Density functional theory study of the {\alpha} --> {\omega} martensitic transformation in titanium induced by hydrostatic pressure

The martensitic {\alpha} --> {\omega} transition was investigated in Ti under hydrostatic pressure. The calculations were carried out using the density functional theory (DFT) framework in combination with the Birch-Murnaghan equation of state. The calculated ground-state properties of {\alpha} and {\omega} phases of Ti, their bulk moduli and pressure derivatives are in agreement with the previous experimental data. The lattice constants of {\alpha} and {\omega}-phase at 0 K were modeled as a function of pressure from 0 to 74 GPa and 0 to 119 GPa, respectively. It is shown that the lattice constants vary in a nonlinear manner upon compression. The calculated lattice parameters were used to describe the {\alpha} --> {\omega} transition and show that the phase transition can be obtained at 0 GPa and 0 K.Comment: 6 pages, 5 figure

Micromechanical model of bovine Haversian bone predicts strain amplification through soft interfaces

Context. Recent observations of brown dwarf spectroscopic variability in the infrared infer the presence of patchy cloud cover. Aims. This paper proposes a mechanism for producing inhomogeneous cloud coverage due to the depletion of cloud particles through the Coulomb explosion of dust in atmospheric plasma regions. Charged dust grains Coulomb-explode when the electrostatic stress of the grain exceeds its mechanical tensile stress, which results in grains below a critical radius a < aCoulcrit being broken up. Methods. This work outlines the criteria required for the Coulomb explosion of dust clouds in substellar atmospheres, the effect on the dust particle size distribution function, and the resulting radiative properties of the atmospheric regions. Results. Our results show that for an atmospheric plasma region with an electron temperature of Te = 10 eV (≈ 105 K), the critical grain radius varies from 10-7 to 10-4 cm, depending on the grains’ tensile strength. Higher critical radii up to 10-3 cm are attainable for higher electron temperatures. We find that the process produces a bimodal particle size distribution composed of stable nanoscale seed particles and dust particles with a ≥ aCoulcrit , with the intervening particle sizes defining a region devoid of dust. As a result, the dust population is depleted, and the clouds become optically thin in the wavelength range 0:1 - 10 μm, with a characteristic peak that shifts to higher wavelengths as more sub-micrometer particles are destroyed. Conclusions. In an atmosphere populated with a distribution of plasma volumes, this will yield regions of contrasting radiative properties, thereby giving a source of inhomogeneous cloud coverage. The results presented here may also be relevant for dust in supernova remnants and protoplanetary disks.PostprintPeer reviewe

A novel framework for Shot number minimization in Quantum Variational Algorithms

Variational Quantum Algorithms (VQAs) have gained significant attention as a potential solution for various quantum computing applications in the near term. However, implementing these algorithms on quantum devices often necessitates a substantial number of measurements, resulting in time-consuming and resource-intensive processes. This paper presents a generalized framework for optimization algorithms aiming to reduce the number of shot evaluations in VQAs. The proposed framework combines an estimator and an optimizer. We investigate two specific case studies within this framework. In the first case, we pair a sample mean estimator with a simulated annealing optimizer, while in the second case, we combine a recursive estimator with a gradient descent optimizer. In both instances, we demonstrate that our proposed approach yields notable performance enhancements compared to conventional methods.Comment: 20 pages, 11 figure

Calculation of the critical energy release rate Gc of the cement line in cortical bone combining experimental tests and finite element models

[EN] In this work, a procedure is proposed to estimate the critical energy release rate Gc of the so-called cement line in cortical bone tissue. Due to the difficulty of direct experimental estimations, relevant elastic and toughness material properties at bone microscale have been inferred by correlating experimental tests and finite element simulations. In particular, three-point bending tests of ovine cortical bone samples have been performed and modeled by finite elements. The initiation and growth of microcracks in the tested samples are simulated through finite elements using a damage model based on a maximum principal strain criterion, showing a good correlation with the experimental results. It is observed that microcracks evolve mainly along the cement lines and through the interstitial material but without crossing osteons. The numerical model allows the calculation of the cement line critical energy release rate Gc by approximating its definition by finite differences. This way, it is possible to estimate this property poorly documented in the literature.The authors wish to thank the Ministerio de Economia y Competitividad for the support received in the framework of the project DPI2013-46641-R and to the Generalitat Valenciana, Programme PROMETEO 2016/007. The authors also thank Dr. Jose Luis Peris, from Instituto de Biomecanica de Valencia (IBV) and Carlos Tudela Desantes for their collaboration within the context of the project.Giner Maravilla, E.; Belda, R.; Arango-Villegas, C.; Vercher Martínez, A.; Tarancón Caro, JE.; Fuenmayor Fernández, FJ. (2017). Calculation of the critical energy release rate Gc of the cement line in cortical bone combining experimental tests and finite element models. Engineering Fracture Mechanics. 184:168-182. https://doi.org/10.1016/j.engfracmech.2017.08.026S16818218

An Integrated Qualitative and Quantitative Biochemical Model Learning Framework Using Evolutionary Strategy and Simulated Annealing

The authors would like to thank the support on this research by the CRISP Project (Combinatorial Responses In Stress Pathways) funded by the BBSRC (BB/F00513X/1) under the Systems Approaches to Biological Research (SABR) Initiative.Peer reviewedPublisher PD

