The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator....The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.展开更多
The hot deformation behavior of 20 Mn Ni Mo low carbon alloy was investigated by isothermal compression tests over wide ranges of temperature(1223-1523 K) and strain rate(0.01-10 s^(-1)). According to the experimental...The hot deformation behavior of 20 Mn Ni Mo low carbon alloy was investigated by isothermal compression tests over wide ranges of temperature(1223-1523 K) and strain rate(0.01-10 s^(-1)). According to the experimental true stress-true strain data, the constitutive relationships were comparatively studied based on the Arrhenius-type model, Johnson-Cook(JC) model and artificial neural network(ANN), respectively. Furthermore, the predictability of the developed models was evaluated by calculating the correlation coefficient(R) and mean absolute relative error(AARE). The results indicate that the flow stress behavior of 20 Mn NiM o low carbon alloy is significantly influenced by the strain rate and deformation temperature. Compared with the Arrhenius-type model and Johnson-Cook(JC) model, the ANN model is more efficient and has much higher accuracy in describing the flow stress behavior during hot compressing deformation for 20 Mn Ni Mo low carbon alloy.展开更多
Total strain controlled cyclic test was performed on 316 LN under uniaxial loadings. Through the partitioning of hysteresis loops, the evolution of two components of cyclic flow stress, the internal and effective stre...Total strain controlled cyclic test was performed on 316 LN under uniaxial loadings. Through the partitioning of hysteresis loops, the evolution of two components of cyclic flow stress, the internal and effective stresses, was reported. The former one determines the cyclic stress response. Based on the transmission electron microscopic（TEM） observation on specimens loaded with scheduled cycles, it is found that planar dislocation structures prevail during the entire cyclic process at low strain amplitude, while a remarkable dislocation rearrangement from planar structures to heterogeneous spatial distributions is companied by a cyclic softening behavior at high strain amplitude. The competition between the evolution of the intergranular and the intragranular components of the internal stress caused by the transition of slip mode induces the cyclic hardening and softening at high strain levels. The intergranular internal stress represents the most part of the internal stress at low strain level.展开更多
A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition(DED)was applied to investigate the microstructure evolution,stress rupture behavior,and deformation mech-anisms at moderate...A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition(DED)was applied to investigate the microstructure evolution,stress rupture behavior,and deformation mech-anisms at moderate-high temperatures and high-low stress conditions.The high Ta/Al ratio induces large misfit lattice stress and low stacking fault energy of alloy,resulting in approximate cubicγ′phases in dendrites and the formation of initial dislocation tangles.After the stress rupture test at 760℃/780 MPa,high content cubicγ′phases,small size of voids as well as preserved dislocation tangles are observed,showing stable structures with high-stress rupture resistance.High content and suitable size of cubicγ′phases,initial dislocation tangles,and L-C locks hinder the dislocation motion,which decreases the minimum strain rate and prolongs life significantly,forming four stress rupture stages.Hence,the defor-mation mechanism is determined by dislocation piled-up onγ/γ′interface,formation of stacking faults inγ′phases,and dislocations shearingγ′phases.However,the microstructure exhibits uneven struc-tures composed of large sizes of raftedγ′phases and voids at 980℃/260 MPa.The rafted structure and high temperature provide continuous channels and enough energy for dislocation motion,resulting in the increase of minimum strain rate,decline of life,and typic three stress rupture stages,even though there are obstacles to dislocation movement caused by dislocation networks.The deformation mecha-nism transforms to form dislocation networks onγ/γ′interface and dislocations shearingγ′phases.Be-sides,the decomposition of carbides on GBs also depends on temperature,which decomposes into harm-ful chain-like M23 C6 carbides at moderate temperatures and reinforced granular-shaped M6 C carbides at high temperatures.The applied stress always decreases mechanical properties due to its degradation of microstructure induced by elongating the precipitates and defects.展开更多
Objective To investigate the relationship between atopic allergy and depression and the role of DBP in the development of depression. Methods BALB/c mice were randomly divided into eight groups：saline;ovalbumin （OVA...Objective To investigate the relationship between atopic allergy and depression and the role of DBP in the development of depression. Methods BALB/c mice were randomly divided into eight groups：saline;ovalbumin （OVA）-immunized;saline＋DBP （0.45 mg/kg·183;d）; saline＋DBP （45 mg/kg·d）; DBP （0.45 mg/kg·d） OVA-immunized; DBP （45 mg/kg·d） OVA-immunized; saline＋hydrocortisone （30 mg/kg·d）; and hydrocortisone （30 mg/kg·d）-exposed OVA-immunized. Behavior （e.g. open-field, tail suspension, and forced swimming tests）, viscera coefficients （brain and spleen）, oxidative damage [e.g. reactive oxygen species （ROS）, malondialdehyde （MDA）, and glutathione （GSH）], as well as levels of IgE and IL-4, were then analyzed. Results In the saline and OVA groups, the degree of depression symptoms in mice increased with increasing DBP concentration. Additionally, the OVA-immunity groups were associated with more serious depressive behavior compared with the same exposure concentration in the saline group. Oxidative damage was associated with a dose-dependent increase in DBP in the different groups. IL-4 and IgE levels were associated with low-dose DBP stimulation, which changed to high-dose inhibition with increasing DBP exposure, possibly due to spleen injury seen at high DBP concentrations.Conclusion Development of an atopic allergy has the potential to increase the risk of depression in mice, and it seems that DBP helps OVA to exert its effect in our present model. Moreover, the results of our study implicate a certain connection between brain oxidative stress and depression, which deserves a further exploration.展开更多
