395 research outputs found
Auxetic anti-tetrachiral materials: equivalent elastic properties and frequency band-gaps
No full textA comprehensive characterization of the novel class of anti-tetrachiral cellular solids, both considering the static and the dynamic response, is provided in the paper. The heterogeneous material is characterized by a periodic microstructure made of equi-spaced rings each interconnected by four ligaments. In the most general case, rings and ligaments are surrounded by a softer matrix and the rings can be filled by a different material. First, the first order linear elastic homogenized constitutive response is estimated resorting to two different microstructural models: a discrete model, in which the ligaments are modeled as beams and the presence of the matrix is neglected and the equivalent elastic properties are evaluated through a simplified analytical approach, and a more detailed continuous model, where the actual properties of matrix, ligaments and rings, varying in the 2D domain, are considered and the first order computational homogenization is adopted. Special attention is given to the dependence of the 2D overall Cauchy-type elastic constants on the mechanical and geometrical parameters characterizing the microstructure. The results, indeed, show the existence of large variations in the linear elastic constants and degree of anisotropy. A comparison with available experimental results confirms the validity of the analytical and numerical approaches adopted. Finally, the rigorous Floquet–Bloch approach is applied to the periodic cell of the cellular solid to evaluate the dispersion of propagation waves along the orthotropic axes in the framework of elasticity and to detect band gaps characterizing the material. A numerical approach, based on the first order computational homogenization, is also adopted and the rigorous and approximate solutions are compared
A COSSERAT BASED MULTI-SCALE MODEL FOR MASONRY STRUCTURES
No full textThis paper presents a multi-scale model for the analysis of the in-plane structural response of regular masonry. It is based on a computational periodic homogenization technique and is characterized by the adoption of the Cosserat continuum model at the macroscopic structural level, taking into account the influence of the microstructure on the global response and correctly describing the localization phenomena; at the microscopic representative volume element (RVE) level, where the nonlinear constitutive behavior, geometry, and arrangement of the masonry constituents are modeled in detail, a standard Cauchy model is employed. An isotropic nonsymmetric damage model is adopted for the bricks and mortar joints. The solution algorithm is based on a parallelization strategy and on the finite-element method. Some numerical applications on typical masonry structures are reported, showing both the global response curves and the stress and damage distributions on the RVEs
NURBS-Based Collocation Methods for the Structural Analysis of Shells of Revolution
No full textIn this work we present a collocation method for the structural analysis of shells of revolution based on Non-Uniform Rational B-Spline (NURBS) interpolation. The method is based on the strong formulation of the equilibrium equations according to Reissner-Mindlin theory, with Fourier series expansion of dependent variables, which makes the problem 1D. Several numerical tests validate convergence, accuracy, and robustness of the proposed methodology, and its feasibility as a tool for the analysis and design of complex shell structures
Auxetic behavior and acoustic properties of microstructured piezoelectric strain sensors
No full textThe use of multifunctional composite materials adopting piezo-electric periodic cellular lattice structures with auxetic elastic behavior is a recent and promising solution in the design of piezoelectric sensors. In the present work, periodic anti-tetrachiral auxetic lattice structures, characterized by different geometries, are taken into account and the mechanical and piezoelectrical response are investigated. The equivalent piezoelectric properties are obtained adopting a first order computational homogenization approach, generalized to the case of electro-mechanical coupling, and various polarization directions are adopted. Two examples of in-plane and out-of-plane strain sensors are proposed as design concepts. Moreover, a piezo-elasto-dynamic dispersion analysis adopting the Floquet–Bloch decomposition is performed. The acoustic behavior of the periodic piezoelectric material with auxetic topology is studied and possible band gaps are detected
A finite element formulation for dynamic systems with frequency-independent material damping
No full textPeroxisomal activities in attached senescing leaves
No full textRecently it has been demonstrated that detached leaves show glyoxysomal enzyme activities when incubated in darkness for several days. In this report glyoxylate-cycle enzymes have been detected in leaves of rice (Oryza sativa L.) and wheat (Triticum durum L.) from either naturally senescing or dark-treated plants. Isolated peroxisomes of rice and wheat show isocitrate lyase (EC 4.1.3.1), malate synthase (EC 4.1.3.2) and β-oxidation activities. Leaf peroxisomes from dark-induced senescing leaves show glyoxylic-acid-cycle enzyme activities two to four times higher than naturally senescing leaves. The glyoxysomal activities detected in leaf peroxisomes during natural foliar senescence may represent a reverse transition of the peroxisomes into glyoxysomes
Evidences of glyoxylate cycle in peroxisomes of senescent cotyledons.
No full textThe metabolic pathway of the glyoxylate cycle has been investigated in peroxisomes isolated from senescent pumpkin (Cucurbita sp.) cotyledons. beta-oxidation activity, as well as activities of glyoxylate cycle enzymes isocitrate lyase (EC 4.1.3.1), malate synthase (EC 4.1.3.2), malate dehydrogenase (EC 1.1.1.37) and citrate synthase (EC 4.1.3.7) were detected. In order to establish if there is a channelling of acetyl CoA into the glyoxylate cycle, peroxisomes have been incubated with various substrates. The incubations show acetyl CoA utilization by the glyoxylate cycle. When the incubation medium for citrate formation is used, all the label from [1-C-14]acetyl CoA is recovered in citrate, whereas only 18% of the added radioactivity is recovered in malic acid (by isocitrate lyase and malate synthase) after a long incubation time (3 h). Only by feeding peroxisomes with [1,5-C-14]citric acid and exogenous aconitase (EC 4.2.1.3) can a weak formation of other organic acids (glyoxylate and succinate) be noted. The requirement for exogenous aconitase to carry out the peroxisomal glyoxylate cycle points towards the isocitric acid step as a crucial factor for the operation of the global cycle
Time domain dynamic analysis in presence of frequency-independent material damping: a finite element formulation
No full textarabidopsis thaliana mRNA for 2-isopropylmalate synthase (ipms gene) GenBank: AJ421793.1
No full textLOCUS AJ421793 1767 bp mRNA linear PLN 13-DEC-2001
DEFINITION Arabidopsis thaliana mRNA for 2-isopropylmalate synthase (IPMS
gene).
ACCESSION AJ421793
VERSION AJ421793.1 GI:17826794
KEYWORDS 2-isopropylmalate synthase; IPMS gene.
SOURCE Arabidopsis thaliana (thale cress
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