| 1. |
- Reinke, Beth A, et al.
(author)
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Diverse aging rates in ectothermic tetrapods provide insights for the evolution of aging and longevity
- 2022
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In: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 376:6600, s. 1459-1466
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Journal article (peer-reviewed)abstract
- Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging.
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| 2. |
- Cayuela, Hugo, et al.
(author)
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Thermal conditions predict intraspecific variation in senescence rate in frogs and toads
- 2024
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In: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:49
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Journal article (peer-reviewed)abstract
- Variation in temperature is known to influence mortality patterns in ectotherms. Even though a few experimental studies on model organisms have reported a positive relationship between temperature and actuarial senescence (i.e., the increase in mortality risk with age), how variation in climate influences the senescence rate across the range of a species is still poorly understood in free-ranging animals. We filled this knowledge gap by investigating the relationships linking senescence rate, adult lifespan, and climatic conditions using long-term capture–recapture data from multiple amphibian populations. We considered two pairs of related anuran species from the Ranidae (Rana luteiventris and Rana temporaria) and Bufonidae (Anaxyrus boreas and Bufo bufo) families, which diverged more than 100 Mya and are broadly distributed in North America and Europe. Senescence rates were positively associated with mean annual temperature in all species. In addition, lifespan was negatively correlated with mean annual temperature in all species except A. boreas. In both R. luteiventris and A. boreas, mean annual precipitation and human environmental footprint both had negligible effects on senescence rates or lifespans. Overall, our findings demonstrate the critical influence of thermal conditions on mortality patterns across anuran species from temperate regions. In the current context of further global temperature increases predicted by Intergovernmental Panel on Climate Change scenarios, a widespread acceleration of aging in amphibians is expected to occur in the decades to come, which might threaten even more seriously the viability of populations and exacerbate global decline.
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| 3. |
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| 4. |
- Bader, Thomas K., 1980-, et al.
(author)
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Numerical modeling of the load distribution in multiple fastener joints
- 2017
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In: International Conference on Connections in Timber Engineering – From Research to Standards. - Graz : Verlag der Technischen Universität Graz. - 9783851255539 ; , s. 136-152
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Conference paper (peer-reviewed)abstract
- Numerical modeling approaches, for the determination of load distribution in laterally loaded joints, as well as for the assignment of stiffness properties of joints for the structural analysis, are summarized in this contribution. The effect of the nonlinearity and the load-to-grain orientation dependence of connection slip, of elastic deformation in the surrounding wood matrix, and of the deviation between load and displacement direction are discussed. Comparison of various models demonstrates the pronounced effect of the load-to-grain orientation dependence and the nonlinearity in connection slip on the load distribution, particularly in case of moment loading. The effect of elastic deformation in the wood matrix on the load distribution increases with increased size of joints, even more pronounced when joints are loaded by a shear force perpendicular to the grain. In case of normal force loading, the non-uniform load distribution due to elastic deformation in the wood matrix reduces rapidly with increased relative joint displacement. Pros and cons of the modeling approaches as well as necessary input data are discussed in relation to the design process and European standardization.
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| 5. |
- Bocquet, Jean-Francois, et al.
(author)
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Design recommendations and example calculations for dowel-type connections with multiple shear planes
- 2018
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In: Design of Connections in Timber Structures. - Aachen : Shaker Verlag. - 9783844061444 ; , s. 241-295
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Book chapter (peer-reviewed)abstract
- Numerical modeling approaches, for the determination of load distribution in later-ally loaded connections, as well as for the assignment of stiffness properties of con-nections for the structural analysis, are summarized in this contribution. The effect of the nonlinearity and the load-to-grain orientation dependence of connection slip, of elastic deformation in the surrounding wood matrix, and of the deviation between load and displacement direction are discussed. Comparison of various models demonstrates the pronounced effect of the load-to-grain orientation dependence and the nonlinearity in connection slip on the load distribution, particularly in case of moment loading. The effect of elastic deformation in the wood matrix on the load distribution increases with increased size of connections, even more pronounced when connections are loaded by a shear force perpendicular to the grain. In case of normal force loading, the non-uniform load distribution due to elastic deformation in the wood matrix reduces rapidly with increased relative connection displacement. Pros and cons of the modeling approaches as well as necessary input data are dis-cussed in relation to the design process and European standardization.
