Статті в журналах з теми "Hypothèse du gradient de stress"
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1
Dubos, Pierre Antoine, Quentin Hatte, Pascal Casari, Mireille Richard-Plouet, Pierre-Yves Jouan, Samuel Branchu, and Nadia Guitter. "Stress Gradient Determination in Anti-Corrosion Multilayer Coating." Materials Science Forum 941 (December 2018): 1632–38. http://dx.doi.org/10.4028/www.scientific.net/msf.941.1632.
Анотація:
To reduce maintenance and to increase the corrosion protection and lifetime of maritimestructures while complying with environmental standards, multilayer coatings are applied to protectsteel sections. A new generation of hybrid sol-gel and/or HiPIMS Ni-based thin films appear toconstitute an efficient pre-treatment before the anti-corrosion paint application. However, increasingthe number of coatings and associated interfaces may lead to coating failure due to stresses inducedby the different deposition processes. Therefore developing smart models to assess the stressdistribution along these multilayers appears of significant importance. The well-known Stoneyformula cannot be used for multilayers and owing to the large dimensions of the object to be protected.To assess an easily measurable curvature after deposition, thin steel sheets are used but do not respectany more the Stoney hypotheses. So we set up an analytical thermo-elasto-plastic model to evaluatethe stresses induced by depositions in each layer. This model is based on the various thermalexpansion coefficients of every coat. After extrapolation along the complete thickness, combiningsol-gel and PVD deposition smoothens the stress difference between steel and paint. The shearstresses at interface seems thus to be reduced. The evolution of the stress difference between layerswith the imposed deflection can predict the mechanical strength and the interface failure. In order toevaluate the quality of the model, in-situ four-point bending in SEM was performed to study of theadhesion between the various layers. The results deduced from the model are in good agreement withSEM images.
2
López, Ramiro Pablo, Sergio Valdivia, Mónica L. Rivera, and Rodrigo S. Rios. "Co-occurrence Patterns along a Regional Aridity Gradient of the Subtropical Andes Do Not Support Stress Gradient Hypotheses." PLoS ONE 8, no. 3 (March 7, 2013): e58518. http://dx.doi.org/10.1371/journal.pone.0058518.
3
Bilek, Anastacia M., Kay C. Dee, and Donald P. Gaver. "Mechanisms of surface-tension-induced epithelial cell damage in a model of pulmonary airway reopening." Journal of Applied Physiology 94, no. 2 (February 1, 2003): 770–83. http://dx.doi.org/10.1152/japplphysiol.00764.2002.
Анотація:
Airway collapse and reopening due to mechanical ventilation exerts mechanical stress on airway walls and injures surfactant-compromised lungs. The reopening of a collapsed airway was modeled experimentally and computationally by the progression of a semi-infinite bubble in a narrow fluid-occluded channel. The extent of injury caused by bubble progression to pulmonary epithelial cells lining the channel was evaluated. Counterintuitively, cell damage increased with decreasing opening velocity. The presence of pulmonary surfactant, Infasurf, completely abated the injury. These results support the hypotheses that mechanical stresses associated with airway reopening injure pulmonary epithelial cells and that pulmonary surfactant protects the epithelium from this injury. Computational simulations identified the magnitudes of components of the stress cycle associated with airway reopening (shear stress, pressure, shear stress gradient, or pressure gradient) that may be injurious to the epithelial cells. By comparing these magnitudes to the observed damage, we conclude that the steep pressure gradient near the bubble front was the most likely cause of the observed cellular damage.
4
Franks, Steven J. "Competitive and facilitative interactions within and between two species of coastal dune perennials." Canadian Journal of Botany 81, no. 4 (April 1, 2003): 330–37. http://dx.doi.org/10.1139/b03-023.
Анотація:
While there is substantial evidence for facilitation, the effects of such factors as stress and species identity on positive interactions remain controversial. At two coastal dune sites, I tested the hypotheses that facilitative interactions increase with increasing stress and disturbance along an environmental gradient and that facilitative interactions are stronger among heterospecific than among conspecific individuals. I transplanted Uniola paniculata and Iva imbricata plants into plots along with four conspecific neighbors, four heterospecific neighbors, or no neighbors across an environmental gradient. Neighbors increased target plant survival, suggesting facilitation, but biomass of targets was reduced by the presence of neighbors, suggesting competition. Unexpectedly, competition was greatest in the purportedly most stressful and disturbed zone. In this study, the outcome of neighbor interactions differed for biomass and survival and depended on position along the environmental gradient, but was independent of neighbor identity.Key words: competition, disturbance, facilitation, Iva imbricata, stress, Uniola paniculata.
5
Mehrabian, Amin, Dale E. Jamison, and Sorin Gabriel Teodorescu. "Geomechanics of Lost-Circulation Events and Wellbore-Strengthening Operations." SPE Journal 20, no. 06 (December 18, 2015): 1305–16. http://dx.doi.org/10.2118/174088-pa.
Анотація:
Summary Lost circulation, a major complication of drilling operations, is commonly treated by adding materials of various types, shapes, and particle-size distributions to the drilling mud. Generally known as wellbore strengthening, this technique often helps the operator to drill with higher mud gradients compared with that suggested by the conventional fracture-gradient or borehole-fracture-limit analysis. The underlying mechanisms through which a wellbore is strengthened, however, are not yet fully understood. This study explores these wellbore-strengthening mechanisms through an analytical solution to the related solid-mechanics model of the wellbore and its adjacent fractures. The provided solution is generic in that it takes into account the mechanical interaction of multiple fractures between one another and the wellbore under an arbitrary state of in-situ stress anisotropy. An additional generality in this solution arises from its unification and quantification of some solid-mechanics aspects of the previous hypotheses that have been published on the subject—i.e., stress cage, as well as the tip isolation and its effect on the fracture-propagation resistance. In relation to the stress-cage theory, the study investigates the wellbore-hoop-stress enhancement upon fracturing. The findings indicate that the induced hoop stress is significant at some regions near the wellbore, especially in the general vicinity of the fracture(s). However, given the strong dependency of wellbore stress on the mechanical and geometrical parameters of the problem, generalizing these results to the entire region around the wellbore may not always be trivial. The study also examines tip isolation, a common feature of fracture-closure and propagation-resistance hypotheses, through the analysis of partially reduced fracture pressures and a breakdown criterion, defined by the critical stress-intensity factor of the formation rock.
6
Humphrey, Charlotte, and Jonathan Elford. "Social class differences in infant mortality: the problem of competing hypotheses." Journal of Biosocial Science 20, no. 4 (October 1988): 497–504. http://dx.doi.org/10.1017/s0021932000017624.
Анотація:
SummaryThere is no agreed explanation of the social class gradient in infant mortality. The longstanding debate continues between those who favour explanations based on natural or social selection and those who stress the influence of environmental circumstances. These explanations are often presented as competing hypotheses between which it is necessary to make an absolute choice. An article which takes this approach is critically examined. It is argued that such an approach may lead to erroneous conclusions, and may divert attention away from the primary task of understanding how to bring about further improvements in the survival of infants in the manual social classes.
7
Godivier, Josepha, Elizabeth A. Lawrence, Mengdi Wang, Chrissy L. Hammond, and Niamh C. Nowlan. "Compressive stress gradients direct mechanoregulation of anisotropic growth in the zebrafish jaw joint." PLOS Computational Biology 20, no. 2 (February 8, 2024): e1010940. http://dx.doi.org/10.1371/journal.pcbi.1010940.
