Immersed-Boundary Fluid-Structure Interaction of Membranes and Shells

This paper presents a general and robust method for the fluid-structure interaction of membranes and shells undergoing large displacement and large added-mass effects by coupling an immersed-boundary method with a shell finite-element model. The immersed boundary method can accurately simulate the fluid velocity and pressure induced by dynamic bodies undergoing large displacements using a computationally efficient pressure projection finite volume solver. The structural solver can be applied to bending and membrane-related problems, making our partitioned solver very general. We use a strongly-coupled algorithm that avoids the expensive computation of the inverse Jacobian within the root-finding iterations by constructing it from input-output pairs of the coupling variables from the previous time steps. Using two examples with large deformations and added mass contributions, we demonstrate that the resulting quasi-Newton scheme is stable, accurate, and computationally efficient.Comment: 11 pages, 6 figures, paper presented at EuroDyn 202

Genetic Ablation of PLA2G6 in Mice Leads to Cerebellar Atrophy Characterized by Purkinje Cell Loss and Glial Cell Activation

Infantile neuroaxonal dystrophy (INAD) is a progressive, autosomal recessive neurodegenerative disease characterized by axonal dystrophy, abnormal iron deposition and cerebellar atrophy. This disease was recently mapped to PLA2G6, which encodes group VI Ca2+-independent phospholipase A2 (iPLA2 or iPLA2β). Here we show that genetic ablation of PLA2G6 in mice (iPLA2β-/-) leads to the development of cerebellar atrophy by the age of 13 months. Atrophied cerebella exhibited significant loss of Purkinje cells, as well as reactive astrogliosis, the activation of microglial cells, and the pronounced up-regulation of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Moreover, glial cell activation and the elevation in TNF-α and IL-1β expression occurred before apparent cerebellar atrophy. Our findings indicate that the absence of PLA2G6 causes neuroinflammation and Purkinje cell loss and ultimately leads to cerebellar atrophy. Our study suggests that iPLA2β-/- mice are a valuable model for cerebellar atrophy in INAD and that early anti-inflammatory therapy may help slow the progression of cerebellar atrophy in this deadly neurodegenerative disease

Firm Heterogeneity and Choice of Ownership Structure: An Empirical Analysis of German FDI in India

We contribute to the nascent literature on the heterogeneity of multinational enterprises (MNEs) and the relevance of firm characteristics for analyzing the determinants of outward foreign direct investment (FDI). The focus is on the role of firm-level heterogeneity when MNEs decide on the share of ownership in foreign affiliates. We combine two firm-specific datasets on German MNEs with varying equity stakes in Indian affiliates. The impact of firm characteristics on ownership shares is assessed in the context of OLS and fractional logit models, controlling for industry and location characteristics. We show that the effect of several characteristics differs between the establishment of new affiliates by German MNEs and their engagement in already existing Indian firms. Most notably, the productivity of the German parents matters only for ownership shares in new affiliates

A critical review of fear tests used on cattle, pigs, sheep, poultry and horses

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Cortical Gray Matter Injury in Encephalopathy of Prematurity: Link to Neurodevelopmental Disorders

Preterm-born infants frequently suffer from an array of neurological damage, collectively termed encephalopathy of prematurity (EoP). They also have an increased risk of presenting with a neurodevelopmental disorder (e.g., autism spectrum disorder; attention deficit hyperactivity disorder) later in life. It is hypothesized that it is the gray matter injury to the cortex, in addition to white matter injury, in EoP that is responsible for the altered behavior and cognition in these individuals. However, although it is established that gray matter injury occurs in infants following preterm birth, the exact nature of these changes is not fully elucidated. Here we will review the current state of knowledge in this field, amalgamating data from both clinical and preclinical studies. This will be placed in the context of normal processes of developmental biology and the known pathophysiology of neurodevelopmental disorders. Novel diagnostic and therapeutic tactics required integration of this information so that in the future we can combine mechanism-based approaches with patient stratification to ensure the most efficacious and cost-effective clinical practice

Computational fluid-structure Interaction of membranes and shells with application to bat flight