Laser shock processing is a very new technique and an emerging modern process that generates compressive stresses much deeper into the surfaces of metals or alloys. A brief parametric study of the effect of laser para...Laser shock processing is a very new technique and an emerging modern process that generates compressive stresses much deeper into the surfaces of metals or alloys. A brief parametric study of the effect of laser parameters on fatigue behavior and residual stress state generated in 6061-T651 alloy specimens was summarized. Residual stress of 6061-T651 alloy was analyzed both before and after laser processing with multishocks. The material remains in compressive residual stress of approximate 1mm in depth which is approximately 10 times deeper than that can be achieved with the conventional technique, and the maximal compressive residual stress at the surface of the sample is about -350MPa. Near the surface, yield strength and hardness are found to be increased by the laser shock. The ratio of fatigue crack initiation life for the laser-shocked to unshocked specimens is found to be 4.9 for specimens. The results clearly show that LSP is an effective surface treatment technique for improving the fatigue performance of aluminum alloys.展开更多
This study proposes a novel approach to study stress field distribution and overlying ground pressure behavior in shallow seam mining in gully terrain.This approach combines numerical simulations and field tests based...This study proposes a novel approach to study stress field distribution and overlying ground pressure behavior in shallow seam mining in gully terrain.This approach combines numerical simulations and field tests based on the conditions of gully terrain in the Chuancao Gedan Mine.The effects of gully terrain on the in situ stress field of coal beds can be identified by the ratio of self-weight stress to vertical stress(η) at the location corresponding to the maximum vertical stress.Based on the function η =j(h),the effect of gully terrain on the stress field of overlying strata of the entire field can be characterized as a significantly affected area,moderately affected area,or non-affected area.Working face 6106 in the Chuancao Gedan Mine had a coal bed Jepth <80 m and was located in what was identified as a significantly affected area.Hence,mining may cause sliding of the gully slope and increased loading(including significant dynamic loading) on the roof strata.Field tests suggest that significant dynamic pressures were observed at the body and foot of the gully slope,and that dynamic loadings were observed upslope of the working face expansion,provided that the expanding direction of the working face is parallel to the gully.展开更多
Using large strain two dimension axisymmetric elasto plastic finite element method and the modified law of mixture, the effects of thermal residual stresses on the yielding behavior of short fiber reinforced metal mat...Using large strain two dimension axisymmetric elasto plastic finite element method and the modified law of mixture, the effects of thermal residual stresses on the yielding behavior of short fiber reinforced metal matrix composite and their dependencies on the material structure parameters (fiber volume fraction, fiber aspect ratio and fiber end distance) were studied. It is demonstrated that the stress strain partition parameter can be used to describe the stress transfer from the matrix to the fiber. The variation of the second derivation of the stress strain partition parameter can be used to determine the elastic modulus, the proportion limit, the initial and final yield strengths. In the presence of thermal residual stress, these yielding properties are asymmetric and are influenced differently by the material structure parameters under tensile and compressive loadings.展开更多
Long-lasting constant loading commonly exists in silicon-based microelectronic contact and can lead to the appearance of plastic deformation.Stress relaxation behaviors of monocrystalline silicon coated with amorphous...Long-lasting constant loading commonly exists in silicon-based microelectronic contact and can lead to the appearance of plastic deformation.Stress relaxation behaviors of monocrystalline silicon coated with amorphous SiO_(2)film during nanoindentation are probed using molecular dynamics simulation by varying the indenter’s size.The results show that the indentation force(stress)declines sharply at the initial and decreases almost linearly toward the end of holding for tested samples.The amount of stress relaxation of SiO_(2)/Si samples indented with different indenters during holding increases with growing indenter size,and the corresponding plastic deformation characteristics are carefully analyzed.The deformation mechanism for confined amorphous SiO_(2)film is depicted based on the amorphous plasticity theories,revealing that the more activated shear transformation zones(STZs)and free volume within indented SiO_(2)film promote stress relaxation.The phase transformation takes place to monocrystalline silicon,the generated atoms of Si-II and bct-5 phases within monocrystalline silicon substrate during holding are much higher than those for smaller indenter.展开更多
This study aims to clarify what kinds of resilience and coping strategies students employ to successfully complete their clinical practicum and provide suggestions for instruction that will allow students to carry out...This study aims to clarify what kinds of resilience and coping strategies students employ to successfully complete their clinical practicum and provide suggestions for instruction that will allow students to carry out effective learning activities. The study subjects were 86 students enrolled at Nursing University A for the 2019 school year and planning to take the integrated nursing practicum. The survey was conducted using an anonymous, self-administered questionnaire. The Wilcoxon signed-rank test was used to determine the amount of change in resilience factors from the surveys before and after the practicum. Subsequently, multiple regression analysis was carried out with stress coping behaviors that were significantly associated with resilience factors in univariate analysis as independent variables and the amount of change in resilience factors before and after the practicum as dependent variables. A total of 56 responses were received (response rate 65.8%) from the 85 survey subjects. Innate resilience factors increased significantly from 41 pre-practicums to 44 post-practicums. Acquired resilience factors also increased significantly from 32 pre-practicums to 35 post-practicums (p < 0.01). The results of multiple regression analysis found that the stress coping behavior of “changing point of view” (β = 0.361, p < 0.01) and pre-practicum innate resilience factors (β = <span style="white-space:nowrap;">−</span>0.456, p < 0.01) were significantly associated with innate resilience factors. Examining the relationship between the amount of change in student resilience and stress coping behaviors revealed that the stress coping behavior of “changing point of view” was associated with innate resilience. This finding suggests that resilience may be increased by changing one’s perspective on an event by taking on a new way of thinking. The results suggested that helping students transform realizations made during reflection into learning and create a sense of meaning may lead to fostering innate resilience during integrated nursing practicums.展开更多