Анотація:
Mechanical stimuli arising from fetal movements are critical factors underlying joint growth. Abnormal fetal movements negatively affect joint shape features with important implications for joint health, but the mechanisms by which mechanical forces from fetal movements influence joint growth are still unclear. In this research, we quantify zebrafish jaw joint growth in 3D in free-to-move and immobilised fish larvae between four and five days post fertilisation. We found that the main changes in size and shape in normally moving fish were in the ventrodorsal axis, while growth anisotropy was lost in the immobilised larvae. We next sought to determine the cell level activities underlying mechanoregulated growth anisotropy by tracking individual cells in the presence or absence of jaw movements, finding that the most dramatic changes in growth rates due to jaw immobility were in the ventrodorsal axis. Finally, we implemented mechanobiological simulations of joint growth with which we tested hypotheses relating specific mechanical stimuli to mechanoregulated growth anisotropy. Different types of mechanical stimulation were incorporated into the simulation to provide the mechanoregulated component of growth, in addition to the baseline (non-mechanoregulated) growth which occurs in the immobilised animals. We found that when average tissue stress over the opening and closing cycle of the joint was used as the stimulus for mechanoregulated growth, joint morphogenesis was not accurately predicted. Predictions were improved when using the stress gradients along the rudiment axes (i.e., the variation in magnitude of compression to magnitude of tension between local regions). However, the most accurate predictions were obtained when using the compressive stress gradients (i.e., the variation in compressive stress magnitude) along the rudiment axes. We conclude therefore that the dominant biophysical stimulus contributing to growth anisotropy during early joint development is the gradient of compressive stress experienced along the growth axes under cyclical loading.
8
Yakovenko, Sergey. "Modeling The Turbulent Scalar Fluxes In An Internal Wave Breaking Region In Stratified Flow With Obstacle." Siberian Journal of Physics 12, no. 1 (March 1, 2017): 79–90. http://dx.doi.org/10.54362/1818-7919-2017-12-1-79-90.
Анотація:
Based on averaging of the direct numerical simulation data obtained earlier, statistical moments are calculated in a turbulent patch arising after internal wave overturning in a flow with obstacle and stable stratification. Temporal evolution and spatial behavior of the turbulent-scalar-flux transport equation budget have been studied. A priori estimations of approximations for the pressure-scalar-gradient correlation and turbulent-diffusion processes in this equation have been carried out. The performed analysis is helpful to explore the turbulent patch in terms of statistical moments, and to verify closure hypotheses in turbulence models. It is shown that, in the global balance of the turbulent-scalar-flux equation, the mean-shear and buoyancy productions and the pressure-scalargradient correlation are roughly balanced, as for the shear Reynolds stress equation, and in contrast to the scalar variance and normal Reynolds stress equations. The algebraic turbulent-scalar-flux relations of the gradient diffusion type, as well as those derived in local-equilibrium and nonequilibrium assumptions are incorrect; therefore the use of the full turbulent-scalar-flux equation is justified.
9
Gutiérrez-Cánovas, Cayetano, David Sánchez-Fernández, Miguel Cañedo-Argüelles, Andrés Millán, Josefa Velasco, Raúl Acosta, Pau Fortuño, Neus Otero, Albert Soler, and Núria Bonada. "Do all roads lead to Rome? Exploring community trajectories in response to anthropogenic salinization and dilution of rivers." Philosophical Transactions of the Royal Society B: Biological Sciences 374, no. 1764 (December 3, 2018): 20180009. http://dx.doi.org/10.1098/rstb.2018.0009.
Анотація:
Abiotic stress shapes how communities assemble and support ecological functions. However, it remains unclear whether artificially increasing or decreasing stress levels would lead to communities assembling predictably along a single axis of variation or along multiple context-dependent trajectories of change. In response to stress intensity alterations, we hypothesize that a single trajectory of change occurs when trait-based assembly prevails, while multiple trajectories of change arise when dispersal-related processes modify colonization and trait-filtering dynamics. Here, we tested these hypotheses using aquatic macroinvertebrates from rivers exposed to gradients of natural salinity and artificially diluted or salinized ion contents. Our results showed that trait-filtering was important in driving community assembly in natural and diluted rivers, while dispersal-related processes seemed to play a relevant role in response to salinization. Salinized rivers showed novel communities with different trait composition, while natural and diluted communities exhibited similar taxonomic and trait compositional patterns along the conductivity gradient. Our findings suggest that the artificial modification of chemical stressors can result in different biological communities, depending on the direction of the change (salinization or dilution), with trait-filtering, and organism dispersal and colonization dynamics having differential roles in community assembly. The approach presented here provides both empirical and conceptual insights that can help in anticipating the ecological effects of global change, especially for those stressors with both natural and anthropogenic origins. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.
10
Le, Aurora B., Abas Shkembi, Anna C. Sturgis, Anupon Tadee, Shawn G. Gibbs, and Richard L. Neitzel. "Effort–Reward Imbalance among a Sample of Formal US Solid Waste Workers." International Journal of Environmental Research and Public Health 19, no. 11 (June 1, 2022): 6791. http://dx.doi.org/10.3390/ijerph19116791.
Анотація:
Background: Solid waste workers are exposed to a plethora of occupational hazards and may also experience work-related stress. Our study had three specific hypotheses: (1) waste workers experience effort–reward imbalance (ERI) with high self-reported effort but low reward, (2) unionized workers experience greater ERI, and (3) workers with higher income have lower ERI. Methods: Waste workers from three solid waste sites in Michigan participated in this cross-sectional study. We characterized perceived work stress using the short-version ERI questionnaire. Descriptive statistics and linear tests for trend were assessed for each scale. Linear regression models were constructed to examine the relationship between structural factors of work stress and ERI. Gradient-boosted regression trees evaluated which factors of effort or reward best characterize workers’ stress. Results: Among 68 participants, 37% of workers reported high effort and low reward from work (ERI > 1). Constant pressure due to heavy workload was most indicative of ERI among the solid waste workers. Union workers experienced 79% times higher ERI than non-unionized workers, while no significant differences were observed by income, after adjusting for confounders. Conclusions: Organizational-level interventions, such as changes related to workload, consideration of fair compensation, and increased support from supervisors, can decrease work stress.
11
Savitskii, Alexey, Aleksei Lobasov, Dmitriy Sharaborin, and Vladimir Dulin. "Testing Basic Gradient Turbulent Transport Models for Swirl Burners Using PIV and PLIF." Fluids 6, no. 11 (October 25, 2021): 383. http://dx.doi.org/10.3390/fluids6110383.
Анотація:
The present paper reports on the combined stereoscopic particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) measurements of turbulent transport for model swirl burners without combustion. Two flow types were considered, namely the mixing of a free jet with surrounding air for different swirl rates of the jet (Re = 5 × 103) and the mixing of a pilot jet (Re = 2 × 104) with a high-swirl co-flow of a generic gas turbine burner (Re = 3 × 104). The measured spatial distributions of the turbulent Reynolds stresses and fluxes were compared with their predictions by gradient turbulent transport models. The local values of the turbulent viscosity and turbulent diffusivity coefficients were evaluated based on Boussinesq’s and gradient diffusion hypotheses. The studied flows with high swirl were characterized by a vortex core breakdown and intensive coherent flow fluctuations associated with large-scale vortex structures. Therefore, the contribution of the coherent flow fluctuations to the turbulent transport was evaluated based on proper orthogonal decomposition (POD). The turbulent viscosity and diffusion coefficients were also evaluated for the stochastic (residual) component of the velocity fluctuations. The high-swirl flows with vortex breakdown for the free jet and for the combustion chamber were characterized by intensive turbulent fluctuations, which contributed substantially to the local turbulent transport of mass and momentum. Moreover, the high-swirl flows were characterized by counter-gradient transport for one Reynolds shear stress component near the jet axis and in the outer region of the mixing layer.
12
Bischoff, Norbert, Robert Mikutta, Olga Shibistova, Reiner Dohrmann, Daniel Herdtle, Lukas Gerhard, Franziska Fritzsche, et al. "Organic matter dynamics along a salinity gradient in Siberian steppe soils." Biogeosciences 15, no. 1 (January 3, 2018): 13–29. http://dx.doi.org/10.5194/bg-15-13-2018.
