Term Of Stress Research Articles

Rheological Study of a Copper Feedstock

MIM technique is described in which allows for the production of highly porous metallic foams with porosity levels up to 90%. It makes use of the pressure built up by the decomposition of a foaming agent which is incorporated in a foamable precursor copper material obtained by powder compaction. A suitable behaviors feedstock that refers to its rheological is one of the key factors to ensure the successful of MIM technique and to predict failure, whether due to the binder component and compositions, powder loading or unsuitable process parameters. Potassium carbonate and polyethylene is added and were mixed homogeneously to form a copper feedstock. The rheological results in term of shear rate, shear stress, viscosity, melting rate and softening temperature which related to pseduoplastic behaviors have been conducted using a capillary rheometer (CFT-500D, Shimadzu) at various temperature and loads. The result has indicated that the viscosity of the feedstock is decreased with increasing shear rate thus proved the feedstock to be pseudoplastic.

The influence of inertia on the rheology of a periodic suspension of neutrally buoyant rigid ellipsoids

We investigate the rheological properties of a suspension of neutrally buoyant rigid ellipsoids by fluid–structure interaction simulations of a particle in a periodic domain under simple shear using the curvilinear immersed-boundary (CURVIB) method along with a quaternion–angular velocity technique to calculate the dynamics of the particle’s motion. We calculate all the different terms of particle stress for the first time for non-spherical particles, i.e. in addition to the stresslet, we calculate the acceleration and Reynolds stress, which are typically ignored in previous similar works. Furthermore, we derive analytical expressions for all these terms to verify the numerical results and deduce the effect of inertia by comparing our numerical results with the analytical solution. The effect of particle Reynolds number ($\mathit{Re}$), volume fraction (${\it\phi}$), and the shape of particles has been studied on all mechanisms of stress generation, the intrinsic viscosity, and normal stress differences of the suspension for the range$0.008\leqslant {\it\phi}\leqslant 0.112$and$0.01\leqslant \mathit{Re}\leqslant 10.0$. We found that inertia increases the shear and the second normal difference of the stresslet (dominant term of the particle stress), and decreases the first normal difference that is generated due to the strain field. The contribution of acceleration stress to the total stress is found to be important in the second normal stress difference, with a cycle-average comparable to the stresslet component. We also discovered that the contribution of Reynolds stress in the first normal stress difference becomes important even when inertia is as low as$\mathit{Re}\sim O(0.1)$, and its value can be even greater than the stresslet when inertia increases, i.e. Reynolds stresses cannot be ignored for non-spherical particles. For concentrations in the range from dilute to semi-dilute, the effect of inertia on the intrinsic viscosity of a suspension is found to be comparable to the volume fraction. Furthermore, our calculations show that for a dilute concentration and the low-inertia regime ($\mathit{Re}<1.0$), the intrinsic viscosity of a suspension consisting of ellipsoids with an aspect ratio of five can be 20 % higher than its Stokesian analytical value.

Pullout resistance of bearing reinforcement embedded in marginal lateritic soil at molding water contents

The effect of molding water contents (on dry and wet sides of optimum water content) on the pullout resistance mechanism of the bearing reinforcement embedded in a marginal lateritic soil is investigated in this paper. The total pullout resistance is contributed from the pullout friction and bearing resistances. The pullout friction resistance is approximated from the soil shear strength and interaction factor, α. The peak and residual interaction factors (αp and αr) are independent of molding water contents tested and are approximately 0.63 and 0.46, respectively. The bearing pullout resistance of a single isolated transverse member is dependent upon both shear strength and failure mode and can be approximated from the modified punching shear solution with various angles of transformation, β. The β values of the compacted soil at 0.67≤w/wOWC≤1.0 are essentially constant and equal to π/2 (where wOWC is the optimum water content). For 1.0<w/wOWC≤1.33, the β value decreases polynomial with an increase in w/wOWC. The failure mechanism of the bearing reinforcement is classified into three zones (block, interference and individual), depending upon spacing and dimension of transverse member, S/B ratio. The transverse member interference zone is independent of water content when 0.67≤w/wOWC≤1.0 and decreases as w/wOWC increases when 1.0<w/wOWC≤1.33. Based on a critical analysis of the test results, the pullout resistance equations in term of normal stress, shear strength parameters, S/B and molding water content are proposed. The proposed equations are useful for the internal stability analysis of bearing reinforcement earth walls during construction and at the end of construction.

