288 research outputs found
A mesh morphing computational method for geometry optimization of assembled mechanical systems with flexible components
No full textIn this paper an interactive computational methodology was developed assuming that shape and size optimization of flexible components can significantly improve energy absorption or storage ability in assembled systems with flexible components (AS-FC). A radial basis functions mesh morphing formulation in non-linear numerical finite element analysis, including contact problems and flow interaction, was adopted as optimal design method to optimize shape and size design parameters in AS-FC. Flexible components were assembled in finite element environment according to functional ISO-ASME tolerances specification; non-linear structural analysis with flow interaction analysis was performed. The results of the study showed that the proposed method allows to optimize the shape and size of the flexible components in AS-FC maximizing the system's ability to absorb or store energy. The potentiality of the method and its forecasting capability were discussed for the case study of an automotive crash shock in which the specific energy absorption was increased by over 40%. The case studied refers to a simple flexible component geometry, but the method could be extended to systems with more complex geometries
A method with a statistical approach for the evaluation of tolerance chains
No full textIn this paper a procedure based on a statistical approach to manufacturing for the analysis of tolerance chains is reported. In particular, the proposed approach can be summarised into two main steps. First, each single technological operation (for example, the drilling of a hole) is simulated by extracting, from a statistical distribution typical of the machine tool, the parameters characteristic of the manufacturing procedure. Then, a simulation is performed, to verify if the real features of the part can simultaneously fit the virtual gage. This method of acceptance/rejection of a part is according to the ISO/ASME standards and is representative of the real functional requirements of the part
Advanced 3D photogrammetric surface reconstruction of extensive objects by UAV camera image acquisition
No full textThis paper proposes a replicable methodology to enhance the accuracy of the
photogrammetric reconstruction of large-scale objects based on the optimization of the procedures
for Unmanned Aerial Vehicle (UAV) camera image acquisition. The relationships between the
acquisition grid shapes, the acquisition grid geometric parameters (pitches, image rates, camera
framing, flight heights), and the 3D photogrammetric surface reconstruction accuracy were studied.
Ground Sampling Distance (GSD), the necessary number of photos to assure the desired overlapping,
and the surface reconstruction accuracy were related to grid shapes, image rate, and camera framing
at different flight heights. The established relationships allow to choose the best combination of grid
shapes and acquisition grid geometric parameters to obtain the desired accuracy for the required
GSD. This outcome was assessed by means of a case study related to the ancient arched brick
Bridge of the Saracens in Adrano (Sicily, Italy). The reconstruction of the three-dimensional surfaces of
this structure, obtained by the efficient Structure-From-Motion (SfM) algorithms of the commercial
software Pix4Mapper, supported the study by validating it with experimental data. A comparison
between the surface reconstruction with different acquisition grids at different flight heights and the
measurements obtained with a 3D terrestrial laser and total station-theodolites allowed to evaluate
the accuracy in terms of Euclidean distances
Porous scaffold design based on minimal surfaces: development and assessment of variable architectures
No full textIn tissue engineering, biocompatible porous scaffolds that try to mimic the features and
function of the bone are of great relevance. In this paper, an effective method for the design of 3D
porous scaffolds is applied to the modelling of structures with variable architectures. These structures
are of interest since they are more similar to the stochastic configuration of real bone with respect
to architectures made of a unit cell replicated in three orthogonal directions, which are usually
considered for this kind of applications. This property configures them as, potentially, more suitable
to satisfy simultaneously the biological requirements and those relative to the mechanical strength.
The procedure implemented is based on the implicit surface modelling method and the use of a
triply periodic minimal surface (TPMS), specifically, the Schwarz’s Primitive (P) minimal surface,
whose geometry was considered for the development of scaffolds with different configurations.
The representative structures modelled were numerically analysed by means of finite element analysis
(FEA), considering them made of a biocompatible titanium alloy. The architectures considered were
thus assessed in terms of the relationship between the geometrical configuration and the mechanical
response to compression loading
Design and analysis of tissue engineering scaffolds based on open porous non-stochastic cells
No full textIn orthopaedics, cellular structures can be used as three-dimensional porous biomaterials that try to mimic the characteristics and function of the bone. The progress in manufacturing techniques, mainly in the field of additive manufacturing, can potentially allow the production of highly controlled pore architectures and customized implants that, however, need more sophisticated design methodologies. In this paper, the design of porous biocompatible structures based on mathematically defined surfaces (triply periodic minimal surfaces) has been considered in respect of the approach that considers unit cells entirely modelled in CAD environment. Two types of unit cell have been here considered: the cubic and the P-cell. The cubic cell is created by a 3D CAD s/w from solid features that are combined together. The P-cell is modelled using an implicit function to describe the outer surface of the cell. Two are the design parameters of the P-cell: thickness and radius. The variation of these parameters allows modifying the architecture of the basic unit of the scaffold. The modification of the radius is carried out by a procedure, based on scaling and truncation operations. The thickness of the cell is modified by thickening and closure operations on the P-isosurface. The effect of these variations on the mechanical behaviour of the scaffold has been numerically evaluated by the estimation of the stiffness of each structure considered. The results demonstrated the huge potentiality of the method and stiffness values compatible with those required for biomechanical applications
Uncommitted gastrointestinal stromal tumour. Case report.
