Computational Modeling of Discrete Mechanical Systems and Complex Networks: Where We are and Where We are Going

WHERE WE ARE IN MODELING MECHANICAL, TRAFFIC, AND SOCIO-ECONOMICAL DISCRETE SYSTEMS Discrete systems have been firstly introduced in physics (Fisher and Wiodm, 1969; Noor and Nemeth, 1980; Adhikari et al., 1996; Kornyak, 2009) to simulate materials at the microand nano-scales where a continuum description of matter breaks down. The constituents can be atoms or molecules and their interactions are usually modeled by force fields resulting from chemical potentials or weak van der Waals interactions, depending on the type of bonding. These models have been further exploited in mechanics with the aim of predicting macroscopic properties such as strength and toughness from the non-linear interactions taking place between the constituents at the different scales. Pioneering attempts in mechanics to model discrete mechanical systems are those using lattice models (van Mier et al., 1995; Schlangen and Garboczi, 1997) characterized by a network of nodes connected by links modeled by beams. Although proven to suffer from meshdependency, they have been broadly used for studying the non-linear fracture behavior of concrete at the meso-scale. Another line of research regards the generalizedBorn approach (Pellegrini and Field, 2002; Marenich et al., 2013), firstly used in chemistry to model a solute represented as a set of three-dimensional spheres into a continuum medium solvent, then applied in molecular mechanics (called MM/GBSA) to investigate contact and fracture of bodies at the micro-scale. The high-computational power and the development of powerful open source software allow nowadays the design of wide discrete scalable models composed of up to millions of particles or molecules whose equations of motions and mutual interactions are described by highly nonlinear interatomic potential laws. This is the field of molecular dynamics (MD), which led to the development of specific explicit time integration schemes (like the velocity-verlet integration scheme) to solve large systems of equations with a reduced computational cost. Car and Parrinello (1985) proposed a minimization of the total energy of the system by applying a dynamical simulated annealing based on MD. MD computations can also be coupled with continuum simulations by multi-scale methods. Among the many strategies available in the literature, (Shenoy et al., 1999; Knap and Ortiz, 2001) developed an approach based on the Tadmor's quasi-continuum method (Tadmor et al., 1996) operating on a representative atomistic zone with a reduced number of degrees of freedom. Local minima of the whole system potential energy are determined via the total energy from a cluster of atoms, avoiding the complete calculation of the full atomistic force field. The MD enriched continuum method by Belytschko and Xiao (2003) and Xiao and Belytschko (2003) was also another pioneering approach to couple a potential energy Hamiltonian calculation conducted on a fine scale MD domain with a Lagrangian calculation on a coarse scale continuum domain with an overlapped bridging domain among the two representations. Recently, an implementation of interatomic potential laws within a displacement-based finite element (FE) formulation has also been proposed in Nasdala et al. (2010), with a rigorous implicit solution scheme, aiming at generating models where non-linear discrete and continuous systems can be suitably combined. Discrete systems made of nodes and links are also used in other disciplines than mechanics to model transport or socio-economical networks (Caldarelli and Vespignani, 2007; Whrittle, 2012). Based on a continuum version of traffic conservation along a link, Lighthill and Whitham (1955) and Whitham (1974) and independently Richards (1956) proposed the LWR model where the governing equation describing the dependency of the traffic flux on time and on location along a link is a nonlinear hyperbolic partial differential equation (PDE) analogous to that describing the propagation of the front of a wave inside a medium. For a homogenous link where the velocity of traffic is the same at any location and no shocks on the traffic flow are present, the integration of the LWR PDE leads to a non-linear relation between the traffic flow and the density of vehicles, which fully represents the traffic state. Also, in economics, it is of great interest to quantify the effect of breaking a link over the whole network response by simulating the dynamics of flow redistribution. Again a flow model can be used as suggested in Zhou et al. (2010) to decode a huge human crowd without distinction betwee

Design of thermo-piezoelectric microstructured bending actuators via multi-field asymptotic homogenization

