Gradual Increase In Stress Research Articles

Motion reconstruction and finite element analysis of the temporomandibular joint during swallowing in healthy adults

There is a close physiological connection between swallowing and the temporomandibular joint (TMJ). However, a shortage of quantitative research on the biomechanical behavior of the TMJ during swallowing exists. The purpose of this study was to reconstruct the movement of the temporomandibular joint (TMJ) based on in vivo experiment and analyze the biomechanical responses during swallowing in healthy adults to investigate the role of the TMJ in swallowing. Motion capture of swallowing, computed tomography (CT), and magnet resonance images (MRI) were performed on six healthy subjects. The movements of the TMJ during swallowing were reconstructed from the motion capture data. The three-dimensional finite element model was constructed. The dynamic finite element analysis of the swallowing process was performed based on the motion data. The range of condylar displacement was within 1 mm in all subjects. The left and right condyle movements were asymmetrical in two-thirds of the subjects. The peak stresses of the discs were relatively low, with a maximum of 0.11 MPa. During swallowing, the condylar displacement showed two trends: slow retraction and slow extension. The tendency to extend could lead to a gradual increase in stress on the disc.

Rubber/clay nanocomposites prepared by compounding clay gel with hydrophilically treated styrene-butadiene rubber

In this work, high-performance rubber/clay nanocomposites (NCs) were prepared by hydrophilic modification of styrene-butadiene rubber (SBR) in conjunction with gel compounding method. The hydrophilicity of SBR matrix increased by 76 % with the addition of hexadecyltrimethylammonium chloride (CTAC), which significantly enhanced the clay-rubber compatibility and processing efficiency. The vulcanization rate of the SBR/clay NC was increased by adding CTAC. The addition of CTAC greatly improved the clay dispersion and the rubber-filler interactions. With increasing the clay loading, the SBR/CTAC/clay NCs showed a gradual increase in stress at a certain strain, elongation at break, tensile strength and Shore A hardness, demonstrating an excellent reinforcing effect of the clay. The tensile strength of the SBR/CTAC/clay NC with 40 phr clay loading reached 14.0 MPa, which was 8.8 times that of the pure SBR and even better than the organoclay filled SBR NC.

Hybrid aliphatic and aromatic diisocyanates forming mixed urea segments for high-performance polyurea

Polyurea is gaining more traction in the realm of protective coatings on metal surfaces from corrosion. The properties of polyurea can be controlled by the judicious selection of its reactants. Herein, a series of polyurea based on hybrid aliphatic/aromatic diisocyanates are synthesized from isophorone diisocyanate (IP) and polycarbodiimide-modified diphenylmethane diisocyanate (ISO). The formulation composed of 37.5:62.5 (IP: ISO) weight ratio yields the highest tensile strength at 47.80 MPa, elongation at 500 %, and hardness of 95 HA. The findings are validated through field emission scanning and atomic force microscopic analysis, which reveals phase mixing surface and ductile fracture containing wide-ranging stretching lines due to enhanced resistance to deformation. Furthermore, synthesized polyureas present a unique stress relaxation pattern with gradual increase in stress under constant deformation, due to hydrogen bond reformation and dislocation creations during chain alignment. IP37.5-ISO62.5 demonstrates outstanding corrosion resistance after a 28-day exposure in salt spray test.

Ecological quality of the Alibori River, northern Benin, using macroinvertebrate indicators