Strain response and damage modelling of glass/epoxy pipes under various stress ratios

This paper presents the stress–strain response and general lifetime damage modelling of glass fibre reinforced epoxy (GRE) composite pipes subjected to multi-ratios stress loadings at room temperature (RT). This particular modelling work was developed to predict the non-linear stress–strain response caused by the fatigue static and cyclic loading in the multiaxial ultimate elastic wall stress (UEWS) tests by considering the effects of matrix cracking within the laminates. Although the UEWS procedure is not a standard protocol used for qualification of GRE pipes, it appears to offer an option to existing procedures delineated in ASTM D2992. The ply properties initially expressed as a function of crack density was computed as a function of increasing stress and strain using shear lag approximation. In general lifetime damage model, the effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The predictions from both models are found to be in good agreement with the data from the multiaxial UEWS tests of ±55° filament wound GRE pipes. These models thus enable for the long term performance prediction of the pipes under combined loadings.

Normal faults, layering and elastic properties of rocks

We study mesoscale normal faults cutting alternating limestone and clay-rich layers in several localities in the South-Eastern Mesozoic sedimentary basin (France). The displacement gradients, defined as the displacement variation per unit length along fault profile, and the mean fault dips are correlated to the structural and petrophysical properties of the host rock, including the carbonate content, the stiffness, the layering pattern and the maximum burial depth. Analysis of the fault dips indicates that the faults propagate (downward or upward) from an initial fracture from one unit to another rather than through connections of fractures that nucleated in different units. The fault dips are consistent with shear, mixed mode and tensile failures in limestone units. They are consistent with shear failure or are abnormally low in the clay-rich units. Among the studied attributes, in limestone units the failure mode is related to the contrast of the Young's modulus between the limestone and the clay-rich layers. A high contrast promotes tensile failure, whereas a low contrast promotes mixed mode or shear failures. In clay-rich layers, the dip is related to the layering pattern and abnormally low dips are promoted in thin clay-rich layers surrounded by thick limestone units. Specific displacement gradients characterize each lithology of the layered section. It ranges from 0.06 to 0.2 in the clay-rich units and it increases with Young's modulus. The analyses of the fault dips and the displacement gradients have implications in term of local stress. Both analyses converge and they can be related to a variation in stress controlled by the variation in stiffness through the layering.

Shape memory and stress relaxation behaviour of oriented mono-dispersed polystyrene

The shape memory and stress relaxation behaviour of oriented samples of mono-dispersed polystyrene have been studied. It was found that the transient stress dip of Fotheringham and Cherry could successfully predict the recovery providing that the initial deformation which produces the molecular orientation is undertaken at a sufficiently fast strain rate. This means that if recovery is to be predicted, relaxation of the molecular orientation must not occur during the drawing process. This is attributed to the low fraction of the viscosity term of the total stress for polystyrene. This makes it advantageous to maximise the total stored stress, allowing the smaller component to be more accurately determined. It is proposed that the critical strain rate for maximising the stored stress is related to the smallest relaxation time in the melt, the entanglement time, τe.The stress relaxation results showed two relaxation processes when drawn at a high strain rate (faster than the inverse of τe), but only one when relaxation could occur during drawing. No differences were observed due to molecular weight, indicating that the molecular reorganisation processes affecting shape memory recovery and stress relaxation are local processes and so independent of chain length.

効果的な教育手法の検討を目的としたストレス測定による学習環境評価の試み

When we recognize “learning” as a result of educational service, we should take more care for providing more suitable learning circumstances, especially in case of the education for the sustainable development, adequate circumstances may be more important, such as the way of preparing the nature as a learning material. In this study we tried to quantify the appropriate learning environment using the term of stress. Because the best performance could be obtained under some adequate stresses and arousal shown by the Yerkes-Dodson's law, therefore, we assumed that the relationship between stress and performance could be applied for extending the learning efficiency. From this point of view, stress was measured using activity of salivary amylase when students were enrolled in a lecture. Stresses were measured 4times during the lecture. We were able to consider about problem of the lecture from stresses of the students measured.

