathione reductase, glutathione S-transferase, catalase and superoxide dismutase as modulated by age and oxidative stress in different regions of the kidney. Antioxidant enzymes were examined in different regions of the kidney in male Wistar rats. Kidneys from rats of different ages (5, 12, 36 and 60weeks) were dissected into cortex, outer medulla and inner medulla. Tissues were incubated for 30min with or without 0.2mM H2O2 to induce oxidative stress. Antioxidant enzyme activities progressively decreased with age under both control and stress conditions (P<0.05) after peaking at 12weeks. Antioxidant enzyme activities were greater in the cortex (P<0.05) by comparison with the outer and inner medulla, respectively.

Effect of Ginkgo biloba Extract on Lead-Induced Oxidative Stress in Different Regions of Rat Brain.

Ginkgo biloba extract (GbE) is a well known natural antioxidant. In the present investigation, its ameliorative effects were tested against lead-induced oxidative stress in rat brain. Four groups of male Wistar rats (100 to 120 g) were used, consisting of eight rats per group. Rats in the control group received 500 ppm of sodium acetate through drinking water, and rats in the other three groups received 500 ppm of lead acetate through drinking water for 4 weeks. Rats in the third and fourth groups were administered (oral) 50 and 100 mg/kg of GbE, respectively, along with lead acetate. The rats were sacrificed after treatment and brains were isolated. Each brain was dissected on ice, and different regions, namely the cerebellum, hippocampus, frontal cortex, and brainstem, were separated. The results revealed a significant (P < .001) increase in reactive oxygen species, catalase, superoxide dismutase, lipid peroxidation products, and total protein carbonyl content, relative to their controls, in all four regions of the brain exposed to lead. These results indicate oxidative stress. Partial restoration was observed for all the parameters just mentioned in different brain regions on treatment with 50 mg/kg GbE. This amelioration was higher with 100 mg/kg GbE, showing dose-dependency. Overall the data suggest that GbE protects against lead-induced oxidative stress in specific regions of rat brain.

Multi-Scale Analysis for Automotive PEM Fuel Cell System: Macro-Scale Analysis

Distributions in reactant species concentration in a Proton Exchange Membrane Fuel Cell (PEMFC) cause distributions in local current density, temperature and water over the area of a PEMFC. These can lead to effects such as flooding and dehydration thus causing stresses in different regions of the fuel cell [1]. Changing operating conditions and design parameters including their properties inside PEMFC system such as flow field configurations, gas diffusion layer (GDL), and membrane electrode assembly (MEA) could impact the cell performance and uniformity in distributions [2-4]. Providing high oxygen concentration in the cathode at high current density operations is critically important to enhance the area specific power density [5, 6]. Thus, mass transport overpotential at high current density is the major barrier to achieving high power density with acceptable operational robustness. Experimental investigation of mass transport is not sufficient to understand mass transport overpotential because of its inability to resolve water saturation-dependent properties in the gas diffusion layer (GDL). An objective of this work is to develop a multi-phase modeling capability to simulate fuel cell performance at high current density region where mass transport overpotential is dominant. Material and design solutions arising from the implementation of this mathematical model are expected to enhance area specific power density of conventional state-of-the art PEMFCs.The conventional computational fluid dynamic (CFD) technique will be used to predict the heat and mass transports in macro-scaled flow-field geometry as shown in Fig. 1. The CFD based meso-scaled Thermal Lattice Boltzmann Method (TLBM) will be introduced to give the solution of gas/liquid transport solution in the porous media. A TLMB GDL model with fixed boundary conditions, such as a constant volumetric injection over an entire GDL surface, represents ex-situexperimental conditions very well [7]. Figure 2 shows an image of the simulation for the condensed water percolated through the GDL. A unique aspect of this work will be to integrate the TLBM GDL model with a CFD based fuel cell electrochemistry model so that the GDL boundary conditions will be dynamic and the water flux entering the GDL will be a function of the dynamic and local water production within the catalyst layer. This fully-integrated simulation will yield a direct prediction of the hydrated in-situ performance by enabling the natural development of water distribution within the GDL. This multi-scaled modeling technique will be able to facilitate the development of advanced mass transport design, which is material sets of GDL and flow field interaction, to enhance the performance and the operational robustness.

