Politecnio die Bari - Catalogo di prodotti della Ricerca
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Prediction of Weld Geometry and Size in Low-Frequency Laser Wobble Welding of Dissimilar Automotive Steels
No full textA stable welding mode within the oscillating path is a complex challenge in wobble welding. The formation of a fusion zone involves a complex laser energy distribution along the oscillating path, which is governed by both oscillation (frequency, amplitude) and laser (laser power, welding speed) parameters. In this study, a coupled thermo-fluid dynamical model was developed to investigate the combined effects of oscillation and laser parameters on seam formation during low-frequency laser wobble welding. An experimental result showed the effectiveness of a circular wobble path to bridge the gaps within the plates of dissimilar automotive steels. The microstructure of the fusion zone and heat-affected zone underwent self-tempering along the circular path, resulting in the tempered martensite structure with quasi-uniform microhardness distribution. According to numerical data, the oscillating amplitude and welding speed were found to be the primary factors influencing the distribution of laser energy density, which in turn defines the final shape of the fusion zone. The periodic depth and shape of the weld seam were fixed along the oscillation path. A low amplitude resulted in a concentration of laser energy density at the centerline of the linear motion, leading to the formation of a typical U-shaped seam. Higher welding speed led to the spread of the peak laser energy density along the oscillation path, thereby promoting a more stable weld pool shape even at larger amplitudes. Conversely, lower welding speeds result in strong variations in weld seams with a W-shaped fusion zone
Search for heavy long-lived charged particles with large ionization energy loss in proton-proton collisions at = 13 TeV
No full textBacterial adhesion eradication and biofilm inhibition through laser surface texturing
No full textThe growing problem of bacterial and microbial resistance to antibiotics is closely tied to the ability of such microorganisms to form biofilms, composed of complex microbial communities embedded in an extracellular matrix (EPS). In fact, quorum sensing enables bacteria to coordinate their behaviors within biofilms, further increasing their resistance to external threats compared to free-floating forms, thus complicating the treatment with conventional antibiotics. Therefore, biofilm formation is closely linked to antimicrobial resistance (AMR), which significantly increases health threats and the costs for the healthcare public system. Traditional antibacterial agents, such as silver ion coatings, photocatalytic materials, leaching biocides, and polymer chains, have shown some limitations, such as pathogen resistance, durability issues, and potential health risks. In response to these challenges, laser surface texturing (LST) has emerged as a promising and sustainable antibacterial alternative which consists in modifying the surfaces at the micro- and nanometric scales to inhibit bacterial colonization or destroy bacterial membranes. LST can prevent bacterial adhesion and biofouling or, on the other hand, promote biocidal action after bacterial adhesion. This review examines how laser-treated surfaces influence the behavior of key bacterial strains, such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, exploring the mechanisms by which LST affects bacterial adhesion, morphology, and biofilm formation. The effectiveness of these mechanisms will be assessed both individually and in combination based on the characteristics of each bacterial strain
liBERTa: Local Intelligence via Browser Extensions for Real-Time Applications
No full textAs an application and service platform, the World Wide Web spans from simple informational websites to rich social media and Software-as-a-Service (SaaS) clients. While innovative capabilities are increasingly provided by Deep Learning (DL) Artificial Intelligence (AI) architectures such as pre-trained trans- formers, so far Web applications and services have integrated them only via cloud-based implementations. Deep-Learning-as- a-Service (DLaaS) is establishing itself for professional and personal use, with prevalent business models including pay-per- use and monthly subscriptions. With growing concerns over data privacy, response latency, and service costs, executing DL inference directly within the user’s browser appears as a com- pelling alternative to cloud-based solutions. This paper introduces local intelligence via Browser Extension for Real-Time applications (liBERTa), a modular browser extension-based architecture for real-time client-side DL inference. By operating entirely within the browser, liBERTa reduces reliance on external servers. Its modular design consists of independent layers for data extraction, model inference, and results presentation, granting flexibility and adaptability across different kinds of applications and services. Experimental results from a case study on website privacy policy classification demonstrate the feasibility of the approach, showing that lightweight transformer models can achieve competitive accuracy while maintaining inference times suitable for real- world use on commodity hardware
Different mechanical models for the study of ultrasonic wave dispersion for mechanical characterization of construction materials
No full textIt is well known from the literature that the phase velocity of waves is directly correlated with the stiffness of the material; however, experimental practice shows that this velocity changes significantly with varying frequencies, despite the fact that the elastic modulus of the material is, by definition, a material constant. We explore the dependence on the frequency of longitudinal ultrasonic plane waves velocity in construction materials, both from experimental and modeling points of view. For the sake of simplicity, the dispersive features are modeled by considering the case of a 1D medium, and two different kinds of mechanical models capable of describing wave dispersion phenomena are employed: a non-dissipative strain-gradient elastic model, and a dissipative viscoelastic one. In both cases, by using the extended Rayleigh–Hamilton principle, we derive the governing equations for 1D bulk waves propagation; in particular, in the case of the dissipative viscoelastic model either classical linear damping or Kelvin–Voigt damping is considered. The comparison of theoretical results with experimental findings obtained by ultrasonic tests on natural (sandstone) and artificial (concrete) construction materials shows that both theoretical models can satisfactorily describe the experimental behavior. These results encourage further experimental investigations for a clear and quantitative identification of the model that can be better used for engineering purposes
Il patrimonio moderno: tradizione rinnovata e avanguardia riformatrice nel contesto culturale plastico-murario ed elastico-ligneo
No full textThe article attempts to reflect on the dialectic that animates critical opinions on the recognition of the character of architecture in the modern transitional phase distinguished by geographic-cultural areas. The initial questioning of the sense of historicity, investigated through the judgments of some thinkers, tries to cast a
glance at the relationship that binds the past to the present in its authentic condition of truth, recognized in the identity perspective that persists even beyond the passage of time.