Анотація:
Abstract. Salt-affected soils will become more frequent in the next decades as arid and semiarid ecosystems are predicted to expand as a result of climate change. Nevertheless, little is known about organic matter (OM) dynamics in these soils, though OM is crucial for soil fertility and represents an important carbon sink. We aimed at investigating OM dynamics along a salinity and sodicity gradient in the soils of the southwestern Siberian Kulunda steppe (Kastanozem, non-sodic Solonchak, Sodic Solonchak) by assessing the organic carbon (OC) stocks, the quantity and quality of particulate and mineral-associated OM in terms of non-cellulosic neutral sugar contents and carbon isotopes (δ13C, 14C activity), and the microbial community composition based on phospholipid fatty acid (PLFA) patterns. Aboveground biomass was measured as a proxy for plant growth and soil OC inputs. Our hypotheses were that (i) soil OC stocks decrease along the salinity gradient, (ii) the proportion and stability of particulate OM is larger in salt-affected Solonchaks compared to non-salt-affected Kastanozems, (iii) sodicity reduces the proportion and stability of mineral-associated OM, and (iv) the fungi : bacteria ratio is negatively correlated with salinity. Against our first hypothesis, OC stocks increased along the salinity gradient with the most pronounced differences between topsoils. In contrast to our second hypothesis, the proportion of particulate OM was unaffected by salinity, thereby accounting for only < 10 % in all three soil types, while mineral-associated OM contributed > 90 %. Isotopic data (δ13C, 14C activity) and neutral sugars in the OM fractions indicated a comparable degree of OM transformation along the salinity gradient and that particulate OM was not more persistent under saline conditions. Our third hypothesis was also rejected, as Sodic Solonchaks contained more than twice as much mineral-bound OC than the Kastanozems, which we ascribe to the flocculation of OM and mineral components under higher ionic strength conditions. Contrary to the fourth hypothesis, the fungi : bacteria ratio in the topsoils remained fairly constant along the salinity gradient. A possible explanation for why our hypotheses were not affirmed is that soil moisture covaried with salinity along the transect, i.e., the Solonchaks were generally wetter than the Kastanozems. This might cause comparable water stress conditions for plants and microorganisms, either due to a low osmotic or a low matric potential and resulting in (i) similar plant growth and hence soil OC inputs along the transect, (ii) a comparable persistence of particulate OM, and (iii) unaffected fungi : bacteria ratios. We conclude that salt-affected soils contribute significantly to the OC storage in the semiarid soils of the Kulunda steppe, while most of the OC is associated with minerals and is therefore effectively sequestered in the long term.
13
Andreev, Vladimir. "The stress state of the rock mass with spherical cavity." E3S Web of Conferences 410 (2023): 02051. http://dx.doi.org/10.1051/e3sconf/202341002051.
Анотація:
One of the main hypotheses accepted in the mechanics of deformable solids is the assumption of the homogeneity of materials. This means that all mechanical characteristics of the material (modulus of elasticity, Poisson’s ratio, yield strength, relaxation parameters, etc.) are constant over the volume of the body, in other words, these characteristics are constants. This hypothesis makes it possible not to take into account the natural inhomogeneity of materials at the microlevel - the presence of various fractions in composite materials (concrete, fiberglass, etc.), crystal lattice defects, etc. Examples can be given when various physical phenomena (temperature field, radiation exposure, explosive impact, etc.) lead to a change in the mechanical characteristics along the body. These changes can be quite significant. So, for example, in the presence of high-gradient temperature fields, the deformation characteristics of materials at different points of the body can change dozens of times. Thus, when calculating and designing structures, it is necessary to take into account such macro heterogeneity, since it leads to a significant change in the stress-strain state of bodies. This article considers the problem associated with the continuous inhomogeneity of materials. It means such a heterogeneity that arose in the process of creating an underground cavity with the help of an explosion. In contrast to the classical mechanics of a deformable solid body, the problems of which are reduced to differential equations with constant coefficients, in the mechanics of continuously inhomogeneous bodies we deal with equations with variable coefficients, which greatly complicates their solution. In this case, depending on the type of inhomogeneity functions—functions that describe the change in mechanical characteristics along the coordinates—differential equations turn out to be significantly different.
14
Peng, Wei, and Shinji Toda. "Tests of Remote Dynamic Aftershock Triggering by Small Mainshocks Using Taiwan’s Earthquake Catalog." Seismological Research Letters 92, no. 4 (February 24, 2021): 2464–76. http://dx.doi.org/10.1785/0220200384.
Анотація:
Abstract To understand earthquake interaction and forecast time-dependent seismic hazard, it is essential to determine which static or dynamic stress change due to a mainshock plays a major role in triggering its aftershocks and subsequent mainshocks. Using small mainshocks (2≤M<3) and their aftershocks, Felzer and Brodsky (2006) argued that mainshock induced dynamic stress change is responsible for earthquake triggering in a form of power-law decay within 50 km. Richards-Dinger et al. (2010), however, studied the foreshock decay and claimed that mainshock had no effect at distances outside its static stress triggering range, which required an alternative explanation. We tested these hypotheses using Taiwan’s earthquake catalog by taking advantage of its lack of large events and the absence of active volcano and associated significant seismic swarm. In examining earthquakes occurring in 1994–2010, following Felzer and Brodsky’s method, we found a linear aftershock density with a power-law decay of −1.12±0.38 that is very similar to the one seen in Felzer and Brodsky (2006). None of the mainshock–aftershock pairs were associated with an M 7 rupture event or M 6 event. We further demonstrated that the density decay in a short time period is more likely a randomized behavior than mainshock–aftershock triggering. These pairs were located mostly in high geothermal gradient areas, which are probably triggered by a small-scale aseismic process.
15
Barin, Mohsen, Nasser Aliasgharzad, Pål Axel Olsson, and MirHassan Rasouli-Sadaghiani. "Salinity-induced differences in soil microbial communities around the hypersaline Lake Urmia." Soil Research 53, no. 5 (2015): 494. http://dx.doi.org/10.1071/sr14090.
Анотація:
Lake Urmia in north-western Iran is one of the largest hypersaline lakes in the world, and agricultural production in the surrounding area is limited by soil salinity. We investigated the effects of salinity on belowground microbial communities in soils collected from fields of cultivated onions (Allium cepa L.) and lucerne (Medicago sativa L.), and sites with the native halophyte samphire (Salicornia europaea L.). We tested the hypotheses that salinity reduces microbial biomass and changes the structure of the microbial community. The physical and chemical properties of soil samples were analysed, and phospholipid fatty acids were identified as signatures for various microbial groups. We found that the organic carbon (OC) content was the dominant determinant of microbial biomass. We also found linear relationships between OC and the biomass of various groups of organisms across the wide salinity gradient studied. Salinity, on the other hand, caused changes in the microbial fatty acid composition that indicated adaptation to stress and favoured saprotrophic fungi over bacteria, and Gram-negative bacteria over Gram-positive. Principal component analysis showed that salinity variables and microbial stress indices formed one group, and OC and microbial biomass another. The importance of OC for high microbial biomass in severely stressed soils indicates that OC amendment may be used to mitigate salt stress and as a method of managing saline soils.
16
Frank, Donya, Diane Foster, Pai Chou, Yu-Min Kao, In Mei Sou, and Joseph Calantoni. "Development and Evaluation of an Autonomous Sensor for the Observation of Sediment Motion*." Journal of Atmospheric and Oceanic Technology 31, no. 4 (April 1, 2014): 1012–19. http://dx.doi.org/10.1175/jtech-d-13-00180.1.
