Reverse Stress Research Articles

Effects of variation of holding temperature on physiological and biochemical parameters of juvenile sturgeon fish in the conditions of industrial breeding

Below are presented the results of physiological stress (sudden temperature variations) affecting the physiological and biochemical parameters of juvenile sturgeon fish (sterlet and Siberian sturgeon) in the conditions of industrial breeding. They show that the temperature variations in the range of ±15 °С at the rate of 5 °С/hour towards temperature decrease are reversible physiological stress for physiologically healthy starving juvenile sturgeons, with which the species cope well if corresponding adaptation mechanisms are used (100 % survival rate). According to the examined physiological and biochemical parameters, the temperature variation towards decrease has its impact on the respiratory frequency (if the temperature decreases by 5 °С during the first hour of exposure, it increases by 30 % from the initial frequency; in three hours of exposure it decreases by 15 % from the initial frequency if the temperature decreases by 15 °С) and blood glucose level which increases by 15, 30 and 50 % every hour of exposure. The same temperature variations towards increase lead to irreversible physiological changes accompanied by the manifestations of acute stress reaction and death of juvenile fish depending on the severity and duration of temperature stress. During the first hour of exposure, the respiratory frequency increases twice, during the second hour it increases 2.5-fold, and 3-fold during the third hour. Blood glucose level increases by 10% during the first hour, twice during the second hour, 3-fold during the third hour from the initial level. Blood lactate level increases 5-fold from the initial level between the second and the third hour of exposure. Acute stress reaction beyond the adaptive capabilities manifests itself as a drop in fish survival rate in the second or the third hour of temperature increase, from 80-90% to 0% of general fish quantity in the experiment respectively.

Cyber risk and the U.S. financial system: A pre-mortem analysis

We model how a cyber attack may be amplified through the U.S. financial system, focusing on the wholesale payments network. We estimate that spillovers of an attack on one of the five most active banks would impair 31% of the network, on average, with some days significantly worse. When other banks respond by liquidity hoarding, forgone payment activity can reach more than 2.5 times daily GDP. A reverse stress test shows attacks on groups of small banks can also impair a significant amount of the network. Interconnectedness through third-party providers and financial market utilities poses additional risks.

Role of temperature and strain rate on the stress reversal in dynamic damage of monocrystalline NiTi alloy

This study focuses on the temperature and strain rate dependences on tensile stress reversal in dynamic damage of single-crystal nickel titanium (NiTi) alloy. Molecular dynamics simulations are conducted to investigate the structural phase evolution and void evolution under specified temperatures (2000–3500 K). Interestingly, a transformation of one-two-one peak number is observed in the tensile stress curves. When the temperature (T) is lower than 2350 K, there is just one stress reversal, which is attributed to phase transition. On the contrary, a double-peak structure occurs when T ranges from 2350 to 2700 K. It is believed that the first stress reversal occurs through phase transition, but the second reversal is dependent upon void nucleation. When T is higher than 2700 K, the phase content is insignificantly changed, because the phase transformation has been almost accomplished during the relaxation process. Accordingly, the stress reversal takes place via void nucleation. In addition, it is found that the number of peaks changes from two to one as the strain rate increases from 3.0 × 109 s−1 to 2.0 × 1010 s−1. In such cases, the stress reversal is merely governed by phase transition. Since temperature softening effect is characterized by the constraint of phase transition, the void nucleation threshold decreases as the temperature increases. Contrarily, strain rate strengthening effect is represented by the intensification of phase transition, and then the void nucleation threshold would slightly increase by increasing strain rate.

Study of the reverse I–V in component subcells of III–V multijunction space solar cells

AbstractThe reverse bias operation of triple‐junction solar cells (GaInP/Ga(In)As/Ge), typically used for space photovoltaics, is poorly understood. In this work, we conduct reverse bias stress tests on both isotype subcells (GaInP, Ga(In)As and Ge) as well as in the complete triple‐junction solar cell. After each reverse bias step, forward dark and lighted I–Vs are measured and modelled using Shockley and Spirito and Albergamo models to fit the characteristic parameters of each individual subcell and quantify the variations evolution caused by the stress. The changes in these parameters are thoroughly analysed in order to comprehend the basic physical processes behind the degradation observed after the reverse bias is applied. Finally, we demonstrate that the individual parameters obtained from each subcell can be combined to simulate the final I–V curve of the complete triple junction and understand how it is affected when reverse bias is applied, linking the changes observed to a sudden degradation of the GaInP top subcell at low reverse voltages.

