158 research outputs found
2D finite elements for the computational analysis of crack propagation in brittle materials and the handling of double discontinuities
Crack growth simulations by way of the traditional Finite Element Method claim progressive remeshing to fit the geometry of the fracture, severely increasing the computational effort. Methods such as the eXtended Finite Element Method (XFEM) allow to overcome this limitation by means of nodal shape functions multiplied by Heaviside step function to enrich finite element nodes. Through the medium of a discontinuous field, the entire geometry of the discontinuity can be modelled regardless of
the mesh, avoiding remeshing. In this paper two shell-type XFEM elements (a three-node triangular element and a four-node quadrangular element) to evaluate crack propagation in brittle materials are presented. These elements have been implemented into the widespread opensource framework OpenSees to evaluate crack propagation into a plane shell subjected to monotonically increasing loads. Moreover, in the perspective of fracture propagation simulations, the problem of managing multiple cracks without remeshing or operating subdivisions on the integration domain has been investigated and a four-node quadrangular finite element
for the computational analysis of double crossed discontinuities by the means of equivalent polynomials is presented in this paper.
Equivalent polynomials allow to overcome inaccuracies on the results when performing standard numerical integration (e.g. Gauss-Legendre quadrature rule) over the entire domain of XFEM elements, without the need of defining integration subdomains. The presented work and the computational strategy behind it may be extremely useful not only in the field of fracture mechanics, but also to solve complex geometry problems or material discontinuities
Analisi della resistenza a fatica di giunzioni saldate per sospensioni automobilistiche
La presente tesi si inserisce in uno studio sulla resistenza a fatica delle saldature.
Lo scopo è quello di identificare un criterio scientifico adatto alla previsione di resistenza a fatica dei giunti saldati, indipendentemente dal giunto e dalla tecnica applicata; questo studio è utile in ambito automobilistico per la progettazione di componenti saldati, senza adottare coefficienti di sicurezza eccessivamente cautelativi a causa di una non completa conoscenza del fenomeno, permettendo una costruzione di componenti più leggera.
All’interno dell’elaborato è stata svolta una ricerca bibliografica dove si mettono in evidenza le problematiche che insorgono nella verifica a fatica a causa della tecnica di saldatura. Successivamente è stato fatto un veloce riepilogo delle metodologie di verifica a fatica più frequentemente adoperate.
Lo svolgimento della tesi si incentra sullo studio di provini assimilabili a semplici coprigiunti, sono stati applicati due diversi criteri di verifica a fatica tramite la realizzazione di sottomodelli, simulati con l’ausilio del programma agli elementi finiti Ansys. I risultati ottenuti sono stati adoperati per ricavare le curve di regressione S-N.
Lo scopo ultimo della tesi è verificare l’affidabilità delle curve di progetto fornite in bibliografia a confronto con le curve di resistenza a fatica ottenute, analizzando eventuali incoerenze
Attention-Based Real-Time Defenses for Physical Adversarial Attacks in Vision Applications
Deep neural networks exhibit excellent performance in computer vision tasks,
but their vulnerability to real-world adversarial attacks, achieved through
physical objects that can corrupt their predictions, raises serious security
concerns for their application in safety-critical domains. Existing defense
methods focus on single-frame analysis and are characterized by high
computational costs that limit their applicability in multi-frame scenarios,
where real-time decisions are crucial.
To address this problem, this paper proposes an efficient attention-based
defense mechanism that exploits adversarial channel-attention to quickly
identify and track malicious objects in shallow network layers and mask their
adversarial effects in a multi-frame setting. This work advances the state of
the art by enhancing existing over-activation techniques for real-world
adversarial attacks to make them usable in real-time applications. It also
introduces an efficient multi-frame defense framework, validating its efficacy
through extensive experiments aimed at evaluating both defense performance and
computational cost
Strategic behaviour of Italian fruit and vegetables importers from South Mediterranean Countries faced with food safety standards
The aim of this study was to analyse the heterogeneity of Italian specialized importers in Southern Mediterranean Countries. We analysed a national representative sample and defined a profile of companies according to the safety of fruit and vegetable im- ports, organization of chain by suppliers and clients and efforts in safety controls. We showed that the type of supply chain affects the importers’ strategies encouraging them to implement stricter standards, such as private standards, with respect to pub- lic law in order to meet customer needs and provide a sufficient degree of differentia- tion. These strategies, however, are not always aimed at obtaining a price premium, but are taken above all to ensure the maintenance of the reputation of the companies towards the most demanding customers and stabilize its market share
An Approach for Improving Automatic Mouth Emotion Recognition
The study proposes and tests a technique for automated emotion recognition
through mouth detection via Convolutional Neural Networks (CNN), meant to be
applied for supporting people with health disorders with communication skills
issues (e.g. muscle wasting, stroke, autism, or, more simply, pain) in order to
recognize emotions and generate real-time feedback, or data feeding supporting
systems. The software system starts the computation identifying if a face is
present on the acquired image, then it looks for the mouth location and
extracts the corresponding features. Both tasks are carried out using Haar
Feature-based Classifiers, which guarantee fast execution and promising
performance. If our previous works focused on visual micro-expressions for
personalized training on a single user, this strategy aims to train the system
also on generalized faces data sets
An International Survey on Taking Up a Career in Cardiovascular Research: Opportunities and Biases toward Would-Be Physician-Scientists
Background
Cardiovascular research is the main shaper of clinical evidence underpinning decision making, with its cyclic progression of junior researchers to mature faculty members. Despite efforts at improving cardiovascular research training, several unmet needs persist. We aimed to appraise current perceptions on cardiovascular research training with an international survey.
