Hardware-in-the-Loop Test Bench for Simulation of Catenary-Pantograph Interaction (CPI) with Linear Camera Measurement.

Catenary-pantograph contact force is generally used for assessment of the current collection quality. A good current collection quality not only increases catenary lifetime but also keeps a stable electric supply and helps to avoid accidents. Low contact forces lead to electric arcs that degrade the catenary, and high contact forces generate excessive wear on the sliding surfaces. Railway track operators require track tests to ensure that catenary-pantograph force remains between safe values. However, a direct measure of the contact force requires an instrumented pantograph which is generally costly and complicated. This paper presents a test bench that allows testing virtual catenaries over real pantographs. Therefore, the contact point force behavior can be tested before the track test to guarantee that the test is passed. Moreover, due to its flexibility, the system can be used for model identification and validation, catenary testing, or contact loss simulation. The test bench also explores using computer vision as an additional sensor for each application. Results show that the system has high precision and flexibility in the available tests.

Numerical modelling of cancellous bone damage using an orthotropic failure criterion and tissue elastic properties as a function of the mineral content and microporosity.

BACKGROUND AND OBJECTIVE: Elastic and strength properties of lamellar tissue are essential to analyze the mechanical behaviour of bone at the meso- or macro-scale. Although many efforts have been made to model the architecture of cancellous bone, in general, isotropic elastic constants are assumed for tissue modelling, neglecting its non-isotropic behaviour. Therefore, isotropic damage laws are often used to estimate the bone failure. The main goals of this work are: (1) to present a new model for the estimation of the elastic properties of lamellar tissue which includes the bone mineral density (BMD) and the microporosity, (2) to address the numerical modelling of cancellous bone damage using an orthotropic failure criterion and a discrete damage mechanics analysis, including the novel approach for the tissue elastic properties aforementioned. METHODS: Numerical homogenization has been used to estimate the elastic properties of lamellar bone considering BMD and microporosity. Microcomputed Tomography (µ-CT) scans have been performed to obtain the micro-finite element (µ-FE) model of cancellous bone from a vertebra of swine. In this model, lamellar tissue is orientated by considering a unidirectional layer pattern being the mineralized collagen fibrils aligned with the most representative geometrical feature of the trabeculae network. We have considered the Hashin's failure criterion and the Material Property Degradation (MPDG) method for simulating the onset and evolution of bone damage. RESULTS: The terms of the stiffness matrix for lamellar tissue are derived as functions of the BMD and microporosity at tissue scale. Results obtained for the apparent yield strain values agree with experimental values found in the literature. The influence of the damage parameters on the bone mechanics behaviour is also presented. CONCLUSIONS: Stiffness matrix of lamellar tissue depends on both BMD and microporosity. The new approach presented in this work enables to analyze the influence of the BMD and porosity on the mechanical response of bone. Lamellar tissue orientation has to be considered in the mechanical analysis of the cancellous bone. An orthotropic failure criterion can be used to analyze the bone failure onset instead of isotropic criteria. The elastic property degradation method is an efficient procedure to analyze the failure propagation in a 3D numerical model.

Explicit expressions for the estimation of the elastic constants of lamellar bone as a function of the volumetric mineral content using a multi-scale approach.

In this work, explicit expressions to estimate all the transversely isotropic elastic constants of lamellar bone as a function of the volumetric bone mineral density (BMD) are provided. The methodology presented is based on the direct homogenization procedure using the finite element method, the continuum approach based on the Hill bounds, the least-square method and the mean field technique. Firstly, a detailed description of the volumetric content of the different components of bone is provided. The parameters defined in this step are related to the volumetric BMD considering that bone mineralization process occurs at the smallest scale length of the bone tissue. Then, a thorough description provides the details of the numerical models and the assumptions adopted to estimate the elastic behaviour of the forward scale lengths. The results highlight the noticeable influence of the BMD on the elastic modulus of lamellar bone. Power law regressions fit the Young's moduli, shear stiffness moduli and Poisson ratios. In addition, the explicit expressions obtained are applied to the estimation of the elastic constants of cortical bone. At this scale length, a representative unit cell of cortical bone is analysed including the fibril orientation pattern given by Wagermaier et al. (Biointerphases 1:1-5, 2006) and the BMD distributions observed by Granke et al. (PLoS One 8:e58043, 2012) for the osteon. Results confirm that fibril orientation arrangement governs the anisotropic behaviour of cortical bone instead of the BMD distribution. The novel explicit expressions obtained in this work can be used for improving the accuracy of bone fracture risk assessment.

