Estimate of theoretical shear strength of C60 single crystal by nanoindentation

The onset of plasticity in a single crystal C60 fullerite was investigated by nanoindentation on the (111) crystallographic plane. The transition from elastic to plastic deformation in a contact was observed as pop-in events on loading curves. The respective resolved shear stresses were computed for the octahedral slip systems $$\langle{01}\overline{1}\rangle\left\{ {{111}} \right\}$$ ⟨ 01 1 ¯ ⟩ 111 , supposing that their activation resulted in the onset of plasticity. A finite element analysis was applied, which reproduced the elastic loading until the first pop-in, using a realistic geometry of the Berkovich indenter blunt tip. The obtained estimate of the C60 theoretical shear strength was about $${1}/{11}$$ 1 / 11 of the shear modulus on {111} planes. Graphical abstract

Finite Element Simulations of the ID Venous System to Treat Venous Compression Disorders: From Model Validation to Realistic Implant Prediction

The ID Venous System is an innovative device proposed by ID NEST MEDICAL to treat venous compression disorders that involve bifurcations, such as the May-Thurner syndrome. The system consists of two components, ID Cav and ID Branch, combined through a specific connection that prevents the migration acting locally on the pathological region, thereby preserving the surrounding healthy tissues. Preliminary trials are required to ensure the safety and efficacy of the device, including numerical simulations. In-silico models are intended to corroborate experimental data, providing additional local information not acquirable by other means. The present work outlines the finite element model implementation and illustrates a sequential validation process, involving seven tests of increasing complexity to assess the impact of each numerical uncertainty separately. Following the standard ASME V&V40, the computational results were compared with experimental data in terms of force-displacement curves and deformed configurations, testing the model reliability for the intended context of use (differences < 10%). The deployment in a realistic geometry confirmed the feasibility of the implant procedure, without risk of rupture or plasticity of the components, highlighting the potential of the present technology.

Оптимизация потерь мощности атомарного пучка при его транспортировке в плазму токамака ТУМАН-3М

Paper reports a physical model of the beam transportation through the duct with realistic geometry. The beam losses are explained by interaction of the energetic particles of the beam with the duct walls resulting in strong influx of neutral gas, which interact with beam particles and cause their reionizaton. Using the model new design of the beam duct was developed. Ratio of the neutron fluxes values obtained under similar experimental conditions with the new transition duct and the old one fitted well with the model predictions.

Computational modeling of seizure spread on a cortical surface

In the field of computational epilepsy, neural field models helped to understand some large-scale features of seizure dynamics. These insights however remain on general levels, without translation to the clinical settings via personalization of the model with the patient-specific structure. In particular, a link was suggested between epileptic seizures spreading across the cortical surface and the so-called theta-alpha activity (TAA) pattern seen on intracranial electrographic signals, yet this link was not demonstrated on a patient-specific level. Here we present a single patient computational study linking the seizure spreading across the patient-specific cortical surface with a specific instance of the TAA pattern recorded in the patient. Using the realistic geometry of the cortical surface we perform the simulations of seizure dynamics in The Virtual Brain platform, and we show that the simulated electrographic signals qualitatively agree with the recorded signals. Furthermore, the comparison with the simulations performed on surrogate surfaces reveals that the best quantitative fit is obtained for the real surface. The work illustrates how the patient-specific cortical geometry can be utilized in The Virtual Brain for personalized model building, and the importance of such approach.

An active source seismo-acoustic experiment using tethered balloons to validate instrument concepts and modelling tools for atmospheric seismology

Summary The measurements of acoustic waves created by a quake are of great interest for planets with hot and dense atmospheres, like Venus, because surface deployments of seismometers will last only a few hours whereas free flying balloons could fly many days. Infrasound sensors can also be used to constrain sub-surface properties during active seismic experiments. This study presents a controlled source seismo-acoustic experiment using infrasonic sensors and accelerometers mounted on a tethered helium balloon. Both the acoustic waves generated below the balloon by seismic surface waves, and the ones generated by strong ground motions above the seismic source are clearly observed and separated on the records of the various instruments. This data set allows various validations and investigations. First, it validates the ground to air coupling theory and our numerical modelling tools. Then, it allows us to demonstrate that antenna processing of infrasound sensors deployed below the balloon can estimate the arrival incidence angle of the acoustic waves within 10○. Finally, a polarization analysis of the accelerometers taped on the balloon envelope is presented. It demonstrates that accelerometer records are strongly dependent on their location on the balloon due to its deformations and rotations. However the different acoustic signals can be distinguished through their polarization, and a best sensor location is estimated at the bottom of the balloon envelope. These results are a first step towards detecting and locating seismic activity using airborne acoustic sensors on Venus and elsewhere. However, some observations of earthquake signals in a more realistic geometry are still missing.

Blood Flow Dynamics at the Pulmonary Artery Bifurcation

Knowledge of physiologic hemodynamics is a fundamental requirement to establish pathological findings. However, little is known about the normal flow fields in the pulmonary arteries, especially for children. The purpose of this study is to characterize flow patterns in the pulmonary artery bifurcation of healthy pediatric subjects using direct numerical simulations. A realistic geometry is obtained via statistical shape modeling, by averaging five subject-specific digital models extracted from cardiovascular magnetic resonance datasets of healthy volunteers. Boundary conditions are assigned to mimic physiological conditions at rest, corresponding to a peak Reynolds number equal to 3400 and a Womersley number equal to 15. Results show that the normal bifurcation is highly hemodynamically efficient, as measured by an energy dissipation index. The curvature of the pulmonary arteries is sufficiently small to prevent flow separation along the inner walls, and no signs of a turbulent-like state are found. In line with previous imaging studies, a helical structure protruding into the right pulmonary artery is detected, and its formation mechanism is elucidated in the paper. These findings might help to identify abnormal flow features in patients with altered anatomic and physiologic states, particularly those with repaired congenital heart disease.