Modelling Impact Damage in Sandwich Structures with Folded Composite Cores

The paper describes FE simulation methods for novel folded structural composite cores being developed for sandwich structures with enhanced performance for use in aircraft fuselage and wing primary structures. To support these materials and structural developments, computational methods were developed in the EU project CELPACT based on micromechanics cell models of the core with multiscale FE modelling techniques for understanding progressive damage and collapse mechanisms. The paper discusses the computational models and applies them to analyse the structural integrity of the advanced cellular core sandwich structures under impact load conditions relevant to aircraft structures

Local volume conservation in concentrated electrolytes is governing charge transport in electric fields

While ion transport processes in concentrated electrolytes, e.g. based on ionic liquids (IL), are a subject of intense research, the role of conservation laws and reference frames is still a matter of debate. Employ-ing electrophoretic NMR, we show that momentum conservation, a typical prerequisite in molecular dynamics (MD) simulations, is not governing ion transport. Involving density measurements to deter-mine molar volumes of distinct ion species, we propose that conservation of local molar species volumes is the governing constraint for ion transport. The experimentally quantified net volume flux is found as zero, implying a non-zero local momentum flux, as tested in pure ILs and IL-based electrolytes for a broad variety of concentrations and chemical compositions. This constraint is consistent with incom-pressibility, but not with a local application of momentum conservation. The constraint affects the calcu-lation of transference numbers as well as comparisons of MD results to experimental findings

A volume-based description of transport in incompressible liquid electrolytes and its application to ionic liquids

Transference numbers play an important role in understanding the dynamics of electrolytes and assessing their performance in batteries. Unfortunately, these transport parameters are difficult to measure in highly concentrated liquid electrolytes such as ionic liquids. Also, the interpretation of their sign and magnitude has provoked an ongoing debate in the literature further complicated by the use of different languages. In this work, we highlight the role of the reference frame for the interpretation of transport parameters using our novel thermodynamically consistent theory for highly correlated electrolytes. We argue that local volume conservation is a key principle in incompressible liquid electrolytes and use the volume-based drift velocity as a reference. We apply our general framework to electrophoretic NMR experiments. For ionic liquid based electrolytes, we find that the results of the eNMR measurements can be best described using this volume-based description. This highlights the limitations of the widely used center-of-mass reference frame which for example forms the basis for molecular dynamics simulations – a standard tool for the theoretical calculation of transport parameters. It shows that the assumption of local momentum conservation is incorrect in those systems on the macroscopic scale

From bulk thermodynamics to Nano-structuring near electrified interfaces: a continuum transport theory for ionic liquids incorporating solvation effects

Theoretical studies and simulations are efficient means for the evaluation of materials and for improving the design of electrochemical devices. Here, we present a thermodynamically consistent transport theory of ionic liquids (ILs) and IL-based electrolytes. Our continuum approach offers a holistic framework for the description of highly correlated electrolytes both in the bulk phase and near electrified interfaces, thus spanning a wide range of length-scales from cell-level (micrometers) to microscopic interactions (nanometers). Our transport theory is based on the framework of rational thermodynamics, which couples nonequilibrium thermodynamics with mechanics and elements from electromagnetic theory. Material specific properties are cast into our description via modeling the Helmholtz free energy. This approach yields a consistent description for effects occurring on different length scales. In addition, we use an Onsager Ansatz to obtain the thermodynamic fluxes, and to identify the set of independent transport parameters. Our bulk description comprises the transport mechanisms of diffusion, migration and convection, and predicts the evolution of the electrolyte species. We validated this description by applying it to a secondary zinc ion battery described in the literature, where the simulation results for charging and discharging the cell are in good agreement with the experimental results. From the numerical results we obtain a detailed understanding of the internal dynamics of each electrolyte species during discharging the cell, as well as the influence of enhanced discharge dynamics on the electrolyte performance. In addition, in a joint theoretical and experimental collaboration, we applied our framework to electrophoretic NMR experiments of pure ILs and IL-salt mixtures. Thereby, we rationalized the influence of the reference frame on the sign and magnitude of transference numbers, and clarified the role of convection in incompressible electrolytes. In order to describe highly charged regions in confined geometries, e.g. the EDL, we supplement the bulk description by non-local ion interactions. Thereby we identify three competing energy scales, related to short-ranged ion-correlations (accounting for excluded volume of hardcore ions), to the thermal energy, and to the electrostatic energy of Coulombic interactions, which determine the equilibrium structure of the EDL. We predict the emergence of three screening-phases, consisting either of a saturation-profile (“crowding”) followed by an exponentially decay towards the bulk, a profile of damped oscillations (“overscreening”), and a crystalline phase of undamped oscillations. Our description yields an analytical prediction for the key parameters of the screening, i.e. the damping ratio and the frequency of the oscillations, and for the phase boundaries between the different screening phases. In a joint experimental/theoretical publication, we validated this theoretical approach with AFM experiments. Furthermore, our multiscale methodology relates directly to the methodology used by atomistic models like molecular dynamics simulations, and comprises the seminal BSK theory as limiting case. In addition, we study the influence of a charged and uncharged solvent species on the screening profile and incorporate solvation effects into our description