Protective effect of resveratrol on fluoride induced alteration in protein and nucleic acid metabolism, DNA damage and biogenic amines in rat brain

Fluoride, a well-established environmental carcinogen, has been found to cause various neurodegenerative diseases in human. Sub-acute exposure to fluoride at a dose of 20mg/kgb.w./day for 30 days caused significant alteration in pro-oxidant/anti-oxidant status of brain tissue as reflected by perturbation of reduced glutathione content, increased lipid peroxidation, protein carbonylation, nitric oxide and free hydroxyl radical production and decreased activities of antioxidant enzymes. Decreased proteolytic and transaminase enzymes’ activities, protein and nucleic acid contents and associated DNA damage were observed in the brain of fluoride intoxicated rats. The neurotransmitters dopamine (DA), norepinephrine (NE) and serotonin level was also significantly altered after fluoride exposure. Protective effect of resveratrol on fluoride-induced metabolic and oxidative dysfunctions was evaluated. Resveratrol was found to inhibit changes in metabolic activities restoring antioxidant status, biogenic amine level and structural organization of the brain. Our findings indicated that resveratrol imparted antioxidative role in ameliorating fluoride-induced metabolic and oxidative stress in different regions of the brain.

Hydroalcoholic seed extract of Coriandrum sativum (Coriander) alleviates lead-induced oxidative stress in different regions of rat brain.

Lead exposure is known to cause apoptotic neurodegeneration and neurobehavioral abnormalities in developing and adult brain by impairing cognition and memory. Coriandrum sativum is an herb belonging to Umbelliferae and is reported to have a protective effect against lead toxicity. In the present investigation, an attempt has been made to evaluate the protective activity of the hydroalcoholic extract of C. sativum seed against lead-induced oxidative stress. Male Wistar strain rats (100-120 g) were divided into four groups: control group: 1,000 mg/L of sodium acetate; exposed group: 1,000 mg/L lead acetate for 4 weeks; C. sativum treated 1 (CST1) group: 250 mg/kg body weight/day for seven consecutive days after 4 weeks of lead exposure; C. sativum treated 2 (CST2) group: 500 mg/kg body weight/day for seven consecutive days after 4 weeks of lead exposure. After the exposure and treatment periods, rats were sacrificed by cervical dislocation, and the whole brain was immediately isolated and separated into four regions: cerebellum, hippocampus, frontal cortex, and brain stem along with the control group. After sacrifice, blood was immediately collected into heparinized vials and stored at 4 °C. In all the tissues, reactive oxygen species (ROS), lipid peroxidation products (LPP), and total protein carbonyl content (TPCC) were estimated following standard protocols. An indicator enzyme for lead toxicity namely delta-amino levulinic acid dehydratase (δ-ALAD) activity was determined in the blood. A significant (p<0.05) increase in ROS, LPP, and TPCC levels was observed in exposed rat brain regions, while δ-ALAD showed a decrease indicating lead-induced oxidative stress. Treatment with the hydroalcoholic seed extract of C. sativum resulted in a tissue-specific amelioration of oxidative stress produced by lead.

Mathematical model for silicon electrode – Part I. 2-d model

This paper presents a 2-dimensional transient numerical model to simulate the electrochemical lithium insertion in a silicon nanowire (Si NW) electrode. The model geometry is a cylindrical Si NW electrode anchored to a copper current collector (Cu CC) substrate. The model solves for diffusion of lithium in Si NW, stress generation in the Si NW due to chemical and elastic strains, stress generation in the Cu CC due to elastic strain, and volume expansion in the Si NW and Cu CC geometries. The evolution of stress components, i.e., radial, axial and tangential stresses in different regions in the Si NW are presented and discussed. The effect of radius of Si NW and lithiation rate, on the maximum stresses developed in the Si NW are also discussed.

