During their lifespan, plants respond to a multitude of stressful factors. Dynamic changes in chromatin and concomitant transcriptional variations control stress response and adaptation, with epigenetic memory mechanisms integrating environmental conditions and appropriate developmental programs over the time. Here we analyzed transcriptome and genome‐wide histone modifications of maize plants subjected to a mild and prolonged drought stress just before the flowering transition. Stress was followed by a complete recovery period to evaluate drought memory mechanisms. Three categories of stress‐memory genes were identified: i) “transcriptional memory” genes, with stable transcriptional changes persisting after the recovery; ii) “epigenetic memory candidate” genes in which stress‐induced chromatin changes persist longer than the stimulus, in absence of transcriptional changes; iii) “delayed memory” genes, not immediately affected by the stress, but perceiving and storing stress signal for a delayed response. This last memory mechanism is described for the first time in drought response. In addition, applied drought stress altered floral patterning, possibly by affecting expression and chromatin of flowering regulatory genes. Altogether, we provided a genome‐wide map of the coordination between genes and chromatin marks utilized by plants to adapt to a stressful environment, describing how this serves as a backbone for setting stress memory.
The most common mechanical equipment adopted in the new generation of pumped-hydro power plants is represented by reversible pump-turbines, required to rapidly switch between pumping and generating modes in order to balance the frequent changes in electricity production and consumption caused by unpredictable renewable energy sources. As a consequence, pump-turbines are required to extend their operation under off-design conditions in unstable operating areas.\ud
The paper presents a numerical analysis of the unstable behavior of a pump-turbine operating in turbine mode near the no-load condition. To study in depth the unsteady phenomena which lead to the S-shape of the turbine characteristic, a load rejection scenario at constant and large guide vane opening was numerically analyzed by running through the flow-speed characteristic up to the turbine brake region.\ud
The flow field analysis led to the onset and development of unsteady phenomena progressively evolving in an organized rotating stall (65.1% of the runner rotation frequency) during the turbine brake operation. These phenomena were characterized by frequency and time-frequency analyses of several numerical signals (static pressure, blade torque, mass flow rate in blade passages). \ud
The influence of the development of these unsteady phenomena on the pump-turbine performance in a turbine operation was also analyzed, and the potential causes that generated the S-Shaped characteristic curve were also investigated
Self-start capability is an important feature of wind turbines. It allows to obtain simpler and cheaper\ud
turbines not actively controlled. Different approaches to describe the self-start of an H-blade Darrieus\ud
rotor are presented and compared in the present work. The Blade Element Momentum (BEM) approach\ud
was compared with two and three-dimensional CFD simulations. The tipespeed ratio versus power\ud
coefficient curves and the evolution of the trust forces over a blade revolution highlighted the limits and\ud
the strengths of each approach.\ud
The BEM model showed remarkable limits to describe to describe the self-start behaviour of the tested\ud
geometry. The principal limits of the BEM approach can be ascribed to the absence of well documented\ud
aerofoil databases for low Reynolds number and the inadequate modelling of dynamics effects. The 2D\ud
simulation allowed to highlight the unsteady features of the flow fields, and the presence of a complex\ud
vortices pattern which interact with the blade. Furthermore the comparison between 2D and 3D data\ud
demonstrated the importance of 3D effects such as secondary flows and tip effects. These effects were\ud
proved to have a positive effect on start-up, increasing the torque characteristic for tipespeed ratio of 1.\ud
The start-up capability of H-Darrieus appears to be influenced by many different factors, which include\ud
secondary flows, three-dimensional aerodynamic effects and the finite aspect-ratio of the blades
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