General Lifetime Damage Model for Glass Fibre Reinforced Epoxy (GRE) Composite Pipes under Multiaxial Loading

This paper presents the modelling of a general lifetime performance for glass fibre reinforced epoxy (GRE) composite pipes similar to the well-known Tsai-Hill interactive failure criterion. Tsai Hill criterion is based on the Von Misses distortional energy criterion which was modified to satisfy the orthotropic nature of GRE composite pipes. The effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress through laminate theory. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The modelled envelop shows a good agreement with experimental data from the multiaxial UEWS test of ±55° GRE composite pipes. This indicates that such model can be used to predict the long-term performance of GRE pipes under combine loadings.

Improvement of engineering properties of liquefied soil using Bio-VegeGrout

Lab tests were carried out in order to analyze and investigate the liquefaction behavior of marine deposit soil which was placed in the region of LCCT, Sepang. The soil was found exposed to liquefaction. Step to improvise the soil was to inject Biovege grout into the soil sample. Soil sample was prepared with three different grout amount, 10%, 25% and 50%. The relation between percentage of Biovege grout injected and soil improvement were observed and recorded. The void ratio and the permeability of the soil sample decreased with increasing grout percentage. The soil becomes stiffer as the amount of grout used increase. The results obtained indicate, higher amount of grout injection reflects better soil improvement in term of cohesion, friction angle, shear stress and void ratio. The Biovege grout increases the resistance of soil against liquefaction

Tu2087 Contraction Analysis of Jejunal Segment in Relation to Flow and Ramp Distension in Type 2 Diabetic GK Rats — Responses to Carbachol Stimulation

Background and aims: Intestinal motility disorders have been reported in streptozotocin (STZ)-induced diabetic rats. However, STZ can potentially be neurotoxic. Investigating intestinal motility in GK rats which is a genetic model of non-insulin-dependent diabetes avoid the neurotoxic effect. This study was to compare spontaneous, flow-induced and distension-induced contractions with and without carbachol (CA) application in the jejunal segments between normal and diabetic rats. Methods: Seven GK male rats, 32 weeks old (GK group), and 9 age-matched normal Wistar rats (Normal group) were included in the study. The motility experiments were carried out in the organ bath containing Krebs solution at pH 7.4, 37 degree. Before and after CA (10-5 M) application, jejunal pressure and diameter changes were obtained in relation to spontaneous contraction, flow (1 ml/min)-induced contraction with outlet resistance pressures of 0, 2.5, 5.0, 7.5 and 10 cmH2O, and ramp distension up to pressure 10 cmH2O. The frequency and amplitude of contractions were analyzed from pressure-diameter curves. Immediate responses to the CA stimulation were also analyzed. Distension-induced contraction thresholds and maximal contractions of spontaneous and flow-induced contractions in term of mechanical stress and strain were calculated with reference to the zero-stress state. The incremental elastic modulus (IEM) at distensioninduced contraction threshold was also calculated. Results: 1) Shortly after (,10 sec.) adding CA, the contraction amplitude increased immediately to the peak value, then decreased again as function of time. More than two peaks of reaction were observed in GK group but not in Normal group during the 200 seconds observation period. 2) After CA application, the pressure and stress thresholds (Figure 1) and IEM were significantly decreased in the GK group (P,0.01) but not in Normal group (P.0.05). Furthermore, the pressure and stress thresholds were significantly smaller in the GK group compared with Normal group after CA application (P,0.05 and P,0.01). 3) After CA application, the maximum pressure and stress of flow-induced contractions (Figure 2) were significantly higher at most outlet pressure levels in both Normal and GK groups (P,0.001). Furthermore they were significantly bigger at low outlet pressure levels in the GK group than in Normal group after CA application (P,0.05 and P,0.01). 4) The contraction frequency, the strain threshold, and the maximal contraction strain did not differ between the groups (P .0.05) and between before and after CA application (P.0.05). Conclusion: Jejunal contractions in diabetic animals were more sensitive to flow or distension stimulation after CA application. These may relate to tissue remodeling and mechano-sensory changes and contribute to the diabetic symptoms such as diarrhea.