The kinetics of water absorption in water-borne anticorrosive urethane/epoxy coatings, which were actually introduced in the industrial field, are studied. It is found that the high water affinity of a water-borne coa...The kinetics of water absorption in water-borne anticorrosive urethane/epoxy coatings, which were actually introduced in the industrial field, are studied. It is found that the high water affinity of a water-borne coating supports a higher saturated water content, Mχ, and helps to facilitate absorption D. The three parameters of stretched exponential function called the William-Watt equation, Eo, τ, and β, are determined to fit the degraded stress relaxation behavior in the water absorption process because this function quantitatively describes the relaxing ability and has been successfully used by a number of researchers. An increasing in the water content is shown to correlate strongly with a decrease in Eo and fl early in the absorption process between Mt/M（χ） = 0 and Mt/Mχ≈ 0.5. The adhesive characteristics of the coatings are correlated with water content, and shown to exhibit higher cohesive failure in coating epoxies under saturated conditions. This suggests that water interferes with the intermolecular bonding between polymer chains which degrades the bulk materials ability to diffuse stress concentrations and reduces its overall strength.展开更多
The progressive current degradation and breakdown behaviors of GaN-based light emitting diodes under high reversebias stress are studied by combining the electrical, optical, and surface morphology characterizations. ...The progressive current degradation and breakdown behaviors of GaN-based light emitting diodes under high reversebias stress are studied by combining the electrical, optical, and surface morphology characterizations. The current features a typical “soft breakdown” behavior, which is linearly correlated to an increase of the accumulative number of electroluminescence spots. The time-to-failure for each failure site approximately obeys a Weibull distribution with slopes of about 0.67 and 4.09 at the infant and wear-out periods, respectively. After breakdown, visible craters can be observed at the device surface as a result of transient electrostatic discharge. By performing focused ion beam cuts coupled with scan electron microscope, we observed a local current shunt path in the surface layer, caused by the rapid microstructure deterioration due to significant current heating effect, consistent well with the optical beam induced resistance change observations.展开更多
Stress from dominance ranks in human societies, or that of other social animals, especially nonhuman primates, can have negative influences on health. Individuals holding different social status may be burdened with v...Stress from dominance ranks in human societies, or that of other social animals, especially nonhuman primates, can have negative influences on health. Individuals holding different social status may be burdened with various stress levels. The middle class experiences a special stress situation within the dominance hierarchy due to its position between the higher and lower classes. Behaviorally, questions about where middle-class stress comes from and how individuals adapt to middle-class stress remain poorly understood in nonhuman primates. In the present study, social interactions, including aggression, avoidance, grooming and mounting behaviors, between beta males, as well as among group members holding higher or lower social status, were analyzed in captive male-only cynomolgus monkey groups. We found that aggressive tension from the higher hierarchy members was the main origin of stress for middle- class individuals. However, behaviors such as attacking lower hierarchy members immediately after being the recipient of aggression, as well as increased avoidance, grooming and mounting toward both higher and lower hierarchy members helped alleviate middle-class stress and were particular adaptations to middle-class social status.展开更多
Cadmium (Cd) exposure can induce acute lethal health-related threats to humans since it has an exceptional ability to accumulate in living organisms and cause toxicological effects. Curcumin (Cur) on the other hand ha...Cadmium (Cd) exposure can induce acute lethal health-related threats to humans since it has an exceptional ability to accumulate in living organisms and cause toxicological effects. Curcumin (Cur) on the other hand has a wide variety of biological activities and several animal studies have suggested for a potential therapeutic or preventive effects against several ailments and infections. To study the effect of Cur on the toxicity of Cd, sixty Swiss-Webster strain male mice were divided into 6 groups of ten each at random. Group-1 served as the na?ve control and received no treatment. Group-2, 3 and 4 were the experimental controls and were administered once a day with a single oral dose of 50% dimethyl sulphoxide (DMSO), Cur (300 mg/kg) or Cd (100 mg/kg) respectively, for 2 weeks. Group-5 and 6 received Cur and Cd in combination once a day orally for 2 weeks except that Cur in a dose of 150 and 300 mg/kg to group 5 and 6 respectively, was administered one hour before Cd (100 mg/kg) administration to both groups. After treatment period, the animals were subjected to behavioral tests and thereafter, the animals were sacrificed for the estimation of neurotransmitters like serotonin (5-HT), dopamine (DA) and it’s metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) as well as oxidative stress enzymes like lipid peroxides in the form of thiobarbituric acid–reactive substances (TBARS) and total glutathione (GSH) in the forebrain tissue. Cd reduced significantly the body weight gain, the locomotor activity, anxiety behavior in the plus maze and the learning capability (cognitive effect) in the shuttle-box test. Biochemical analysis further revealed that Cd exposure significantly altered the brain neurotransmitters and the oxidative stress enzymes. However, administration of Cur along with Cd had an ameliorating effect on all the behavioral and biochemical parameters studied herein and reduced the toxicity of Cd significantly and dose-dependently. Thus, Cur may be beneficial for anxiety, neuromuscular, and cognitive problems and protect from Cd intoxication.展开更多