A review on recent advances in numerical modelling of bone cutting

[EN] Common practice of surgical treatments in orthopaedics and traumatology involves cutting processes of bone. These operations introduce risk of thermo-mechanical damage, since the threshold of critical temperature producing thermal osteonecrosis is very low. Therefore, it is important to develop predictive tools capable of simulating accurately the increase of temperature during bone cutting, being the modelling of these processes still a challenge. In addition, the prediction of cutting forces and mechanical damage is also important during machining operations. As the accuracy of simulations depends greatly on the proper choice of the thermo-mechanical properties, an essential part of the numerical model is the constitutive behaviour of the bone tissue, which is considered in different ways in the literature. This paper focuses on the review of the main contributions in modelling of bone cutting with special attention to the bone mechanical behaviour. The aim is to give the reader a complete vision of the approaches commonly presented in the literature in order to help in the development of accurate models for bone cutting.The authors acknowledge to the Ministry of Economy and Competitiveness of Spain the financial support for this work received through the projects DPI2011-25999 and DPI2013-46641-R.Marco, M.; Rodríguez Millán, M.; Santiuste, C.; Giner Maravilla, E.; Henar Miguélez, M. (2015). A review on recent advances in numerical modelling of bone cutting. Journal of the Mechanical Behavior of Biomedical Materials. 44:179-201. https://doi.org/10.1016/j.jmbbm.2014.12.006S1792014

Explicit expressions for the estimation of the elastic constants of lamellar bone as a function of the volumetric mineral content using a multi-scale approach

[EN] In this work, explicit expressions to estimate all the transversely isotropic elastic constants of lamellar bone as a function of the volumetric bone mineral density (BMD) are provided. The methodology presented is based on the direct homogenization procedure using the finite element method, the continuum approach based on the Hill bounds, the least-square method and the mean field technique. Firstly, a detailed description of the volumetric content of the different components of bone is provided. The parameters defined in this step are related to the volumetric BMD considering that bone mineralization process occurs at the smallest scale length of the bone tissue. Then, a thorough description provides the details of the numerical models and the assumptions adopted to estimate the elastic behaviour of the forward scale lengths. The results highlight the noticeable influence of the BMD on the elastic modulus of lamellar bone. Power law regressions fit the Young's moduli, shear stiffness moduli and Poisson ratios. In addition, the explicit expressions obtained are applied to the estimation of the elastic constants of cortical bone. At this scale length, a representative unit cell of cortical bone is analysed including the fibril orientation pattern given by Wagermaier et al. (Biointerphases 1:1-5, 2006) and the BMD distributions observed by Granke et al. (PLoS One 8:e58043, 2012) for the osteon. Results confirm that fibril orientation arrangement governs the anisotropic behaviour of cortical bone instead of the BMD distribution. The novel explicit expressions obtained in this work can be used for improving the accuracy of bone fracture risk assessment.The authors acknowledge the Ministerio de Economia y Competitividad for the financial support received through the project DPI2013-46641-R and to the Generalitat Valenciana for Programme PROMETEO 2016/007. The authors declare that they have no conflict of interestVercher Martínez, A.; Giner Maravilla, E.; Belda, R.; Aigoun, A.; Fuenmayor Fernández, F. (2018). Explicit expressions for the estimation of the elastic constants of lamellar bone as a function of the volumetric mineral content using a multi-scale approach. Biomechanics and Modeling in Mechanobiology. 17(2):449-464. https://doi.org/10.1007/s10237-017-0971-xS449464172Akiva U, Wagner HD, Weiner S (1998) Modelling the three-dimensional elastic constants of parallel-fibred and lamellar bone. J Mater Sci 33:1497–1509Ascenzi A, Bonucci E (1967) The tensile properties of single osteons. Ana Rec 158:375–386Barbour KE, Zmuda JM, Strotmeyer ES, Horwitz MJ, Boudreau R, Evans RW, Ensrud K, Petit MA, Gordon CL, Cauley JA (2013) Correlates of trabecular and cortical volumetric bone mineral density of the radius and tibia older men: the osteoporotic fractures in men study. 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The influence of anisotropy in numerical modelling of orthogonal cutting of cortical bone

Cutting operations in bone are involved in surgical treatments in orthopaedics and traumatology. The importance of guaranteeing the absence of damage in the living workpiece is equivalent in this case to ensuring surface quality. The knowledge in this field is really far from the expertise in industrial cutting of mechanical components. Modeling of bone cutting is a challenge strongly dependent on the accurate modeling of mechanical behaviour of the bone. This paper focuses on modeling of orthogonal cutting of cortical bone. The intrinsic anisotropic nature of the cortical bone that makes it comparable to a composite material is taken into account. The influence of anisotropy is analysed comparing this behaviour with an isotropic approach. It is shown that both chip morphology and temperature are affected by the anisotropy of the cortical bone that acts as a workpiece.The authors acknowledge the financial support for the work to the Ministry of Economy and Competitiveness of Spain under the Project DPI2011-25999 and DPI2013-46643-R.Santiuste, C.; Rodríguez Millán, M.; Giner Maravilla, E.; Miguélez, H. (2014). The influence of anisotropy in numerical modelling of orthogonal cutting of cortical bone. Composite Structures. 116:423-431. doi:10.1016/j.compstruct.2014.05.031S42343111