Fracture in distortion gradient plasticity

In this work, distortion gradient plasticity is used to gain insight into material deformation ahead of a crack tip. This also constitutes the first fracture mechanics analysis of gradient plasticity theories adopting Nye's tensor as primal kinematic variable. First, the asymptotic nature of crack tip fields is analytically investigated. We show that an inner elastic region exists, adjacent to the crack tip, where elastic strains dominate plastic strains and Cauchy stresses follow the linear elastic stress singularity. This finding is verified by detailed finite element analyses using a new numerical framework, which builds upon a viscoplastic constitutive law that enables capturing both rate-dependent and rate-independent behaviour in a computationally efficient manner. Numerical analysis is used to gain further insight into the stress elevation predicted by distortion gradient plasticity, relative to conventional J2 plasticity, and the influence of the plastic spin under both mode I and mixed-mode fracture conditions. It is found that Nye's tensor contributions have a weaker effect in elevating the stresses in the plastic region, while predicting the same asymptotic behaviour as constitutive choices based on the plastic strain gradient tensor. A minor sensitivity to X, the parameter governing the dissipation due to the plastic spin, is observed. Finally, distortion gradient plasticity and suitable higher order boundary conditions are used to appropriately model the phenomenon of brittle failure along elastic-plastic material interfaces. We reproduce paradigmatic experiments on niobium-sapphire interfaces and show that the combination of strain gradient hardening and dislocation blockage leads to interface crack tip stresses that are larger than the theoretical lattice strength, rationalising cleavage in the presence of plasticity at bi-material interfaces

Gradient-enhanced statistical analysis of cleavage fracture

We present a probabilistic framework for brittle fracture that builds upon Weibull statistics and strain gradient plasticity. The constitutive response is given by the mechanism-based strain gradient plasticity theory, aiming to accurately characterize crack tip stresses by accounting for the role of plastic strain gradients in elevating local strengthening ahead of cracks. It is shown that gradients of plastic strain elevate the Weibull stress and the probability of failure for a given choice of the threshold stress and the Weibull parameters. The statistical framework presented is used to estimate failure probabilities across temperatures in ferritic steels. The framework has the capability to estimate the three statistical parameters present in the Weibull-type model without any prior assumptions. The calibration against experimental data shows important differences in the values obtained for strain gradient plasticity and conventional J2 plasticity. Moreover, local probability maps show that potential damage initiation sites are much closer to the crack tip in the case of gradient-enhanced plasticity. Finally, the fracture response across the ductile-to-brittle regime is investigated by computing the cleavage resistance curves with increasing temperature. Gradient plasticity predictions appear to show a better agreement with the experiments

Gradient-enhanced statistical analysis of cleavage fracture

We present a probabilistic framework for brittle fracture that builds upon Weibull statistics and strain gradient plasticity. The constitutive response is given by the mechanism-based strain gradient plasticity theory, aiming to accurately characterize crack tip stresses by accounting for the role of plastic strain gradients in elevating local strengthening ahead of cracks. It is shown that gradients of plastic strain elevate the Weibull stress and the probability of failure for a given choice of the threshold stress and the Weibull parameters. The statistical framework presented is used to estimate failure probabilities across temperatures in ferritic steels. The framework has the capability to estimate the three statistical parameters present in the Weibull-type model without any prior assumptions. The calibration against experimental data shows important differences in the values obtained for strain gradient plasticity and conventional J2 plasticity. Moreover, local probability maps show that potential damage initiation sites are much closer to the crack tip in the case of gradient-enhanced plasticity. Finally, the fracture response across the ductile-to-brittle regime is investigated by computing the cleavage resistance curves with increasing temperature. Gradient plasticity predictions appear to show a better agreement with the experiments

Effects of environmental variables on the distribution of juvenile cubomedusae Carybdea marsupialis in the coastal Western Mediterranean

