Optimal Design of Multiple Stresses Accelerated Life Test Plan Based on Transforming the Multiple Stresses to Single Stress

For planning optimum multiple stresses accelerated life test plans, a commonly followed guiding principle is that all parameters of the life-stress relationship should be estimated, and the number of the stress level combinations must be no less than the number of parameters of the life-stress relationship. However, the general objective of an accelerated life test（ALT） is to assess thep-th quantile of the product life distribution under normal stress. For this objective,estimating all model parameters is not necessary, and this will increase the cost of test. Based on the theoretical conclusion that the stress level combinations of the optimum multiple stresses ALT plan locate on a straight line through the origin of coordinate, it is proposed that a design idea of planning the optimum multiple stresses ALT plan through transforming the problem of designing an optimum multiple stresses ALT plan to designing an optimum single stress ALT plan. Moreover, a method of planning the optimum multiple stresses ALT plan which can avoid estimating all model parameters is established. An example shows that, the proposed plan which only has two stress level combinations could achieve an accuracy no less than the traditional plan, and save the test time and cost on one stress level combination at least; when the actual product life is less than the design value, even the deviation of the model initial parameters value is up to 20%, the variance of the estimation of thep-th quantile of the proposed plan is still smaller than the traditional plans approximately 25%. A design method is provided for planning the optimum multiple stresses ALT which uses the statistical optimum degenerate test plan as the optimum multiple stresses accelerated life test plan.

Increasing concentrations of dietary threonine,tryptophan,and glycine improve growth performance and intestinal health with decreasing stress responses in broiler chickens raised under multiple stress conditions

The current study aimed to compare the effects of increasing concentrations of dietary threonine(Thr),tryptophan(Trp),and glycine(Gly)on growth performance,stress biomarkers,and intestinal function in broiler chickens under multiple stress conditions.Five hundred sixty broiler chickens at 21 d old were randomly allotted to 5 treatments with 8 replicates.Birds in a positive control(PC)treatment were raised under low stock density(16.9 birds/m^(2) per cage)with recommended environmental conditions,whereas birds in 4 treatments were subjected to multiple stress conditions:a cyclic heat stress of 30±0.3℃ for 10 h and 23±0.2℃ for 14 h per day with high stock density(25.3 birds/m^(2) per cage).A basal diet was assigned to both PC and negative control(NC)treatments.Three additional diets were individually formulated to contain double concentrations of digestible Thr,Trp,or Gly+Ser compared with their concentrations in the basal diet.The experiment lasted for 14 d.Results showed that NC treatment had less growth performance(P<0.001),jejunal goblet cell counts(P=0.018),and trans-epithelial electrical resistance(TEER;P<0.001),but greater(P=0.026)feather corticosterone(CORT)concentrations than PC treatment.Thr treatment showed the least(P<0.001)feed conversion ratio(FCR)among treatments under multiple stress conditions.Thr,Trp,and Gly treatments had less(P=0.026)feather CORT concentrations,but had greater(P<0.001)TEER than NC treatment.In conclusion,increasing concentrations of dietary Thr,Trp,or Gly improve the growth performance and intestinal health in broiler chickens with decreasing stress response under multiple stress conditions.

Effects of chronic multiple stress on learning and memory and the expression of Fyn,BDNF,TrkB in the hippocampus of rats

Background The effect of chronic stress on cognitive functions has been one of the hot topics in neuroscience. But there has been much controversy over its mechanism. The aim of this study was to investigate the effects of chronic multiple stress on spatial learning and memory as well as the expression of Fyn, BDNF and TrkB in the hippocampus of rats. Methods Adult rats were randomly divided into control and chronic multiple stressed groups. Rats in the multiple stressed group were irregularly and alternatively exposed to situations of vertical revolution, sleep expropriation and restraint lasting for 6 weeks, 6 hours per day with night illumination for 6 weeks. Before and after the period of chronic multiple stresses, the performance of spatial learning and memory of all rats was measured using the Morris Water Maze （MWM）. The expression of Fyn, BDNF and TrkB proteins in the hippocampus was assayed by Western blotting and immunohistochemical methods. The levels of Fyn and TrkB mRNAs in the hippocampus of rats were detected by RT-PCR technique. Results The escape latency in the control group and the stressed group were 15.63 and 8.27 seconds respectively. The performance of spatial learning and memory of rats was increased in chronic multiple stressed group （P〈0.05）. The levels of Fyn, BDNF and TrkB proteins in the stressed group were higher than those of the control group （P〈0.05）. The results of immunoreactivity showed that Fyn was present in the CA3 region of the hippocampus and BDNF positive particles were distributed in the nuclei of CA1 and CA3 pyramidal cells as well as DG granular cells. Quantitative analysis indicated that level of Fyn mRNA was also upregulated in the hippocampus of the stressed group （P〈0.05）. Conclusions Chronic multiple stress can enhance spatial learning and memory function of rats. The expression of Fyn, BDNF and TrkB proteins and the level of Fyn mRNA are increased in the stessed rat hippocampus. These suggest that Fyn and BDNF/TrkB signal transduction pathways may participate in the process of the enhanced learning and memory durina chronic multiple stress.

INTEGRAL EQUATION METHOD'S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.