Ameliorative effects of Bacopa monniera on lead-induced oxidative stress in different regions of rat brain

Bacopa monniera is a rejuvenating herb for brain cells enhancing learning and cognitive ability. In the present investigation, the ameliorative effects of Bacopa monniera were examined against lead-induced oxidative stress in different regions of rat brain. Male rats were divided into five groups: control (1000 ppm sodium acetate) and exposed (1000 ppm lead acetate) for 4 weeks; DMSA (Meso-2,3-Dimercaptosuccinic acid)-treated (90 mg/kg body weight/day); Bacopa monniera-treated (BM) (10 mg/kg body weight/day) and a combination of BM + DMSA for seven consecutive days after 4 weeks of lead exposure. After treatment, the whole brain was isolated by sacrificing rats and four regions were separated namely cerebellum, hippocampus, frontal cortex and brain stem. Results indicated a significant (p < 0.05) increase in reactive oxygen species (ROS), lipid peroxidation products (LPP) and total protein carbonyl content (TPCC) in association with tissue metal content in all the four regions of brain for exposed group compared with their respective controls. However, the lead-induced ROS, LPP, TPCC and tissue metal content were lowered on treatment with Bacopa monniera, almost reaching the control group values in all the above brain regions compared to DMSA and a combination therapy. Results suggest that Bacopa monniera can mitigate the lead induced-oxidative stress tissue specifically by pharmacologic interventions which encompass both chelation as well as antioxidant functions.

Finite Element Analysis of Thermal Residual Stress in Unidirectional Fiber Reinforced Composite

During the cooling process of composites after curing, thermal residual stress will be produced due to mismatch of the coefficients of thermal expansion between matrix and reinforcement phases. Thermal residual stress is one of the most important factors that affect the mechanical properties of composite materials. The effect of fiber volume fraction on the distribution of thermal residual stress in unidirectional fiber reinforced composite has been investigated with finite element analysis. The results show an inhomogeneous distribution of thermal residual stress in different regions of composites. The longitudinal stress on the interface between matrix and fiber is the main factor resulting in debonding failure of composites. This numerical study can be of great significance in designing new composites with high performance.

Superelastic memory effect in in-situ NbTi-nanowire-NiTi nanocomposite

An in-situ NbTi-nanowire-NiTi composite wire fabricated by conventional metallurgical processing has the remarkable ability of remembering its previous stress/strain states where it was unloaded during multiple-step cyclic loading. In situ synchrotron x-ray diffraction studies revealed that an interactive stress between NbTi nanowires and NiTi matrix was introduced and retained after a load/unload cycle due to their strain mismatch. The different levels of interactive stress in different regions of the specimen resulted in a superelastic memory effect. Furthermore, the final loading curve could remember all previous loading histories, which may be of use in practical applications.

Infection of Vascular Endothelial Cells with Human Cytomegalovirus under Fluid Shear Stress Reveals Preferential Entry and Spread of Virus in Flow Conditions Simulating Atheroprone Regions of the Artery

Atherosclerosis is a major pathogenic factor in cardiovascular diseases, which are the leading cause of mortality in developed countries. While risk factors for atherosclerosis tend to be systemic, the distribution of atherosclerotic plaques within the vasculature is preferentially located at branch points and curves where blood flow is disturbed and shear stress is low. It is now widely accepted that hemodynamic factors can modulate endothelial gene expression and function and influence the pathophysiological changes associated with atherosclerosis. Human cytomegalovirus (HCMV), a ubiquitous pathogen, has long been proposed as a risk factor for atherosclerosis. To date, the role of HCMV in atherogenesis has been explored only in static conditions, and it is not known how HCMV infection is influenced by the physiological context of flow. In this study, we utilized a parallel-plate flow system to simulate the effects of shear stresses in different regions of the vasculature in vitro. We found that endothelial cells cultured under low shear stress, which simulates the flow condition of atheroprone regions in vivo, are more permissive to HCMV infection than cells experiencing high shear stress or static conditions. Cells exposed to low shear stress show increased entry of HCMV compared to cells exposed to high shear stress or static conditions. Viral structural gene expression, viral titers, and viral spread are also enhanced in endothelial cells exposed to low shear stress. These results suggest that hemodynamic factors modulate HCMV infection of endothelial cells, thus providing new insights into the induction/acceleration of atherosclerosis by HCMV.