Arbuscular mycorrhizal fungi reverse selenium stress in Zea mays seedlings by improving plant and soil characteristics

Selenium (Se) is a beneficial trace element for certain animals including humans, while remaining controversial for plants. High Se concentration in soil is toxic to plants especially at seedling stage of the plants. Although, arbuscular mycorrhizal fungi (AMF) are important for plant stress resistance; but the mechanisms by which AMF alleviate Se stress in crop seedlings are unclear. Therefore, we investigated the potential strategies of AMF symbiosis to alleviate Se stress in maize (Zea mays) from plants and soil perspectives. Results showed that Se stress (Se application level > 5 mg kg−1) significantly inhibited leaf area, shoot dry weight, and root dry weight of maize (P < 0.05). In contrast, AM symbiosis significantly improved root morphology, increased nitrogen and phosphorus nutrition, promoted shoot growth, inhibited the transport of Se from soil/roots to shoots, and then diluted the concentration of Se in shoots (32.65–52.80%). In general, the response of maize growth to AMF was mainly observed in shoots rather than roots. In addition, AMF inoculation significantly increased the easily extractable glomalin-related soil protein and organic matter contents and decreased the availability of soil Se to the plant. Principal component analysis showed that AMF promoted growth and nutrition uptake of maize was the most dominant effect of Se stress alleviation, followed by the decrease of soil Se availability, limiting Se transport from soil/roots to shoots. Moreover, the expression of Se uptake-related ion transporter genes (ZmPht2, ZmNIP2;1, and ZmSultr1;3) in maize roots were down-regulated upon AM symbiosis which resultantly inhibited the uptake and transport of Se from soil to maize roots. Thus, AMF could impede Se stress in maize seedlings by improving plant and soil characteristics.

Involvement of Ethylene in Reversal of Salt Stress by Salicylic Acid in the Presence of Sulfur in Mustard (Brassica juncea L.)

The involvement of ethylene in reversal of salt (NaCl; 50 mM) stress on photosynthetic activity and growth by salicylic acid (SA; 0.5 mM) together with sulfur (S; 2.0 mM) was studied in mustard (Brassica juncea L. cv. Pusa Vijay). Application of SA plus SO42− improved photosynthetic activity through markedly increased S-assimilation, strengthening antioxidant defense system and limiting NaCl-accrued oxidative consequences more conspicuously than their individual effect in B. juncea under 50 mM NaCl stress. Since SA acts as an inhibitor of ethylene and S-assimilation is associated with ethylene synthesis, we tried to figure out the interaction of ethylene in SA and SO42−-mediated salt tolerance. The involvement of ethylene was studied by supplementing salt-treated plants with 200 µL L−1 ethephon (an ethylene-releasing compound) or 100 µM norbornadiene (NBD, ethylene action inhibitor) to SA and SO42− treatments. Ethephon supplemented to NaCl-treated plants showed optimal ethylene formation, increasing ethylene sensitivity to enhance photosynthesis by affecting antioxidative capacity of plants. SA plus SO42− treatment decreased stress ethylene production and optimized ethylene formation under NaCl stress that contributed in the maintenance of high photosynthetic rate, which was reversed with NBD. NaCl-treated plants receiving SA plus SO42− and supplemented with NBD showed inhibited photosynthetic characteristics and growth, with minimal S-assimilation capacity, activity of antioxidant enzymes and GSH content. This showed that the reversal of salt stress by SA plus SO42− was through ethylene involvement. Overall, ethylene intervened the effect of SA in the presence of SO42− to induce S-assimilation, upregulated the enzymatic and non-enzymatic antioxidants, and imparted NaCl tolerance in plants.

