Radial or bilateral? The molecular basis of floral symmetry.

In the plant kingdom, the flower is one of the most relevant evolutionary novelties. Floral symmetry has evolved multiple times from the ancestral condition of radial to bilateral symmetry. During evolution, several transcription factors have been recruited by the different developmental pathways in relation to the increase of plant complexity. The MYB proteins are among the most ancient plant transcription factor families and are implicated in different metabolic and developmental processes. In the model plant Antirrhinum majus, three MYB transcription factors (DIVARICATA, DRIF, and RADIALIS) have a pivotal function in the establishment of floral dorsoventral asymmetry. Here, we present an updated report of the role of the DIV, DRIF, and RAD transcription factors in both eudicots and monocots, pointing out their functional changes during plant evolution. In addition, we discuss the molecular models of the establishment of flower symmetry in different flowering plants

Limit state analysis of RC structures

The inelastic static pushover analysis has become a popular tool for evaluating the seismic capacity of structures. It is able of predicting the seismic force and deformation demands by accounting in an approximate manner for the inelastic redistribution of internal forces. Though approximate in nature and based on static loading, if properly used the pushover analysis can provide many significant insights into the structural behaviour and also put forward the design weaknesses that may be hidden in the elastic analysis. The main features of the conventional pushover analysis are well described in [1], where are also emphasized limitations and possible causes that may produce loss of accuracy of the method. A basic prerequisite for successful applications of the method is an adequate knowledge of the inelastic behaviour of structural elements. This is particularly true for those structures containing shear walls that, if not properly described, may render the results of the analysis completely meaningless. In this work we show how, under appropriate hypotheses, one can introduce steel reinforcement into shear walls by appealing to a semi-analytical multi-scale approach. In particular, reinforcements are taken into account using an embedded beam approach, the usual conventional material behaviour, i.e. the the so-called parabolic-rectangular stress block for concrete and ideal elastic-plastic for steel as of Eurocode 2, and a fiber-free integration, that provides the exact solution for stress resultants over the cross section of the beam itself. Representative numerical simulations are shown that illustrate the capabilities of the proposed approach, that allows one to carry out accurate nonlinear analyses of full-scale reinforced concrete structures with relatively reduced computational effort

Analysis of the genes involved in floral symmetry of the orchid Orchis italica

Orchis italica è un’orchidea selvatica mediterranea appartenente alla sottofamiglia Orchidoideae delle Orchidaceae, una delle più vaste famiglie di piante a fiore. Lo scopo di questo lavoro è lo studio dei geni coinvolti nella determinazione della simmetria bilaterale del fiore di O. italica. Studi sulla determinazione della simmetria fiorale effettuati sulla specie modello Antirrhinum majus hanno evidenziato che cinque geni, due appartenenti alla famiglia TCP (CYC e DICH) e tre appartenenti alla famiglia MYB di fattori di trascrizione (DIV, RAD e DRIF), svolgono un ruolo cruciale nella formazione del fiore zigomorfo. In A. majus queste proteine interagiscono tra di loro attraverso un meccanismo antagonistico che permette la formazione nel fiore di una regione dorsale e una ventrale. In O. italica, l’analisi del trascrittoma dell’infiorescenza matura ha evidenziato la presenza di 8 trascritti DIV-like, 4 trascritti RAD-like e due trascritti DRIF1/2. L’organizzazione genomica dei geni DIV-like e RAD-like presenta un singolo introne, fatta eccezione per un unico gene RAD-like che risulta essere privo di introni. L’analisi evolutiva ha evidenziato che sulle regioni codificanti dei geni DIV-like e RAD-like agisce selezione purificante. I geni DIV, RAD e DRIF di O. italica hanno un’espressione conservata rispetto ad A. majus. L’analisi delle interazioni proteiche tra i fattori di trascrizione MYB di O. italica ha dimostrato che il modello alla base della determinazione della simmetria bilaterale sembra essere conservato anche in orchidea. I geni MADS-box di tipo II MIKCC, classificati in cinque classi funzionali ABCDE, hanno un ruolo cruciale della determinazione della struttura e dell’organizzazione fiorale. In particolare, in orchidea, secondo il modello “orchid code”, i geni MADS-box appartenenti alla classe B hanno un ruolo fondamentale nella formazione della struttura zigomorfa del fiore di orchidea. Nell’infiorescenza matura di O. italica sono espressi 29 trascritti MADS-box appartenenti al tipo I e al tipo II. I geni MADS-box di O. italica hanno un profilo di espressione in linea con il modello di sviluppo fiorale “fading borders”. Poiché entrambe le famiglie geniche, MADS-box e MYB, sono alla base della determinazione fiorale è stato effettuato uno studio sull’interazione proteica tra i fattori di trascrizione MYB (DIV, RAD e DRIF) e le proteine MADS-box di classe B di O. italica. L’analisi condotta ha evidenziato che le singole proteine MADS-box appartenenti alla classe B non sono in grado di interagire con i fattori di trascrizione MYB

