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The paper focuses on the problem of evaluating analytically the electric and elastic fields in a piezoelectric material of the symmetry class 6 containing a penny-shaped crack loaded by both normal and tangential tractions and by electric charges. A solution of this kind has been developed for symmetry class 6 mm by Karapetian et al. (Arch. Appl. Mech. 70: 201–229, 2000). To the best of our knowledge, it has never been derived for a material of class 6. The research is motivated by needs in evaluation of damage accumulated in bone tissue, which possesses such a symmetry. The problem is solved by the method of potential functions developed by Fabrikant (Applications of Potential Theory in Mechanics: Selection of New Results. Kluwer, Dordrecht,1989). Closed form solutions are obtained for the full electric and elastic fields. The approach is first verified by comparison with the results of Karapetian et al. (Arch. Appl. Mech. 70: 201–229, 2000) for the limiting case of piezoceramic of class 6 mm (PZT-6B) and then applied to calculation of the electroelastic fields associated with a penny-shaped crack in cortical bone (material of class 6).

Stroke is considered one of the leading causes of death worldwide. The treatment is limited; however, the Brazilian flora has a great source of natural products with therapeutic potentials. Studies with the medicinal plant Polygala sabulosa W. Bennett provided evidence for its use as an anti-inflammatory and neuroprotective drug. In the case of ischemic stroke due to lack of oxygen, both acute and chronic inflammatory processes are activated. Thus, we hypothesized that P. sabulosa (HEPs) has the potential to treat the motor and cognitive deficits generated by ischemic stroke. Male mice were subjected to global ischemia for 60 min, followed by reperfusion and orally treated with HEPs (100 mg/kg in saline + 3% tween 20) twice a day (12 h apart) for 48 h starting 3 h after surgery. Motor skills were assessed using grip force and open field tasks. Hippocampi were then collected for mRNA quantification of the cytokines IL-1-β and TNF-α levels. After 48 h of acute treatment, spatial reference memory was evaluated in a Morris water maze test for another group of animals. We show that HEPs treatment significantly prevented motor weakness induced by ischemia. Brain infarct area was reduced by 22.25% with downregulation of the levels of IL-1β and TNF-α mRNA. Learning performance and memory ability on Morris water maze task were similar to the sham group. Our data demonstrates the neuroprotective properties of HEPs through its anti-inflammatory activities, which prevent motor and cognitive impairments, suggesting that HEPs may be an effective therapy for ischemic stroke.

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The evaluation of the effective properties of nonhomogeneous solids using analytical methods is, in general, based on the assumption that these solids have infinite dimensions. Here, we investigate the influence of both the number of holes and the boundary layer of a solid with finite dimensions on the determination of these properties. We use the Asymptotic Homogenization Method (AHM) to determine the effective shear modulus of an elastic solid with infinite dimensions containing a uniform and periodic distribution of circular cylindrical holes arranged on a hexagonal lattice. We also use the Finite Element Method (FEM) to determine this modulus in the case of a solid with finite dimensions containing the same uniform distribution of cylindrical holes away from its boundary. Near the boundary, we consider a layer of material with no holes, which is usually left in the fabrication process of samples. Both solids have the same elastic properties and are subjected to similar anti-plane shear loadings. For the finite medium, we study two sequences of domains discretized by the FEM, which are called the Fixed Layer Sequence (FLS) and the Fixed Domain Sequence (FDS). For the FLS, the layer thickness is kept fixed and both the dimensions of the domain and the number of holes vary. For the FDS, the dimensions of the domain are kept fixed and both the number of holes and the layer thickness vary. Results obtained from numerical simulations are then used to generate graphs of the effective shear modulus versus void volume fraction. It is observed that, in the FLS case, the shear modulus obtained from the numerical simulations converges to the analytical solution obtained via AHM. It is also observed that, in the FDS case, the shear modulus obtained from the numerical simulations converges to a limit function, which is close to the analytical solution obtained via AHM. For comparison purposes, we have also calculated the effective shear modulus of porous elastic solids containing a square array of circular cylindrical holes. We then show graphs of this modulus versus void volume fraction for both hexagonal and square arrangements that are very close to each other up to void volume fraction of 0.5.