Анотація:
Abstract Measurements within the mobile bed layer have been limited by previous Eulerian-based technologies. A microelectromechanical system device, called a smart sediment grain (SSG), that can measure and record Lagrangian observations of coastal sediments at incipient motion has been developed. These sensors have the potential to resolve fundamental hypotheses regarding the incipient motion of coastal sediments. Angle of repose experiments verified that the sensor enclosure has mobility characteristics similar to coarse gravel. Experiments conducted in a small oscillating flow tunnel verified that the sensors detect incipient motion under various hydrodynamic conditions. Evidence suggests the influence of pressure-gradient-induced sediment motion, contrary to the more commonly assumed bed shear stress criterion. Lagrangian measurements of rotation measured with the newly developed SSG agreed to within 5% of the rotation estimates made simultaneously with high-speed video cameras.
17
Popp, Manuel R., and Jesse M. Kalwij. "Abiotic conditions shape the relationship between indigenous and exotic species richness in a montane biodiversity hotspot." Plant Ecology 222, no. 4 (February 20, 2021): 421–32. http://dx.doi.org/10.1007/s11258-021-01116-6.
Анотація:
AbstractMontane ecosystems are more prone to invasions by exotic plant species than previously thought. Besides abiotic factors, such as climate and soil properties, plant-plant interactions within communities are likely to affect the performance of potential invaders in their exotic range. The biotic resistance hypothesis predicts that high indigenous species richness hampers plant invasions. The biotic acceptance hypothesis, on the other hand, predicts a positive relationship between indigenous and exotic species richness. We tested these two hypotheses using observational data along an elevational gradient in a southern African biodiversity hotspot. Species composition data of indigenous and exotic plants were recorded in 20 road verge plots along a gradient of 1775–2775 m a.s.l. in the Drakensberg, South Africa. Plots were 2 × 50 m in size and positioned at 50 m elevational intervals. We found a negative correlation between indigenous and exotic richness for locations with poorly developed mineral soils, suggesting biotic resistance through competitive interactions. A strong positive correlation for plots with very shallow soils at high elevations indicated a lack of biotic resistance and the possibility of facilitating interactions in harsher environments. These results suggest that biotic resistance is restricted to the lower and mid elevations while biotic acceptance prevails in presence of severe abiotic stress, potentially increasing the risk of plant invasions into montane biodiversity hotspots.
18
Frick, N. T., and P. A. Wright. "Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus I. The influence of environmental salinity and external ammonia." Journal of Experimental Biology 205, no. 1 (January 1, 2002): 79–89. http://dx.doi.org/10.1242/jeb.205.1.79.
Анотація:
SUMMARY At a field site in Belize, mangrove killifish Rivulus marmoratus inhabit hypersaline waters (up to 48 ‰) containing approximately 1 mmol l–1 ammonia. We tested the hypotheses that R. marmoratus modify their nitrogen metabolism and excretion (i) by accumulating free amino acids (FAAs) and urea in the tissues during hyperosmotic stress and (ii) by shifting to ureotelism and accumulating FAAs during hyperammonia stress. Urea excretion (JUrea) (but not ammonia excretion, JAmm) displayed a diurnal pattern, with significantly less (75 %) urea excreted at night than during the day in both laboratory-reared clones and wild-caught killifish. When fish were exposed to hypersaline conditions (45 ‰ sea water), JUrea was significantly reduced and tissue urea and FAA levels were elevated compared with those of control fish (15 ‰ sea water). When R. marmoratus were exposed to 0, 1, 2, 5 and 10 mmol l–1 NH4Cl (pH 8) for 48 h, no differences were found in JUrea. Remarkably, prolonged exposure (10 days) to 5 mmol l–1 NH4Cl (pH 8) did not result in an elevation of tissue ammonia levels. In addition, tissue urea and total FAA levels did not differ between control and ammonia-exposed fish after ⩾4 days. We propose that the euryhaline R. marmoratus retain urea and FAAs within their tissues in response to extreme osmotic stress. In contrast to many ammonia-tolerant fishes, R. marmoratus do not shift to ureotelism during prolonged hyperammonia stress, nor do they convert nitrogenous wastes into FAAs. The data suggest that killifish continue to eliminate ammonia despite an unfavourable blood-to-water gradient, thereby avoiding accumulation of ammonia.
19
Hwang, Willy, Neil G. Kelly, and Aladin M. Boriek. "Passive mechanics of muscle tendinous junction of canine diaphragm." Journal of Applied Physiology 98, no. 4 (April 2005): 1328–33. http://dx.doi.org/10.1152/japplphysiol.00816.2004.
Анотація:
The diaphragmatic muscle tendon is a biaxially loaded junction in vivo. Stress-strain relations along and transverse to the fiber directions are important in understanding its mechanical properties. We hypothesized that 1) the central tendon possesses greater passive stiffness than adjacent muscle, 2) the diaphragm muscle is anisotropic, whereas the central tendon near the junction is essentially isotropic, and 3) a gradient in passive stiffness exists as one approaches the muscle-tendinous junction (MTJ). To investigate these hypotheses, we conducted uniaxial and biaxial mechanical loading on samples of the MTJ excised from the midcostal region of dog diaphragm. We measured passive length-tension relationships of the muscle, tendon, and MTJ in the direction along the muscle fibers as well as transverse to the fibers. The MTJ was slack in the unloaded state, resulting in a J-shaped passive tension-strain curve. Generally, muscle strain was greater than that of MTJ, which was greater than tendon strain. In the muscular region, stiffness in the direction transverse to the fibers is much greater than that along the fibers. The central tendon is essentially inextensible in the direction transverse to the fibers as well as along the fibers. Our data demonstrate the existence of more pronounced anisotropy in the muscle than in the tendon near the junction. Furthermore, a gradient in muscle stiffness exists as one approaches the MTJ, consistent with the hypothesis of continuous passive stiffness across the MTJ.
20
Chen, Henry Y., Issam D. Moussa, Charles Davidson, and Ghassan S. Kassab. "Impact of main branch stenting on endothelial shear stress: role of side branch diameter, angle and lesion." Journal of The Royal Society Interface 9, no. 71 (November 23, 2011): 1187–93. http://dx.doi.org/10.1098/rsif.2011.0675.
Анотація:
In-stent restenosis and stent thrombosis remain clinically significant problems for bifurcation lesions. The objective of this study is to determine the haemodynamic effect of the side branch (SB) on main branch (MB) stenting. We hypothesize that the presence of a SB has a negative effect on MB wall shear stress (WSS), wall shear stress gradient (WSSG) and oscillatory shear index (OSI); and that the bifurcation diameter ratio (SB diameter/MB diameter) and angle are important contributors. We further hypothesized that stent undersizing exaggerates the negative effects on WSS, WSSG and OSI. To test these hypotheses, we developed computational models of stents and non-Newtonian blood. The models were then interfaced, meshed and solved in a validated finite-element package. Stents at bifurcation models were created with 30° and 70° bifurcation angles and bifurcations with diameter ratios of SB/MB = 1/2 and 3/4. It was found that stents placed in the MB at a bifurcation lowered WSS dramatically, while elevating WSSG and OSI. Undersizing the stent exaggerated the decrease in WSS, increase in WSSG and OSI, and disturbed the flow between the struts and the vessel wall. Stenting the MB at bifurcations with larger SB/MB ratios or smaller SB angles (30°) resulted in lower WSS, higher WSSG and OSI. Stenosis at the SB lowered WSS and elevated WSSG and OSI. These findings highlight the effects of major biomechanical factors in MB stenting on endothelial WSS, WSSG, OSI and suggests potential mechanisms for the potentially higher adverse clinical events associated with bifurcation stenting.
21
Orozova-Bekkevold, Ivanka, and Thomas Guldborg Petersen. "Numerical forward modelling of the overpressure build-up in the Cenozoic section of the Central Graben in the North Sea." Journal of Petroleum Exploration and Production Technology 11, no. 4 (March 26, 2021): 1621–42. http://dx.doi.org/10.1007/s13202-021-01135-z.