[EN] Relationships between environmental factors and oscillations in jellyfish abundance, especially in the early life stages, could help to interpret past increases and also predict scenarios in a changing future. For the first time, we present cubozoan spatial and temporal distributions in the earliest stages and their relationships with different factors. Abundances ofCarybdea marsupialismedusae showed high interannual variability from 2008 to 2014 along the Denia coast (SE Spain, W Mediterranean). During 2015, samples were collected from 11 beaches along 17 km of coastline, 8 times from January to November in order to determine the effects of environmental factors on the distribution of juvenileC.marsupialis. Juveniles (<= 15 mm diagonal bell width) were present from May to July, with more sampled near shore (0-15 m). Most of them occurred in June when their numbers were unequal among beaches (average 0.05 ind m(-3), maximum 6.71 ind m(-3)). We tested distributions of juveniles over time and space versus temperature, salinity, nutrients (N, P and Si), chlorophyll-a(Chl-a), and zooplankton abundance. Temperature and cladocerans (zooplankton group) were significantly positively correlated with juvenile distribution, whereas Chl-aconcentration was weakly negative. By contrast, in 2014, high productivity areas (Chl-aand zooplankton) overlapped the maximum adult abundance (5.2 ind m(-3)). The distribution of juveniles during 2015 did not spatially coincide with the areas where ripe adults were located the previous year, suggesting that juveniles drift with the currents upon release from the cubopolyps. Our results yield important insights into the complexity of cubozoan distributions.This study has received funding through European Commission's LIFE programme [LIFE08 NAT ES64 CUBOMED.eu to C.B. from the Alicante University and V.L.F. from the Institute of Marine Science, CSIC, Spain], and from the D.G Sostenibilidad de la Costa y el Mar from the Spanish Ministry of Agriculture, Food and the Environment, the Fundacion Biodiversidad, and the D.G. Agua -Generalitat Valenciana. It has also received support from Parques Nacionales and Ajuntament de Denia. We are grateful for the collaboration of Fundació Baleària, Marina El Portet de Dénia and Marina de Dénia. This work is a contribution from the ¿Ramon Margalef¿ Environmental Research Institute (IMEM) from the University of Alicante, Spain. We are especially grateful for the sampling and laboratory support provided in the Montgó Research Station by NGO ACIF Marina Alta volunteers: Ángela Alba, Ainara Ballesteros, Miguel Escolano, Ángel Fernández, Marta Gil, Héctor Gutiérrez, Ainara Lacalle and Alba Pérez. We would also like to extend our thanks to Jordi Alventosa and Júlia Escrivá from IGIC-Polytechnic Valencia University for their contribution to nutrient analysis. Editing services were provided by Sea Pen Scientific Writing.Bordehore, C.; Fonfría, E.; Alonso, C.; Rubio-Tortosa, B.; Acevedo, M.; Canepa, A.; Falco, S.... (2020). Effects of environmental variables on the distribution of juvenile cubomedusae Carybdea marsupialis in the coastal Western Mediterranean. PLoS ONE. 15(6):1-20. https://doi.org/10.1371/journal.pone.0230768S120156Purcell, J., Uye, S., & Lo, W. (2007). Anthropogenic causes of jellyfish blooms and their direct consequences for humans: a review. Marine Ecology Progress Series, 350, 153-174. doi:10.3354/meps07093Graham, W. M., Gelcich, S., Robinson, K. L., Duarte, C. M., Brotz, L., Purcell, J. E., … Condon, R. H. (2014). Linking human well-being and jellyfish: ecosystem services, impacts, and societal responses. Frontiers in Ecology and the Environment, 12(9), 515-523. doi:10.1890/130298Cegolon, L., Heymann, W., Lange, J., & Mastrangelo, G. (2013). Jellyfish Stings and Their Management: A Review. Marine Drugs, 11(12), 523-550. doi:10.3390/md11020523Hartwick, R. F. (1991). Distributional ecology and behaviour of the early life stages of the box-jellyfish Chironex fleckeri. Hydrobiologia, 216-217(1), 181-188. doi:10.1007/bf00026460Mooney, C. J., & Kingsford, M. J. (2016). The influence of salinity on box jellyfish (Chironex fleckeri, Cubozoa) statolith elemental chemistry. Marine Biology, 163(5). doi:10.1007/s00227-016-2867-1Kingsford, M. J., Seymour, J. E., & O’Callaghan, M. D. (2012). Abundance patterns of cubozoans on and near the Great Barrier Reef. Hydrobiologia, 690(1), 257-268. doi:10.1007/s10750-012-1041-0ACEVEDO, M. J., STRAEHLER-POHL, I., MORANDINI, A. C., STAMPAR, S. N., BENTLAGE, B., MATSUMOTO, G. I., … FUENTES, V. L. (2019). Revision of the genus Carybdea (Cnidaria: Cubozoa: Carybdeidae): clarifying the identity of its type species Carybdea marsupialis. Zootaxa, 4543(4), 515. doi:10.11646/zootaxa.4543.4.3Bordehore, C., Fuentes, V. L., Atienza, D., Barberá, C., Fernandez-Jover, D., Roig, M., … Gili, J. M. (2011). Detection of an unusual presence of the cubozoan Carybdea marsupialis at shallow beaches located near Denia, Spain (south-western Mediterranean). Marine Biodiversity Records, 4. doi:10.1017/s1755267211000650Canepa, A., Fuentes, V., Bosch-Belmar, M., Acevedo, M., Toledo-Guedes, K., Ortiz, A., … Gili, J.