Microposit S1813 is very popular photoresist due to high resolution, simplicity of deposition methods, and high adhesion to semiconductors. The least controlled parameter of photoresist thin films deposition is the tanning process, where everything depends on the operator and therefore it is quite difficult to ensure perfect reproducibility of the process. In this work, we studied thin films of Microposit S1813, deposited by spin coating on silicon substrates, and then tanned in 30, 45, 60, 75, and 90 s at 110 \(^\circ \)C. The thickness of the films was studied using optical microscopy. The waviness and surface roughness were investigated by atomic force microscopy. To evaluate the mechanical properties of Microposit S1813 thin films, the nanoindentation method in the quasistatic mode was used. The results obtained will help to determine the region of the indenter-sample contact area as well as the measurement error, which is necessary for modern analytical mathematical models used to study the mechanical characteristics of multilayer coatings.

Necessary and sufficient conditions for strong ellipticity of the equilibrium equations governing finite plane deformations are established for the class of orthotropic and compressible hyperelastic materials. The conditions are then specialized to the case of an orthotropic material having the symmetry axes parallel to the principal directions of deformation. This case is relevant in experimental protocols employed in the characterization of constitutive relations of rubber-like materials and biological tissues. The classical conditions for infinitesimal linear elasticity and isotropic finite elasticity are recovered as particular cases.

Complex regional pain syndrome type-I (CRPS-I) is a chronic painful condition resulting from trauma. Bradykinin (BK) is an important inflammatory mediator required in acute and chronic pain response. The objective of this study was to evaluate the association between BK receptors (B

We determine the minimum number of independent invariants that are needed to characterize completely the strain energy density of a compressible hyperelastic solid having two distinct material symmetry directions. We use a theory of representation of isotropic functions to express this energy density in terms of eighteen invariants, from which we extract ten invariants to analyze two cases of material symmetry. In the case of orthogonal directions, we recover the classical result of seven invariants and offer a justification for the choice of invariants found in the literature. If the directions are not orthogonal, we find that the minimum number is also seven and correct a mistake in a formula found in the literature. An energy density of this type is used to model, on the macroscopic scale, engineering materials, such as fiber-reinforced composites, and biological tissues, such as bones.

This work concerns the behavior of a two-phase periodic laminate composed of homogeneous, isotropic, and hyperelastic layers in equilibrium in the absence of body force and subjected to a finite deformation on its boundary. The effective behavior of unbounded laminates is studied elsewhere using the tangent second-order homogenization method. In the case of a laminate composed of penalty compressible Neo-Hookean phases and subjected to pure shear deformation on its boundary, analytical results indicate that a combination of loading conditions, material properties, and phase concentrations may lead to a reduction of the overall stiffness of the laminate, which may be related to the loss of overall strong ellipticity of the corresponding effective medium, in spite of the fact that the layers are strongly elliptic. Here, the Asymptotic Homogenization Method (AHM) and the Finite Element Method (FEM) are used to verify and extend these results for laminates subjected to similar boundary conditions and compressible Neo-Hookean phases. Using FEM, the rotation angles of the layers at the center of the laminate are calculated and compared to the rotation angles obtained analytically. For certain loading conditions and material properties, the rotation angles are very close to each other up to a critical shear deformation predicted analytically, after which, the angle obtained via FEM changes abruptly from the angle obtained analytically, suggesting a bifurcation-like behavior. This critical deformation depends strongly on the heterogeneity contrast ratio between the phases. For a contrast ratio close to one, no such behavior is observed. As we increase this ratio, the critical deformation becomes smaller and tends to the identity deformation as the contrast ratio tends to infinity. This work may be of interest to practitioners doing numerical simulation of problems involving composites and to researchers interested in material instabilities of effective nonlinear elastic media.