Influence of the mineral staggering on the elastic properties of the mineralized collagen fibril in lamellar bone.

In this work, a three-dimensional finite element model of the staggered distribution of the mineral within the mineralized collagen fibril has been developed to characterize the lamellar bone elastic behavior at the sub-micro length scale. Minerals have been assumed to be embedded in a collagen matrix, and different degrees of mineralization have been considered allowing the growth of platelet-shaped minerals both in the axial and the transverse directions of the fibril, through the variation of the lateral space between platelets. We provide numerical values and trends for all the elastic constants of the mineralized collagen fibril as a function of the volume fraction of mineral. In our results, we verify the high influence of the mineral overlapping on the mechanical response of the fibril and we highlight that the lateral distance between crystals is relevant to the mechanical behavior of the fibril and not only the mineral overlapping in the axial direction.

Numerical modelling of the mechanical behaviour of an osteon with microcracks.

In this work, we present two strategies for the numerical modelling of microcracks and damage within an osteon. A numerical model of a single osteon under compressive diametral load is developed, including lamellae organized concentrically around the haversian canal and the presence of lacunae. Elastic properties have been estimated from micromechanical models that consider the mineralized collagen fibrils reinforced with hydroxyapatite crystals and the dominating orientation of the fibrils in each lamella. Microcracks are simulated through the node release technique, enabling propagation along the lamellae interfaces by application of failure criteria initially conceived for composite materials, in particular the Brewer and Lagacé criterion for delamination. A second approach is also presented, which is based on the progressive degradation of the stiffness at the element level as the damage increases. Both strategies are discussed, showing a good agreement with experimental evidence reported by other authors. It is concluded that interlaminar shear stresses are the main cause of failure of an osteon under compressive diametral load.

Homogenized stiffness matrices for mineralized collagen fibrils and lamellar bone using unit cell finite element models.

Mineralized collagen fibrils have been usually analyzed like a two-phase composite material where crystals are considered as platelets that constitute the reinforcement phase. Different models have been used to describe the elastic behavior of the material. In this work, it is shown that when Halpin-Tsai equations are applied to estimate elastic constants from typical constituent properties, not all crystal dimensions yield a model that satisfy thermodynamic restrictions. We provide the ranges of platelet dimensions that lead to positive definite stiffness matrices. On the other hand, a finite element model of a mineralized collagen fibril unit cell under periodic boundary conditions is analyzed. By applying six canonical load cases, homogenized stiffness matrices are numerically calculated. Results show a monoclinic behavior of the mineralized collagen fibril. In addition, a 5-layer lamellar structure is also considered where crystals rotate in adjacent layers of a lamella. The stiffness matrix of each layer is calculated applying Lekhnitskii transformations, and a new finite element model under periodic boundary conditions is analyzed to calculate the homogenized 3D anisotropic stiffness matrix of a unit cell of lamellar bone. Results are compared with the rule-of-mixtures showing in general good agreement.

First Report of Fusarium denticulatum from Sweet Potato in Venezuela.