-M. (2017). Environmental factors influencing the spatio-temporal distribution of Carybdea marsupialis (Lineo, 1978, Cubozoa) in South-Western Mediterranean coasts. PLOS ONE, 12(7), e0181611. doi:10.1371/journal.pone.0181611Acevedo MJ. Biology, ecology and ecophysiology of the box jellyfish Carybdea marsupialis (Cnidaria: Cubozoa). PhD dissertation. Universitat Politècnica de Catalunya, Barcelona. 2016.Pulis K. A preliminary study of the population, ecology and genetic characters of the Mediterranean box jellyfish (Carybdea marsupialis) in the island of Malta. MSc dissertation. University of Malta, Malta. 2015.Bordehore C. Studies on the ecology of Carybdea marsupialis (Cubozoa) and jellyfish sting risk management. PhD dissertation. Universidad de Alicante, Alicante. 2014.Straehler-Pohl, I., & Jarms, G. (2005). Life cycle of Carybdea marsupialis Linnaeus, 1758 (Cubozoa, Carybdeidae) reveals metamorphosis to be a modified strobilation. Marine Biology, 147(6), 1271-1277. doi:10.1007/s00227-005-0031-4Gordon, M., & Seymour, J. (2012). Growth, Development and Temporal Variation in the Onset of Six Chironex fleckeri Medusae Seasons: A Contribution to Understanding Jellyfish Ecology. PLoS ONE, 7(2), e31277. doi:10.1371/journal.pone.0031277Canepa, A., Purcell, J. E., Belmar, M. B., Acevedo, M., Gentile, M., & Fuentes, V. (2013). Salinity effects on asexual reproduction of Carybdea sp. (Cnidaria: Cubozoa). Journal of Plankton Research, 36(2), 585-590. doi:10.1093/plankt/fbt124Canepa A. Jellyfish of the Spanish Mediterranean coast: effects of environmental factors on their spatio-temporal dynamics and economic impacts. PhD dissertation, Universitat de Barcelona, Barcelona. 2014.Aminot A, Chaussepied M. Manuel des analyses chimiques en milieu marin. Brest: Centre national pour l’exploitation des océans; 1983.APHA, AWWA, WEF. Standard methods for the examination of water and wastewater. 22 edition. Washington: American Public Health Association; 2012.Zuur, A. F., Ieno, E. N., Walker, N., Saveliev, A. A., & Smith, G. M. (2009). Mixed effects models and extensions in ecology with R. Statistics for Biology and Health. doi:10.1007/978-0-387-87458-6Zuur, A. F., Ieno, E. N., & Smith, G. M. (2007). Analysing Ecological Data. Statistics for Biology and Health. doi:10.1007/978-0-387-45972-1Yang C, Szu-Pyng K, Fen-Bin L, Pen-Shan H. Twelve different interpolation methods: a case study of Surfer 8.0. ISPRS Congr Istanbul. 2004; 778–783.STRAEHLER-POHL, I., & JARMS, G. (2011). Morphology and life cycle of Carybdea morandinii, sp. nov. (Cnidaria), a cubozoan with zooxanthellae and peculiar polyp anatomy. Zootaxa, 2755(1), 36. doi:10.11646/zootaxa.2755.1.2Chiaverano, L. M., Holland, B. S., Crow, G. L., Blair, L., & Yanagihara, A. A. (2013). Long-Term Fluctuations in Circalunar Beach Aggregations of the Box Jellyfish Alatina moseri in Hawaii, with Links to Environmental Variability. PLoS ONE, 8(10), e77039. doi:10.1371/journal.pone.0077039Hamner, W. M., Gilmer, R. W., & Hamner, P. P. (1982). The physical, chemical, and biological characteristics of a stratified, saline, sulfide lake in Palau1. Limnology and Oceanography, 27(5), 896-909. doi:10.4319/lo.1982.27.5.0896Gordon, M. R., & Seymour, J. E. (2008). Quantifying movement of the tropical Australian cubozoan Chironex fleckeri using acoustic telemetry. Hydrobiologia, 616(1), 87-97. doi:10.1007/s10750-008-9594-7Colin, S. P., Costello, J. H., Katija, K., Seymour, J., & Kiefer, K. (2013). Propulsion in Cubomedusae: Mechanisms and Utility. PLoS ONE, 8(2), e56393. doi:10.1371/journal.pone.0056393Coates, M. M. (2003). Visual Ecology and Functional Morphology of Cubozoa (Cnidaria). Integrative and Comparative Biology, 43(4), 542-548. doi:10.1093/icb/43.4.542Garm, A., O’Connor, M., Parkefelt, L., & Nilsson, D.-E. (2007). Visually guided obstacle avoidance in the box jellyfish Tripedalia cystophora and Chiropsella bronzie. Journal of Experimental Biology, 210(20), 3616-3623. doi:10.1242/jeb.004044Lewin, R. (1986). Supply-Side Ecology. Science, 234(4772), 25-27. doi:10.1126/science.234.4772.25Marcus, N. H., & Marcus, N. H. (1998). Minireview: The importance of benthic-pelagic coupling and the forgotten role of life cycles in coastal aquatic systems. Limnology and Oceanography, 43(5), 763-768. doi:10.4319/lo.1998.43.5.0763Bordehore, C., Fuentes, V. L., Segarra, J. G., Acevedo, M., Canepa, A., & Raventós, J. (2015). Use of an Inverse Method for Time Series to Estimate the Dynamics of and Management Strategies for the Box Jellyfish Carybdea marsupialis. PLOS ONE, 10(9), e0137272. doi:10.1371/journal.pone.013727

