In multicellular organisms, a long-standing question is how spatial patterns of distinct cell types are initiated and maintained during continuous cell division and proliferation. Along the vertical axis of plant shoot apical meristems (SAMs), stem cells are located at the top while cells specifying the stem cells are located more basally, forming a robust apical-basal pattern. We previously found that in Arabidopsis SAMs, the HAIRY MERISTEM (HAM) family transcription factors form a concentration gradient from the epidermis to the interior cell layers, and this gradient is essential for the stem cell specification and the apical-basal patterning of the SAMs. Here, we uncover that epidermis specific transcription factors, ARABIDOPSIS THALIANA MERISTEM LAYER 1 (ATML1) and its close homolog, define the concentration gradient of HAM in the SAM through activating a group of microRNAs. This study provides a molecular framework linking the epidermis-derived signal to the stem cell homeostasis in plants.

Despite the huge expansion of electric vehicle sales in the market, customers are discouraged by the possible catastrophic consequences brought by the safety issues of lithium-ion batteries, such as internal...

With the increasing number of electric vehicles, inevitable crash accidents, vibration and foreign objective penetration potentially generate catastrophic consequences such as fire or explosion. Unlike traditional engineering materials or structures, LIBs exhibit multiphysical behaviors including mechanical deformation/failure, thermal conduction, series of electrochemical and chemical reactions, upon mechanical abusive loading. Therefore, developing computational frameworks capable of describing multiphysical behaviors of cylindrical batteries in crash safety design of electric vehicles based on commercially available platform is in pressing need. In this paper, based on the widely used LS-DYNA software platform, a multiphysics model with the comprehensive coupling of mechanical, battery, short-circuit, exothermic and thermal models are established. Models are validated by the in-house designed experiments. Further, parametric studies based on the established model demonstrates that a larger indentor leads to a later onset of internal short circuit (ISC) for LIBs but result in a higher peak battery temperature. On the other hand, an ISC will be triggered early if the compressive loading is applied near the ends of battery cells. This study provides an accessible, fast and accurate computational framework for safety design, assessment and improvement of lithium-ion batteries and electric vehicles in harsh mechanical scenarios.

More and more polymers and polymer composite materials are used in automotive industry to reduce cost and weight of vehicles to meet the environmental requirement. However, the fatigue behaviour for these materials is less understanding than metallic materials. The current work is focussed on the fatigue behaviour for a range of thermoplastic polymer/composite materials. It reveals that the fatigue behaviour of these materials can be described by S-N curves using the Basquin Equation. All the materials exhibit significant mean stress effect. The most commonly used mean stress correction equations developed in metal fatigue were evaluated with the current test results. It reveals that Goodman, Gerber and Soderberg cannot be used as generic equations for the materials investigated, whereas Smith-Watson-Topper can correlate the test data reasonably well, but the best correlation is given by Walker with material constant γ = 0.4.