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| 6. |
- Fujio, Kazuki, et al.
(author)
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TALYS calculations of prompt fission observables and independent fission product yields for the neutron-induced fission of 235U
- 2023
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In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59
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Journal article (peer-reviewed)abstract
- The TALYS nuclear reaction code’s Hauser-Feshbach statistical decay model has been adapted in order to calculate prompt fission neutron and γ-ray observables by iterating over deexciting fission fragments. Several fission fragment generators such as GEF, HF3D, and SPY were employed to provide TALYS with databases. These databases contain standardized tables with fission fragment yields, mean excitation energies and their widths, and average total kinetic energy, as a function of charge and mass number of primary fission fragments. The resulting calculations, including prompt particle multiplicities, spectra, average energies, and independent fission product yields, were compared with experimental and evaluated data. This work first outlines the new methodology implemented in TALYS and examines the effects of three important parameters on the final evaporation data. Furthermore, the neutron-induced fission of 235U is investigated in detail as a function of incident energy. The results from TALYS, with input from GEF and HF3D, were compared with available experimental data and the results of the stand-alone GEF code. The proposed methodology contributes to an improved capability to model the fission process.
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| 7. |
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| 8. |
- Lemaitre, Romain, et al.
(author)
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Beam-on-foundation modelling as an alternative design method for timber joints with dowel-type fasteners : Part 1: Strength and stiffness per shear plane of single-fastener joints.
- 2018
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In: INTER Proceedings, 2018. - : Karlsruher Institut für Technologie.
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Conference paper (peer-reviewed)abstract
- Optimised manufacturing processes made possible the production of larger dimensions timber products, which allow for the design of remarkable structures. In the last version of the EN 1995-1-1, it seemed important to its drafters to propose design formulas to estimate stiffness of joints in accordance with the needs of that time. Aware of the technical jump that had to be managed, the proposed rules remained simple. However, simple design equations became insufficient to cope with present-day challenges, which are, e.g., related to the design of high-rise wooden buildings. In EN 1995-1-1, the resistant capacity of dowel-type timber joints is no longer determined by empirical formulas but it is based on the limit analysis proposed by Johansen (1949). This methodology however shows limits for complex joints even though many improvements have been made since its introduction (Blaß and Laskewitz 2000). In parallel with these analytical approaches, developments in computational mechanics made it possible to develop simple numerical methods (Foschi 1974, Hirai 1983), which taken even into account nonlinear phenomena. These approaches have remained unused in practical design due to their complex implementation and their high running time, at the time of their invention, while todays computational resources strongly reduced corresponding limitations. Thus, numerical modelling of connections can help engineers to fill the gaps of the EN 1995-1-1 and to cope with variability in connection design. For this purpose, dowel-type fasteners are numerically modelled as elastoplastic beams on a nonlinear foundation in engineered in wood-based products (Sawata and Yasumura 2003, Hochreiner et al. 2013). This method is called Beam-On-Foundation (BOF) modelling and shows huge potential for engineering design. The purpose of this paper is to show how this method can substitute and complement limit analysis and empirical stiffness formulas of timber joints with dowel-type fasteners.
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| 9. |
- Lemaitre, Romain, et al.
(author)
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Beam-on-Foundation Modelling as an Alternative Design Method for Timber Joints with Dowel-Type Fasteners : Part 2: Modelling Techniques for Multiple Fastener Connections
- 2019
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In: INTER: International Network on Timber Engineering Research. - Karlsruhe, Germany : Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen.