On the suitability of slow strain rate tensile testing for assessing hydrogen embrittlement susceptibility

The onset of sub-critical crack growth during slow strain rate tensile testing (SSRT) is assessed through a combined experimental and modeling approach. A systematic comparison of the extent of intergranular fracture and expected hydrogen ingress suggests that hydrogen diffusion alone is insufficient to explain the intergranular fracture depths observed after SSRT experiments in a Ni-Cu superalloy. Simulations of these experiments using a new phase field formulation indicate that crack initiation occurs as low as 40% of the time to failure. The implications of such sub-critical crack growth on the validity and interpretation of SSRT metrics are then explored

Timing of Exposure and Bisphenol-A: Implications for Diabetes Development

Bisphenol-A (BPA) is one of the most widespread endocrine disrupting chemicals (EDCs). It is used as the base compound in the production of polycarbonate and other plastics present in many consumer products. It is also used as a building block in epoxy can coating and the thermal paper of cash register receipts. Humans are consistently exposed to BPA and, in consequence, this compound has been detected in the majority of individuals examined. Over the last decade, an enlarging body of evidence has provided a strong support for the role of BPA in the etiology of diabetes and other metabolic disorders. Timing of exposure to EDCs results crucial since it has important implications on the resulting adverse effects. It is now well established that the developing organisms are particularly sensitive to environmental influences. Exposure to EDCs during early life may result in permanent adverse consequences, which increases the risk of developing chronic diseases like diabetes in adult life. In addition to that, developmental abnormalities can be transmitted from one generation to the next, thus affecting future generations. More recently, it has been proposed that gestational environment may also program long-term susceptibility to metabolic disorders in the mother. In the present review, we will comment and discuss the contributing role of BPA in the etiology of diabetes. We will address the metabolic consequences of BPA exposure at different stages of life and comment on the final phenotype observed in different whole-animal models of study