The recognition of the established characters in the Mediterranean architectural-linguistic culture (plastic-masonry) and in the Central-Nordic culture (elastic-ligneous) explains the phenomenology that has connoted the transition to the
modern differently manifested because of the nature of the places in which it persists, respectively, the heavy “masonry” and light “discrete” essence, generated by a dialectic that tends to reveal the self-conscious contribution aimed at
preserving the value of autochthony, proposed – in these notes – through the critical thinking of some of the main author of the time
Pixels-to-Graph: Real-time Integration of Building Information Models and Scene Graphs for Semantic-Geometric Human-Robot Understanding
No full textAutonomous robots are increasingly playing key roles as support platforms for
human operators in high-risk, dangerous applications. To accomplish challenging
tasks, an efficient human-robot cooperation and understanding is required.
While typically robotic planning leverages 3D geometric information, human
operators are accustomed to a high-level compact representation of the
environment, like top-down 2D maps representing the Building Information Model
(BIM). 3D scene graphs have emerged as a powerful tool to bridge the gap
between human readable 2D BIM and the robot 3D maps. In this work, we introduce
Pixels-to-Graph (Pix2G), a novel lightweight method to generate structured
scene graphs from image pixels and LiDAR maps in real-time for the autonomous
exploration of unknown environments on resource-constrained robot platforms. To
satisfy onboard compute constraints, the framework is designed to perform all
operation on CPU only. The method output are a de-noised 2D top-down
environment map and a structure-segmented 3D pointcloud which are seamlessly
connected using a multi-layer graph abstracting information from object-level
up to the building-level. The proposed method is quantitatively and
qualitatively evaluated during real-world experiments performed using the NASA
JPL NeBula-Spot legged robot to autonomously explore and map cluttered garage
and urban office like environments in real-time
A Hybrid Approach for Heat Source Identification and Heat Diffusion–Related Issues in the Fatigue Loading
No full textOver the past decades, thermographic methods have become a viable substitute for conventional approaches in the analysis of material fatigue behavior, due to their efficiency, cost-effectiveness, and nondestructive nature. By examining the temperature signature generated by intrinsic heat dissipations during the fatigue loading, valuable insights into the behavior of the materials can be investigated. Substantial intrinsic dissipation—a marker of material damage—is linked to a transition from anelastic to inelastic strains. The main aim of this work is to explore heat dissipations during fatigue of materials by combining experimental techniques and numerical simulations, focusing on the fundamental temperature component in fully reversed loading, known as the second amplitude harmonic (SAH) of temperature. The hybrid method combines experimental data with numerical modeling to identify the specific volume generating heat during fatigue testing. Additionally, the effect of the mechanical loading frequency on SAH of temperature was also examined
On the effect of force isotropy in a multiphase cascaded lattice Boltzmann scheme with entropic stabilization
No full textThe study of multiphase flows is a pivotal topic in natural sciences and engineering. A modeling approach to depict such phenomena combines the Lattice Boltzmann Method (LBM), a mesoscopic Navier-Stokes solver, and the Shan-Chen (SC) pseudopotential method, the latter postulating an interparticle interaction force inducing a spontaneous phase separation within a diffuse interface. To handle the inaccuracy and instability of the naive SC-LBM at high density ratio (DR) and dynamic viscosity ratio (VR), a twofold approach is proposed in recent literature: enhancing the collision process by a Cascaded Lattice Boltzmann Method (CLBM) constrained by a post-collision entropy minimization (KBC), and extending the formulation while tuning parameters of the interaction force to aid thermodynamic consistency, thus damping parasitic discretization effects and enabling surface tension tuning. In our work, we investigate how the interplay between the interparticle force isotropy order and key modeling parameters affects the KBC-CLBM discretization artifacts and stability. The nontrivial results achieved in terms of isotropy effectiveness hierarchy would guide future applied research in the adoption of suitable force stencils, complying with the required physical parameters (DR and VR), while limiting the computational burden. Static tests yield thermodynamically consistent results with the spurious currents magnitude lower than 10−3 lattice units at DR ≈3000 and VR ≈600 in the E8 isotropy order case. The compliance with the Laplace law has been proven, even at tuned surface tension. Droplet oscillation test results show consistency with transient analytical models, especially at E8 and even at higher DR and VR, also with surface tension modulation. Given the model's capabilities, we consider the outcome of our work as a step towards gaining a deeper understanding of natural phenomena and solving engineering problems
On the solutions for the Kudryashov-Sinelshchikov equation
No full textThe Kudryashov-Sinelshchikov equation models the evolution of the long weakly nonlinear waves, taking into consideration liquid viscosity, inter-phase heat transfer and surface tension. It models also the evolution of nonlinear sound wave propagation in bubbly liquids. Under appropriate assumptions of the coefficients of such equation, in this paper, we prove the well–posedness of the solutions for the Cauchy problem, associated with this equation