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Conference paper (peer-reviewed)abstract
- In many design codes for timber structures (e.g. Eurocode 5 and SIA 265), the stiffness of a connection is given by empirical equations for a single dowel-type fastener per shear plane. The global stiffness of the connection is then given by multiplication with the number of dowels and shear planes. In the codes cited above, the empirical equations to estimate stiffness only depend on two parameters, namely the dowel diameter and the wood density. The main difference between different codes and stiffness of different types of fasteners is the choice of the exponent on these two parameters. Development and background of empirical equations for stiffness in different codes were recently reported in Jockwer and Jorissen (2018), who analysed about one thousand double shear timber-to-timber connection tests to evaluate the influence of further parameters on stiffness, such as number of fasteners in a row, number of rows of fasteners and dowel slenderness. From this huge database, they have been able to estimate another empirical stiffness equation, that includes dowel slenderness as an additional parameter. Effects of the latter have even been reported in Lemaître et al. (2018), by using a phenomenological numerical model instead ofexperiments. Sandhaas and van de Kuilen (2017) reported that using the slip modulus Kser, calculated according to Eurocode 5 for stiffness prediction of multiple fastener joints, considerably overestimates the experimentally observed stiffness and they proposed to introduce an effective number of dowels in their design, which was also recommended in Jockwer and Jorissen (2018).This paper continues the work presented in Lemaître et al. (2018) on strength and stiffness estimations of single-fastener connections using a beam-on-foundation (BOF) modelling. In Lemaître et al (2018), the beam-on-foundation model calculations were compared to design equations of Eurocode 5, i.e. the load-carrying capacity and slip modulus. By these comparisons, the validity of the method for the design of single-fastener connections was highlighted. Moreover, effects that are not explicitly covered in the empirical design equations, namely the influence of the dowel slenderness and the nonlinear dowel diameter on the slip modulus were demonstrated.In the present paper, the same comparisons are made for multiple dowelled connections. Moreover, load distribution between dowels in this type of connection, which was shown to be non-uniform by Blass (1995), is studied by means of the BOF model. Different approaches to estimate the load distribution have been proposed by Cramer (1968), Lantos (1969) and Wilkinson (1986).
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| 10. |
- Lemaitre, Romain, et al.
(author)
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Beam-on-Foundation Modelling as an Alternative Design Method for Timber Joints with Dowel-Type Fasteners : Part 4: Joints Subjected to In-Plane Loading
- 2021
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In: INTER Proceedings, 2021: International Network on Timber Engineering Research 2021. - : Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen.
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Conference paper (peer-reviewed)abstract
- Several different modelling techniques to analyse the mechanical behaviour of the fastener-wood interaction, and thus indirectly to model a dowel-type timber connection,have been developed. However, due to the complex mechanical behaviour of thewood material, no model is capable to satisfactorily analysis the complex stress stateand to predict the brittle fracture due to splitting of timber elements around the drilledhole. In addition, most of the advanced material models are based on a complex mathematical formalism, which makes their application in engineering work cumbersomeand their integration in a design standard such as Eurocode 5 challenging. Furthermore, their high computing times hinder application in engineering practice (Lemaître,2020).This paper continues the work presented in Lemaître et al. (2018, 2019) on strengthand stiffness estimation of multiple dowel joints using a Beam-on-Foundation (BoF)model. In the two previous papers, the modelling was inspired by Hirai’s work presented in 1983, see Hirai (1983). Even though Lemaître et al. (2018, 2019) were limitedto joints subjected to normal force, they showed that numerical modelling can helpengineers to fill the gaps of current regulations in Eurocode 5 and to improve the design process. Moreover, the use of engineered wood materials in structures with large spans and in tall timber buildings increase even more the gap between the engineer’sneeds and currently available regulations in Eurocode 5. Due to their shapes and sizes,the global mechanical behaviour of large timber structures highly dependents on thestiffness of their connections, which influences eigenmodes and eigenfrequencies, deformation and internal load distribution. In addition, the connections are subjected tomore complex loading. For this reason, the BoF model is herein extended to dowelledtimber connections subjected to in-plane loading, in the connection shear planes (inplane bending moment, forces parallel and perpendicular to the neutral axis of theconnected timber elements).Applying a BoF model means to idealize the fastener-wood interaction by non-linearsprings. The stiffness of these springs is expressed by mathematical functions, whichare empirically determined. Several authors have worked on this type of modelling,see Lemaître (2020) for a review. Previous works however were limited to one-dimensional foundation, which limits the applicability of the model to connections subjectedto pure normal or shear loading. The objectives of this paper are to (i) propose techniques to extend this approach to a three-dimensional modelling of the fastener-woodinteraction, (ii) show the suitability of the model for estimating the connection stiffness, plastic capacity (no brittle failure can be considered) as well as the load distribution and (iii) highlight the advantages of this type of model for the design of dowelledtimber joints in the context of Eurocode 5.This paper is limited to dowel fasteners. No normal force is considered along the fasteners axis, and thus, neither screwed connections (with inclined or not inclinedscrews) nor bolted connections were calculated, since the rope effect is not considered.
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