Nuclear activity in galaxy pairs: a spectroscopic analysis of 48 UZC-BGPs

Galaxy pairs are ideal sites in which to investigate the role of interaction on nuclear activity. For this reason we have undertaken a spectroscopic survey of a large homogeneous sample of galaxy pairs (UZC-BGP) and we present the results of the nuclear spectral classification of 48 pairs (more than half of the whole sample). The fraction of emission line galaxies is extremely large, especially among spirals (84 % and 95 %, for early and late spirals respectively). SB is the most frequent type of nuclear activity encountered (30 % of galaxies) while AGNs are only 19%. The fractions raise to 45 % and 22 % when considering only spirals. Late spirals are characterized by both an unusual increase (35 %) of AGN activity and high luminosity (44 % have M_B <-20.0 + 5log h). LLAGNs are only 8% of the total number of galaxies, but this activity could be present in another 10 % of the galaxies (LLAGN candidates). Absorption line galaxies reside mostly (61 %) in S0 galaxies and display the lowest B luminosity in the sample, only 18 % of them have M_B < -20 + 5 log h, but together with LLAGNs they are the most massive galaxies in the sample. Intense-SB nuclei are found in galaxy pairs with galaxy-galaxy projected separations up to 160 h^{-1} kpc suggesting that in bright isolated galaxy pairs interaction may be at work and effective up to that distance. AGNs are characterized by an advanced morphology while SB phenomenon occurs with the same frequency in early and late spirals. LLAGNs and LLAGN candidates do not always show similar properties, a finding which might confirm the heterogeneous nature of this class of objects. Half LLAGNs are hosted in galaxies showing visible signs of interaction with fainter companions, suggesting that minor interactions might be a driving mechanism for a relevant fraction of LLAGNs.Comment: 19 pages, 11 figures, accepted by A&

AINUR: Atlas of Images of NUclear Rings

We present the most complete atlas of nuclear rings to date. We include 113 rings found in 107 galaxies, six of which are elliptical galaxies, five are highly inclined disc galaxies, 18 are unbarred disc galaxies, and 78 are barred disc galaxies. Star-forming nuclear rings occur in 20% of disc galaxies with types between T=-3 and T=7. We aim to explore possible relationships between the size and morphology of the rings and various galactic parameters. We produce colour index and structure maps, as well as Halpha and Paalpha continuum-subtracted images from HST archival data. We derive ellipticity profiles from H-band 2MASS images in order to detect bars and find their metric parameters. We measure the non-axisymmetric torque parameter, Qg, and search for correlations between bar, ring metric parameters, and Qg. Our atlas of nuclear rings includes star-forming and dust rings. Nuclear rings span a range from a few tens of parsecs to a few kiloparsecs in radius. Star-forming nuclear rings can be found in a wide range of morphological types, from S0 to Sd, with a peak in the distribution between Sab and Sb, and without strong preference for barred galaxies. Dust nuclear rings are found in elliptical and S0 galaxies. For barred galaxies, the maximum radius that a nuclear ring can reach is a quarter of the bar radius. We found a nearly random distribution of PA offsets between nuclear rings and bars. There is some evidence that nuclear ring ellipticity is limited by bar ellipticity. We confirm that the maximum relative size of a star-forming nuclear ring is inversely proportional to the non-axisymmetric torque parameter, Qg, and that the origin of nuclear rings, even the ones in non-barred hosts, are closely linked to the existence of dynamical resonances.Comment: Accepted for publication in MNRAS. A full resolution version of the manuscript with high resolution figures can be found at http://www.iac.es/folleto/research/preprints

Vision, challenges and opportunities for a Plant Cell Atlas

With growing populations and pressing environmental problems, future economies will be increasingly plant-based. Now is the time to reimagine plant science as a critical component of fundamental science, agriculture, environmental stewardship, energy, technology and healthcare. This effort requires a conceptual and technological framework to identify and map all cell types, and to comprehensively annotate the localization and organization of molecules at cellular and tissue levels. This framework, called the Plant Cell Atlas (PCA), will be critical for understanding and engineering plant development, physiology and environmental responses. A workshop was convened to discuss the purpose and utility of such an initiative, resulting in a roadmap that acknowledges the current knowledge gaps and technical challenges, and underscores how the PCA initiative can help to overcome them.National Science Foundation 1916797 David W Ehrhardt, Kenneth D Birnbaum, Seung Yon Rhee; National Science Foundation 2052590 Seung Yon Rhe