The Alibori River, which flows through Benin’s cotton crop regions, receives surface water from much of the cultivated land that is situated along its banks. Chemical pollution in surface runoff from this land use threatens the ecological quality of the river. This study aimed to characterise the ecological status of the Alibori River under such agricultural pressures using biological indices and macroinvertebrate metrics. Water and macroinvertebrate samples were taken monthly from fifteen sites along the river between June 2015 and May 2016. The measured physico-chemical parameters and biological indices were subjected to descriptive statistics, bivariate correlations and partial least squares regression (PLSR). Taxonomic richness decreased from the upstream to the downstream reaches of the river. Sampling sites with high mineral content and organic load were home to more pollution-tolerant taxa, such as Chironomidae and Oligochaeta, with a high abundance of Thiaridae. Diversity indices reveal an unbalanced community and macroinvertebrate distribution characterised by the development of opportunistic taxa such as the gastropod Melanoides tuberculata. Decreases in taxonomic composition and community organisation between the upstream and downstream reaches of the river appear to be linked to less stable environmental conditions at the downstream sampling sites, and were compounded with a gradual increase in stress for organisms from the upper to lower reaches of the river. The composition, distribution and diversity characteristics of taxa collected is an indication that the ecological status of the Alibori River is under pressure, as a result of the agricultural activities along its banks.

Variation of Elastic Energy Shows Reliable Signal of Upcoming Catastrophic Failure

We consider the Equal-Load-Sharing Fiber Bundle Model as a model for composite materials under stress and derive elastic energy and damage energy as a function of strain. With gradual increase of stress (or strain) the bundle approaches a catastrophic failure point where the elastic energy is always larger than the damage energy. We observe that elastic energy has a maximum that appears after the catastrophic failure point is passed, i.e., in the unstable phase of the system. However, the slope of elastic energy {\it vs.\/} strain curve has a maximum which always appears before the catastrophic failure point and therefore this can be used as a reliable signal of upcoming catastrophic failure. We study this behavior analytically for power-law type and Weibull type distributions of fiber thresholds and compare the results with numerical simulations on a single bundle with large number of fibers.

Modelling and simulation of myocardial infarction in the human cardiovascular system

Modelling the physiological processes leading to myocardial infarction can help ameliorate the severity of the condition by improving early detection. Thus, the aim of this study was to model the cardiovascular system and simulate its response to myocardial infarction. Two methods were deployed for this simulation. The first method is the Computational Fluid Mechanics approach, simulated using Mathematica and the solutions of the resulting equations were obtained using Differential Transform Method. The second method is the Lumped Parameter method, simulated using MATLAB/Simulink. With Computational Fluid Mechanics, at 0% blockage within the arteries, no significant stress on the arterial wall was observed. At 10% and 50% blockage levels, a gradual increase in stress from the inlet through the entire arteries’ length was observed. 100% blockage resulted in an exponential increase in the stress. A similar output was seen with the Lumped Parameter approach. The blood flow decreases rapidly and reaches zero at a pressure of about 170mmHg. The responses of the different arteries to myocardial infarction as simulated can be applied in the early detection of heart diseases. Keywords: myocardial infarction, stress, pressure, blood flow, arterial blockage

Improvement of Strength and Energy Absorption Properties of Porous Aluminum Alloy with Aligned Unidirectional Pores Using Equal-Channel Angular Extrusion

Porous aluminum alloy with aligned unidirectional pores was fabricated by dipping A1050 tubes into A6061 semi-solid slurry. The porous aluminum alloy was processed through Equal-channel Angular Extrusion (ECAE) while preventing cracking and maintaining both the pore size and porosity by setting the insert material and loading back pressure. The specific compressive yield strength of the sample aged after 13 passes of ECAE was approximately 2.5 times higher than that of the solid-solutionized sample without ECAE. Both the energy absorption EV and energy absorption efficiency ηV after four passes of ECAE were approximately 1.2 times higher than that of the solid-solutionized sample without ECAE. The specific yield strength was improved via work hardening and precipitation following dynamic aging during ECAE. EV was improved by the application of high compressive stress at the beginning of the compression owing to work hardening via ECAE. ηV was improved by a steep increase of stress at low compressive strain and by a gradual increase of stress in the range up to 50 pct of compressive strain. The gradual increase of stress was caused by continuous shear fracture in the metallic part, which was due to the high dislocation density and existence of unidirectional pores parallel to the compressive direction in the structure.