The evolution of local stress during deformation twinning in a Mg-Gd-Y-Zn alloy

In this study, we perform in-situ tensile testing and high-resolution electron backscatter diffraction (HR-EBSD) to monitor the twin local stresses at different stages: (i) before twinning, (ii) twins that have propagated into the parent crystal, and (iii) thickening of the twin lamella. The resolved shear stress (RSS) at the twin interface is calculated during deformation twinning, which indicates that the RSS evolution is a dynamic process. Negative shear stress is observed during the propagation stage, which provides evidence for the twinning shear transformation-induced stress reversal. Furthermore, a local Schmid factor (LSF) is used to evaluate the extent to which the local stress is dominated by the RSS on the identified twin plane. The experimental results indicate that the LSFs evolve with strain and are at their maximum level before twinning. The initiated twins are correlated with the highest LSFs compared with the unactivated variants. In addition, the product of the Luster Morris m′ value times the LSF of the twin variant may reveal a threshold for the slip-induced twinning process.

Laws Governing Free and Actual Drying Shrinkage of 50 mm Thick Mongolian Scotch Pine Timber

The relationships between free shrinkage and actual shrinkage of different layers in Mongolian Scotch pine (Pinus sylvestris var. mongolica Litv.) were explored to provide basic data for the further study of drying shrinkage properties. The free shrinkage coefficients at different temperatures and the actual shrinkage strain of each layer were examined under conventional drying. The results showed high precision of free drying shrinkage of corresponding layers of thin small test strips in each layer of sawn timber. The free shrinkage increased linearly as moisture content declined. At the same temperature, the free shrinkage coefficient reached the largest values for the first layer (above 0.267%), while the smallest values were recorded for the ninth layer (below 0.249%). Except for the ninth layer, the free shrinkage coefficients in width directions of other representative layers decreased as temperature increased. At constant temperature, the difference in free shrinkage coefficient of test materials in the length direction of sawn timber was small for the first layer, but slightly larger and changed irregularly in the fifth and ninth layer direction. At the end of conventional drying, the plastic deformation of each layer in the early stage of drying showed a reducing trend or even reversal due to the effects of reverse stress and later damp heat. In sum, these findings look promising for future optimization of wood drying process.

Directional shear jamming of frictionless ellipses.

In this work we study shear reversals of dense non-Brownian suspensions composed of cohesionless elliptical particles. By numerical simulations, we show that a new fragility appears for frictionless ellipses in the flowing states, where particles can flow indefinitely in one direction at applied shear stresses but shear jam in the other direction upon shear stress reversal. This new fragility, absent in the isotropic particle case, is linked to the directional order of the elongated particles at steady shear and its reorientation at shear stress reversal, which forces the suspensions to pass through a more disordered state with an increased number of contacts in which it might get arrested.

Phenomenological hysteretic model for superelastic NiTi shape memory alloys accounting for functional degradation

AbstractThis study presents a simple hysteretic model to reproduce the stress–strain relationship of superelastic NiTi shape memory alloys (SMAs). The proposed model explicitly includes the functional degradation of SMAs, which has been ignored in earthquake engineering applications. This effect causes a reduction in the transformation stress and accumulation of residual strain. Because SMA devices are mainly used for seismic retrofit and account for a small portion of the structural system, their numerical model should not increase the computational time needed to perform nonlinear dynamic analyses. Computational efficiency can be achieved by representing their stress–strain response in a phenomenological way. Additionally, practitioners who may not have a professional background in materials science can easily manipulate the proposed model for the appropriate reproduction of model parameters such as transformation stress and residual strain. The ability to properly reproduce the experimental stress–strain response is validated for the test results of 65 NiTi SMA specimens. The amount of forward and reverse transformation stress degradation and the amount of residual strain accumulation per cycle, which are observed in the experimental results, are captured with reasonable accuracy in the proposed model. Additionally, the response of SMA braces in a four‐story steel moment frame is modeled using the proposed model to examine the residual story drift of the SMA braced frame under a set of ground motions. At higher intensity levels, the functional degradation of SMA braces increased the residual story drift up to 60% in comparison to the SMA‐braced model without functional degradation.