The conventional Arrhenius-type model was adopted to identify the deformation characteristic of Ti6 A14 V(TC4) titanium alloy based on the stress-strain curves of isothermal compression test. A new flow stress model b...The conventional Arrhenius-type model was adopted to identify the deformation characteristic of Ti6 A14 V(TC4) titanium alloy based on the stress-strain curves of isothermal compression test. A new flow stress model based on Arrhenius equation was proposed for TC4,which is composed of peak flow stress(PFS) prediction and strain compensation. The predicted PFS is set as a reference to derive the flow stress model at any strain ranging from approximately 0 to 0.7. The predictability and efficiency among the proposed model, conventional model,and an existing physical-based model of TC4 were comparatively evaluated. It is found that the newly proposed model can simultaneously track the hardening and softening behaviors of TC4 through a single expression while the other existing models are only valid in the softening region.Besides, the wider application range and acceptable accuracy of the new model have been achieved by fewer material constants with much-simplified modeling procedure than the other models.展开更多
The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the ...The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.展开更多
Objective: To investigate the effects of cognitive behavioral intervention on psychological stress response in breast cancer patients by cognitive behavioral intervention in breast cancer patients. Methods: Adopting t...Objective: To investigate the effects of cognitive behavioral intervention on psychological stress response in breast cancer patients by cognitive behavioral intervention in breast cancer patients. Methods: Adopting the random comparison method, 100 patients with breast cancer were divided into comparison group and intervention group by 50 cases. The intervention group underwent cognitive behavioral intervention at the same time as the comparison group only received conventional treatment without cognitive behavioral intervention. Two groups of breast cancer patients were enrolled in the general questionnaire, the Self-Rating Anxiety Scale (SAS), and the Medical Coping Modes Questionnaire (MCMQ) within one week after admission and one month after treatment to understand the psychological stress levels of the two groups. Results: There was no significant difference in the scores of SAS and MCMQ between the intervention group and the comparison group before intervention (P > 0.05). But after intervention, the scores of SAS and MCMQ in the comparison group were significantly higher than those in the intervention group (P 0.05). It shows that the implementation of cognitive behavioral intervention therapy for breast cancer patients has the effect of improving their psychological status. Conclusion: Cognitive behavioral intervention therapy combined with psychology for breast cancer patients can effectively reduce their stress level, improve mental health status and improve their positive coping ability.展开更多
Objective: To evaluate the effects of prenatal and postnatal stress on the sexual behavior of rats. Methods: Thirty-two 2-month-old male Wistar rats were divided as follows: the EG Group (comprised of 10 rats whose mo...Objective: To evaluate the effects of prenatal and postnatal stress on the sexual behavior of rats. Methods: Thirty-two 2-month-old male Wistar rats were divided as follows: the EG Group (comprised of 10 rats whose mothers underwent gestational stress), the EO Group (11 rats subjected to postnatal stress), and the SE Group (control group, comprised of 11 animals that went through no stress whatsoever). Upon reaching adulthood, these male rates were introduced to females and had their sexual behavior assessed based on the number of mounts. Results: The animals from the EP Group showed significantly fewer mounts (74 ± 24.77, p < 0.05) when compared to those from the EG (108.9 ± 35.27) and SE (99.6 ± 20.76) Groups. Conclusion: The rats that underwent stress during the first days of life mated fewer times than those whose mothers were subjected to stress during pregnancy. The latter had their sexual behavior unaltered.展开更多
Nursing students are facing more and more stress in their course of study especially in clinical practicum. The study aimed to predict nursing students’ stress level in clinical practicum with coping behaviors. It wa...Nursing students are facing more and more stress in their course of study especially in clinical practicum. The study aimed to predict nursing students’ stress level in clinical practicum with coping behaviors. It was a retrospective cross-sectional study conducting in a self-financing institution in Hong Kong. Nursing students who were studying the pre-registration baccalaureate nursing program and completed all the practicum blocks were recruited. Those who had extended the study and failed any of the practicum blocks were excluded. Convenience sampling was used to recruit subjects. Participants were required to fill out the demographic sheet, COPE Inventory and Assessment of Stress among Nursing Students scale during lecture at the commencement of a semester. The whole data collection lasted for 30 minutes. Stepwise multiple regression was used to do the modeling with p-value being set at 0.05. 131 eligible nursing students were recruited with about half of female students. The regression model accounted for 50% of the variance in the perceived stress level. Gender, focus on and venting of emo-tions, restraint, use of emotional social support and denial were positively associated with perceived stress level (R squared = 0.52, p = 0.001). It is to conclude that nurse educators can refer to the findings to screen out students with higher risk of being overwhelmed by clinical learning and ineffective coping. Proactive measures should be taken to prevent poor health outcomes.展开更多
Stress studies frequently utilize physical stressors to establish animal models of stress. In the majority of cases, these models are not consistent with human circumstances. The present study simulated a social isola...Stress studies frequently utilize physical stressors to establish animal models of stress. In the majority of cases, these models are not consistent with human circumstances. The present study simulated a social isolation plus resident intruder stress model in the rat. The rats were subjected to daily social isolation and resident intruder stress for 2 weeks. Behaviors were then tested. Rats subjected to social stress exhibited different aggressive behavior styles; some rats had greater scores on composite aggression behaviors, as well as locomotor and exploratory activity, but lower scores on latency than others. The high-aggressive group exhibited predominantly anger-out, while the low-aggressive group exhibited anger-in. Results suggest that social isolation plus resident intruder may serve as an appropriate model for anger-in and anger-out emotion modeling in the rat.展开更多
基金the National Basic Research Program of China(No.2005CB623705)
文摘The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.
