Fractographic study of transverse cracks in a fibre composite

Transverse fracture of unidirectional fibre composites was studied in a model glass/epoxy composite in which 1 mm-diameter rods had been used in place of fibres. The fracture surface resulting from transverse cracking in this model system was studied by scanning electron microscopy (SEM). The interaction of the crack with the epoxy matrix resin and the glass rods was the following: Cracks in the resin appeared to have effected a debonding at the glassmatrix interface before reaching the glass. The debonding then propagated along the interface and induced secondary cracks ahead of the primary debonding crack. The confluence of the secondary and primary cracks resulted in sharp ridges being formed on the matrix resin surface, produced by plastic deformation of the rigid epoxy resin. These appeared as a field of parabolic marks. Considering the brittleness of the resin, the amount of plastic deformation indicated by the ridges was astonishing. As the debonding continued around the glass rod, a transverse corrugated texture developed on the resin surface, again produced by plastic deformation. Finally, the cracks reentered the matrix from small patches of polymer adhering especially strongly to the glass surface. The overall fracture energy of transverse cracking of unidirectional fibre composites is suggested to consist, therefore, of the following elements in addition to crack propagation in the matrix resin: (a) the glass-resin debonding before the incoming cracks reach the glass, (b) the initiation of secondary cracks or debonds at the interface, (c) the plastic deformation in generating the ridges on the rigid resin surface, appearing both as the paraboloids and the transverse corrugation, and (d) cracking of the matrix reinitiated at the opposite side of the glass. The use of an enlarged glass reinforcement in this study provided a more direct observation of the properties of transverse crack propagation in composite materials than would have been possible with the small, roughly 10 μ m fibres.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44691/1/10853_2005_Article_BF01111915.pd

Facile Synthesis, Geometry, and 2′-Substituent-Dependent in Vivo Activity of 5′‑(<i>E</i>)- and 5′‑(<i>Z</i>)‑Vinylphosphonate-Modified siRNA Conjugates

(<i>E</i>)-Vinylphosphonate ((<i>E</i>)-VP), a metabolically stable phosphate mimic at the 5′-end of the antisense strand, enhances the in vivo potency of siRNA. Here we describe a straightforward synthetic approach to incorporate a nucleotide carrying a vinylphosphonate (VP) moiety at the 5′-end of oligonucleotides under standard solid-phase synthesis and deprotection conditions by utilizing pivaloyloxymethyl (POM) protected VP-nucleoside phosphoramidites. The POM protection enhances scope and scalability of 5′-VP-modified oligonucleotides and, in a broader sense, the synthesis of oligonucleotides modified with phosphonate moieties. Trivalent <i>N</i>-acetylgalactosamine-conjugated small interfering RNA (GalNAc-siRNA) comprising (<i>E</i>)-geometrical isomer of VP showed improved RISC loading with robust RNAi-mediated gene silencing in mice compared to the corresponding (<i>Z</i>)-isomer despite similar tissue accumulation. We also obtained structural insights into why bulkier 2′-ribosugar substitutions such as 2′-<i>O</i>-[2-(methylamino)-2-oxoethyl] are well tolerated only when combined with 5′-(<i>E</i>)-VP

Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies

The standard Λ Cold Dark Matter (ΛCDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant H0, the σ8–S8 tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the 5.0σ tension between the Planck CMB estimate of the Hubble constant H0 and the SH0ES collaboration measurements. After showing the H0 evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density Ωm, and the amplitude or rate of the growth of structure (σ8,fσ8). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the H0–S8 tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questions