The use of integrated MicroElectroMechanical systems (MEMS) is recently spread thanks to their improved sensitivity, accuracy and reliability. Accurate preliminary computations born from the need of high precision in the manufacturing process of such devices. Piezoelectric materials are broadly employed in this field as direct converters between mechanical and electrical signals and some of these piezoelectric materials show pyroelectric features, which involve thermo-electrical interactions. Pyroelectric bending actuators are analyzed in the present study in plane conditions. They consists of active PZT layers with in-plane polarization and a microstructured composite layer characterized by a periodic microstructure where PZT fibers with an out of plane polarization are immersed in a polymeric matrix. The constitutive law of the composite layer at the macroscale has been determined by means of a multi-field asymptotic homogenization technique, recently developed for thermo-piezoelectric materials. Overall constitutive equations characterizing the behavior of the microstructured layer at the macroscale have been derived and the closed form of the overall constitutive tensors has been provided for the equivalent first-order (Cauchy) homogenized continuum. Deflection of unimorph and bimorph bender actuators has been investigated in relation to their geometrical features, exploiting the out of plane piezoelectric properties of the composite layer, which modify the stiffness of the entire bender. An accurate description of benders behavior at the structural length scale is of fundamental importance in order to design devices with high performances. In this regard, the influence of the microstructure on the global response of the actuator is investigated in the present study in order to understand how the composite material can be tailored to meet specific design requirements

Simulated hail impacts on flexible photovoltaic laminates: testing and modelling

The problem of simulated low-velocity hail impacts on flexible photovoltaic (PV) modules resting on a substrate with variable stiffness is investigated. For this type of PV module it is shown that the prescriptions of the IEC 61215 International Standard for quality control used for rigid (glass-covered) PV modules should be augmented by taking into account their real mounting condition and the stiffness of the substrate in the simulated hail impact tests. Moreover, electroluminescence inspection of the crack pattern should be made in addition to electric power output measurements.An implicit finite element simulation of the contact problem in dynamics is also proposed, with two different degrees of accuracy, to interpret the experimentally observed extension of cracking. Results pinpoint the important role of stress wave propagation and reflection in the case of soft substrates

Transrectal ultrasonography of the adrenal glands in donkeys (Equus asinus)

Little information is available for medical imaging in donkeys and no report about adrenal glands ultrasonography can be found in scientific literature. The feasibility of transrectal ultrasonography of the adrenal glands was tested on 30 healthy donkeys using a 10 MHz linear transducer. Mean age of animals was 10.7 ±4.8 years, mean weight 275.0 ±62.9 Kg and mean height 126.7 ±7.1 cm. The left adrenal gland was visualized in all donkeys. The right gland ultrasonography was not feasible in seven animals with a height less than 116 cm. The left gland was visualized as a linear or slightly curved structure, the right gland was most often S-shaped. In both glands, an hypechoic peripheral zone was identified as the cortex with an inner, hyperechoic medulla. The length was 5.49 ±1.90 cm and 5.15 ±1.10 cm for right and left gland, respectively. Right gland whole and medullary thickness were 0.71 ±0.11 cm and 0.24 ±0.09 cm, 0.65 ±0.13 cm and 0.21 ±0.07 cm, 0.56 ±0.17 cm and 0.25 ±0.07 cm for cranial pole, middle point and caudal pole respectively. Left gland whole and medullary thickness were 0.69 ±0.13 cm and 0.25 ±0.09 cm, 0.66 ±0.13 cm and 0.23 ±0.09 cm, 0.57 ±0.15 cm and 0.26 ±0.09 cm for cranial pole, middle point and caudal pole respectively. There was a significant correlation between height and the entire length of the left gland. Ultrasonography of the adrenal glands is a suitable tool for evaluation of both adrenal glands in most of the donkey. The size is a limiting factor for proper visualization of the right gland

Effects of Single-Dose Prucalopride on Intestinal Hypomotility in Horses: Preliminary Observations

