Politecnio die Bari - Catalogo di prodotti della Ricerca
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Mode-Group Selective Photonic Lantern based on Indium Fluoride Optical Fibers for Mid-Infrared
No full textThis manuscript illustrates the design and characterization of the first fiber-based photonic lantern, tailored for an efficient operation in the Mid-Infrared spectral range. The design and fabrication of the proposed device involve the use of three distinct indium fluoride optical fibers into a surrounding low refractive index glass capillary. An adiabatic transition is achieved through a controlled manufacturing process based on heating and drawing. The modal behavior of the photonic lantern is investigated along the transition via electromagnetic modal analysis, at the wavelength λ = 3.34 μm. Mode-group selectivity is obtained through the use of optical fibers with different characteristics. This implies that the light launched into a particular optical fiber evolves into specific mode groups at the photonic lantern multi-mode end. Experimental results demonstrate the possibility to excite the LP01 mode and two, odd and even, LP11 propagation modes, with losses below 1.3 dB and 1.7 dB, respectively. These results emphasize the feasibility of the proposed photonic lantern based on indium fluoride glass, with potentials for diverse applications, e.g. in communications, astrophotonics, remote sensing and spectroscopy
Novel hybrid nanocomposites based on graphene derivatives and colloidal nanoparticles for sensing applications
Get PDFThe research activity of this PhD course reports on the synthesis and chemical physical characterization of a novel hybrid nanocomposite formed of Histidine (His) functionalized Reduced Graphene Oxide (RGO) sheets, decorated with Ag nanowires (NWs) (His-RGO/Ag NWs), and its applications in sensors devices.
Graphene is among the carbonaceous nanostructures, one of the most interesting for its high specific surface area, high conductivity, high electrocatalytic activity, SERS activity, high Young’s modulus and mechanical strength, high thermal and electrical conductivity, all amiable properties that have been exploited in electrochemical and SERS sensors, devices for energy conversion and storage, Field-Effect Transistors (FETs), touch panels, and membranes. On the other hand, Ag NWs show interesting plasmonic properties, high electric and thermal conductivity, optical transparency and good mechanical flexibility, properties that have been exploited in Surface Enhanced Raman Scattering (SERS), electrochemical, pressure and temperature sensors, transparent heaters, electrodes for solar cells and touch screen panels.
Our interest in developing hybrid nanocomposites formed of graphene and Ag NWs, relays on the possibility to merge their outstanding properties, resulting in materials with novel properties or with enhanced the functionalities of the pristine components. In particular, nanocomposites based on inorganic nanoparticles and graphene derivatives found wide applications in the aerospace industry for the manufacturing of composites having high Young’s modulus to integrate in vehicles, advanced thermoregulatory textiles for manufacturing sophisticated clothes for individual thermal comfort in extreme thermal conditions, components for energy storage as battery and supercapacitors, electromagnetic shielding materials, sensors for monitoring atmosphere conditions, temperature and pressure and individual physiological parameters.
In the frame of this research project, the hybrid nanocomposite has been synthesized starting from the exfoliation of RGO sheets with His in water. The amino acid intercalates among the RGO multilayers, anchors onto the RGO basal plane by π-π interactions and grafts it by -COOH and -NH2 groups allowing its exfoliation. The use of His prevented the use of the toxic organic solvents that are typically used in the exfoliation of RGO, because its binding to the RGO scaffold allows RGO dispersion in aqueous solutions. Then, the Ag NWs were synthesized in situ onto the RGO basal plane by the polyol approach, using AgNO3 as precursor, ethylene glycol (EG) as solvent and reducing agent, and polyvinylpyrrolidone (PVP) as capping and steric stabilizing agent. The synthesized NWs anchor RGO basal plane binding, by coordination, the -COOH groups of His, and RGO behaves as support and protective coating layer, avoiding NWs aggregation and oxidation thanks to its gas and moisture barrier properties. The synthesis of the His-RGO/Ag NWs has been optimized by using PVP of 360 kDa, and ca. 3.4 ± 0.9 μm long and 0.06 ± 0.01 μm thick Ag NWs, with aspect ratio of 57, were achieved. The synthesized nanocomposite His-RGO/Ag NWs have been tested for the electrochemical detection of the pesticide carbofuran and for the SERS detection of probe molecules. Such a study has been conceived to test and validate, as a proof-of-concept demonstration, the potentialities of the novel engineered nanocomposite material, opening perspectives to its leveraging in sensors having applications closer to those related to aerospace industry.