Анотація:
AbstractOne of the most widespread hypotheses for the origin of the present-day overpressure in the shale Post-Chalk section in the North Sea is the very rapid sedimentation from Neogene to present day. We tested this hypothesis by the means of numerical forward finite elements modelling and successfully simulated the overpressure build-up during the Cenozoic filling of the North Sea with relatively simple model set-up. Our model shows that overpressure of approximately 28% above hydrostatic developed in the Neogene, while during the Quaternary, it reached up to 36% above hydrostatic. At present day, the predicted onset of overpressure starts at about 800–1000 m below seafloor, while the maximum (magnitude about 1.36 sg, i.e. 36% above the normal hydrostatic pressure) is at approximately 2100 m. This overpressure profile fits reasonably well with data from wells drilled in the Central Graben. The exact magnitude of the overpressure depends on the used assumptions, the model set-up and the values of the input parameters. Especially the dynamic interaction between high sedimentation rates, clay permeability and low horizontal pressure gradient seems to be a key factor in the efficiency of dewatering of saturated clays during burial. The results indicate that, the assumption of horizontal stress isotropy results in nearly no horizontal fluid flow, despite the same magnitude for the vertical and the horizontal permeability. In these conditions, the vertical permeability plays much bigger role than the horizontal one in the effective de-watering of the sediments during burial. Further investigation is needed to explore the role of horizontal pressure gradient in fluid migration in passive sedimentary basins.
22
Andreev, Vladimir Igorevich, Robert Alekseevich Turusov, and Nikita Yur’evich Tsybin. "DETERMINATION OF STRESS-STRAIN STATE OF A THREE-LAYER BEAM WITH APPLICATION OF CONTACT LAYER METHOD." Vestnik MGSU, no. 4 (April 2016): 17–26. http://dx.doi.org/10.22227/1997-0935.2016.4.17-26.
Анотація:
The article deals with the solution for the stress-strain state of a multilayer composite beam with rectangular cross-section, which is bended by normally distributed load. The intermolecular interaction between layers is accomplished by the contact layer, in which the substances of adhesive and substrate are mixed. We consider the contact layer as a transversal anisotropic medium with such parameters that it can be represented as a set of short elastic rods, which are not connected to each other. For simplicity, we assume that the rods are normally oriented to the contact surface. The contact layer method allows us to solve the problem of determining the concentration of tangential stresses arising at the boundaries between the layers and the corner points, their changes, as well as to determine the physical properties of the contact layer basing on experimental data. Resolving the equations obtained in this article can be used for the solution of many problems of the theory of layered substances. These equations were derived from the fundamental laws of the theory of elasticity and generally accepted hypotheses of the theory of plates for the general case of the bending problem of a multilayer beam with any number of layers. The article deals with the example of the numerical solution of the problem of bending of a three-layer beam. On the basis of this solution the curves were obtained, which reflect the stress-strain state of one of the layers. All these curves have a narrow area of the edge effect. The edge effect is associated with a large gradient tangential stresses in the contact layer. The experimental data suggest that in this zone the destruction of the samples occurs. This fact allows us to say that the equations obtained in this article can be used to construct a theory of the strength layered beams under bending.
23
Heymans, Lyse, Jean-Yves Meyer, Claudine Ah-Peng, Quentin Ethève, Olivier Flores, Christophe Lavergne, Bertrand Mallet, Hilde Parlevliet, Dominique Strasberg, and Robin Pouteau. "Do Native and Alien Species Differ in Their Ecological Strategies? A Test with Woody Plants in Tropical Rainforests on Réunion Island (Mascarene Archipelago, Indian Ocean)." Plants 12, no. 23 (November 27, 2023): 3990. http://dx.doi.org/10.3390/plants12233990.
Анотація:
Understanding the mechanisms of biological invasions (e.g., competitive exclusion) is a key conservation challenge, especially on islands. Many mechanisms have been tested by comparing the characteristics of native and alien species, but few studies have considered ecological strategies. Here we aim at comparing the competitive ability, stress tolerance, and ruderalism (CSR) of native and alien trees in the tropical rainforests of Réunion Island. A total of sixteen 100 m2 plots (eight ‘near-trail’ and eight ‘off-trail’, at less disturbed sites) were established over a 2100 m elevational gradient. Three traits were measured in 1093 leaves from 237 trees: leaf area, leaf dry matter content and specific leaf area. They were converted into a CSR score assigned to each of the 80 surveyed tree species (70 native and 10 alien) using the ‘Stratefy’ ordination approach. C scores increased with basal area and S scores with elevation, but R scores were not higher along the trail, thus only partially validating Stratefy. Native and alien trees had similar CS strategies, thus challenging invasion hypotheses predicting a difference in ecological strategies and rather demonstrating the importance of environmental filtering. However, other differences falling outside the CSR theory may also explain the success of alien species on Réunion.
24
Hunter, John T. "Changes in Allometric Attributes and Biomass of Forests and Woodlands across an Altitudinal and Rainfall Gradient: What Are the Implications of Increasing Seasonality due to Anthropogenic Climate Change?" International Journal of Ecology 2015 (2015): 1–10. http://dx.doi.org/10.1155/2015/208975.
Анотація:
Canonical correspondence analysis and linear regressions were used to relate height, diameter, and dispersion measurements of 36,380 stems from 197 species recorded in 2,341 plots against both climatic and landscape variables. Above ground biomass increased in wetter and cooler locations that ameliorate the seasonal rainfall deficits. Taller and greater diameter trees with lower wood densities occur at higher altitudes. Differences between locations are based on a change in the composition of species rather than a change in the allometric properties within a species. The results support the hydraulic limitation and species packing hypotheses. These interrelationships may be affected by the interactions of fire frequency and drought which are a common feature of much of the study area. Under current climate change scenarios it is likely that there will be a reduction in above ground biomass, the number of stems per hectare, average height, average diameter, and basal area due to increasing seasonality of rainfall, temperatures, and the intensity and frequency of fires. The largest of trees are likely to be removed early due to their inability to cope with increased drought stress. The results suggest a marked reduction in carbon storage will occur across the study region in eastern Australia.
25
Hickey, David R. "Shell shape plasticity in Late Pennsylvanian myalinids (Bivalvia)." Journal of Paleontology 61, no. 2 (March 1987): 290–311. http://dx.doi.org/10.1017/s002233600002847x.
Анотація:
Analyses of shell shape variation in epifaunal and semi-infaunal myalinids from the LaSalle “cyclothem” attest to the extensive shape plasticity of some Late Pennsylvanian myalinids. Mean shell shapes differ significantly within and among species across three nearshore facies. Discriminant analyses of Fourier biometric data categorized by taxonomic, populational (habitat), life-mode, and “multi-species habitat assemblage”” discriminant groups reveal patterns of shape change and variation across an inferred environmental stress gradient in addition to taxonomic and life-mode shape differences. Fourier harmonic data are good indicators of shape differences between epifaunal and semi-infaunal life modes. Mean shapes of epifaunal species vary among habitats. Within-habitat shell shape convergence occurred between Myalina glossoidea and M. (Orthomyalina) slocomi. Interpopulational shape divergence occurred among all populations of M. (Orthomyalina) slocomi, M. glossoidea, and M. wyomingensis. Within-species variation among habitats produced significant mean shape differences among each of three “multi-species habitat assemblages.” Results indicate that a portion of the variation is of ecophenotypic origin.Mean interspecific shape differences reflect internal functional organization and life modes. Intraspecific shape differences among epifaunal species could reflect physical and biotic habitat variables. Several harmonic amplitudes vary in concert with inferred environmental variation among habitats. Although biologic interpretation of harmonic data is problematic, parallel trends in fifth harmonic amplitudes of epifaunal species mirror inferred differences in water turbulence among habitats and could reflect shape variation related to byssal attachment.Stress gradient trends in intraspecific shape variability cannot be collectively explained by either of the antithetical stability-diversity-variation hypotheses. Each species exhibits a different nonmonotonic trend. Maximal levels of intraspecific variation within each species occurred within different habitats. Within-species differences in levels of variation could result from genetic variation among populations as well as ecophenotypic influences. Comparative studies of ontogenetic shape change between valves of individuals, among individuals, and among populations are necessary to determine the relative influence of environmental variables on shape variation and evolutionary significance of phenotypic plasticity.