Poly(n-Alkyl Itaconate-Co-Vinyl Acetate) as Pour Point Depressants for Lube Oil in Relation to Rheological Flow Properties

In the present work, poly(n-alkyl itaconate-co-vinyl acetate) comb-like polymers were synthesized by radical copolymerization of n-alkyl itaconates of various alkyl chain length and vinyl acetate monomers for use as pour point depressants in lubricant oil. Initially four n-alkyl itaconate monomers were synthesized by esterification of itaconic acid with a series of n-alkyl alcohol, having different alkyl chain length C16/C18/NAFOL 20 + A (Cav = 20)/NAFOL 1822 B (Cav = 22). The copolymerization of these monomers with vinyl acetate was then performed using dibenzoyl peroxide in toluene at 120°C up to high conversion, with molar ratios of 0.25:0.75, 0.50:0.50, and 0.75:0.25 for alkyl itaconate: vinyl acetate. All products were characterized by FTIR, 1H NMR and gel permeation chromatography (GPC). These copolymers were tested in terms of their suitability as pour point depressants and flow improvers for lube oil. The obtained data revealed that the prepared compounds depress the pour point of the lube oil successfully and the additive efficiency on the pour point reduction of the lube oil increases by increasing the concentration of these additives and by decreasing the alkyl chain length of n-alkyl itaconate. The rheological properties of lube oil (with and without copolymer additive) were studied in term of shear rate, shear stress and viscosity. The results indicated that the performance of flow improver was dependent on the copolymer compositions and the size of alkyl chain length of n-alkyl itaconate monomers. Poly(hexadecyl itaconate-co-vinyl acetate) with high content of vinyl acetate showed the best flow improver properties of lube oil. Comparison of morphologies and structures of wax crystals or aggregates in untreated and treated lube oil was also done by micro photographic studies which showed the modification in wax crystal morphology due to additives.

Assessment on hermetic property and mechanical compatibility of various groove-gasket sealing designs for solid oxide fuel cell stack

Assessment among various groove-gasket designs under solid oxide fuel cell operating condition is presented. The gasket is deformable under the stress applied by external loading between 0.13–0.67 MPa. The operating temperature is from 30 to 800 °C. It has an indicated width of 1.95 mm and depth of 2.1 mm., which is accommodated in a square, triangular and U groove channel having the dimension of 2.0 × 2.0 mm2. From the results, the U shape configuration provides the best performance with immeasurable leak rate under the applying load represented in term of global stress of 0.67 MPa. A stress analysis using Finite Element Method (FEM) tool, ABAQUS™, suggests sufficiently high compressive stress far exceeding the elastic limit with enough coverage of such high-stress area for U-shape design. In contrast, those from square and triangular designs posses relatively lower well-distributed stress and smaller region of highly concentrated stress, respectively. The associated deformed cross section suggests that the gasket has plastically deformed toward the U-shape wall surface at a greater degree than those for triangular-shape design. It can be concluded that the greater region in deformed gasket surface can more effectively reduce interconnectivity of micro channel on the interface between the gasket and the interconnector surfaces.

Optimal data scheduling for P2P video-on-demand streaming systems

Peer-to-peer (P2P) overlay-based streaming services have became more and more attractive. However, it is still challenging to provide scalable streaming services over large-scale Internet environment beacause of the stringent quality of service requirements as well as the dynamic nature of P2P overlay network. In this study, the authors focus on the optimisation of streaming data scheduling in P2P video-on-demand (VoD) system, with the objective of minimising the server stress and maximising the playback continuity. The authors first model the data scheduling problem to the maximum network flow problem where the schedule scheme is transformed to find an optimal supplier-consumer relationship assigment among peers with minimal server strees, and then present two max-flow-based streaming data scheduling algorithms by combining the upload capacity of peers as well as the path capacity between peers. The authors prove that the computing complexing of the proposed scheduling algorithms is polynomial. The practicability of the proposal is evaluated via simulations. Simulation results indicate that the proposed scheduling scheme could distribute bandwidth load among peers well while keeping the node degree low. Simulation results also show that the novel proposal has better performance than previous work in term of the server stress and the playback continuity.

Is it oxidative or free radical stress and why does it matter?

