Steady-state fracture toughness of elastic-plastic solids: Isotropic versus kinematic hardening

The fracture toughness for a mode I/II crack propagating in a ductile material has been subject to numerous investigations. However, the influence of the material hardening law has received very limited attention, with isotropic hardening being the default choice if cyclic loads are absent. The present work extends the existing studies of monotonic mode I/II steady-state crack propagation with the goal to compare the predictions from an isotropic hardening model with that of a kinematic hardening model. The work is conducted through a purpose-built steady-state framework that directly delivers the steady-state solution. In order to provide a fracture criterion, a cohesive zone model is adopted and embedded at the crack tip in the steady-state framework, while a control algorithm for the far-field, that significantly reduces the number of equilibrium iterations is employed to couple the far-field loading to the correct crack tip opening. Results show that the steady-state fracture toughness (shielding ratio) obtained for a kinematic hardening material is larger than for the corresponding isotropic hardening case. The difference between the isotropic and kinematic model is tied to the nonproportional loading conditions and reverse plasticity. This also explains the vanishing difference in the shielding ratio when considering mode II crack propagation as the non-proportional loading is less pronounced and the reverse plasticity is absent

Increased isobutanol production in Saccharomyces cerevisiae by overexpression of genes in valine metabolism

<p>Abstract</p> <p>Background</p> <p>Isobutanol can be a better biofuel than ethanol due to its higher energy density and lower hygroscopicity. Furthermore, the branched-chain structure of isobutanol gives a higher octane number than the isomeric <it>n</it>-butanol. <it>Saccharomyces cerevisiae </it>was chosen as the production host because of its relative tolerance to alcohols, robustness in industrial fermentations, and the possibility for future combination of isobutanol production with fermentation of lignocellulosic materials.</p> <p>Results</p> <p>The yield of isobutanol was improved from 0.16 to 0.97 mg per g glucose by simultaneous overexpression of biosynthetic genes <it>ILV2, ILV3</it>, and <it>ILV5 </it>in valine metabolism in anaerobic fermentation of glucose in mineral medium in <it>S. cerevisiae</it>. Isobutanol yield was further improved by twofold by the additional overexpression of <it>BAT2</it>, encoding the cytoplasmic branched-chain amino-acid aminotransferase. Overexpression of <it>ILV6</it>, encoding the regulatory subunit of Ilv2, in the <it>ILV2 ILV3 ILV5 </it>overexpression strain decreased isobutanol production yield by threefold. In aerobic cultivations in shake flasks in mineral medium, the isobutanol yield of the <it>ILV2 ILV3 ILV5 </it>overexpression strain and the reference strain were 3.86 and 0.28 mg per g glucose, respectively. They increased to 4.12 and 2.4 mg per g glucose in yeast extract/peptone/dextrose (YPD) complex medium under aerobic conditions, respectively.</p> <p>Conclusions</p> <p>Overexpression of genes <it>ILV2, ILV3, ILV5</it>, and <it>BAT2 </it>in valine metabolism led to an increase in isobutanol production in <it>S. cerevisiae</it>. Additional overexpression of <it>ILV6 </it>in the <it>ILV2 ILV3 ILV5 </it>overexpression strain had a negative effect, presumably by increasing the sensitivity of Ilv2 to valine inhibition, thus weakening the positive impact of overexpression of <it>ILV2, ILV3</it>, and <it>ILV5 </it>on isobutanol production. Aerobic cultivations of the <it>ILV2 ILV3 ILV5 </it>overexpression strain and the reference strain showed that supplying amino acids in cultivation media gave a substantial improvement in isobutanol production for the reference strain, but not for the <it>ILV2 ILV3 ILV5 </it>overexpression strain. This result implies that other constraints besides the enzyme activities for the supply of 2-ketoisovalerate may become bottlenecks for isobutanol production after <it>ILV2, ILV3</it>, and <it>ILV5 </it>have been overexpressed, which most probably includes the valine inhibition to Ilv2.</p

Effect of temperature and water activity on the production of fumonisins by Aspergillus niger and different Fusarium species

<p>Abstract</p> <p>Background</p> <p>Fumonisins are economically important mycotoxins which until recently were considered to originate from only a few <it>Fusarium </it>species. However recently a putative fumonisin gene cluster was discovered in two different <it>Aspergillus niger </it>strains followed by detection of an actual fumonisin B₂(FB₂) production in four strains of this biotechnologically important workhorse.</p> <p>Results</p> <p>In the present study, a screening of 5 <it>A. niger </it>strains and 25 assumed fumonisin producing <it>Fusarium </it>strains from 6 species, showed that all 5 <it>A. niger </it>strains produced FB₂and 23 of 25 <it>Fusarium </it>produced fumonisin B₁and other isoforms (fumonisin B₂and B₃). Five <it>A. niger </it>and five <it>Fusarium </it>spp. were incubated at six different temperatures from 15-42°C on Czapek Yeast Agar +5% salt or Potato Dextrose Agar. <it>A. niger </it>had the highest production of FB₂at 25-30°C whereas <it>Fusarium </it>spp. had the maximal production of FB₁and FB₂at 20-25°C. Addition of 2.5-5% NaCl, or 10-20% sucrose increased the FB₂production of <it>A. niger</it>, whereas addition of glycerol reduced FB₂production. All three water activity lowering solutes reduced the fumonisin production of the <it>Fusarium </it>species.</p> <p>Conclusion</p> <p>The present study shows that the regulation of fumonisin production is very different in <it>A. niger </it>and <it>Fusarium</it>, and that food and feeds preserved by addition of sugar or salts may be good substrates for fumonisin B₂production by <it>A. niger</it>.</p