Fluid-Structure Interaction of thin, flexible structures is omnipresent in nature and engineering. Numerical simulation of this kind of system is challenging due to the large non-linear deformations and the strong added-mass effect. In this thesis, we develop a novel immersed boundary fluid-structure structure interaction solver to deal with those challenging cases. First, we show that immersed boundary methods must explicitly impose the Neumann condition on the pressure field for accurate results when the structure is thin and dynamic. We develop an extension to an existing immersed boundary method, BDIM-sigma, that enforces this boundary condition regardless of the body's thickness. The method relies on a variable coefficient Poisson equation to impose the Neumann condition on the interface. Standard linear algebra methods solve the resulting linear system. The method drastically outperforms Direct-Forcing methods and the standard immersed boundary method for problems with thin dynamic structures. We couple our immersed boundary method with a three-dimensional shell solver via an implicit partitioned approach. A quasi-Newton method solves the resulting fixed-point problem. The method constructs an approximation of the Jacobian of the interface via input-output pairs of the coupling variables from the previously converged time steps. These pairs form an inverse least-square problem whose solution is the (inverse) Jacobian of the interface. With various fluid-structure interaction examples, we show that the method possesses excellent spatial convergence properties, is stable and efficient for a large range of flexibility and mass ratios and outperforms standard Gauss-Seidel relaxation methods.Finally, we demonstrate the capability of our coupled solver to deal with practical examples by simulating bat flight. We investigate the effects of Strouhal number, membrane elasticity and fibre reinforcement on the aerodynamic efficiencies of bats. We show that the three-dimensional nature of the kinematics results in aerodynamic efficiencies peaking well outside the optimal Strouhal number range. Additionally, we show that propulsive efficiency is well correlated with membrane elasticity, where elastic membranes outperform stiff ones until flutter occurs. To extend the flutter envelope of the wing, we reinforce the isotropic membrane with anisotropic fibres. The response of this modified membrane shows a drastic reduction in the flutter and large improvements in aerodynamic efficiencies

Immersed boundary simulations of flows driven by moving thin membranes

Immersed boundary methods are extensively used for simulations of dynamicsolid objects interacting with fluids due to their computational efficiency andmodelling flexibility compared to body-fitted grid methods. However, thingeometries, such as shells and membranes, cause a violation of the boundaryconditions across the surface for many immersed boundary projection algorithms. Using a one-dimensional analytical derivation and multi-dimensional numerical simulations, this manuscript shows that adjustment of the Poisson matrix itself is require to avoid large velocity, pressure, and force prediction errors when the pressure jump across the interface is substantial and that these errors increase with Reynolds number. A new minimal thickness modication is developed for the Boundary Data Immersion Method (BDIM-),which avoids these issues while still enabling the use of efficient projectionalgorithms for high-speed immersed surface simulations

Dataset in support of the Southampton doctoral thesis 'Computational Fluid-Structure Interaction of Membranes and Shells with Application to Bat Flight'

Dataset containing the data used in generating all the analysis in the thesis: Computational Fluid Structure Interaction of Membranes and Shells with Application to bat Flight</span

Rapid flapping and fiber-reinforced membrane wings are key to high-performance bat flight

Bats fly using significantly different wing motions than other fliers, stemming from the complex interplay of their membrane wings’ motion and structural properties. Biological studies show that many bats fly at Strouhal numbers, the ratio of flapping to flight speed, 50-150% above the range typically associated with optimal locomotion. We use high-resolution fluid-structure interaction simulations of a bat wing to independently study the role of kinematics and material/structural properties on aerodynamic performance and show that peak propulsive and lift efficiencies for a bat-like wing motion require flapping 66% faster than for a symmetric motion, agreeing with the increased flapping frequency observed in zoological studies. In addition, we find that reduced membrane stiffness is associated with improved propulsive efficiency until the membrane flutters, but that incorporating microstructural anisotropy arising from biological fiber reinforcement enables a tenfold reduction of the flutter energy whilst maintaining high aerodynamic efficiency. Our results indicate that animals with specialized flapping motions may have correspondingly specialized flapping speeds, in contrast to arguments for a universally efficient Strouhal range. Additionally, our study demonstrates the significant role that the microstructural constitutive properties of the membrane wing of a bat can have on its propulsive performance