Although oxidative stress is generally considered to be caused by reactive oxygen species endowed with electrophilic properties, non-oxidizing free radicals also play a role in numerous degenerative diseases. The most biologically active is hydroxyl radical known to be produced in vivo under hypoxic conditions. In addition, as shown in this paper, hydroxyl radicals can be generated in vitro in the presence of ferric ions without any additional redox agents. This free radical can convert soluble human fibrinogen into an insoluble fibrin-like aggregate. It is argued that this novel phenomenon can explain the in vivo association of iron overload with fibrin-like deposits observed in degenerative diseases. In view of the fact that hydroxyl radials are also formed under the reductive conditions, true antioxidants i.e. reducing substances, may enhance rather than diminish free radical stress. On the other hand, numerous natural substances, such as polyphenols considered to be antioxidants, can reduce free radical stress by virtue of their direct scavenging of hydroxyl radicals and/or chelation of body free iron. In conclusion, it is suggested in this overview to revise the concept of oxidative stress and introduce a more adequate term of free radical stress.

Health and cellular impacts of air pollutants: from cytoprotection to cytotoxicity.

Air pollution as one of the ravages of our modern societies is primarily linked to urban centers, industrial activities, or road traffic. These atmospheric pollutants have been incriminated in deleterious health effects by numerous epidemiological and in vitro studies. Environmental air pollutants are a heterogeneous mixture of particles suspended into a liquid and gaseous phase which trigger the disruption of redox homeostasis—known under the term of cellular oxidative stress—in relation with the establishment of inflammation and cell death via necrosis, apoptosis, or autophagy. Activation or repression of the apoptotic process as an adaptative response to xenobiotics might lead to either acute or chronic toxicity. The purpose of this paper is to highlight the central role of oxidative stress induced by air pollutants and to focus on the subsequent cellular impacts ranging from cytoprotection to cytotoxicity by decreasing or stimulating apoptosis, respectively.

Team-based working and employee well-being: A cross-cultural comparison of United Kingdom and Hong Kong health services

This study examined the impact of team-based working, team structure, and job design on employee well-being (in term of job satisfaction and work stress) in staff working in healthcare organizations in Hong Kong. Cross-cultural differences in the impact of job design, team structure, and employee well-being outcomes between United Kingdom and Hong Kong were also investigated. A group of 197 staff from two Hong Kong hospitals were compared to a sample of 270 UK staff working in National Health Service organizations in the UK. Results showed that team structure and job design were significantly associated with greater employee satisfaction and lower stress for Hong Kong healthcare staff. Culture was also found to moderate the impact of team structure and job design on employee well-being. The findings suggest that although team structure and job design contribute to employee well-being, they have differential impacts across cultures. This provides insights to policy planning on building team-based organizations in the healthcare sector involving multinational collaboration.

The Comparison of the Effectiveness of Hyperbaric Oxygen and Medical Ozone Therapy Against Acute Distal Colitis in a Rat Model

Purpose: Previous studies have shown that hiperbaric oxygen (HBO) is effective in reducing severity of acute distal colitis (ADC). On the other hand, ozone therapy (OT) is shown to reduce inflammation in several pathological entities. Thus, we designed a study to evaluate the efficacy of OT in an experimental rat model of ADC and to compare effects of both HBO and OT in this entity. Methods: Forty Sprague-Dawley rats were divided into four groups: sham, ADC, ADC+HBO, ADC+OT groups. All groups except sham group were subjected to ADC procedure, which was induced by intracolonic installation of %4 acetic acid to investigate acute phase of inflamation. ADC+HBO group underwent to hyperbaric oxygen chamber at 2.8 atmosphere absolute pressure with 100 % O2 inhalation for 90 minutes twice in a day and ADC+OT group received 0.7 mg/kg/day ozone/oxygen mixture intraperitoneally for a total of 4 days after induction of colitis. The surviving animals were killed at the 5th day and their distal colons were harvested for biochemical and histopathologic analysis. Results: The Malondialdehyde (MDA) levels in the ADC group were significantly higher when comparing with the other groups indicating increased damage in tissue with colitis (p<0.05, ADC vs. the other groups). Althougt the MDA levels were decreased in the ADC+HBO and the ADC+OT groups, only that of ADC+OT group was statistically significant (p<0.005, ADC+OT vs. AP). The tissue Superoxydedismutase (SOD) activity in ADC group were significantly lower than the sham-operated group (p<0.05, ADC vs. sham-operated). There is no significantly difference for the tissue SOD activities between the treatment groups and the sham-operated group. The difference between all groups in terms of the values of the Gluthatione dismutase (GSH-Px) activity were not statistically significant. At the histopathological evaluation, there is a significant improvement in the ADC+OT group. Conclusion: Our data showed that OT reduced severity in the experimental ADC compared with HBO in term of oxidative stress, histopathologic damage score. These findings suggest that it is possible to improve the outcome of ADC by using ozone therapy as an adjuvant therapy.FigureTable: [1215] Histopathological score of the each group