Covid-19 Combined with Stress Cardiomyopathy: Case Report and Review of the Literature

Introduction: Severe COVID-19 can cause multiple organ dysfunction or failure, often associated with cardiac dysfunction, known as stress cardiomyopathy or apical spherical syndrome. Patient Concerns: Severe COVID-19 patients in Hebei province have 5 cases of stress cardiomyopathy. Two cases in Cangzhou are summarized from Feb 2020 to May 2020. Diagnosis: Based on the precipitating factor, pathophysiology, Mayo diagnostic criteria and differential diagnosis of stress cardiomyopathy, the patients were diagnosed with stress cardiomyopathy, which is characterized by elevated biomarkers, hemodynamic instability, and cardiomyopathy. Interventions: Early and dynamic monitoring of ECG, myocardial enzymes, cardiac troponin and echocardiography are needed to predict and assess the risk of stress-induced cardiomyopathy. Noradrenaline and dobutamine were continued to be given, and neokine, levosimendan, Cediland and other drugs were given successively to strengthen the heart. Outcomes: After several days of supportive care, the patients’s cardiac output and the apical movement were gradually improved. Conclusion: Reversible stress cardiomyopathy may occur in the setting of COVID-19 infection with elevated cardiac biomarkers and an abnormal ECG and echocardiographic. We should pay more attention to the treatment of stress cardiomyopathy.

Covid-19 Combined with Stress Cardiomyopathy: Case Report and Review of the Literature

Introduction: Severe COVID-19 can cause multiple organ dysfunction or failure, often associated with cardiac dysfunction, known as stress cardiomyopathy or apical spherical syndrome. Patient Concerns: Severe COVID-19 patients in Hebei province have 5 cases of stress cardiomyopathy. Two cases in Cangzhou are summarized from Feb 2020 to May 2020. Diagnosis: Based on the precipitating factor, pathophysiology, Mayo diagnostic criteria and differential diagnosis of stress cardiomyopathy, the patients were diagnosed with stress cardiomyopathy, which is characterized by elevated biomarkers, hemodynamic instability, and cardiomyopathy. Interventions: Early and dynamic monitoring of ECG, myocardial enzymes, cardiac troponin and echocardiography are needed to predict and assess the risk of stress-induced cardiomyopathy. Noradrenaline and dobutamine were continued to be given, and neokine, levosimendan, Cediland and other drugs were given successively to strengthen the heart. Outcomes: After several days of supportive care, the patients’s cardiac output and the apical movement were gradually improved. Conclusion: Reversible stress cardiomyopathy may occur in the setting of COVID-19 infection with elevated cardiac biomarkers and an abnormal ECG and echocardiographic. We should pay more attention to the treatment of stress cardiomyopathy.

Erythrocytes of Little Ground Squirrels Undergo Reversible Oxidative Stress During Arousal From Hibernation.

The hibernation of small mammals is characterized by long torpor bouts alternating with short periods of arousal. During arousal, due to a significant increase in oxygen consumption, tissue perfusion, and the launch of thermogenesis in cells, a large amount of reactive oxygen species (ROS) and nitrogen (RNS) can be formed, which can trigger oxidative stress in cells. To estimate this possibility, we studied the intensity of free-radical processes in the red blood cells (RBCs) of little ground squirrels (LGS; Spermophilus pygmaeus) in the dynamics of arousal from hibernation. We found that in the torpid state, the degree of generation of ROS and RNS (8.3%, p>0.09; 20.7%, p<0.001, respectively), the degree of oxidative modification of membrane lipids and RBC proteins is at a low level (47%, p<0.001; 82.7%, p<0.001, respectively) compared to the summer control. At the same time, the activity of superoxide dismutase (SOD) and catalase (CAT) in RBC is significantly reduced (32.8%, p<0.001; 22.2%, p<0.001, respectively), but not the level of glutathione (GSH). In the torpid state, SOD is activated by exogenous GSH in concentration-dependent manner, which indicates reversible enzyme inhibition. During the arousal of ground squirrels, when the body temperature reaches 25°C, RBCs are exposed oxidative stress. This is confirmed by the maximum increase in the level of uric acid (25.4%, p<0.001) in plasma, a marker of oxidative modification of lipids [thiobarbituric acid reactive substances (TBARS); 82%, p < 0.001] and proteins (carbonyl groups; 499%, p < 0.001) in RBC membranes, as well as the decrease in the level of GSH (19.7%, p < 0.001) in erythrocytes relative to the torpid state and activity of SOD and CAT in erythrocytes to values at the Tb 20°C. After full recovery of body temperature, the level of GSH increases, the ratio of SOD/CAT is restored, which significantly reduces the degree of oxidative damage of lipids and proteins of RBC membranes. Thus, the oxidative stress detected at Tb 25°C was transient and physiologically regulated.