Abnormalities of gastrointestinal motility are often a challenge in horses; however, the use of prokinetic drugs in such conditions must be firmly established yet. For this reason we carried out a preliminary study on the effects of prucalopride on intestinal motor activity of horses with gut hypomotility. The effect of prucalopride per os by oral dose syringe (2 mg/100 kg body weight) was assessed by abdominal ultrasound (evaluating duodenal, cecal, and colonic motor activity) in six horses with gut hypomotility. After administration of prucalopride, a significant increase of contractile activity was found in the duodenum at 30 minutes (p = 0.0005), 60 minutes (p = 0.01) and 90 minutes (p = 0.01), whereas in the cecum and in the left colon the increase was only present at 60 minutes (p = 0.03, and p = 0.02, respectively). No changes from baseline heart and respiratory rate or behavior side effects were observed after administration of the drug and throughout the observation period. Prucalopride may be a useful adjunct to the therapeutic armamentary for treating hypomotile upper gut conditions of horses. Dosing information is however needed to establish its actual clinical efficacy and its proper effects on the large bowel in these animals

Trabajar en/desde/con el territorio en los barrios : una reconstrucción de experiencias problematizadas por el territorio

Este trabajo apunta a reconstruir la acción-investigación que se viene desarrollando desde la organización ArqCom La Plata (LP). Apuntamos a sistematizar y conceptualizar las prácticas territoriales llevadas adelante entorno a los problemas del hábitat, apostando y aportando a una construcción dinámica y dialéctica entre reflexión y acción. En contextos donde la desigualdad social se profundiza cada vez más, es necesario que los profesionales de la Universidad Pública podamos reconocer qué aportamos, a quiénes dirigimos nuestros esfuerzos e ideas, sobre qué problemáticas de la sociedad trabajamos. Es desde esta perspectiva crítica entorno a qué conocimiento se genera desde la Universidad, que se construyen las prácticas de ArqCom LP, articulando desde prácticas concretas que discutan con las reflexiones conceptuales y discusiones contemporáneas, entendiendo la urgencia de generar propuestas de acción que permitan divisar un horizonte de transformación. Este trabajo, construido y pensado mayormente desde la arquitectura, pretende discutir con otras disciplinas, nuevas preguntas, herramientas y reflexiones en torno al abordaje de lo urbano, de la ciudad, el territorio y el habitar de la misma. En la necesaria auto- reflexión constante y construcción de nuevas miradas, de reconstrucción de las disciplinas mismas, creemos indispensable poder dialogar con diferentes actores que nos permitan ampliar las perspectivas, apuntando a detectar esfuerzos que puedan aportar y construir en conjunto.Fil: Durante, María Eugenia. Universidad Nacional de La PlataFil: Di Croce Garay, Andrea. Universidad Nacional de La PlataFil: Paggi, María Guillermina. Universidad Nacional de La Plat

Transrectal ultrasonography of the adrenal glands in donkeys (Equus asinus)

Little information is available for medical imaging in donkeys and no report about adrenal glands ultrasonography can be found in scientific literature. The feasibility of transrectal ultrasonography of the adrenal glands was tested on 30 healthy donkeys using a 10 MHz linear transducer. Mean age of animals was 10.7 ±4.8 years, mean weight 275.0 ±62.9 Kg and mean height 126.7 ±7.1 cm. The left adrenal gland was visualized in all donkeys. The right gland ultrasonography was not feasible in seven animals with a height less than 116 cm. The left gland was visualized as a linear or slightly curved structure, the right gland was most often S-shaped. In both glands, an hypechoic peripheral zone was identified as the cortex with an inner, hyperechoic medulla. The length was 5.49 ±1.90 cm and 5.15 ±1.10 cm for right and left gland, respectively. Right gland whole and medullary thickness were 0.71 ±0.11 cm and 0.24 ±0.09 cm, 0.65 ±0.13 cm and 0.21 ±0.07 cm, 0.56 ±0.17 cm and 0.25 ±0.07 cm for cranial pole, middle point and caudal pole respectively. Left gland whole and medullary thickness were 0.69 ±0.13 cm and 0.25 ±0.09 cm, 0.66 ±0.13 cm and 0.23 ±0.09 cm, 0.57 ±0.15 cm and 0.26 ±0.09 cm for cranial pole, middle point and caudal pole respectively. There was a significant correlation between height and the entire length of the left gland. Ultrasonography of the adrenal glands is a suitable tool for evaluation of both adrenal glands in most of the donkey. The size is a limiting factor for proper visualization of the right gland