Evaluation of Different Drought Stress Regimens on Growth, Leaf Gas Exchange Properties, and Carboxylation Activity in Purple Passionflower Plants

A greenhouse experiment was conducted to evaluate the effects of water stress on leaf water potential, plant growth, and photosynthesis in purple passionflower (Passiflora incarnata). Twenty 4-L pots with two plants in each pot were arranged in a completely randomized design. Ten pots received a daily irrigation dose of 100% evapotranspiration (ET) throughout the 43-day experiment (control). The other 10 pots were subjected to a reduced irrigation (RI) treatment, which was implemented stepwise to achieve a gradual increase in stress, by irrigating them with 50% ET first, then with 25% ET and, finally, with 10% ET. The last stress phase was followed by a recovery phase in which all treatments received the same amount of water (100% ET). A lower water potential was obtained at 10% ET compared with control plants (−2.51 and −0.98 MPa, respectively). Plants in both 25% and 10% ET irrigation treatments had reduced net CO2 assimilation rates (4.25 and 3.50 μmol·m−2·s−1, respectively) than plants watered with 100% ET (8.53 and 6.77 μmol·m−2·s−1, respectively). Values of maximum carboxylation rate allowed by rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), calculated 31 days after treatment (DAT) application (when RI plants were irrigated with 10% ET) decreased by ≈60%, whereas rate of photosynthetic electron transport and triose phosphate use (TPU) were reduced by ≈30% and ≈45% in the stress treatment compared with the control during the 10% ET irrigation period, respectively. Values of water potential and net CO2 assimilation rates in previously stressed plants were not different from the control treatment in the recovery phase, suggesting that P. incarnata plants could adapt well to landscaping situations where periods of extreme drought can be expected.

Learning Environment to Take Operational Decision in Emergency Situation

In psychological and human factors engineering sciences have been strengthened research on the way in which social and demographic variables influence the cognitive functioning of the employee at the time of decision. It is understood that performing tasks at work seeks continuous satisfaction of demands for physical and material security, social and emotional comfort as well as economic and productive stability. Due to the complexity of living systems in the global community, involving increasing environmental changes and limit natural resources, intolerance and social violence, political and economic crises, the demand is presented by investigations of such dimensions on decision making, between designated professional to decide in emergency situations. In the high-risk process industry can happen emergency situations where the lives of many people depend on the decision of a few actors. Extrapolating limits of a model that is not only rational (manage) or emotional (preserve) or instinctual (flee, freeze or fight), the model indicated by the API 770 and discussed in this article indicates that there is an optimal range of stress level to maintain the effectiveness of the task. This paper proposes: a mental model to address emergencies that differs from the model used in the routine decision, and a method to assess technical and intuitive decision and the right profile of the teams for the actions in emergency situations. A case of the liquefied petroleum gas industry (LPG) was analyzed, which makes up a projection of behavior, learning environment, with the gradual increase of stress on the staff of operators and the effects on mental model for decision.

Generalized Concept of the Reinforcement of Elastomers. Part 3: Self-Reinforcement by the Formation of Continuous Hard Phase in Segmented Polyurethane Elastomer

Abstract The author proposed the third concept in the reinforcement of elastomers for segmented polyurethane with the direct observation by microscopic techniques. The structure in segmented polyurethane elastomers fundamentally consists of three domains of different sizes, two kinds of micro-domain, cluster of 100 nm in diameter and spherulite of µm order. Of the micro-domains, one is the hard-segment (HS)-rich micro-domain consisting of hard segment (4 nm thickness) and soft segment (7 nm) and the other is the hard-segment (HS)-poor micro-domain of hard segment (4 nm) and soft segment (15∼20 nm). The HS cluster is constructed by the assembly of the HS-rich micro-domains. The spherulite seems to be composed of the dense packing of the HS cluster, growing up radially or circularly from the center to the outside surface. From physical and mechanical points of view, we can regard the above structures in the segmented polyurethane as bi-continuous structure of the HS clusters whose volume fraction is 0.2, and the matrix phase consisting of the HS-poor domains (0.8 in the volume fraction). The characteristic stress-strain relation of the segmented polyurethane is generated by the combination of both the continuous structures. That is, the initial very high stress (modulus) at small extension and the following gradual increase in stress at medium extension mainly result from the extension and the sliding of the HS cluster, respectively. The very large stress-upturn at large extension and the final great tensile strength are generated by the contribution of both the continuous structures. Thus, the third reinforcement is achieved by the formation of bicontinuous structure of the hard and strong cluster and also the strong matrix phase, in which the absolute structural defects seem not to be included.