Effect of pulsed electric field on diabetes-induced glycated enzyme, oxidative stress, and inflammatory markers in vitro and in vivo

This study focused on the effect of pulsed electric field (PEF) on the modification of superoxide dismutase (SOD) to recover its activity (in vitro) and thereby reverse oxidative stress in diabetic mice (in vivo). The result of the in vitro assay demonstrated that PEF could modify the glycated SOD structure through a change in the electrostatic environment of the protein. This modification leads to an 83% and 31% increase in the enzymatic activity of in vitro and in vivo assays, respectively. The in vivo assessment results show a decrease in oxidative stress biomarker indices, advanced glycation end products content, and inflammatory cytokines concentrations. However, the change in blood glucose level is not significant. According to the results, PEF would be effective in diabetes therapy and could be employed as a complementary method.

Effects of shot peening on the tribological properties of aluminum alloys with T6 treatment

Aluminum alloy has many excellent properties such as light texture, corrosion resistance, and easy processing, etc., so it is widely used on the market. The shot peening method can effectively eliminate residual stress and increase its reverse stress, so as to achieve the purpose of anti-fatigue and prolong service life. Therefore, the effects of shot peening on the tribological properties of aluminum alloys with T6 Treatment are investigated in this study. The reciprocating friction test was carried out with three different aluminum alloy mid-plate test pieces, two different shot peening impact parameters and two different loads. Moreover, the macroscopic and microscopic methods are used to discuss the tribological performance of friction and wear. The experimental results show that the plastic deformation is formed on the surface of the material by the shot peening impact method. Although the hardness increases, it also causes inelastic and brittle properties. It can be seen that although the ball striking method can improve the performance of bending, tensile, compression and impact resistance to achieve the purpose of prolonging the service life, when repeated stress is applied, the fatigue resistance will decrease and it will not resist wear. The results will be beneficial to the future of the aerospace industry to develop more internationally competitive products.

Effect of the post-gate annealing on the gate reliability of AlGaN/GaN HEMTs

In this paper, we investigated the effect of post-gate annealing (PGA) on reverse gate leakage and the reverse bias reliability of Al0.23Ga0.77N/GaN high electron mobility transistors (HEMTs). We found that the Poole–Frenkel (PF) emission is dominant in the reverse gate leakage current at the low reverse bias region (V th < V G < 0 V) for the unannealed and annealed HEMTs. The emission barrier height of HEMT is increased from 0.139 to 0.256 eV after the PGA process, which results in a reduction of the reverse leakage current by more than one order. Besides, the reverse step stress was conducted to study the gate reliability of both HEMTs. After the stress, the unannealed HEMT shows a higher reverse leakage current due to the permanent damage of the Schottky gate. In contrast, the annealed HEMT shows a little change in reverse leakage current. This indicates that the PGA can reduce the reverse gate leakage and improve the gate reliability.

Quantification of vertical, lateral, and longitudinal fastener demand in broken spike track: Inputs to mechanistic-empirical design

To address a recent challenge related to broken spikes in premium elastic fastening systems that have led to at least ten derailments and require manual walking inspections as well as build upon mechanistic-empirical (M-E) design principles for future fastening system component design, this paper quantifies the vertical, lateral, and longitudinal fastening system loads under revenue service traffic in a curve that has regularly experienced spike fastener fatigue failures. Previous data has indicated that the high rail of Track 3 experienced the most failures at this location. The data from this investigation sheds light into why failures are more predominant at this location than others and how the vertical, lateral, and longitudinal loads cannot be considered independently. Specifically, while the magnitude of the applied loading was the lowest on the high rail of Track 3, the threshold for failure was also the lowest given the operations at this location led to unloading of the high rail, thus indirectly highlighting the importance of friction within a fastening system. The data also show the high rail of Track 3 was subjected to the highest L/V load ratios and was an outlier in the typical lateral load reversals applied likely leading to spike stress reversals and thus a shorter fatigue life. Finally, based upon the data, it is recommended that to mitigate spike failures, as well as similar fastener challenges in other track types (e.g. rail seat deterioration, etc.) railroads should ensure trains operate close to the balance speed and use fastening system that transfer loads through friction. This study also provides novel data for M-E design of fastening systems.