Evaluation of rutting performance of stone matrix asphalt mixtures containing warm mix additives

Permanent deformation or rutting, one of the most important distresses in flexible pavements, has long been a problem in asphalt mixtures and thus a great deal of research has been focused on the development of a rheological parameter that would address the rutting susceptibility of both unmodified and modified bituminous binders. In this research, three warm mix additives(Sasobit, Rheofalt and Zycotherm) were used to modify 60-70 penetration grade base binder. The rutting potential of both modified and unmodified binders were evaluated through the multiple stress creep recovery(MSCR)-based parameter, nonrecoverable compliance(Jnr) and recovery parameter(R). Several performance tests carried on stone matrix asphalt(SMA) mixtures comprising different nominal maximum aggregate sizes(NMASs, 9.5, 12.5 and 19 mm), like Marshall stability, dynamic and static creep and Hamburg wheel tracking tests to evaluate their rutting performance. The objective of this work is to correlate MSCR test results to performance. Results indicate that for the range of the gradations investigated in this work, increasing the nominal maximum aggregate size of the gradation would increase the permanent deformation resistance of the SMA mixture. Addition of 3% sasobit to base binder leads an increase in Jnr100 about 82%. Addition of 2% rheofalt to base binder leads an recovery increase of about 9.76 % and 27.44% in stress levels of 100 and 3200 Pa, respectively. The results reveal that rutting resistance of mixtures improves as Jnr decreases. The use of the MSCR test in the rutting characterization of bituminous binders is highly recommended based on the results of this work.

Differential manifestation of RONS and antioxidant enzymes in response to singular versus combinatorial stress in Chironomus ramosus

In nature,organisms face multiple abiotic stress concurrently.Our previous study has indicated how threshold level of lethality depends on the type and combination of stressors.Many mechanisms exist by which organisms respond to stressors and maintain homeostasis.We examined the homeostatic pliability in an extremophilic oriental midge Chironomus ramosus larvae under various combinatorial stress conditions of desiccation(DS),heat(HS)and starvation(SS).Exposure to these stressors led to activation of a common response pathway of oxidative stress.Abundance of antioxidant enzymes like superoxide dismutase,catalase,glutathione reductase and glutathione peroxidase along with selective as well as stressor specific increase in total antioxidant capacity were reflected from the corresponding level of reactive oxygen and nitrogen species(RONS)in larvae exposed to various combinatorial stress.Additionally,we found stressor specific increment in lipid peroxidation level,protein carbonyl content and advanced oxidative protein products during the stress regime.Further investigation revealed a sharp decline in the activity of mitochondrial aconitase enzyme activity in response to abiotic stress induced oxidative stress.The combinatorial stressor specific comparative study based on biochemical and fluorescence based redox-endpoint assays confirmed that the generation of oxidative stress is the consequential convergent pathway of DS,HS and SS,but the quantum of RONS decides the redox potential of homeostatic response and survival rate.

Cowpea NAC1/NAC2 transcription factors improve growth and tolerance to drought and heat in transgenic cowpea through combined activation of photosynthetic and antioxidant mechanisms

NAC(NAM/ATAF1/2/CUC2)transcription factors are central switches of growth and stress responses in plants.However,unpredictable interspecies conservation of function and regulatory targets makes the well-studied NAC orthologs inapt for pulse engineering.The knowledge of suitable NAC candidates in hardy pulses like cowpea(Vigna unguiculata(L.)Walp.)is still in infancy,hence warrants immediate biotechnological intervention.Here,we showed that overexpression of two native NAC genes(VuNAC1and VuNAC2)promoted germinative,vegetative,and reproductive growth and conferred multiple abiotic stress tolerance in a commercial cowpea variety.The transgenic lines displayed increased leaf area,thicker stem,nodule-rich denser root system,early flowering,higher pod production(~3.2-fold and~2.1-fold),and greater seed weight(10.3%and 6.0%).In contrast,transient suppression of VuNAC1/2 caused severe growth retardation and flower inhibition.The overexpressor lines showed remarkable tolerance to major yielddeclining terminal stresses,such as drought,salinity,heat,and cold,and recovered growth and seed production by boosting photosynthetic activity,water use efficiency,membrane integrity,Na^(+)/K^(+)homeostasis,and antioxidant activity.The comparative transcriptome study indicated consolidated activation of genes involved in chloroplast development,photosynthetic complexes,cell division and expansion,cell wall biogenesis,nutrient uptake and metabolism,stress response,abscisic acid,and auxin signaling.Unlike their orthologs,VuNAC1/2 direct synergistic transcriptional tuning of stress and developmental signaling to avoid unwanted trade-offs.Their overexpression governs the favorable interplay of photosynthesis and reactive oxygen species regulation to improve stress recovery,nutritional sufficiency,biomass,and production.This unconventional balance of strong stress tolerance and agronomic quality is useful for translational crop research and molecular breeding of pulses.

Molecular mechanisms of plant adaptation to acid soils: A review

Acid soils are widespread and limit global plant production.Aluminum(Al)/manganese(Mn)toxicity and phosphorus(P)deficiency are the major limiting factors affecting plant growth and productivity on acid soils.Plants,however,have evolved various strategies to adapt to these stresses.These strategies include using both external and internal mechanisms to adapt to Al toxicity,regulating Mn uptake,translocation,and distribution to avoid Mn toxicity,and orchestrating a set of P transport mechanisms to efficiently take up P from the soil.Here,we review the current state of knowledge about the molecular mechanisms of plant adaptation to these constraints in acid soils,focusing on the roles of transporters involved in Al/Mn tolerance and P efficiency.Gene manipulation combined with other biotechnology will contribute to the development of novel strategies to improve plant adaptation to acid soils.The molecular mechanisms of plant coadaptation to multiple stresses in acid soils are largely unknown and require further investigation.