基金Project(CDJZR14130006)supported by the Fundamental Research Funds for the Central Universities,China
文摘The hot deformation behavior of 20 Mn Ni Mo low carbon alloy was investigated by isothermal compression tests over wide ranges of temperature(1223-1523 K) and strain rate(0.01-10 s^(-1)). According to the experimental true stress-true strain data, the constitutive relationships were comparatively studied based on the Arrhenius-type model, Johnson-Cook(JC) model and artificial neural network(ANN), respectively. Furthermore, the predictability of the developed models was evaluated by calculating the correlation coefficient(R) and mean absolute relative error(AARE). The results indicate that the flow stress behavior of 20 Mn NiM o low carbon alloy is significantly influenced by the strain rate and deformation temperature. Compared with the Arrhenius-type model and Johnson-Cook(JC) model, the ANN model is more efficient and has much higher accuracy in describing the flow stress behavior during hot compressing deformation for 20 Mn Ni Mo low carbon alloy.
基金Funded by the Nuclear Power Major Project(No.2011zx06004-002)
文摘Total strain controlled cyclic test was performed on 316 LN under uniaxial loadings. Through the partitioning of hysteresis loops, the evolution of two components of cyclic flow stress, the internal and effective stresses, was reported. The former one determines the cyclic stress response. Based on the transmission electron microscopic（TEM） observation on specimens loaded with scheduled cycles, it is found that planar dislocation structures prevail during the entire cyclic process at low strain amplitude, while a remarkable dislocation rearrangement from planar structures to heterogeneous spatial distributions is companied by a cyclic softening behavior at high strain amplitude. The competition between the evolution of the intergranular and the intragranular components of the internal stress caused by the transition of slip mode induces the cyclic hardening and softening at high strain levels. The intergranular internal stress represents the most part of the internal stress at low strain level.
基金financially supported by the Technology Area Fund of the Basic Strengthening Program(No.2021-JCJQ-JJ-0092)the Science Center for Gas Turbine Project(Project No.P2022-C-Ⅳ-002-001)+2 种基金the Defense Industrial Technology Development Program(No.JCKY2020130C024)the National Key R&D Program of China(Grant No.2021YFB3702503)the National Science and Tech-nology Major Project(No.Y2019-VII-0011-0151).
文摘A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition(DED)was applied to investigate the microstructure evolution,stress rupture behavior,and deformation mech-anisms at moderate-high temperatures and high-low stress conditions.The high Ta/Al ratio induces large misfit lattice stress and low stacking fault energy of alloy,resulting in approximate cubicγ′phases in dendrites and the formation of initial dislocation tangles.After the stress rupture test at 760℃/780 MPa,high content cubicγ′phases,small size of voids as well as preserved dislocation tangles are observed,showing stable structures with high-stress rupture resistance.High content and suitable size of cubicγ′phases,initial dislocation tangles,and L-C locks hinder the dislocation motion,which decreases the minimum strain rate and prolongs life significantly,forming four stress rupture stages.Hence,the defor-mation mechanism is determined by dislocation piled-up onγ/γ′interface,formation of stacking faults inγ′phases,and dislocations shearingγ′phases.However,the microstructure exhibits uneven struc-tures composed of large sizes of raftedγ′phases and voids at 980℃/260 MPa.The rafted structure and high temperature provide continuous channels and enough energy for dislocation motion,resulting in the increase of minimum strain rate,decline of life,and typic three stress rupture stages,even though there are obstacles to dislocation movement caused by dislocation networks.The deformation mecha-nism transforms to form dislocation networks onγ/γ′interface and dislocations shearingγ′phases.Be-sides,the decomposition of carbides on GBs also depends on temperature,which decomposes into harm-ful chain-like M23 C6 carbides at moderate temperatures and reinforced granular-shaped M6 C carbides at high temperatures.The applied stress always decreases mechanical properties due to its degradation of microstructure induced by elongating the precipitates and defects.