Reply to Jensen, O.K. On the Use of Quantitative Sensory Testing to Estimate Central Sensitization in Humans. Comment on "Schuttert et al. The Definition, Assessment, and Prevalence of (Human Assumed) Central Sensitisation in Patients with Chronic Low Back Pain: A Systematic Review. J. Clin. Med. 2021, 10, 5931":A Systematic Review. J. Clin. Med. 2021, 10, 5931"

We thank Dr. Jensen for his interest [...]

Technologies for restricting mould growth on baled silage

End of project reportSilage is made on approximately 86% of Irish farms, and 85% of these make some baled silage. Baled silage is particularly important as the primary silage making, storage and feeding system on many beef and smaller sized farms, but is also employed as a secondary system (often associated with facilitating grazing management during mid-summer) on many dairy and larger sized farms (O’Kiely et al., 2002). Previous surveys on farms indicated that the extent of visible fungal growth on baled silage was sometimes quite large, and could be a cause for concern. Whereas some improvements could come from applying existing knowledge and technologies, the circumstances surrounding the making and storage of baled silage suggested that environmental conditions within the bale differed from those in conventional silos, and that further knowledge was required in order to arrive at a secure set of recommendations for baled silage systems. This report deals with the final in a series (O’Kiely et al., 1999; O’Kiely et al., 2002) of three consecutive research projects investigating numerous aspect of the science and technology of baled silage. The success of each depended on extensive, integrated collaboration between the Teagasc research centres at Grange and Oak Park, and with University College Dublin. As the series progressed the multidisciplinary team needed to underpin the programme expanded, and this greatly improved the amount and detail of the research undertaken. The major objective of the project recorded in this report was to develop technologies to improve the “hygienic value” of baled silage

Phaeobacter gallaeciensis Reduces Vibrio anguillarum in Cultures of Microalgae and Rotifers, and Prevents Vibriosis in Cod Larvae

Phaeobacter gallaeciensis can antagonize fish-pathogenic bacteria in vitro, and the purpose of this study was to evaluate the organism as a probiont for marine fish larvae and their feed cultures. An in vivo mechanism of action of the antagonistic probiotic bacterium is suggested using a non-antagonistic mutant. P. gallaeciensis was readily established in axenic cultures of the two microalgae Tetraselmis suecica and Nannochloropsis oculata, and of the rotifer Brachionus plicatilis. P. gallaeciensis reached densities of 107 cfu/ml and did not adversely affect growth of algae or rotifers. Vibrio anguillarum was significantly reduced by wild-type P. gallaeciensis, when introduced into these cultures. A P. gallaeciensis mutant that did not produce the antibacterial compound tropodithietic acid (TDA) did not reduce V. anguillarum numbers, suggesting that production of the antibacterial compound is important for the antagonistic properties of P. gallaeciensis. The ability of P. gallaeciensis to protect fish larvae from vibriosis was determined in a bath challenge experiment using a multidish system with 1 larva per well. Unchallenged larvae reached 40% accumulated mortality which increased to 100% when infected with V. anguillarum. P. gallaeciensis reduced the mortality of challenged cod larvae (Gadus morhua) to 10%, significantly below the levels of both the challenged and the unchallenged larvae. The TDA mutant reduced mortality of the cod larvae in some of the replicates, although to a much lesser extent than the wild type. It is concluded that P. gallaeciensis is a promising probiont in marine larviculture and that TDA production likely contributes to its probiotic effect

Utilising thermal annealing for multiplexing and sensitivity enhancement of polymer optical fibre sensors

Thermal annealing was initially introduced for multiplexing purposes, since it can induce a permanent negative Bragg wavelength shift for polymer fibre grating sensors. At a later stage, it is shown that annealing can also provide additional benefits, such as strain and humidity sensitivity enhancement and augmented temperature operational range. In this paper, we report additional usage of thermal annealing on PMMA fibre Bragg grating sensors. We show the possibility to tune Bragg wavelengths to longer wavelengths permanently by stretching the polymer optical fibre during the thermal annealing process. An array of sensors fabricated with only one phase-mask, demonstrates the concept by having Bragg wavelengths below and above the original inscribed spectral position. In addition, we report that thermal annealing can be also used to enhance the performance of sensors when used for stress and force monitoring