During 2001and 2002, 53 accessions of sweet potato (Ipomoea batatas L.) from a germ plasm collection maintained in the field at Centro Nacional de Investigaciones Agropecuarias, Maracay, Venezuela, were evaluated for diseases. Sweet potato accessions Catemaco and 2878 were symptomatic for chlorotic leaf distortion with deformation of young leaves and stunted vines. Symptomatic nodes and shoot tips were excised, surface disinfested in 0.5% sodium hypochlorite, cultured on potato dextrose agar (PDA), and incubated at 28°C. Pale pink colonies with white aerial mycelium developed from symptomatic tissues. At 20°C, pure cultures on PDA developed slow-growing, aerial, white-to-pink mycelium. Pigmentation in reverse was light orange. Conidia aggregated in false heads, and orange sporodochia were abundant. Conidiophores in aerial mycelium were prostrate, short, and sometimes branched. Sporodochial conidiophores were branched. Phialides were mostly monophialidic but occasionally polyphialidic and averaged 25.0 × 3.0 µm. Microconidia were abundant, long, oval to allantoid, and 0 to 1 septate. Macroconidia were fusiform to falcate with a beaked apical cell and a footlike basal cell, 3 to 5 sepate, and 38 to 45 × 3.6 to 4.0 µm. Chlamydospores were absent. The fungus was identified as Fusarium denticulatum Nirenberg and O'Donnell (1). Ten 25-cm-long vine-tip cuttings of accessions Catemaco and 2878 were immersed in a conidial suspension (1 × 106 conidia per ml) of F. denticulatum. As a control, vines were immersed in sterile, distilled water. After inoculation, each cutting was planted in a 13-cm plastic pot containing a soil/sand (1:1) mixture. Inoculated plants were covered with plastic bags for 48 h and grown in a greenhouse at temperatures ranging from 30 to 38°C. After 3 months, three inoculated plants of accession Catemaco and two plants of accession 2878 developed purple terminals and moderate interveinal chlorosis. Leaf distortion was not observed. F. denticulatum was recovered from both symptomatic and asymptomatic inoculated plants. To our knowledge, this is the first report of F. denticulatum from sweet potato germ plasm in Venezuela. Dried, pure cultures and slides of the fungus are being deposited in the Albert S. Muller Herbario Micologico (VIA). Reference: (1) H. I. Nirenberg and K. O'Donnell. Mycologia 90:434, 1998.

Biodisponibilidad del Hierro en alimentos ecuatorianos fortificados

Un billón de personas se encuentran afectadas por deficiencia de hierro en el mundo entero, en el Ecuador también constituye un problema de salud pública especialmente en la mujeres en edad reproductiva, embarazadas, nodrizas y niños, por lo que se refiere urgente atención. La carencia de hierro se debe esencialmente a un insuficiente aporte de este mineral en la dieta, lo cual impide la satisfacción de los requerimientos del organismo. Dada la magnitud de dediciencia de hierro, actualmente se propone un conjunto de medidas de intervención orientadas a su control y prevención , a saber; suplementación, fortificación de los alimentos, diversificación de la dieta y tratmiento y prevención de la parssitosis. Según La O.M.S, la fortificación de los alimentos es la mei}jor forma de prevenir la deficiencia de hierro a nivel comunitario, en el largo plazo. De acuerdo a ls tendencias de consumo, en el Ecuador uno de los vehículos más apropiados para la fortificación es la harina de trigo, tanto por su procesamiento centralizado cuanto por su acceso generalizado y consumo masivo. El presente estudio se realizó bajo el auspicio de la Universidad de las Naciones Unidas (UNU), en colaboración con la Facultad de Ciencias Médicas de la Universidad Central del Ecuador, y el Instituto de Nutrición y Tecnología de los Alimentos de la Universidad de Chile INTA (Santiago de Chile) durante 4 meses, período en el cual recibí la asistencia y formación necesarias de especialistas y expertos en este campo. El procesamiento de datos y los análisis se realizaron en la Unidad de Hematología y Nutrición de la Facultad de Ciencias Médicas de la Universidad Central del Ecuador.

Paracoccidioidomicosis cutanea. / Cutaneous paracoccidioidomycosis

El Paracoccidioides brasiliensis, agente causal de la Paracoccidioidomicosis, penetra al organismo por via inhalatoria, ocasionando frecuentemente lesiones muco-cutanea; sin embargo, parece existir la posibilidad de la infeccion por la via cutanea, la cual quedaria localizada al sitio del traumatismo, habiendo sobre el particular 4 publicaciones de autores brasileleros. El caso que a continuacion se presenta, parece confirmar una vez mas esta posibilidad en base a: imposibilidad de demostrar la presencia del hongo en otra parte del organismo; reaccion celular el estudio histopatologico y resultados de su estudio inmunologico. Se hace mencion de otro caso de paracoccidioidomicosis cutanea, con iguales caracteristicas que el caso presentado