基金financially supported by the Key Project of International Cooperation from the Chinese Ministry of Science and Technology(2010DFA31790)the China National Natural Science Foundation of China(51136002)China Key Technologies R&D Program(2012BAJ02B03)
文摘Objective To investigate the relationship between atopic allergy and depression and the role of DBP in the development of depression. Methods BALB/c mice were randomly divided into eight groups：saline;ovalbumin （OVA）-immunized;saline＋DBP （0.45 mg/kg·183;d）; saline＋DBP （45 mg/kg·d）; DBP （0.45 mg/kg·d） OVA-immunized; DBP （45 mg/kg·d） OVA-immunized; saline＋hydrocortisone （30 mg/kg·d）; and hydrocortisone （30 mg/kg·d）-exposed OVA-immunized. Behavior （e.g. open-field, tail suspension, and forced swimming tests）, viscera coefficients （brain and spleen）, oxidative damage [e.g. reactive oxygen species （ROS）, malondialdehyde （MDA）, and glutathione （GSH）], as well as levels of IgE and IL-4, were then analyzed. Results In the saline and OVA groups, the degree of depression symptoms in mice increased with increasing DBP concentration. Additionally, the OVA-immunity groups were associated with more serious depressive behavior compared with the same exposure concentration in the saline group. Oxidative damage was associated with a dose-dependent increase in DBP in the different groups. IL-4 and IgE levels were associated with low-dose DBP stimulation, which changed to high-dose inhibition with increasing DBP exposure, possibly due to spleen injury seen at high DBP concentrations.Conclusion Development of an atopic allergy has the potential to increase the risk of depression in mice, and it seems that DBP helps OVA to exert its effect in our present model. Moreover, the results of our study implicate a certain connection between brain oxidative stress and depression, which deserves a further exploration.
基金Project(50275068) supported by the National Natural Science Foundation of China
文摘Laser shock processing is a very new technique and an emerging modern process that generates compressive stresses much deeper into the surfaces of metals or alloys. A brief parametric study of the effect of laser parameters on fatigue behavior and residual stress state generated in 6061-T651 alloy specimens was summarized. Residual stress of 6061-T651 alloy was analyzed both before and after laser processing with multishocks. The material remains in compressive residual stress of approximate 1mm in depth which is approximately 10 times deeper than that can be achieved with the conventional technique, and the maximal compressive residual stress at the surface of the sample is about -350MPa. Near the surface, yield strength and hardness are found to be increased by the laser shock. The ratio of fatigue crack initiation life for the laser-shocked to unshocked specimens is found to be 4.9 for specimens. The results clearly show that LSP is an effective surface treatment technique for improving the fatigue performance of aluminum alloys.
基金supported by the Fundamental Research Funds for the Central Universities of China University of Mining and Technology(No.2014ZDPY21)
文摘This study proposes a novel approach to study stress field distribution and overlying ground pressure behavior in shallow seam mining in gully terrain.This approach combines numerical simulations and field tests based on the conditions of gully terrain in the Chuancao Gedan Mine.The effects of gully terrain on the in situ stress field of coal beds can be identified by the ratio of self-weight stress to vertical stress(η) at the location corresponding to the maximum vertical stress.Based on the function η =j(h),the effect of gully terrain on the stress field of overlying strata of the entire field can be characterized as a significantly affected area,moderately affected area,or non-affected area.Working face 6106 in the Chuancao Gedan Mine had a coal bed Jepth <80 m and was located in what was identified as a significantly affected area.Hence,mining may cause sliding of the gully slope and increased loading(including significant dynamic loading) on the roof strata.Field tests suggest that significant dynamic pressures were observed at the body and foot of the gully slope,and that dynamic loadings were observed upslope of the working face expansion,provided that the expanding direction of the working face is parallel to the gully.
文摘Using large strain two dimension axisymmetric elasto plastic finite element method and the modified law of mixture, the effects of thermal residual stresses on the yielding behavior of short fiber reinforced metal matrix composite and their dependencies on the material structure parameters (fiber volume fraction, fiber aspect ratio and fiber end distance) were studied. It is demonstrated that the stress strain partition parameter can be used to describe the stress transfer from the matrix to the fiber. The variation of the second derivation of the stress strain partition parameter can be used to determine the elastic modulus, the proportion limit, the initial and final yield strengths. In the presence of thermal residual stress, these yielding properties are asymmetric and are influenced differently by the material structure parameters under tensile and compressive loadings.
基金the National Natural Science Foundation of China(Nos.51375364,51575372)Doctor Funds of Taiyuan University of Science and Technology(No.20202004)。
文摘Long-lasting constant loading commonly exists in silicon-based microelectronic contact and can lead to the appearance of plastic deformation.Stress relaxation behaviors of monocrystalline silicon coated with amorphous SiO_(2)film during nanoindentation are probed using molecular dynamics simulation by varying the indenter’s size.The results show that the indentation force(stress)declines sharply at the initial and decreases almost linearly toward the end of holding for tested samples.The amount of stress relaxation of SiO_(2)/Si samples indented with different indenters during holding increases with growing indenter size,and the corresponding plastic deformation characteristics are carefully analyzed.The deformation mechanism for confined amorphous SiO_(2)film is depicted based on the amorphous plasticity theories,revealing that the more activated shear transformation zones(STZs)and free volume within indented SiO_(2)film promote stress relaxation.The phase transformation takes place to monocrystalline silicon,the generated atoms of Si-II and bct-5 phases within monocrystalline silicon substrate during holding are much higher than those for smaller indenter.