Stress–strain responses for continuous orthogonal strain path changes with increasing sharpness

In this article a series of non-proportional orthogonal tests with continuous strain paths are presented. Mild steel was investigated on a biaxial test device that was specifically developed to examine strain path sensitivity. It is shown that a gradual strain path change shows a gradual increase in stress. However, experiments with increasing sharpness in the strain path change show an overshoot in stress which is a typical feature of stress–strain curves from discontinuous strain path changes.

A constitutive model for the tensile deformation of a binary aluminum alloy at high fractions of solid

Tensile tests were performed on alloy Al-4.5 pct Cu with a solidification unit dubbed the direct chill surface simulator (DCSS) that simulates the primary cooling conditions encountered during the direct chill (DC) casting process of sheet ingots. The curves obtained showed a near linear increase of the load with strain up to the point where nonlinearity induced by hot tearing prevented further increase of the load. A constitutive model based on the Lahaie-Bouchard stress-strain theoretical model was generalized by assuming a nonsingular channel thickness distribution. This approach considers a fully lubricated arrangement that allows grain boundary sliding as the most important mechanism of accommodation. As the strain increases, the grain boundaries become more and more subjected to friction sliding and oppose a higher resistance than a fully lubricated sliding condition. This results in a gradual increase of stress with strain. The important variables of the model include solid fraction, channel thickness, geometric standard deviation, and creep law parameters. The model seems appropriate to correlate the tensile behavior of semisolid microstructures having up to 30 pct liquid phase distributed over a large spectrum of grain morphologies.

Surface stresses and the hardness of ion implanted aluminium

The stresses resulting from the implantation of nitrogen into aluminium were measured using a strain gauge technique. The strains resulting from 400 keV and 200 keV N+ implantation were measured at doses of between 5*1015 and 1017 ions cm-2 and the corresponding stresses were calculated. Hardness measurements were made on a Vickers microhardness tester. The stresses were observed to increase linearly with dose up to about 4*1016 ions cm-2 above which they relieved. No corresponding drop in hardness was observed. The relief of stress at high doses is considered to result from plastic yielding of the implanted material and not blistering or bubble formation as reported by other research workers. For the 400 keV N+ implant there was a gradual increase in stress after the stress relief, suggesting the operation of work hardening mechanisms.

Salt Stress and Comparative Physiology in the Gramineae. I. Ion Relations of Two Salt- and Water-Stressed Barley Cultivars, California Mariout and Arimar

Two barley cultivars, California Mariout and the somewhat more salt-sensitive Arimar, were grown under different salinity regimes and in isosmotic polyethylene glycol (PEG) solutions. Shoot growth of both cultivars was inhibited more by NaCl than by PEG. The effects of various salt and osmotic stress regimes on the K+, Na+ and Cl- status, the fresh weight : dry weight ratio and osmotic potential of the tissue were determined. The changes in these parameters were dependent on the rate at which the stress was applied. A gradual increase in stress led to K+/Na+ exchange in the shoot so as to maintain an almost constant (K+ + Na+) content on a dry weight basis. Tissue dehydration largely accounted for the increase in osmotic pressure. In contrast, salt shock resulted in a rapid nonselective accumulation of salt. Both osmotic stress and shock similarly brought about a dehydration of shoot tissue. A gradual osmotic stress slightly enhanced K+ accumulation in the roots. The greater salt sensitivity of the Arimar cultivar appeared to be related to a poorer ability to regulate Na+ plus Cl- accumulation in shoots.