Electrochemical sensors
When integrated on screen-printed carbon electrodes (SPCEs) and further modified by the electropolymerization of the polymer PEDOT:PSS, the achieved SPCE/His-RGO/Ag NW/PEDOT:PSS electrodes have shown an increased conductivity, a higher heterogeneous charge transfer constant and an higher electrocatalytic activity, favoring oxidation of carbofuran at the electrode surface. Thus, the fabricated SPCEs/His-RGO/Ag NW/PEDOT:PSS electrodes have shown a high sensitivity in the detection of carbofuran, with a limit of detection of 17.3 nM, that is lower than the U.S. EPA recommended concentration in drinking water with a relatively good %RSD of selectivity, repeatability, reproducibility and storage stability. This improved sensitivity is due to the electrocatalytic properties of Ag NWs and the high conductivity of both the nanocomposite and the electropolymerized PEDOT:PSS film, opening the venue to the application of the fabricated electrode in the detection of other molecules of environment interest.
SERS sensors
When deposited by drop-casting onto hydrophobic paper substrates, the nanocomposite has been tested in the SERS detection of model molecules having a different chemical structure, namely 1-naphthalenethiol (1-Nat), rhodamine 6G (R6G), and benzo[a]pyrene), against paper substrates modified by neat Ag NWs based samples. The study reveals that 1-Nat, possessing a high affinity for silver, exhibits strong SERS signals on both His-RGO/Ag NWs and the neat Ag NWs substrates. Meanwhile, R6G generates even more intense SERS peaks compared to 1-Nat on both substrates due to its high affinity with silver and its interaction with RGO. Both molecules 1-Nat and R6G reach a limit of detection (LOD) of 10−7 M on both His-RGO/Ag NWs and Ag NWs substrates. In contrast, benzo[a]pyrene produced no detectable SERS signal. This absence of response was attributed to the absence of functional groups in benzo[a]pyrene having chemical affinity for silver and to the reduced number of aromatic rings in the molecule's structure that undergoes weak aromatic π- π stacking interactions.
The developed hybrid nanocomposite materials designed for the detection of pollutant molecules hold significant potential in the aerospace sector, which increasingly relies on advanced sensing technologies to enhance operational safety, environmental compliance, and crew health in complex environments. Monitoring air quality in aircraft cabins and space vehicles is crucial due to the potential accumulation of toxic chemicals, which may arise from system-related emissions, prolonged closed-loop life support, and even contaminants like pesticides in agricultural aviation settings. Detecting and managing these pollutants in real-time requires sensor technologies that are both highly sensitive and robust under challenging aerospace conditions
On the embedding of weighted Sobolev spaces with applications to a planar nonlinear Schrödinger equation
No full textIn this paper we study the embedding's properties for the weighted Sobolev space HV1(RN) into the Lebesgue weighted space LWτ(RN). Here V and W are diverging weight functions. The different behaviour of V with respect to W at infinity plays a crucial role. Particular attention is paid to the case V=W. This situation is very delicate since it depends strongly on the dimension and, in particular, N=2 is somewhat a limit case. As an application, an existence result for a planar nonlinear Schrödinger equation in presence of coercive potentials is provided
Enhancing Reproducibility and Replicability in Information Retrieval: A Path Towards Scientific Integrity and Effective Research
No full textA Finite Element Study of Simulated Fusion in an L4-L5 Model: Influence of the Combination of Materials in the Screw-and-Rod Fixation System on Reproducing Natural Bone Behavior
Get PDFThe mechanical properties of materials for spinal fixation can significantly affect spinal surgical outcomes. Traditional materials such as titanium exhibit high stiffness, which can lead to stress shielding and adjacent segment degeneration. This study investigates the biomechanical performance of titanium and PEEK (polyetheretherketone) in spinal fixation using finite element analysis, through the evaluation of the Shielding Strength Factor (SSF). Methods: A three-dimensional finite element analysis (FEA) model of an L4/L5 functional spinal unit was developed to simulate the mechanical behavior of three fixation systems: titanium screws and rods (model A), titanium screws with PEEK rods (model B), and PEEK screws and rods (model C). The analysis evaluated stress distribution and load transfer under physiological conditions, in comparison with the intact spine (baseline model). Results: The analysis showed that titanium fixation systems resulted in higher stress shielding effects, with a significant difference in stress distribution compared to PEEK. The maximum stress recorded in the neutral position was 24.145 MPa for PEEK, indicating better biomechanical compatibility. Conclusions: The results suggest that PEEK may be an attractive alternative to titanium for spinal fixation, promoting more healthy load transfer and minimizing the risk of stress shielding complications
Immobilized Saccharomyces cerevisiae viable cells for electrochemical biosensing of Cu(II)