The combination of organoselenium compounds and guanosine prevents glutamate-induced oxidative stress in different regions of rat brains

This study was designed to investigate the protective effects of the combination of guanosine and 2 organoselenium compounds (ebselen and diphenyl diselenide) against glutamate-induced oxidative stress in different regions of rat brains. Glutamate caused an increase in reactive oxygen species (ROS) generation and a decrease in [3H]-glutamate uptake in striatal, cortical, and hippocampal slices. Guanosine, ebselen, and diphenyl diselenide prevented glutamate-induced ROS production in striatal, cortical and hippocampal slices. The combination of guanosine with organoselenium compounds was more effective against glutamate-induced ROS production than the individual compounds alone. Guanosine prevented [3H]-glutamate uptake inhibition in striatal, cortical, and hippocampal slices. Thus, protection against the harmful effects of glutamate is possibly due to the combination of the antioxidant properties of organoselenium compounds and the stimulatory effect of guanosine on glutamate uptake. In conclusion, the combination of antioxidants and glutamatergic system modulators could be considered a potential therapy against the prooxidant effects of glutamate.

The Effect of Ginkgo biloba extract (EGb 761) on parameters of oxidative stress in different regions of aging rat brains after acute hypoxia

Neurodegenerative processes of aging seem to be associated with oxidative stress by reactive oxygen species (ROS). This study investigates the influence of age and of acute respiratoric hypoxia on parameters of oxidative stress in different brain regions of Wistar rats and the protective effects of Ginkgo extract (EGb 761) as a radical scavenger. Biopsies of frontal and temporal cortices, the cerebellum, and the brainstem of young and old rats (each group n=6-8: normoxic - hypoxic; unprotected - EGb-protected) were analyzed for malondialdehyde (MDA) levels, superoxide dismutase (SOD) activity, glutathione (GSH) content, and creatine kinase (CK) activity. Experimental hypoxia: downregulation of oxygen partial pressure to 5 vol. % for 20 minutes. EGb administration: daily 100 mg/kg of body weight in drinking water for 3 months. Effects of age: While most oxidative stress parameters in the temporal cortex, the cerebellum, and the brainstem are increased, this is not the case in the frontal cortex; after additional hypoxia SOD and GSH are diminished in the temporal cortex and the brainstem of old rats. EGb treatment causes contradictory alterations in young, old, and hypoxic brain regions. Minor effects are seen in old hypoxic brains, while there are some protective effects in old normoxic brainstems and cerebellums. The old brain appears to adapt appropriately to chronic oxidative stress and to the specific conditions of shortterm hypoxia. EGb's protective effect is especially notable in the brainstem and the cerebellum.

Understanding the effect of channel tolerances on performance of PEMFCs

Distributions in the concentration of reactant species in a PEMFC can cause distributions in local current density, temperature, and water content over the area of a PEMFC. These distributions can lead to effects such as flooding and MEA dehydration thus causing stresses in different regions of the fuel cell. Changing flow-field configurations and channel characteristics have been shown to also affect the cell performance and uniformity in distributions. This work investigates how performance and distributions in a baseline laboratory cell prepared by a precise machining method compared with others from alternative manufacturing processes (e.g., stamping, electrochemical etching, hydroforming, etc.). Specifically we examine “typical” variations in the channel width, height, and undercut that may occur with alternatively manufactured metal plates and compare those with sample-to-sample variations that may occur with between laboratory-scale graphite plates. This work will provide fundamental information that can be used to develop tolerance and design principles for manufacturing PEMFC bipolar plates.