04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
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Item Open Access Heat waves alter carbon allocation and increase mortality of Aleppo pine under dry conditions(2018) Birami, Benjamin; Gattmann, Marielle; Heyer, Arnd G.; Grote, Rüdiger; Arneth, Almut; Ruehr, Nadine K.Climate extremes are likely to occur more frequently in the future, including a combination of heat waves and drought. However, the responses of trees to combined stress and their post-stress recovery are not fully understood yet. Therefore, this study investigated the responses of semi-arid Pinus halepensis seedlings to moderate drought, heat and combined heat-drought stress, as well as post-stress recovery. The seedlings were grown under controlled conditions and exposed to two 4-days-long heat periods, reaching air temperature maxima of 42°C and vapor pressure deficit (VPD) of 7 kPa. Day- and nighttime canopy gas exchange was measured and differences in shoot and root allocation of non-structural carbohydrate (NSC) compounds (soluble sugars, starch, cyclitols, and carboxylic acids) assessed. Fluorescence parameters, nitrate levels, proline content and shoot water potential (ψ) provided additional indicators for stress severity and recovery performance. During the heat periods, net photosynthesis and stomatal conductance decreased immediately. This decline was modest under well-watered conditions, with transpiration and dark respiration rates remaining high and despite reductions in root NSC content, trees recovered following heat release. This was not the case in the heat-drought treatment, where stress resulted in high mortality rates and the few surviving seedlings showed reduced gas exchange rates and low root NSC content, while leaf nitrate and proline remained elevated even 3 weeks after heat release. Shoot ψ indicated that hydraulic failure was not the reason for mortality in the heat-drought seedlings. Instead, we argue that low transpiration rates, which resulted in needle temperatures >47°C during heat stress (6°C above air temperature) have caused irreversible damage. In summary, it could be demonstrated that heat waves in combination with moderate drought can either result in increased mortality or, if the seedlings survive, in delayed recovery. This highlights the potential of an increase in heat wave temperatures to trigger forest decline in semi-arid regions.Item Open Access Acoustic streaming‐induced multimodal locomotion of bubble‐based microrobots(2023) Mahkam, Nima; Aghakhani, Amirreza; Sheehan, Devin; Gardi, Gaurav; Katzschmann, Robert; Sitti, MetinAcoustically‐driven bubbles at the micron scale can generate strong microstreaming flows in its surrounding fluidic medium. The tunable acoustic streaming strength of oscillating microbubbles and the diversity of the generated flow patterns enable the design of fast‐moving microrobots with multimodal locomotion suitable for biomedical applications. The acoustic microrobots holding two coupled microbubbles inside a rigid body are presented; trapped bubbles inside the L‐shaped structure with different orifices generate various streaming flows, thus allowing multiple degrees of freedom in locomotion. The streaming pattern and mean streaming speed depend on the intensity and frequency of the acoustic wave, which can trigger four dominant locomotion modes in the microrobot, denoted as translational and rotational, spinning, rotational, and translational modes. Next, the effect of various geometrical and actuation parameters on the control and navigation of the microrobot is investigated. Furthermore, the surface‐slipping multimodal locomotion, flow mixing, particle manipulation capabilities, the effective interaction of high flow rates with cells, and subsequent cancerous cell lysing abilities of the proposed microrobot are demonstrated. Overall, these results introduce a design toolbox for the next generation of acoustic microrobots with higher degrees of freedom with multimodal locomotion in biomedical applications.Item Open Access In situ laboratory for plastic degradation in the Red Sea(2022) Brümmer, Franz; Schnepf, Uwe; Resch, Julia; Jemmali, Raouf; Abdi, Rahma; Kamel, Hesham Mostafa; Bonten, Christian; Müller, Ralph-WalterDegradation and fragmentation of plastics in the environment are still poorly understood. This is partly caused by the lack of long-term studies and methods that determine weathering duration. We here present a novel study object that preserves information on plastic age: microplastic (MP) resin pellets from the wreck of the SS Hamada, a ship that foundered twenty-nine years ago at the coast of Wadi el Gemal national park, Egypt. Its sinking date enabled us to precisely determine how long MP rested in the wreck and a nearby beach, on which part of the load was washed off. Pellets from both sampling sites were analyzed by microscopy, X-ray tomography, spectroscopy, calorimetry, gel permeation chromatography, and rheology. Most pellets were made of low-density polyethylene, but a minor proportion also consisted of high-density polyethylene. MP from inside the wreck showed no signs of degradation compared to pristine reference samples. Contrary, beached plastics exhibited changes on all structural levels, which sometimes caused fragmentation. These findings provide further evidence that plastic degradation under saltwater conditions is comparatively slow, whereas UV radiation and high temperatures on beaches are major drivers of that process. Future long-term studies should focus on underlying mechanisms and timescales of plastic degradation.