26
Shavnin, Sergey A., Irek A. Yusupov, Andrey A. Montile, Dmitry Yu Golikov, and Nataliya V. Marina. "Seasonal Dynamics of Content of Antioxidant System Component in Needles of Scots Pine (Pinus sylvestris L.) Trees Situated in the Local Warming Impact Zone." Lesnoy Zhurnal (Forestry Journal), no. 2 (April 15, 2023): 38–57. http://dx.doi.org/10.37482/0536-1036-2023-2-38-57.
Анотація:
The seasonal changes in a period of low temperatures and characteristic correlations of some antioxidant system (AOS) components in pine needles influenced by a gas flare are investigated in this study. The parameters taken are total water content (TWC) in needles, peroxidase activity (AP) and selected elements of the antioxidant system of needles, such as content of carotenoids (Car), ascorbic acid (AA), catechins (Cat) and flavanols (Fl). The needles come from Scots pine trees (Pinus sylvestris L.), which grow in a gradient of environmental conditions formed in the zone of thermal field of the gas flare impact (at various distances). The gas flare is situated on the territory of the Khanty-Mansiysk Autonomous Okrug (UGRA) of Russia. Three hypotheses were subject to verification: 1) the thermal field of the gas flare during the low temperature period affects the water exchange and the AOS state of needles; 2) increase in temperature of the environment in the flare impact zone during the autumn-winter period causes the decrease in amount of moisture in needles, which is a trait of oxidative stress in cells; 3) in the functioning of а needle’s AOS, there are correlations between its components, which values depend on distance from the gas flare and environment created by it. It was found that in the thermal field gradient of the flare, there is neither an additional reduction in TWC in needles compared to the background nor signs of change in the state of AOS corresponding to the oxidative stress in the cells. The greatest impact of the gas flare on characteristics of the physiological state of pine needles is observed in the section closest to the flare. It reveals in the higher values of AP, TWC, Car and decrease in concentration of Fl and AA. The seasonal dynamics of the studied traits values do not correlate with the temperature of the environment. It indicates the indirect effect on the regulation of needle’s AOS activity. The factor and correlation analysis of the data indicate a difference in physiological state of pine needles at different distances from the flare. There is no domination of any processes in the functioning of AOS components. The observed correlations between the studied properties change according to distance to the flare. The most stable is a negative AP relationship with ofter parameters, which rise with the increased distance from the flare. The consistency degree of separate AOS components functioning is maximal in background conditions and decreases when approaching the flare. This fact is explained by the modifying effect of the flare on physiological and biochemical processes of the needle’s adaptation to specific climatic conditions of the environment. For citation: Shavnin S.A., Yusupov I.A., Montile A.A., Golikov D.Yu., Marina N.V. Seasonal Dynamics of Content of Antioxidant System Components in Needles of Scots Pine (Pinus sylvestris L.) Trees Situated in the Local Warming Impact Zone. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 2, pp. 38–57. (In Russ.). https://doi.org/10.37482/0536-1036-2023-2-38-57
27
Chakravarthy, S. S., and W. A. Curtin. "Stress-gradient plasticity." Proceedings of the National Academy of Sciences 108, no. 38 (September 12, 2011): 15716–20. http://dx.doi.org/10.1073/pnas.1107035108.
28
Leccia, Dominique. "Les urgences un sismographe urbain. Témoignage." Santé mentale au Québec 37, no. 1 (October 3, 2012): 203–11. http://dx.doi.org/10.7202/1012652ar.
Анотація:
Notre hypothèse : la ville accélère ou provoque des états de stress spécifiques, et génère sa propre clinique. Les Urgences vont nous indiquer, comment l’incertitude des lieux, l’accélération des trajets et la labilité des frontières, inhérentes aux métropoles sont intériorisées en symptômes pouvant affecter durablement notre équilibre mental.
29
Codo, Sylvie, and Richard Soparnot. "Des conflits de rôle au stress perçu." Articles 68, no. 3 (September 24, 2013): 507–30. http://dx.doi.org/10.7202/1018438ar.
Анотація:
De nombreuses recherches présentent le soutien social perçu comme un levier efficace de gestion du stress au travail. Notre recherche propose de vérifier cette hypothèse en interrogeant le rôle modérateur attribué au soutien social perçu provenant des supérieurs et des subordonnés dans les relations entre les conflits de rôle et le stress chez des managers intermédiaires (MI) et des managers de proximité (MP) du secteur public. Le modèle exigences-ressources professionnelles (Bakker et Demerouti, 2007) nous a servi de cadre théorique. D’après ce modèle, le soutien social perçu constitue une ressource professionnelle permettant d’atténuer les effets délétères des exigences professionnelles sur la santé mentale. Les données collectées auprès de 310 managers dans des administrations publiques locales confirment partiellement cette hypothèse. En effet, notre recherche ne permet pas d’appuyer dans un premier temps l’influence modératrice du soutien social perçu provenant des supérieurs et du soutien social perçu provenant des subordonnés dans la relation entre les conflits de rôle et le stress perçu chez les MI. Des résultats similaires sont observés dans certains cas chez des MP. Conséquemment, l’hypothèse de la non-mobilisation du soutien social comme une ressource professionnelle par les managers dans certaines conditions est avancée pour discuter ces résultats. Ces derniers révèlent dans un second temps que l’efficacité du soutien social perçu dépend de plusieurs facteurs : la nature et la source du soutien social perçu, le type de conflit de rôle en présence et le niveau hiérarchique des managers bénéficiaires (MI et MP). Ainsi, plus que MI, les MP semblent plus réceptifs au soutien social d’estime perçu provenant de leurs supérieurs lorsqu’ils sont confrontés aux conflits de rôle. Par conséquent, leur niveau de stress diminue. Afin de gérer le stress des MP occasionné par les conflits de rôle, nos implications managériales sont orientées vers une reconnaissance de leurs compétences professionnelles.
30
Forest, Samuel, and Karam Sab. "Stress gradient continuum theory." Mechanics Research Communications 40 (March 2012): 16–25. http://dx.doi.org/10.1016/j.mechrescom.2011.12.002.
31
Riad, Tomas. "The Origin of Scandinavian Tone Accents." Diachronica 15, no. 1 (January 1, 1998): 63–98. http://dx.doi.org/10.1075/dia.15.1.04ria.