文摘This study aims to clarify what kinds of resilience and coping strategies students employ to successfully complete their clinical practicum and provide suggestions for instruction that will allow students to carry out effective learning activities. The study subjects were 86 students enrolled at Nursing University A for the 2019 school year and planning to take the integrated nursing practicum. The survey was conducted using an anonymous, self-administered questionnaire. The Wilcoxon signed-rank test was used to determine the amount of change in resilience factors from the surveys before and after the practicum. Subsequently, multiple regression analysis was carried out with stress coping behaviors that were significantly associated with resilience factors in univariate analysis as independent variables and the amount of change in resilience factors before and after the practicum as dependent variables. A total of 56 responses were received (response rate 65.8%) from the 85 survey subjects. Innate resilience factors increased significantly from 41 pre-practicums to 44 post-practicums. Acquired resilience factors also increased significantly from 32 pre-practicums to 35 post-practicums (p < 0.01). The results of multiple regression analysis found that the stress coping behavior of “changing point of view” (β = 0.361, p < 0.01) and pre-practicum innate resilience factors (β = <span style="white-space:nowrap;">−</span>0.456, p < 0.01) were significantly associated with innate resilience factors. Examining the relationship between the amount of change in student resilience and stress coping behaviors revealed that the stress coping behavior of “changing point of view” was associated with innate resilience. This finding suggests that resilience may be increased by changing one’s perspective on an event by taking on a new way of thinking. The results suggested that helping students transform realizations made during reflection into learning and create a sense of meaning may lead to fostering innate resilience during integrated nursing practicums.
文摘The kinetics of water absorption in water-borne anticorrosive urethane/epoxy coatings, which were actually introduced in the industrial field, are studied. It is found that the high water affinity of a water-borne coating supports a higher saturated water content, Mχ, and helps to facilitate absorption D. The three parameters of stretched exponential function called the William-Watt equation, Eo, τ, and β, are determined to fit the degraded stress relaxation behavior in the water absorption process because this function quantitatively describes the relaxing ability and has been successfully used by a number of researchers. An increasing in the water content is shown to correlate strongly with a decrease in Eo and fl early in the absorption process between Mt/M（χ） = 0 and Mt/Mχ≈ 0.5. The adhesive characteristics of the coatings are correlated with water content, and shown to exhibit higher cohesive failure in coating epoxies under saturated conditions. This suggests that water interferes with the intermolecular bonding between polymer chains which degrades the bulk materials ability to diffuse stress concentrations and reduces its overall strength.
基金supported by the National Natural Science Foundation of China(Grant Nos.61504050 and 11604124)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK20140168 and BK20150158)the Fundamental Research Funds for the Central Universities,China(Grant Nos.JUSRP51628B and JUSRP51510)
文摘The progressive current degradation and breakdown behaviors of GaN-based light emitting diodes under high reversebias stress are studied by combining the electrical, optical, and surface morphology characterizations. The current features a typical “soft breakdown” behavior, which is linearly correlated to an increase of the accumulative number of electroluminescence spots. The time-to-failure for each failure site approximately obeys a Weibull distribution with slopes of about 0.67 and 4.09 at the infant and wear-out periods, respectively. After breakdown, visible craters can be observed at the device surface as a result of transient electrostatic discharge. By performing focused ion beam cuts coupled with scan electron microscope, we observed a local current shunt path in the surface layer, caused by the rapid microstructure deterioration due to significant current heating effect, consistent well with the optical beam induced resistance change observations.
基金Foundation items： This study was supported by the Ministry of Science and Technology of China Grant （2012CB825500） and the Youth Innovation Promotion Association of Chinese Academy of Sciences （2012075）
文摘Stress from dominance ranks in human societies, or that of other social animals, especially nonhuman primates, can have negative influences on health. Individuals holding different social status may be burdened with various stress levels. The middle class experiences a special stress situation within the dominance hierarchy due to its position between the higher and lower classes. Behaviorally, questions about where middle-class stress comes from and how individuals adapt to middle-class stress remain poorly understood in nonhuman primates. In the present study, social interactions, including aggression, avoidance, grooming and mounting behaviors, between beta males, as well as among group members holding higher or lower social status, were analyzed in captive male-only cynomolgus monkey groups. We found that aggressive tension from the higher hierarchy members was the main origin of stress for middle- class individuals. However, behaviors such as attacking lower hierarchy members immediately after being the recipient of aggression, as well as increased avoidance, grooming and mounting toward both higher and lower hierarchy members helped alleviate middle-class stress and were particular adaptations to middle-class social status.
文摘Cadmium (Cd) exposure can induce acute lethal health-related threats to humans since it has an exceptional ability to accumulate in living organisms and cause toxicological effects. Curcumin (Cur) on the other hand has a wide variety of biological activities and several animal studies have suggested for a potential therapeutic or preventive effects against several ailments and infections. To study the effect of Cur on the toxicity of Cd, sixty Swiss-Webster strain male mice were divided into 6 groups of ten each at random. Group-1 served as the na?ve control and received no treatment. Group-2, 3 and 4 were the experimental controls and were administered once a day with a single oral dose of 50% dimethyl sulphoxide (DMSO), Cur (300 mg/kg) or Cd (100 mg/kg) respectively, for 2 weeks. Group-5 and 6 received Cur and Cd in combination once a day orally for 2 weeks except that Cur in a dose of 150 and 300 mg/kg to group 5 and 6 respectively, was administered one hour before Cd (100 mg/kg) administration to both groups. After treatment period, the animals were subjected to behavioral tests and thereafter, the animals were sacrificed for the estimation of neurotransmitters like serotonin (5-HT), dopamine (DA) and it’s metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) as well as oxidative stress enzymes like lipid peroxides in the form of thiobarbituric acid–reactive substances (TBARS) and total glutathione (GSH) in the forebrain tissue. Cd reduced significantly the body weight gain, the locomotor activity, anxiety behavior in the plus maze and the learning capability (cognitive effect) in the shuttle-box test. Biochemical analysis further revealed that Cd exposure significantly altered the brain neurotransmitters and the oxidative stress enzymes. However, administration of Cur along with Cd had an ameliorating effect on all the behavioral and biochemical parameters studied herein and reduced the toxicity of Cd significantly and dose-dependently. Thus, Cur may be beneficial for anxiety, neuromuscular, and cognitive problems and protect from Cd intoxication.