A three-dimensional numerical analysis of moisture flow in wood and of the wood\u2019s hygro-mechanical and visco-elastic behaviour

A three-dimensional numerical model was employed in simulating nonlinear transient moisture flow in wood and the wood’s hygro-mechanical and visco-elastic behaviour under such conditions. The model was developed using the finite element software Abaqus FEA®, while taking account of the fibre orientation of the wood. The purpose of the study was to assess the ability of the model to simulate the response of wood beams to bending and to the climate of northern Europe. Four-point bending tests of small and clear wood specimens exposed to a constant temperature and to systematic changes in relative humidity were conducted to calibrate the numerical model. A validation of the model was then performed on the basis of a four-point bending test of solid timber beams subjected to natural climatic conditions but sheltered from the direct effects of rain, wind and sunlight. The three-dimensional character of the model enabled a full analysis of the effects of changes in moisture content and in fibre orientation on stress developments in the wood. The results obtained showed a clear distinction between the effects of moisture on the stress developments caused by mechanical loads and the stress developments caused solely by changes in climate. The changes in moisture that occurred were found to have the strongest effect on the stress state that developed in areas in which the tangential direction of the material was aligned with the exchange surface of the beams. Such areas were found to be exposed to high-tension stress during drying and to stress reversal brought about by the uneven drying and shrinkage differences that developed between the outer surface and the inner sections of the beams.

The effects of initial static deviatoric stress on liquefaction and pre-failure deformation characteristics of saturated sand under cyclic loading

Initial static deviatoric stress can affect the liquefaction behaviour and deformation characteristics of saturated sand under cyclic loading. A series of cyclic triaxial tests were performed on a saturated sand consolidated under a constant vertical stress but different lateral stresses. The dependence of failure mechanism, liquefaction resistance, and stiffness evolution of the sand on initial static deviatoric stress ratio was investigated on medium dense to dense sand samples (Dr = 0.44 to 0.82). The pre-failure deformation and the direction of strain accumulation were analysed under different static deviatoric stress ratios. The results indicate that under cyclic loading with stress reversal condition, the effective mean stress in the samples could reduce to zero, which leads to cyclic mobility failure and completely loss of stiffness due to liquefaction. The stress state after cyclic loading could be above critical state line. Under non reversal loading condition, however, the effective mean stress cannot reduce to zero and therefore the samples fail under shear due to large strain accumulation. In this condition, the stress state at the end of the cyclic loading is approximately at the critical state line and hardly affected by initial deviatoric stress. The failure resistance of medium dense to dense sand is not greatly affected by initial static deviatoric stress until it is large enough to meet non-reverse loading condition. The ratio of axial stain to excess pore water pressure accumulation (or Δϵacc a/Δϵacc v) increases with the average static deviatoric stress ratio ηav. The strain accumulation direction roughly follows the flow rule of Modified Cam Clay model, independent of relative density and failure mechanism.

Constitutive models for well-entangled living polymers beyond the fast-breaking limit

In well-entangled living polymers, there is a complex relationship between reversible polymerization reactions and stress relaxation dynamics. This relationship is already well-understood in the “fast-breaking” limit, where polymers tend to break apart much faster than they can relax interior tube segments by reptation. For well-entangled living polymers that are not necessarily fast-breaking, we introduce a new suite of computationally efficient partial differential equation models for linear and nonlinear rheology. For linear rheology calculations, we retain full-chain depictions of standard stress relaxation processes (reptation, double reptation, contour length fluctuations, etc.) and replace the reaction terms with a simple “shuffling” approximation. Besides predicting bulk rheology, these shuffling models also yield new insights into the rheological contribution from chains at different sectors of the molecular weight distribution. Generalizing to nonlinear rheology models, additional approximations must be made with respect to reptation and constraint release in order to facilitate applications in computational fluid dynamics. To evaluate... a pair of constitutive models with complementary strengths and weaknesses: LRP-f (living Rolie-Poly, fitted) and STARM-E (simplified tube approximation for rapid-breaking micelles, extended). Nonlinear rheology calculations are provided for both models over a range of flow conditions in both fast-breaking and semi-slow breaking systems. In spite of their differing assumptions and approximations, we find that both models are capable of producing similar results. From this, we conclude that the predictions of the LRP-f and STARM-E models reflect their shared physical basis, and hence either model can be used with reasonable confidence for describing nonlinear rheology in systems of well-entangled living polymers across the fast/slow breaking spectrum.