System-wide analyses of the fission yeast poly(A)+ RNA interactome reveal insights into organization and function of RNA–protein complexes

Large RNA-binding complexes play a central role in gene expression and orchestrate production, function, and turnover of mRNAs. The accuracy and dynamics of RNA–protein interactions within these molecular machines are essential for their function and are mediated by RNA-binding proteins (RBPs). Here, we show that fission yeast whole-cell poly(A)+ RNA–protein crosslinking data provide information on the organization of RNA–protein complexes. To evaluate the relative enrichment of cellular RBPs on poly(A)+ RNA, we combine poly(A)+ RNA interactome capture with a whole-cell extract normalization procedure. This approach yields estimates of in vivo RNA-binding activities that identify subunits within multiprotein complexes that directly contact RNA. As validation, we trace RNA interactions of different functional modules of the 3′ end processing machinery and reveal additional contacts. Extending our analysis to different mutants of the RNA exosome complex, we explore how substrate channeling through the complex is affected by mutation. Our data highlight the central role of the RNA helicase Mtl1 in regulation of the complex and provide insights into how different components contribute to engagement of the complex with substrate RNA. In addition, we characterize RNA-binding activities of novel RBPs that have been recurrently detected in the RNA interactomes of multiple species. We find that many of these, including cyclophilins and thioredoxins, are substoichiometric RNA interactors in vivo. Because RBPomes show very good overall agreement between species, we propose that the RNA-binding characteristics we observe in fission yeast are likely to apply to related proteins in higher eukaryotes as well

Spliceosome-mediated decay (SMD) regulates expression of nonintronic genes in budding yeast

We uncovered a novel role for the spliceosome in regulating mRNA expression levels that involves splicing coupled to RNA decay, which we refer to as spliceosome-mediated decay (SMD). Our transcriptome-wide studies identified numerous transcripts that are not known to have introns but are spliced by the spliceosome at canonical splice sites in Saccharomyces cerevisiae. Products of SMD are primarily degraded by the nuclear RNA surveillance machinery. We demonstrate that SMD can significantly down-regulate mRNA levels; splicing at canonical splice sites in the bromodomain factor 2 (BDF2) transcript reduced transcript levels roughly threefold by generating unstable products that are rapidly degraded by the nuclear surveillance machinery. Regulation of BDF2 mRNA levels by SMD requires Bdf1, a functionally redundant Bdf2 paralog that plays a role in recruiting the spliceosome to the BDF2 mRNA. Interestingly, mutating BDF2 5' splice site and branch point consensus sequences partially suppresses the bdf1Δ temperature-sensitive phenotype, suggesting that maintaining proper levels of Bdf2 via SMD is biologically important. We propose that the spliceosome can also repress protein-coding gene expression by promoting nuclear turnover of spliced RNA products and provide an insight for coordinated regulation of Bdf1 and Bdf2 levels in the cell