Experimental Calibration of a Numerical Model of Prepreg Tack for Predicting AFP Process Related Defects

Wrinkles, puckers, and fiber bridging are among the major defects encountered in the Automated Fiber Placement (AFP) process, and are all different manifestations of fiber misalignment. The main driver for these defects are the residual stresses introduced in the tow during the deposition stage by the AFP head. In contrast, the tack between the deposited tape and the substrate is the resisting force against the formation of such defects. Tack may be defined as the ability of a material to form a bond immediately on contact with another surface. Tack is a very complex phenomenon that is influenced by a variety of process parameters including temperature, head pressure and speed, as well as degree of cure, moisture content, and surface roughness A physics-based modeling framework for simulation of tack was developed in this study that allows for prediction of tack response. The developed tack model is incorporated in the AFP placement modelling framework developed to simulate AFP defects

Tack Measurements of Prepreg Tape at Variable Temperature and Humidity

NASAs Advanced Composites Project has established the goal of achieving a 30 percent reduction in the timeline for certification of primary composite structures for application on commercial aircraft. Prepreg tack is one of several critical parameters affecting composite manufacturing by automated fiber placement (AFP). Tack plays a central role in the prevention of wrinkles and puckers that can occur during AFP, thus knowledge of tack variation arising from a myriad of manufacturing and environmental conditions is imperative for the prediction of defects during AFP. A full design of experiments was performed to experimentally characterize tack on 0.25-inch slit-tape tow IM7/8552-1 prepreg using probe tack testing. Several process parameters (contact force, contact time, retraction speed, and probe diameter) as well as environmental parameters (temperature and humidity) were varied such that the entire parameter space could be efficiently evaluated. Mid-point experimental conditions (i.e., parameters not at either extrema) were included to enable prediction of curvature in relationships and repeat measurements were performed to characterize experimental error. Collectively, these experiments enable determination of primary dependencies as well as multi-parameter relationships. Slit-tape tow samples were mounted to the bottom plate of a rheometer parallel plate fixture using a jig to prevent modification of the active area to be interrogated with the top plate, a polished stainless steel probe, during tack testing. The probe surface was slowly brought into contact with the pre-preg surface until a pre-determined normal force was achieved (2-30 newtons). After a specified dwell time (0.02-10 seconds), during which the probe substrate interaction was maintained under displacement control, the probe was retracted from the surface (0.1-50 millimeters per second). Initial results indicated a clear dependence of tack strength on several parameters, with a particularly strong dependence on temperature and humidity. Although an increase in either of these parameters reduces tack strength, a maximum in tack was predicted to occur under conditions of low temperature and moderate humidity

Fluorinated Tags to Study Protein Conformation and Interactions Using 19F NMR

The incorporation of fluorine atoms into a biomacromolecule provides a background-free and environmentally sensitive reporter of structure, conformation and interactions using 19F NMR. There are several methods to introduce the 19F reporter – either by synthetic incorporation via solid phase peptide synthesis; by suppressing the incorporation or biosynthesis of a natural amino acid and supplementing the growth media with a fluorinated counterpart during protein expression; and by genetic code expansion to add new amino acids to the amino acid alphabet. This review aims to discuss progress in the field of introducing fluorinated handles into biomolecules for NMR studies by post-translational bioconjugation or ‘fluorine-tagging’. We will discuss the range of chemical tagging ‘warheads’ that have been used, explore the applications of fluorine tags, discuss ways to enhance reporter sensitivity and how the signal to noise ratios can be boosted. Finally, we consider some key challenges of the field and offer some ideas for future directions

Increases in plasma sheet temperature with solar wind driving during substorm growth phases

During the substorm growth phase, magnetic reconnection extracts ~10^15 J from the solar wind through magnetic reconnection at the magnetopause, which is then stored in the magnetotail lobes. Plasma sheet pressure then increases to balance magnetic flux density increases in the lobes. We examine plasma sheet pressure, density and temperature during substorm growth phases using nine years of Cluster data (>316,000 data points). We show that plasma sheet pressure and temperature are higher during growth phases with higher solar wind driving whereas the density is approximately constant. We also show a weak correlation between plasma sheet temperature before onset and the minimum SuperMAG SML auroral index in the subsequent substorm. We discuss how energization of the plasma sheet before onset may result from thermodynamically adiabatic processes; how hotter plasma sheets may result in magnetotail instabilities and how this relates to the onset and size of the subsequent substorm expansion phase