Non-syndromic cleft lip and palate: Could stress be a causal factor?

The aetiology of non-syndromic cleft lip and palate has as yet not been clearly defined. Familial relationships, environmental toxins and nutritional status have all been considered without conclusive results, although in some studies a potential link between non-syndromic cleft lip and palate and any one or more of these factors has been proposed. Elevated stress, particularly an extended term of traumatic stress, can lead to oxidative damage at the cellular level via hypothalamus-pituitary-adrenal (HPA) axis dysregulation, high cortisol and cytokine production. The effect of this hormonal shift is to re-direct the blood supply to the mother's muscles, thereby reducing the supply to the placenta, causing a potential nutritional deficiency which may then result in a genetic alteration in the foetus. Mothers with a child aged two years or younger who had been born with a cleft, who were members of CleftPals, a family support group, volunteered to be participants in this qualitative study. The research first called for a survey to be completed by the mother and this was then followed by an interview conducted by the researcher. The study involved families living in the three eastern States of Australia. The results suggest that physical and/or emotional stress may well be implicated in clefting. While little work has been done in considering stress as a causal factor, the existing literature suggests, as does this study, that elevated stress levels at, or soon after, conception appear to affect foetal development.

A new expression for the velocity profile in the turbulent pipe flows of fiber suspension

The equation of Reynolds averaged Navier-Stokes with the term of additional stress resulted from fibers and the equation of probability distribution function for mean fiber orientation with the second- and fourth-order orientation tensor of the fiber were derived and solved to explore the characteristics of turbulent fiber suspension in the turbulent pipe flows of fiber suspension. The effect of Reynolds number, fiber concentration and fiber aspect-ratio on the mean velocity were presented and analyzed. It was found that the velocity profile of fiber suspension becomes sharper with decreasing the flow rate and/or increasing the fiber concentration, which agrees with the corresponding experimental ones. The velocity profile becomes steeper as fiber aspect-ratio increases. Fibers at this range of concentration and scales play a role in the increase of viscosity. Finally, the prediction formula of velocity profile involving the effect of Reynolds number, fiber concentration, and aspect-ratio for the turbulent pipe flows of fiber suspension was derived.

A new formula for predicting the velocity distribution in the turbulent fiber suspensions of a channel flow

The equation of Reynolds averaged Navier-Stokes with the term of additional stress resulted from fibers and the equation of probability distribution function for mean fiber orientation are derived and solved numerically to explore the characteristics of fiber suspension flow in a channel. The mathematical model and numerical code are validated by comparing the computational results with the corresponding experimental ones. The effect of Reynolds number, fiber concentration and fiber aspect-ratio on the velocity profile, turbulent intensity, and turbulent dissipation rate is analyzed. The results show that the effect of fibers on turbulent channel flow is equivalent to an additional viscosity, but at this range of fiber concentration, the effect of the presence of fibers was small. The turbulent velocity profiles of fiber suspension become gradually sharper in the central region of channel by increasing the fiber concentration and/or decreasing the Reynolds number. The velocity gradient near the wall decreases gradually as the fiber aspect-ratio increased. The turbulent kinetic energy will increase with increasing Reynolds number, fiber concentration, and fiber aspect-ratio. The turbulent dissipation rate will increase with increasing fiber concentration or decreasing fiber aspect-ratio. Finally, the equation of velocity profile for turbulent fiber suspension channel flow, involving the effect of Reynolds number, fiber concentration, and aspect-ratio, is derived.