50 research outputs found
Adapted raised cosine window function for array factor control with dynamic range ratio limitation
The use of window functions to improve the side
lobe level of antenna arrays is hindered by high value of
excitation currents dynamic range ratio. This paper proposes a
fast and iterative window function generation strategy aimed
at achieving improved side lobe level starting from a preset
current dynamic range ratio. Based on this strategy a new
window function is developed for standard set of conditions.info:eu-repo/semantics/publishedVersio
Object oriented programming : data preparation and visualization of FEM models
In this paper two object oriented applications are described. The former is intended to
generate data associated with the finite element method (FEM) and the later is a
three-dimensional visualization tool named 3DMesh. Both are based on the principles of
object oriented programming, namely encapsulation, inheritance and polymorphism. To
support the preparation of FEM data, a language named 3DO was developed. Its syntax is
similar to a subset of the C++ programming language. 3DO is based on object construction
and modification by methods that require a small number of arguments. With this tool, mesh
generation, definition of properties and loads and mesh refinement can be performed with
limited user effort, even when the model is complex. All the generated information can be
visualized with the program 3DMesh. This application is based on the OpenGL library and
uses the Microsoft Foundation Classes to simplify its integration in the MS-Windows
environment. 3DMesh implements an interactive navigation technique that allows the
visualization of the model interior, preserving its integrity. Model attributes and the results of
the FEM analysis can also be visualized
Near surface mounted CFRP strips for the flexural strengthening of RC columns: experimental and numerical research
In the present work, a strengthening technique based on near surface mounted (NSM) carbon fibre
laminate strips bonded into slits opened on the concrete cover is used to improve the flexural capacity of
columns subjected to bending and compression. This technique avoids the occurrence of the peeling
phenomenon, is able to mobilize the full strengthening capacity of the strips, and provides higher
protection against fire and vandalism acts. The present paper describes the adopted strengthening
technique and reports the experimental characterization of the materials involved in the strengthening
process. The results obtained in two series of reinforced concrete columns, subjected to axial compression
and lateral cyclic loading, show that a significant increase on the load carrying capacity can be achieved
by using the NSM technique. Cyclic material constitutive laws were implemented in a finite element
program and the tests with reinforced concrete columns strengthened with the NSM technique were
numerically simulated under cyclic loading. These numerical simulations reproduce the experimental
load-displacement diagrams satisfactorily.The study reported in this paper is included in the research program "CUTINSHEAR-Performance assessment of an innovative Structural FRP strengthening technique using an integrated system based oil optical fiber sensors" Supported by FCT, POCTI/ECM/59033/2004. The second author acknowledges the support provided by the grant in the ambit of this research project
Stress-crack opening relationship of enhanced performance concrete
Force-deflection responses obtained from three-point bending tests with notched beams of
enhanced performance concrete were used to determine, by means of an inverse analysis, the stress at
crack initiation, the shape of the stress-crack opening relationship and the fracture energy of this
material. This inverse analysis was performed with non-linear finite element software where crack
opening and crack propagation were simulated by discrete crack models using interface finite elements.
The influence of both the concrete age and the percentage of binder replaced by fly-ash on the fracture
parameters was analysed. In the present work, the numerical strategy is described, and the obtained
results are presented and analysed.ADI - PABERFIA
Novel hydroxyapatite/chitosan bilayered scaffold for osteochondral tissue-engineering applications : scaffold design and its performance when seeded with goat bone marrow stromal cells
Recent studies suggest that bone marrow stromal cells are a potential source of osteoblasts and chondrocytes and can be used to
regenerate damaged tissues using a tissue-engineering (TE) approach. However, these strategies require the use of an appropriate scaffold
architecture that can support the formation de novo of either bone and cartilage tissue, or both, as in the case of osteochondral defects.
The later has been attracting a great deal of attention since it is considered a difficult goal to achieve. This work consisted on developing
novel hydroxyapatite/chitosan (HA/CS) bilayered scaffold by combining a sintering and a freeze-drying technique, and aims to show the
potential of such type of scaffolds for being used in TE of osteochondral defects. The developed HA/CS bilayered scaffolds were
characterized by Fourier transform infra-red spectroscopy, X-ray diffraction analysis, micro-computed tomography, and scanning
electron microscopy (SEM). Additionally, the mechanical properties of HA/CS bilayered scaffolds were assessed under compression. In
vitro tests were also carried out, in order to study the water-uptake and weight loss profile of the HA/CS bilayered scaffolds. This was
done by means of soaking the scaffolds into a phosphate buffered saline for 1 up to 30 days. The intrinsic cytotoxicity of the HA scaffolds
and HA/CS bilayered scaffolds extract fluids was investigated by carrying out a cellular viability assay (MTS test) using Mouse
fibroblastic-like cells. Results have shown that materials do not exert any cytotoxic effect. Complementarily, in vitro (phase I) cell culture
studies were carried out to evaluate the capacity of HA and CS layers to separately, support the growth and differentiation of goat
marrow stromal cells (GBMCs) into osteoblasts and chondrocytes, respectively. Cell adhesion and morphology were analysed by SEM
while the cell viability and proliferation were assessed by MTS test and DNA quantification. The chondrogenic differentiation of
GBMCs was evaluated measuring the glucosaminoglycans synthesis. Data showed that GBMCs were able to adhere, proliferate and
osteogenic differentiation was evaluated by alkaline phosphatase activity and immunocytochemistry assays after 14 days in osteogenic
medium and into chondrocytes after 21 days in culture with chondrogenic medium. The obtained results concerning the physicochemical
and biological properties of the developed HA/CS bilayered scaffolds, show that these constructs exhibit great potential for their use in
TE strategies leading to the formation of adequate tissue substitutes for the regeneration of osteochondral defects