A new tool for the chemical genetic investigation of the Plasmodium falciparum Pfnek-2 NIMA-related kinase

Background: Examining essential biochemical pathways in Plasmodium falciparum presents serious challenges, as standard molecular techniques such as siRNA cannot be employed in this organism, and generating gene knock-outs of essential proteins requires specialized conditional approaches. In the study of protein kinases, pharmacological inhibition presents a feasible alternative option. However, as in mammalian systems, inhibitors often lack the desired selectivity. Described here is a chemical genetic approach to selectively inhibit Pfnek-2 in P. falciparum, a member of the NIMA-related kinase family that is essential for completion of the sexual development of the parasite. Results: Introduction of a valine to cysteine mutation at position 24 in the glycine rich loop of Pfnek-2 does not affect kinase activity but confers sensitivity to the protein kinase inhibitor 4-(6-ethynyl-9H-purin-2-ylamino) benzene sulfonamide (NCL-00016066). Using a combination of in vitro kinase assays and mass spectrometry, (including phosphoproteomics) the study shows that this compound acts as an irreversible inhibitor to the mutant Pfnek2 likely through a covalent link with the introduced cysteine residue. In particular, this was shown by analysis of total protein mass using mass spectrometry which showed a shift in molecular weight of the mutant kinase in the presence of the inhibitor to be precisely equivalent to the molecular weight of NCL-00016066. A similar molecular weight shift was not observed in the wild type kinase. Importantly, this inhibitor has little activity towards the wild type Pfnek-2 and, therefore, has all the properties of an effective chemical genetic tool that could be employed to determine the cellular targets for Pfnek-2. Conclusions: Allelic replacement of wild-type Pfnek-2 with the mutated kinase will allow for targeted inhibition of Pfnek-2 with NCL-00016066 and hence pave the way for comparative studies aimed at understanding the biological role and transmission-blocking potential of Pfnek-2. © 2016 The Author(s)

Hydrology in the 21st century : challenges in science, to policy and practice

To mark the 40th anniversary of the British Hydrological Society, a landmark Discussion Meeting was held at the Royal Society in June 2024, bringing together a transdisciplinary community, including hydrologists, policymakers and practitioners, to reflect on four decades of progress and chart future directions for hydrology. This special issue presents a collection of papers from that meeting, addressing advances in data, modelling, forecasting and decision-making in the context of intensifying climate and hydrological extremes. Key themes include the need for open, reproducible science, greater integration of machine learning, AI and convection-permitting models and a shift towards transdisciplinary, co-produced knowledge that better supports adaptation, resilience and policy impact. The issue highlights the critical roles of education, collaboration and equity in shaping a hydrology that is not only technically advanced but socially and environmentally responsive to the challenges of the 21st century. This article is part of the discussion meeting issue ‘Hydrology in the 21st century: challenges in science, to policy and practice’

19F NMR-tags for peptidyl prolyl conformation analysis

Proline cis/trans isomerism plays an important role in protein folding and mediating protein–protein interactions in short linear interacting motifs within intrinsically disordered protein regions. The slow exchange rate between cis and trans prolyl bonds provides distinct signals in 19F NMR analysis of fluorinated peptides, allowing for simple quantification of each population. However, fluorine is not naturally found in proteins but can be introduced using chemical tags. In this study, we evaluate a range of fluorinated cysteine-reactive 19F NMR tags to assess their ability to react with short, linear proline-containing peptides and accurately report on the equilibrium cis/trans-Pro populations. Several fluorinated electrophilic tags, including nitrobenzenes, sulfonylpyrimidines, and acrylamides, were found to react chemoselectively and reliably report on the %cis-Pro in the model peptide Ac-LPAAC. Other 19F NMR tags were found to be poor reporters of local proline conformation. Although pentafluoropyridine was non-chemoselective, it still reliably reported on %cis-Pro when conjugated via cysteine or tyrosine in Ac-LPAAX (X = Cys, Tyr, Lys) peptides. 3,4-Difluoronitrobenzene was found to be compatible with protein tagging, albeit it had modest reactivity and afforded a pair of regioisimeric tagging-products when reacted with a cysteine mutant of α-synuclein. These tools may be valuable for probing cis/trans-Pro populations in proteins