基金financially supported by the National Natural Science Foundation of China (No. 51475295)
文摘The conventional Arrhenius-type model was adopted to identify the deformation characteristic of Ti6 A14 V(TC4) titanium alloy based on the stress-strain curves of isothermal compression test. A new flow stress model based on Arrhenius equation was proposed for TC4,which is composed of peak flow stress(PFS) prediction and strain compensation. The predicted PFS is set as a reference to derive the flow stress model at any strain ranging from approximately 0 to 0.7. The predictability and efficiency among the proposed model, conventional model,and an existing physical-based model of TC4 were comparatively evaluated. It is found that the newly proposed model can simultaneously track the hardening and softening behaviors of TC4 through a single expression while the other existing models are only valid in the softening region.Besides, the wider application range and acceptable accuracy of the new model have been achieved by fewer material constants with much-simplified modeling procedure than the other models.
基金Supported by the West Region Communication Construction Technology Project of the Ministry of Communications (2009318000001)the National Natural Science Foundation of China (50808187)
文摘The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.
文摘Objective: To investigate the effects of cognitive behavioral intervention on psychological stress response in breast cancer patients by cognitive behavioral intervention in breast cancer patients. Methods: Adopting the random comparison method, 100 patients with breast cancer were divided into comparison group and intervention group by 50 cases. The intervention group underwent cognitive behavioral intervention at the same time as the comparison group only received conventional treatment without cognitive behavioral intervention. Two groups of breast cancer patients were enrolled in the general questionnaire, the Self-Rating Anxiety Scale (SAS), and the Medical Coping Modes Questionnaire (MCMQ) within one week after admission and one month after treatment to understand the psychological stress levels of the two groups. Results: There was no significant difference in the scores of SAS and MCMQ between the intervention group and the comparison group before intervention (P > 0.05). But after intervention, the scores of SAS and MCMQ in the comparison group were significantly higher than those in the intervention group (P 0.05). It shows that the implementation of cognitive behavioral intervention therapy for breast cancer patients has the effect of improving their psychological status. Conclusion: Cognitive behavioral intervention therapy combined with psychology for breast cancer patients can effectively reduce their stress level, improve mental health status and improve their positive coping ability.
文摘Objective: To evaluate the effects of prenatal and postnatal stress on the sexual behavior of rats. Methods: Thirty-two 2-month-old male Wistar rats were divided as follows: the EG Group (comprised of 10 rats whose mothers underwent gestational stress), the EO Group (11 rats subjected to postnatal stress), and the SE Group (control group, comprised of 11 animals that went through no stress whatsoever). Upon reaching adulthood, these male rates were introduced to females and had their sexual behavior assessed based on the number of mounts. Results: The animals from the EP Group showed significantly fewer mounts (74 ± 24.77, p < 0.05) when compared to those from the EG (108.9 ± 35.27) and SE (99.6 ± 20.76) Groups. Conclusion: The rats that underwent stress during the first days of life mated fewer times than those whose mothers were subjected to stress during pregnancy. The latter had their sexual behavior unaltered.
文摘Nursing students are facing more and more stress in their course of study especially in clinical practicum. The study aimed to predict nursing students’ stress level in clinical practicum with coping behaviors. It was a retrospective cross-sectional study conducting in a self-financing institution in Hong Kong. Nursing students who were studying the pre-registration baccalaureate nursing program and completed all the practicum blocks were recruited. Those who had extended the study and failed any of the practicum blocks were excluded. Convenience sampling was used to recruit subjects. Participants were required to fill out the demographic sheet, COPE Inventory and Assessment of Stress among Nursing Students scale during lecture at the commencement of a semester. The whole data collection lasted for 30 minutes. Stepwise multiple regression was used to do the modeling with p-value being set at 0.05. 131 eligible nursing students were recruited with about half of female students. The regression model accounted for 50% of the variance in the perceived stress level. Gender, focus on and venting of emo-tions, restraint, use of emotional social support and denial were positively associated with perceived stress level (R squared = 0.52, p = 0.001). It is to conclude that nurse educators can refer to the findings to screen out students with higher risk of being overwhelmed by clinical learning and ineffective coping. Proactive measures should be taken to prevent poor health outcomes.
基金the National Natural Science Foundation of China,No.30973688the National Program of Key Basic Research Project(973Program),No.2006CB504804
文摘Stress studies frequently utilize physical stressors to establish animal models of stress. In the majority of cases, these models are not consistent with human circumstances. The present study simulated a social isolation plus resident intruder stress model in the rat. The rats were subjected to daily social isolation and resident intruder stress for 2 weeks. Behaviors were then tested. Rats subjected to social stress exhibited different aggressive behavior styles; some rats had greater scores on composite aggression behaviors, as well as locomotor and exploratory activity, but lower scores on latency than others. The high-aggressive group exhibited predominantly anger-out, while the low-aggressive group exhibited anger-in. Results suggest that social isolation plus resident intruder may serve as an appropriate model for anger-in and anger-out emotion modeling in the rat.
