64 research outputs found
Redesign of an auto-levelling base for submarine seismic sensor
The OBS (acronym of Ocean Bottom Seismometer) is a system to monitor the submarine
seismic activity. To properly work, an OBS system needs a suitable auto-levelling base to
maintain a fixed (horizontal) position during the measurement phases.
In this work a new auto-levelling base for submarine seismic sensors has been designed.
During the redesign process a preliminary phase of analysis of the state of art has been
made. Afterwards, the technological solutions chosen by different manufactures have been
critically analysed, and a full description of their functionalities, working principles and system
performances has been carried out. Later, some innovative concepts have been proposed.
Among these ones, the most interesting are the auto-levelling bases with spherical joint,
based on: air bearings, ball bearings and magnetic levitation systems.
The concept scoring method has been used to identify. as best concept, the auto-levelling
base with spherical joint and air bearings system.
Successively, the chosen concept has been implemented: the technical working principles
have been studied to choose the best solutions in terms of dimensions, shapes, materials of
all base components. A full parametric CAD model of the auto-levelling base has been also
created.
The new designed base, by using a very innovative auto-levelling system, allows to obtain
very good results as regards the accuracy of positioning, so ensuring a remarkable
improvement of the performances of the ocean bottom seismometers
Influence of the Screw Positioning on the Stability of Locking Plate for Proximal Tibial Fractures: A Numerical Approach
Tibial fractures are common injuries in people. The proper treatment of these fractures is important in order to recover complete mobility. The aim of this work was to investigate if screw positioning in plates for proximal tibial fractures can affect the stability of the system, and if it can consequently influence the patient healing time. In fact, a more stable construct could allow the reduction of the non-weight-bearing period and consequently speed up the healing process. For that purpose, virtual models of fractured bone/plate assemblies were created, and numerical simulations were performed to evaluate the reaction forces and the maximum value of the contact pressure at the screw/bone interface. A Schatzker type I tibial fracture was considered, and four different screw configurations were investigated. The obtained results demonstrated that, for this specific case study, screw orientation affected the pressure distribution at the screw/bone interface. The proposed approach could be used effectively to investigate different fracture types in order to give orthopaedists useful guidelines for the treatment of proximal tibial fracture
Parametric Hull Design with Rational Bézier Curves and Estimation of Performances
In this paper, a tool able to support the sailing yacht designer during the early stage of the
design process has been developed. Cubic Rational Bézier curves have been selected to describe the
main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of
a set of parameters, say the length of waterline, the beam of the waterline, canoe body draft and some
dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical
constraints imposed on the curves (e.g., continuity, endpoint angles, curvature) have been conceived
aimed to avoid unreasonable shapes. These curves can be imported into any commercial Computer
Aided Design (CAD) software and used as a frame to fit with a surface. The resistance of the hull can
be calculated and plotted in order to have a real time estimation of the performances. The algorithm
and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the
usability and the precision of the tool, two existing sailboats with different characteristics have been
successfully replicated and a new design, taking advantages of both the hulls, has been developed.
The new design shows good performances in terms of resistance values in a wide range of Froude
numbers with respect to the original hulls
Study of a constrained finite element elbow prosthesis: the influence of the implant placement
BackgroundThe functional results of total elbow arthroplasty (TEA) are controversial and the medium- to long-term revision rates are relatively high. The aim of the present study was to analyze the stresses of TEA in its classic configuration, identify the areas of greatest stress in the prosthesis-bone-cement interface, and evaluate the most wearing working conditions.Materials and methodsBy means of a reverse engineering process and using a 3D laser scanner, CAD (computer-aided drafting) models of a constrained elbow prosthesis were acquired. These CAD models were developed and their elastic properties, resistance, and stresses were studied through finite element analysis (finite element method-FEM). The obtained 3D elbow-prosthesis model was then evaluated in cyclic flexion-extension movements (> 10 million cycles). We highlighted the configuration of the angle at which the highest stresses and the areas most at risk of implant mobilization develop. Finally, we performed a quantitative study of the stress state after varying the positioning of the stem of the ulnar component in the sagittal plane by +/- 3 degrees.ResultsThe greatest von Mises stress state in the bone component for the 90 degrees working configuration was 3.1635 MPa, which occurred in the most proximal portion of the humeral blade and in the proximal middle third of the shaft. At the ulnar level, peaks of 4.1763 MPa were recorded at the proximal coronoid/metaepiphysis level. The minimum elastic resistance and therefore the greatest stress states were recorded in the bone region at the apex of the ulnar stem (0.001967 MPa). The results of the analysis for the working configurations at 0 degrees and 145 degrees showed significant reductions in the stress states for both prosthetic components; similarly, varying the positioning of the ulnar component at 90 degrees (- 3 degrees in the sagittal plane, 0 degrees in the frontal plane) resulted in better working conditions with a greater resulting developed force and a lower stress peak in the ulnar cement.ConclusionThe areas of greatest stress occur in specific regions of the ulnar and humeral components at the bone-cement-prosthesis interface. The heaviest configuration in terms of stresses was when the elbow was flexed at 90 degrees. Variations in the positioning in the sagittal plane can mechanically affect the movement, possibly resulting in longer survival of the implant.Level of evidence:
Characterization of Brain Lysosomal Activities in GBA-Related and Sporadic Parkinson’s Disease and Dementia with Lewy Bodies
Mutations in the GBA gene, encoding the lysosomal hydrolase glucocerebrosidase (GCase), are the most common known genetic risk factor for Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). The present study aims to gain more insight into changes in lysosomal activity in different brain regions of sporadic PD and DLB patients, screened for GBA variants. Enzymatic activities of GCase, β-hexosaminidase, and cathepsin D were measured in the frontal cortex, putamen, and substantia nigra (SN) of a cohort of patients with advanced PD and DLB as well as age-matched non-demented controls (n = 15/group) using fluorometric assays. Decreased activity of GCase (− 21%) and of cathepsin D (− 15%) was found in the SN and frontal cortex of patients with PD and DLB compared to controls, respectively. Population stratification was applied based on GBA genotype, showing substantially lower GCase activity (~ − 40%) in GBA variant carriers in all regions. GCase activity was further significantly decreased in the SN of PD and DLB patients without GBA variants in comparison to controls without GBA variants. Our results show decreased GCase activity in brains of PD and DLB patients with and without GBA variants, most pronounced in the SN. The results of our study confirm findings from previous studies, suggesting a role for GCase in GBA-associated as well as sporadic PD and DLB
Influence of the Screw Positioning on the Stability of Locking Plate for Proximal Tibial Fractures: A Numerical Approach
Tibial fractures are common injuries in people. The proper treatment of these fractures is important in order to recover complete mobility. The aim of this work was to investigate if screw positioning in plates for proximal tibial fractures can affect the stability of the system, and if it can consequently influence the patient healing time. In fact, a more stable construct could allow the reduction of the non-weight-bearing period and consequently speed up the healing process. For that purpose, virtual models of fractured bone/plate assemblies were created, and numerical simulations were performed to evaluate the reaction forces and the maximum value of the contact pressure at the screw/bone interface. A Schatzker type I tibial fracture was considered, and four different screw configurations were investigated. The obtained results demonstrated that, for this specific case study, screw orientation affected the pressure distribution at the screw/bone interface. The proposed approach could be used effectively to investigate different fracture types in order to give orthopaedists useful guidelines for the treatment of proximal tibial fractures
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