Анотація:
SUMMARY This article presents a hypothesis about the origin of tone accent in Swedish and Norwegian. The main idea is that the presence of Proto-Nordic secondary stress and its subsequent reduction is essential to the development of accent 2. Developing an earlier proposal (Riad 1988), it is argued that stress clash is critical in the phonologization of tonal information. Support for the major claims is provided by the correlation of Proto-Nordic secondary stress and accent 2 in the modern languages, the synchronic behaviour of accent 2 in Modern Standard Swedish, its manifestation in conservative dialects, and distributional differences between three Scandinavian varieties, which reflect different stages of development. Other, earlier theories of the origin of the accents are discussed in the appendix. RÉSUMÉ Cet article présente une hypothèse de l'origine des accents tonaux en suédois et en norvégien. L'idée principale est que la présence de l'accent dynamique secondaire en proto-nordique et sa réduction subséquente sont essentielles pour le développement de l'accent 2. Ici l'auteur développe la proposition de Riad (1988) selon laquelle le facteur qui cause la phonologisation d'information tonale est le 'stress clash' (le conflit de l'accent tonique). À l'appui des aspects principaux de l'hypothèse il y a la corrélation entre l'accent dynamique secondaire en proto-nordique et l'accent 2 (tonal) dans les langues modernes, la comportement synchronique d'accent 2 en suédois moderne, sa manifestation dans les dialectes conservateurs, et des différences distribu-tionelles entre trois dialectes Scandinaves, qui présentent les différents étapes du développement. On discute d'autres théories de l'origine des accents dans un appendice. ZUSAMMENFASSUNG In diesem Aufsatz wird eine Hypothèse zur ÖEntstehung der schwedischen und norwegischen tonalen Akzente vorgelegt. Ihr Kernpunkt ist, daß sekun-dare Betonungen im Urnordischen und ihre spätere Reduktion eng mit der Ent-wicklung des Akzents 2 verbunden sind. Als auslösenden Faktor in der Pho-nologisierung tonaler Information wird hier ein sog. 'Stress Clash' (nach Riad 1988) angenommen. Stütze für die hauptsächlichen Aspekte dieser Hypothèse finden wir in der Korrelation zwischen urnordischer sekundärer Betonung und Akzent 2 in den modernen Sprachen, dem synchronischen Verhalten des Ak-zent 2 im modernen Standardschwedischen, ihrer Manifestation in konserva-tiven Dialekten und auch in den distributionellen Kontrasten in drei skandi-navischen Varietäten, denen verschiedene Stadien der Entwicklung des Tons entsprechen. Andere Theorien zum Ursprung der Akzente werden in einem Anhang diskutiert.
32
Wood, S. C., and G. M. Malvin. "Physiological significance of behavioral hypothermia in hypoxic toads (Bufo marinus)." Journal of Experimental Biology 159, no. 1 (September 1, 1991): 203–15. http://dx.doi.org/10.1242/jeb.159.1.203.
Анотація:
We tested the hypotheses that hypoxic toads (Bufo marinus) in a thermal gradient would select a lower than normal temperature and that this behavioral response would be beneficial. Under normoxic conditions, selected body temperature was 24.2 +/− 3.6 degrees C. When inspired O2 was 10% or less, mean selected temperature decreased to 15.3 +/− 2.4 degrees C. The theoretical advantages of hypoxia-induced hypothermia we tested include (1) a reduction of oxygen uptake (VO2) by a Q10 effect; (2) increased arterial saturation (SaO2), (3) a decreased ventilatory response, and (4) a decreased stress response. Gas exchange, hematocrit, hemoglobin, SaO2, PaO2 and pH were measured at 25 degrees C (normal preferred temperature) and 15 degrees C (hypoxia preferred temperature) in toads breathing normoxic or hypoxic gas mixtures. During graded hypoxia at 15 degrees C, SaO2 was significantly increased and VO2 was significantly reduced compared with 25 degrees C. Graded hypoxia did not significantly affect VO2 at 25 degrees C, despite evidence for increased ventilation at that temperature (increased pH and respiratory exchange ratio, RE). At 15 degrees C, graded hypoxia had a significant effect on VO2 only at an inspired O2 of 4%. Increased RE with hypoxia was significant at 25 degrees C but not at 15 degrees C. Hematocrit and [hemoglobin] rose significantly during graded hypoxia at 25 degrees C but did not change at 15 degrees C. Toads exposed to 10% O2 (the value that elicits behavioral hypothermia) showed a significant respiratory alkalosis at 25 degrees C but not at 15 degrees C. Likewise, hypoxia caused a significant drop in SaO2 and PO2 at 25 degrees C. Cooling to 15 degrees C during hypoxia caused a significant rise in SaO2 but no change in PaO2. In conclusion, behavioral hypothermia is a beneficial response to hypoxia in Bufo marinus.
33
Torre, I., A. Arrizabalaga, C. Feliu, and A. Ribas. "The helminth infracommunities of the wood mouse (Apodemus sylvaticus) two years after the fire in Mediterranean forests." Helminthologia 50, no. 1 (May 1, 2013): 27–38. http://dx.doi.org/10.2478/s11687-013-0104-8.
Анотація:
AbstractParasites have been recognized as indicators for natural or man-induced environmental stress and perturbation. In this article, we investigated the role of two non-exclusive hypotheses on the response of helminths of wood mice to fire perturbation: 1) a reduction of the helminth infracommunity (species richness) in post-fire areas due to the temporal lack of worms with indirect (complex) life cycles linked to intermediate hosts that are more specialized than the final host, and 2) an increase of the abundance of helminths with direct (simple) life cycles as a response of increasing abundances of the final host, may be in stressful conditions linked to the post-fire recolonization process.We studied the helminth infracommunities of 97 wood mice in two recently burned plots (two years after the fire) and two control plots in Mediterranean forests of NE Spain. Species richness of helminths found in control plots (n = 14) was twice large than in burned ones (n = 7). Six helminth species were negatively affected by fire perturbation and were mainly or only found in unburned plots. Fire increased the homogeneity of helminth infracommunities, and burned plots were characterised by higher dominance, and higher parasitation intensity. We found a gradient of frequency of occurrence of helminth species according to life cycle complexity in burned areas, being more frequent monoxenous (66.6 %), than diheteroxenous (33.3 %) and triheteroxenous (0 %), confirming the utility of helminths as bioindicators for ecosystem perturbations. Despite the short period studied, our results pointed out an increase in the abundance and prevalence of some direct life cycle helminths in early postfire stages, whereas indirect life cycle helminths were almost absent. A mismatch between the final host (that showed a fast recovery shortly after the fire), and the intermediate hosts (that showed slow recoveries shortly after the fire), was responsible for the loss of half of the helminth species.
34
Hafsi, Alma. "Le stress au travail chez les enseignants des collèges en Tunisie." Swiss Journal of Educational Research 39, no. 1 (September 13, 2018): 57–74. http://dx.doi.org/10.24452/sjer.39.1.4999.
Анотація:
L’objectif de l’étude est d’identifier les situations de travail les plus génératrices de stress professionnel chez des enseignants des collèges en Tunisie. Le cadre théorique mobilise les modèles du stress psychologique en milieu professionnel, en particulier celui de Karasek. Nous avons émis l’hypothèse que les conditions de travail des enseignants des collèges d’enseignement général engendreraient un stress professionnel. Cette hypothèse a été testée en administrant le JCQ de Karasek à 351 enseignants des trois types de collèges existants. Les résultats montrent que 18% d’entre eux s’estiment stressés. Toutefois, les enseignants des collèges professionnels sont moins exposés au stress que les autres, en raison d’une forte latitude décisionnelle et de contrôle dans la réalisation de leurs tâches.
35
Polizzotto, Castrenze. "Stress gradient versus strain gradient constitutive models within elasticity." International Journal of Solids and Structures 51, no. 9 (May 2014): 1809–18. http://dx.doi.org/10.1016/j.ijsolstr.2014.01.021.
36
Filippini, M. "Stress gradient calculations at notches." International Journal of Fatigue 22, no. 5 (May 2000): 397–409. http://dx.doi.org/10.1016/s0142-1123(00)00010-4.
37
Zhao, Zhiye. "Stress and stress gradient evaluation — a BEM approach." Advances in Engineering Software 19, no. 1 (January 1994): 45–52. http://dx.doi.org/10.1016/0965-9978(94)90046-9.
38
Chinthakindi, Anil K., Dhananjay Bhusari, Brian P. Dusch, Jürgen Musolf, Balam A. Willemsen, Eric Prophet, Mark Roberson, and Paul A. Kohl. "Electrostatic Actuators with Intrinsic Stress Gradient." Journal of The Electrochemical Society 149, no. 8 (2002): H139. http://dx.doi.org/10.1149/1.1486454.