No full textGastrointestinal Stromal Tumours (GIST) are mesenchymal tumours with uncertain prognosis. Malignant variety represents about 2.0% of malignant gastroenteric tumours. The Authors report a clinical case of malignant gastric and duodenojejunal GIST, in which the only surgical treatment seems to be definitive. R. S., a 69-year-old female, was admitted for asthenia and fever in January 1997. Endoscopic exploration, ultrasonography and CT-scan of the abdomen demonstrated an exophytic tumour in the greater gastric curvature and one tumour of 5.5 cm of diameter in the Treitz's angle. We performed a resection of the gastric tumour and the duodenojejunal angle. Postoperative course was uneventful and the patient was discharged after 14 postoperative hospital days. Histological analysis showed two spindle cells stromal tumours with mitotic rate > 20/10 HPF. The immunohistochemistry demonstrated the uncommitted origin of tumour cells. The patient refused the chemotherapy treatment. There was no local recurrence or metastasis at a follow up of 47 months, in spite the high malignancy degree. For this reason and because of the uncertain behaviour of benign GIST, the authors propose a lifelong follow up of the patients managed with potentially curative surgical resection
Modeling, assessment, and design of porous cells based on schwartz primitive surface for bone scaffolds
No full textThe design of bone scafolds for tissue regeneration is a topic of great interest, which involves diferent issues related to geometry of architectures, mechanical behavior, and biological requirements, whose optimal combination determines the success of an implant. Additive manufacturing (AM) has widened the capability to produce structures with complex geometries, which should potentially satisfy the diferent requirements. These architectures can be obtained by means of refned methods and have to be assessed in terms of geometrical and mechanical properties. In this paper a triply periodic minimal surface (TPMS), the Schwarz's Primitive surface (P-surface), has been considered as scafold unit cell and conveniently parameterized in order to investigate the efect of modulation of analytical parameters on the P-cell geometry and on its properties. Several are the cell properties, which can afect the scafold performance. Due to the important biofunctional role that the surface curvature plays in mechanisms of cellular proliferation and diferentiation, in this paper, in addition to properties considering the cell geometry in its whole (such as volume fraction or pore size), new properties were proposed. Tese properties involve, particularly, the evaluation of local geometrical-diferential properties of the P-surface. Te results of this P-cell comprehensive characterization are very useful for the design of customized bone scafolds able to satisfy both biological and mechanical requirements. A numerical structural evaluation, by means of fnite element method (FEM), was performed in order to assess the stifness of solid P-cells as a function of the changes of the analytical parameters of outer surface and the thickness of cell. Finally, the relationship between stifness and porosity has been analyzed, given the relevance that this property has for bone scafolds design
Design and analysis of tissue engineering scaffolds based on open porous non-stochastic cells
No full textBrain-derived neurotrophic factor (BDNF) and polysialylated-neural cell adhesion molecule (PSA-NCAM) in the human brainstem precerebellar nuclei from prenatal to adult age.
No full textOccurrence and distribution of the neurotrophin brain-derived neurotrophic factor (BDNF)
and polysialylated-neural cell adhesion molecule (PSA-NCAM), a neuroplasticity marker
known to modulate BDNF signalling, were examined by immunohistochemistry in the
human brainstem precerebellar nuclei at prenatal, perinatal and adult age. Western blot
analysis performed in human brainstem showed for both molecules a single protein band
compatible with the molecular weight of the dimeric form of mature BDNF and with that of
PSA-NCAM. Detectability of both molecules up to 72 h post-mortem was also assessed in rat
brain. In neuronal perikarya, BDNF-like immunoreactivity (LI) appeared as intracytoplasmic
granules, whereas PSA-NCAM-LI appeared mostly as peripheral staining, indicative of
membrane labelling; immunoreactivity to both substances also labelled nerve fibres and
terminals. BDNF- and PSA-NCAM-LI occurred in the external cuneate nucleus,
perihypoglossal nuclei, inferior olive complex, arcuate nucleus, lateral reticular formation,
vestibular nuclei, pontine reticulotegmental and paramedian reticular nuclei, and pontine
basilar nuclei. With few exceptions, for both substances the distribution pattern detected at
prenatal age persisted later on, though the immunoreactivity appeared often higher in preand
full-term newborns than in adult specimens. The results obtained suggest that BDNF
operates in the development, maturation, maintenance and plasticity of human brainstem
precerebellar neuronal systems. They also imply a multiple origin for the BDNF-LI of the
human cerebellum. The codistribution of BDNF- and PSA-NCAM-LI in analyzed regions
suggests that PSA-NCAM may modulate the functional interaction between BDNF and its
high and low affinity receptors, an issue worth further analysis, particularly in view of the
possible clinical significance of neuronal trophism in cerebellar neurodegenerative
disorders.
A lunar rover leg: Optimal design of a decoupling joint
No full textThe development of vehicles for the exploration in the lunar environment is a topic of great interest. In particular, recently, there has been a growing attention toward the lunar rovers for working missions since the building of lunar bases is a primary objective for the lunar exploration. However, these vehicles have peculiar requirements to be taken into account in the design of each component. In this paper a particular component of a worker rover, developed as a collaboration between two academic institutions, has been designed for an optimal functionality. Each leg of this rover comprises a mechanism for lifting weights and the component considered, a decoupling joint, is a part of this mechanism. The design optimization was performed by means of parametric modelling and numerical simulations
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