The 2009MW6.1 L’Aquila fault system imaged by 64k earthquake locations

On April 6 2009, a MW 6.1 normal-faulting earthquake struck the axial area of the Abruzzo region in central Italy. We investigate the complex architecture and mechanics of the activated fault system by using 64k high-resolution foreshock and aftershock locations. The fault system is composed by two major SW dipping segments forming an en-echelon NW trending system about 50 km long: the high-angle L’Aquila fault and the listric Campotosto fault, located in the first 10 km depth. From the beginning of 2009, foreshocks activated the deepest portion of the mainshock fault. A week before the MW 6.1 event, the largest (MW 4.0) foreshock triggered seismicity migration along a minor off-fault segment. Seismicity jumped back to the main plane a few hours before the mainshock. High-precision locations allowed us to peer into the fault zone showing complex geological structures from the metre to the kilometre scale, analogous to those observed by field studies and seismic profiles. Also, we were able to investigate important aspects of earthquakes nucleation and propagation through the upper crust in carbonate-bearing rocks such as: the role of fluids in normal-faulting earthquakes; how crustal faults terminate at depths; the key role of fault zone structure in the earthquake rupture evolution processes

To be or not to be quadratic (with X-Fem)

A novel implementation of the eXtended Finite Element Method that makes use of quadratic elements is discussed. The present formulation is shown to behave fairly better compared to usual quadratic elements enriched with Heaviside functions in that both the number of unknowns and the condition number of element matrices considerably decrease with respect to a classical second order scheme. A representative example demonstrates the capabilities of the proposed approach

Evaluation of Conjugate Stresses to Seth’s Strain Tensors

An explicit expression providing the symmetric stress tensor T(m) conjugate to the Seth’s strain measure E(m) for each integer m unequal 0 is presented. The result is obtained by exploiting an original approach for the solution of a tensor equation in the unknown T(m) expressed as function of the powers of the right stretch tensor U. The proposed approach is based upon the spectral decomposition of U and exploits some peculiar features of the set of fourth-order tensors obtained as linear combination of dyadic and square tensor products of the eigenprojectors of U. On the basis of such properties it is shown that the unknown T(m) can be expressed in the given reference frame as linear combination of six fourth-order tensors scaled through coefficients which are rational functions of the eigenvalues of U

GRADIENT OF DAMAGE ENHANCEMENT FOR A COHESIVE MODEL

International audienceGradient enhancements have become increasingly popular in the last decades for dealing with problems in mechanics suffering from spurious mesh sensitivity induced by strain softening. Many proposals exist in this sense and various regularization techniques have been presented and successfully applied to study localization and fracture. In short, the idea underlying almost all such techniques is that of using some extended con-stitutive equations in which information about the material microstructure is represented through a length scale-related parameter. The physical interpretation of this quantity on a micromechanical basis is still the object of an open debate, whereby its interpretation as a mere numerical regularization parameter is certainly more appropriate. From a computational standpoint, once spatial gradients and/or length scales are introduced in the constitutive equations the latter are no longer defined at the local (quadra-ture point) level but they are established at a larger scale, i.e. the scale of the structural model, in a form that could be rephrased in an integral format. Basically, for usual local models stresses, strains and internal variables are defined in a point-wise fashion whereby, as outlined in [1], their values can be regarded as the parameters of a piece-wise constant interpolation. Hence, variables computed at the Gauss point level in classical displacement-based finite element methods can be understood as fields that are in general discontinuous across elements boundaries and inside elements as well. This discontinuous pattern is indeed one of the most striking consequences of the strictly local character of the constitutive law

Graded damage in quasi-brittle solids

A novel approach to damage modeling for quasi-brittle solids is presented relying upon a differential inclusion that is closely related to the one of implicit gradient models. The proposed formulation naturally fits in the so-called nonlocal standard approach, whereby the framework of generalized standard materials is extended to include gradients of internal variables to account for the physics of the fracture phenomenon in a regularized sense, that is, via extended constitutive equations in which a length scale parameter brings to the macro level information about material microstructure. This concept is fully embodied into the present approach to quasi-brittle fracture, whereby progressive damage occurs in layers of finite thickness where the gradient of damage is bounded and a fully damaged region is understood as a fracture with no ambiguity. Key to the effective implementation of the model are the choice of two constitutive functions and the implicit tracking of regions in a state of progressive damage via Lagrange multipliers acting on internal constraints. The ideas are developed for a general Cauchy continuum and representative numerical simulations are included that demonstrate the model capabilities

Use of kriging to surrogate finite element models of bonded double cantilever beams

An algorithm based on kriging statistical interpolation for computing the surrogate response of a Finite Element model is presented. The interpolation model is calibrated via computation of Finite Element responses at a set of random occurrences of a material parameter. Such random generation concentrates at locations where the numerical model requires a higher amount of data to get the desired accuracy. As a model problem a standard fracture propagation test is analyzed. The proposed procedure is shown to be robust and accurate since responses obtained via a direct computation and use of the surrogate model turn out to be undistinguishable