39
Chinthakindi, Anil K., and Paul A. Kohl. "Electrostatic Actuators with Intrinsic Stress Gradient." Journal of The Electrochemical Society 149, no. 8 (2002): H146. http://dx.doi.org/10.1149/1.1486455.
40
Chakravarthy, Srinath S., and William A. Curtin. "Stress Gradient Plasticity: Concept and Applications." Procedia IUTAM 10 (2014): 453–61. http://dx.doi.org/10.1016/j.piutam.2014.01.040.
41
Nowell, D., and D. Dini. "Stress gradient effects in fretting fatigue." Tribology International 36, no. 2 (February 2003): 71–78. http://dx.doi.org/10.1016/s0301-679x(02)00134-2.
42
Lazopoulos, K. A., and A. K. Lazopoulos. "Strain gradient elasticity and stress fibers." Archive of Applied Mechanics 83, no. 9 (April 24, 2013): 1371–81. http://dx.doi.org/10.1007/s00419-013-0752-7.
43
Seely, Andrew J. E. "Optimizing Our Patients’ Entropy Production as Therapy? Hypotheses Originating from the Physics of Physiology." Entropy 22, no. 10 (September 29, 2020): 1095. http://dx.doi.org/10.3390/e22101095.
Анотація:
Understanding how nature drives entropy production offers novel insights regarding patient care. Whilst energy is always preserved and energy gradients irreversibly dissipate (thus producing entropy), increasing evidence suggests that they do so in the most optimal means possible. For living complex non-equilibrium systems to create a healthy internal emergent order, they must continuously produce entropy over time. The Maximum Entropy Production Principle (MEPP) highlights nature’s drive for non-equilibrium systems to augment their entropy production if possible. This physical drive is hypothesized to be responsible for the spontaneous formation of fractal structures in space (e.g., multi-scale self-similar tree-like vascular structures that optimize delivery to and clearance from an organ system) and time (e.g., complex heart and respiratory rate variability); both are ubiquitous and essential for physiology and health. Second, human entropy production, measured by heat production divided by temperature, is hypothesized to relate to both metabolism and consciousness, dissipating oxidative energy gradients and reducing information into meaning and memory, respectively. Third, both MEPP and natural selection are hypothesized to drive enhanced functioning and adaptability, selecting states with robust basilar entropy production, as well as the capacity to enhance entropy production in response to exercise, heat stress, and illness. Finally, a targeted focus on optimizing our patients’ entropy production has the potential to improve health and clinical outcomes. With the implications of developing a novel understanding of health, illness, and treatment strategies, further exploration of this uncharted ground will offer value.
44
Tang, Yiheng, Yanxuan Song, Guofu Yin, and Ying Nie. "Notch Fatigue Life Prediction Model Considering Stress Gradient Influence Depth and Weight Function." Metals 13, no. 3 (March 7, 2023): 539. http://dx.doi.org/10.3390/met13030539.
Анотація:
Notch characteristics significantly affect the fatigue performance of engineered components, for which the stress gradient effect is worth careful consideration. The traditional stress gradient analysis method based on the Coffin–Manson equation does not take into account the stress gradient influence range regarding the definition of the stress gradient correction factor, nor the high-stress gradient region, which has a greater influence on fatigue life. To address the aforementioned problems, a new notch fatigue life model is proposed in this paper. First, the stress–strain field at the root of the notch is analyzed to define the depth of stress gradient influence, following which the influence of the low-stress gradient region is reduced by a weighting function in the calculation of the stress gradient correction factor. Finally, to validate the method, three sets of experimental data, including TC4, GH4169, and EN8B, were used and compared with three other models. The results demonstrate that the predicted lifetimes of the new model are all within a 2-fold dispersion band, and the prediction ability is better than that of the other three models.
45
Ohtsuka, Masaaki, Hideaki Matsuoka, Yukio Hirose, and Hitoshi Ishii. "The Influence of Stress Gradient on X-ray Stress Measurement." Advances in X-ray Analysis 38 (1994): 463–70. http://dx.doi.org/10.1154/s0376030800018115.
Анотація:
The various machine parts made of fine ceramics are usually finished by grinding. The X-ray elastic constants in ground ceramics are measured by the X-ray diffraction method, as a result a measurement error can occur. The cause of the error is the stress gradient in the material produced by the grinding. In the case of material in which a stress gradient is present, X-ray stress measurement data show non-linear 2θφψ- sin2 ψ diagrams. Until now, the X-ray stress measurement by the sin2ψ method makes use of effectively linear 2θφψ - sin2 ψ diagrams. In the case of 2θφψ - sin2 ψ diagrams showing non-linear behavior, however, good analysis method are generally not available.
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Klaasse, G., R. Puers, and H. A. C. Tilmans. "Stress release structures for actuator beams with a stress gradient." Journal of Micromechanics and Microengineering 17, no. 10 (September 12, 2007): 2093–101. http://dx.doi.org/10.1088/0960-1317/17/10/022.
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Kwon, Young W., Emma K. Markoff, and Stanley DeFisher. "Unified Failure Criterion Based on Stress and Stress Gradient Conditions." Materials 17, no. 3 (January 25, 2024): 569. http://dx.doi.org/10.3390/ma17030569.
Анотація:
Specimens made of various materials with different geometric features were investigated to predict the failure loads using the recently proposed criterion comprised of both stress and stress gradient conditions. The notch types were cracks and holes, and the materials were brittle, ductile, isotropic, orthotropic, or fibrous composites. The predicted failure stresses or loads were compared to experimental results, and both experimental and theoretically predicted results agreed well for all the different cases. This suggests that the stress and stress-gradient-based failure criterion is both versatile and accurate in predicting the failure of various materials and geometric features.
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Armas, Cristina, Susana Rodríguez-Echeverría, and Francisco I. Pugnaire. "A field test of the stress-gradient hypothesis along an aridity gradient." Journal of Vegetation Science 22, no. 5 (May 18, 2011): 818–27. http://dx.doi.org/10.1111/j.1654-1103.2011.01301.x.
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Polizzotto, Castrenze. "A unifying variational framework for stress gradient and strain gradient elasticity theories." European Journal of Mechanics - A/Solids 49 (January 2015): 430–40. http://dx.doi.org/10.1016/j.euromechsol.2014.08.013.
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KOLCHUNOV, VL I. "DEPLANATION HYPOTHESES FOR ANGULAR DEFORMATIONS IN REINFORCED CONCRETE STRUCTURES UNDER COMBINED TORSION AND BENDING." Building and reconstruction 100, no. 2 (2022): 3–12. http://dx.doi.org/10.33979/2073-7416-2022-100-2-3-12.
Анотація:
The article analyzes the hypothesis of deplanation of angular deformations in reinforced concrete structures during bending with torsion. A simple method from the field of the grid methods for approximating the deformations of complex functions under the 3D stress state is considered. Diagrams of angular and linear deformations in such structures were built and analyzed to find these deformations, bending and torques perceived by the concrete of the compressed area using the accepted hypotheses and coefficients for projecting normal and shear stresses (strains) through diagrams of compressed concrete and working reinforcement. Approximating the calculated section by small squares, a spatial surface of deformations was constructed. This is with the corresponding gradients of these deformations in the section with a crack, and on this basis, expressions were written for the total longitudinal deformations in the section and shear deformations in the section of the element during bending with torsion. Using the membrane analogy of the Timoshenko-Goodyear stress functions and the proposed version of new complex functions from the field of the grid method, an analysis was made of its error, when we find the value of complex functions at the considered characteristic points (2%) and at any points of the cross section (7%). The use of the proposed hypotheses and the given version of complex functions makes it possible considering the warping of the 3D stressed section of a reinforced concrete element with cracks undergoing bending with torsion.