Methods and Results
We administered a 20-closed-question survey to mentors and mentees belonging to different international institutions. A total of 247 (12%) surveys were available (out of 2,000 invitations). Overall, mentees and mentors were reasonably satisfied with the educational and research resources. Significant differences were found analyzing results according to gender, geographic area, training and full-time researcher status. Specifically, women proved significantly less satisfied than men, disclosed access to fewer resources and less support from mentors (all P
Conclusions
Several potential biases appear to be present in the way training in cardiovascular research is provided worldwide, including one against women. If confirmed, these data require proactive measures to decrease discriminations and improve the cardiovascular research training quality
Spring forth diversity: Specialist species contribute to the conservation value of headwater springs and streams at the landscape scale
Headwater springs and streams often occur in relatively remote areas, reducing their exposure to human influences and thus increasing their collective capacity to support high biodiversity. Their aquatic macroinvertebrate communities can include species of conservation interest, some of which are specialists associated with groundwater inputs, low water temperature or temporary flow. However, the inaccessibility of some spring and stream networks has left their communities poorly characterized, limiting our capacity to implement effective conservation strategies. We characterized the biodiversity and conservation value of macroinvertebrate communities in a network of 51 relatively inaccessible and unimpacted headwater spring and stream sites spanning multiple catchments in a single landscape type: the chalk downland of south England. At each site, we kick sampled macroinvertebrate communities and recorded environmental variables, including flow permanence. To represent each community, we calculated taxa richness, coverage‐adjusted Hill‐Shannon diversity, the local contribution to beta diversity, and an index of richness and species rarity. We used the latter three metrics to rank sites based on their biodiversity and conservation value and analyzed relationships between metrics and environmental variables. We found specialists of springs, cold waters, groundwaters and temporary flow regimes, including rare species of conservation value. Some metrics responded to environmental variables, but top‐ranking sites had highly variable environmental characteristics. We highlight the value of individual headwater streams with contrasting characteristics as contributors to ecologically heterogeneous site networks. Our results can inform landscape‐scale management strategies that protect headwaters as refuges that support biodiverse communities, including rare species, as they adapt to global change
MITS: the Multi-Imaging Transient Spectrograph for SOXS
The Son Of X-Shooter (SOXS) is a medium resolution spectrograph R~4500
proposed for the ESO 3.6 m NTT. We present the optical design of the UV-VIS arm
of SOXS which employs high efficiency ion-etched gratings used in first order
(m=1) as the main dispersers. The spectral band is split into four channels
which are directed to individual gratings, and imaged simultaneously by a
single three-element catadioptric camera. The expected throughput of our design
is >60% including contingency. The SOXS collaboration expects first light in
early 2021. This paper is one of several papers presented in these proceedings
describing the full SOXS instrument
The VIS detector system of SOXS
SOXS will be a unique spectroscopic facility for the ESO NTT telescope able
to cover the optical and NIR bands thanks to two different arms: the UV-VIS
(350-850 nm), and the NIR (800-1800 nm). In this article, we describe the
design of the visible camera cryostat and the architecture of the acquisition
system. The UV-VIS detector system is based on a e2v CCD 44-82, a custom
detector head coupled with the ESO continuous ow cryostats (CFC) cooling system
and the NGC CCD controller developed by ESO. This paper outlines the status of
the system and describes the design of the different parts that made up the
UV-VIS arm and is accompanied by a series of contributions describing the SOXS
design solutions.Comment: 9 pages, 13 figures, to be published in SPIE Proceedings 1070
The Acquisition Camera System for SOXS at NTT
SOXS (Son of X-Shooter) will be the new medium resolution (R4500 for a
1 arcsec slit), high-efficiency, wide band spectrograph for the ESO-NTT
telescope on La Silla. It will be able to cover simultaneously optical and NIR
bands (350-2000nm) using two different arms and a pre-slit Common Path feeding
system. SOXS will provide an unique facility to follow up any kind of transient
event with the best possible response time in addition to high efficiency and
availability. Furthermore, a Calibration Unit and an Acquisition Camera System
with all the necessary relay optics will be connected to the Common Path
sub-system. The Acquisition Camera, working in optical regime, will be
primarily focused on target acquisition and secondary guiding, but will also
provide an imaging mode for scientific photometry. In this work we give an
overview of the Acquisition Camera System for SOXS with all the different
functionalities. The optical and mechanical design of the system are also
presented together with the preliminary performances in terms of optical
quality, throughput, magnitude limits and photometric properties.Comment: 9 pages, 7 figures, SPIE conferenc
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