The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.

Ultrafast laser processing of transparent materials supported by in-situ diagnostics

For the development of industrial NIR ultrafast laser processing of transparent materials, the absorption inside the bulk material has to be controlled. Applications we aim for are front and rear side ablation, drilling and inscription of modifications for cleaving and selective laser etching of glass and sapphire in sheet geometry. We applied pump probe technology and in situ stress birefringence microscopy for fundamental studies on the influence of energy and duration (100 fs – 20 ps), temporal and spatial spacing, focusing and beam shaping of the laser pulses. Applying pump probe technique we are able to visualize differences of spatio-temporal build up of absorption, self focusing, shock wave generation for standard, multispot and beam shaped focusing. Incubation effects and disturbance of beam propagation due to modifications or ablation can be observed. In-situ imaging of stress birefringence gained insight in transient build up of stress with and without translation. The results achieved so far, demonstrate that transient stress has to be taken into account in scaling the laser machining throughput of brittle materials. Furthermore it points out that transient stress birefringence is a good indicator for accumulation effects, supporting tailored processing strategies.Cutting results achieved for selective laser etching by single pass laser modification exemplifies the benefits of process development supported by in situ diagnostics.

Experimental and Modeling Studies on the Stress Relaxation Behaviour of Ti-6Al-4V Alloy

The transient mechanical behavior of materials during stress relaxation has evoked interest in manufacturing applications because of the effect of stress relaxation on formability enhancement. However, most of the previous studies have focused on advanced high strength steels and aluminum alloys. Limited transient stress relaxation studies have been conducted on titanium alloys in order to understand the influence of stress relaxation on forming behavior. Titanium alloys are widely used in aerospace components because of their high strength to weight ratios and excellent fatigue strengths. However, room temperature formability of Ti alloys is an important concern, which restricts their widespread use in various applications. To address these challenges, the present study is aimed to understand the role of transient stress relaxation on formability of Ti alloys. Toward this end, stress relaxation of a dual phase titanium alloy (Ti-6Al-4V) has been investigated experimentally. Stress relaxation tests were performed by interrupting uniaxial tensile tests in the uniform deformation regime for a pre-defined strain and hold time after which tests were continued monotonically until fracture. Single step, room temperature stress relaxation experiments were performed systematically to study the effect of hold time, pre-strain, and strain rate on mechanical properties. The stress relaxation phenomenon was found to contribute positively to the ductility improvement. The mechanisms responsible for enhancing the formability are discussed. The experimentally obtained stress vs. time data were analyzed using a advanced constitutive model for stress relaxation available in literature.

Characterization and Expression Profiling of Glutathione Peroxidase 1 gene (GPX1) and Activity of GPX in Onychostoma macrolepis suffered from Thermal Stress

In this study, full-length cDNA of glutathione peroxidases 1 (GPX1) of Onychostoma macrolepis was cloned by RACE, and expression of GPX1 and activity of GPX in O. macrolepis suffered from heat stress were analyzed. Compared with the control group (24°C), the experimental fish were stressed for 0, 1, 3, 6, 12, 24, and 48 hours at the heated water (30°C). Liver had highest level and response speed in GPX1 expression among various tissues after heat stress, indicated that liver was the highest sensitive tissue to heat stress. When the water was raised to the heating temperature (30°C), the GPX activity decreased in fish serum, and the consumption of GPX eliminated the increase of ROS caused by heat stress within 3h. However, after 6h and 12h stress at 30°C, GPX activity was significantly higher than that at 0h (P<0.05), which is due to the rapid response of GPX to heat stress. In summary, fish showed a transient stress response and was acclimated to the new temperature after 24 h according to the overall expression of the GPX1 and the serum GPX activity, and both GPX1 and GPX play crucial roles in this process.

Impact of Heat Transfer on Transient Stress Fields in Power Plant Boiler Components

In boilers operating in modern power plants, thick-walled elements of complex shapes, such as valves, superheater headers, T-pipes, Y-pipes, four-way pipes, and elbows, are especially prone to fatigue processes. Higher operation parameters and more frequent startups may speed up fatigue damage in these elements. Such damage is a local phenomenon and is caused by thermomechanical fatigue (TMF). This paper presents a method designed for predicting the behavior of components subjected to variable temperature and mechanical loading conditions. This method combines the results of measurements of operating parameters of devices under industrial conditions with those obtained using finite element modeling (FEM). Particular attention was given to the influence of the time-dependent heat transfer coefficient on the local thermomechanical stress–strain behavior of the material. It was stated that heat transfer conditions have a significant impact on local transient stresses and depend on the operation parameters of boilers. Consistency of the temperature changes as a function of time, determined in industrial conditions and calculated on the basis of the model approach, was obtained. This developed and described in the work approach enables defining the conditions of heat transfer on the surface of models of considered components.

Changes in rearfoot strike patterns over childhood

Rearfoot strike (RFS) in children running produces impact forces that give rise to a transient stress wave traveling through the body. It could contribute to the development of injuries. The purpose of this study was to determine RFS prevalence during childhood while running at a self-selected velocity in a prospective longitudinal cohort study. A total of 175 children (68 girls), aged 6 to 14 years, participated in this study. The sample was divided into three age groups (age in 2016): 6-8 years, 9-11 years, and 12-14 years which were analysed three years later (2019). 2D video-based was used to record the RFS Taking into account all samples, in the jogging trial the prevalence of RFS (an average of both feet) was 86.9% in 2016 and 94.7% three years later; in the running trial the prevalence was 82.6 and 94.4%, respectively. In all samples a significant increase of RFS prevalence was found in both the jogging and running trials for both feet over three years (jogging, left foot, p=.011, right foot, p=.023; running, left foot, p=.001, right foot, p&lt;.001). In girls, there were no significant differences in any conditions. In boys, a significant increase of RFS prevalence was found after three years in both feet (p&lt;.01) in the running trial. This study shows that RFS prevalence in children increases with age and the results may be used to characterize typical running development in children population.

Thermal strength of retention compartment interacting with exhaust gas

The thermal strength of the retention compartment is calculated to analyze the possibility of multiple use for a rocket start. The transient heat field of the retention compartment, which is induced by the interaction of the exhaust gas with the retention compartment, is analyzed. The part of the retention compartment undergoes significant heat action with a high-temperature gradient when the rocket is started. This heat action essentially changes in time. This leads to the generation of significant transient stress fields. The aim of the present paper is the calculation of the maximal values of stresses induced by the heat field. We analyze the stress state induced by the steady-state heat field. This field corresponds to the transient heat field at the time when the maximal temperature gradient is observed. The upper bound of stresses in the retention compartment is obtained by the suggested method.