Get PDFElectrodes functionalised with weak electroactive microorganisms offer a viable alternative to conventional chemical sensors for detecting priority pollutants in bioremediation processes. Biofilm-based biosensors have been proposed for this purpose. However, biofilm formation and maturation require 24–48 h, and the microstructure and coverage of the electrode surface cannot be controlled, leading to poorly reproducible signal and sensitivity. Alternatively, semiconductive biocompatible coatings can be used for viable cell immobilization, achieving reproducible coverage and resulting in a stable biosensor response. In this work, we use a polydopamine (PDA)-based coating to immobilize Saccharomyces cerevisiae yeast viable cells on carbon screen printed electrodes (SPE) for Cu(II) detection, with potassium ferricyanide (K3[Fe (CN)6]) as a redox mediator. Under these conditions, the current output correlates with Cu (II) concentration, reaching a limit of detection of 2.2 μM, as calculated from the chronoamperometric response. The bioelectrochemical results are supported by standard viability assays, microscopy, and electrochemical impedance spectroscopy. The PDA coatings can be functionalised with different mutant strains, thus expanding the toolbox for biosensor design in bioremediation
Enhancement of adhesion strength through microvibrations: Modeling and experiments
No full textHigh-frequency micrometrical vibrations have been shown to greatly influence the adhesive performance of soft interfaces, however a detailed comparison between theoretical predictions and experimental results is still missing. Here, the problem of a rigid spherical indenter, hung on a soft spring, that is unloaded from an adhesive viscoelastic vibrating substrate is considered. The experimental tests were performed by unloading a borosilicate glass lens from a soft PDMS substrate excited by high-frequency micrometrical vibrations. We show that as soon as the vibration starts, the contact area increases abruptly and during unloading it decreases following approximately the JKR classical model, but with a much increased work of adhesion with respect to its thermodynamic value. We find that the pull-off force increases with the amplitude of vibration up to a certain saturation level, which appeared to be frequency dependent. Under the hypothesis of short range adhesion, a lumped mechanical model was derived, which, starting from an independent characterization of the rate-dependent interfacial adhesion, predicted qualitatively and quantitatively the experimental results, without the need of any adjustable parameters
Study and design of process parameters for additive manufacturing of PEEK and C-PEEK parts for aeronautical applications
Get PDFThe growing need for more sustainable solutions has led research in the aeronautical and aerospace fields to the production of increasingly lighter and more efficient aircraft. For lightening purposes, advanced composite materials made of carbon fibers and epoxy resins were developed. Nevertheless, the use of thermoplastics as a valid alternative to thermosets, has the advantage of being easily processable, repairable and recyclable. The most interesting thermoplastic materials for the aerospace industry are the so-called “ technopolymers”, such as polyariletherketones (PAEK) family, which combine high mechanical, thermal and chemical resistance with very low weight. One of the most sustainable ways to process these materials are Additive Manufacturing technologies (AM), and in particular the Fused Filament Fabrication (FFF) technique.
The present work is an in-depth study on the optimization of FFF process parameters and possible strategies aimed at resolving the technological limitations for the printing of Polyether-ether ketone (PEEK) and Carbon-PEEK parts making them usable for lightening purposes in the aeronautical sector.
In the first part of the study, the optimal process conditions for the 3D printing of 100% dense PEEK parts are found by characterizing both mechanical and structural properties of printed coupons. It was discovered that the mechanical performances are strongly dependent on PEEK degree of crystallinity. Therefore, by varying the process temperatures and the printing speed, it is possible to control the crystallization, customizing the mechanical properties and possible applications.
Subsequently, the research activity was focused on the enhancement of the interlayer adhesion in 3D printed parts by means of atmospheric plasma superficial treatments. The study was carried out on both Polycarbonate (PC) and PEEK because they have very similar features and processing issues. The choice of treatment parameters was made by studying the plasma-induced improvement in wettability through several analyses. The interlayer adhesion of both untreated and treated PC samples was verified by mechanical tests, and an improvement of about 30% in strength was achieved.
The last part was dedicated on the study of 3D printed Gyroid structures made of Carbon PEEK for both the optimization of the compressive strength-to-weight ratio and the enhancement of mechanical isotropy. The specimens were printed by varying the infill density, and the results were compared to the Gibson-Ashby model, finding a compressive behavior similar to bending-dominated lattice structures. The strength-to-weight ratio was optimized for a density of 70% allowing a saving of 30% of material and time and it was found that isotropy in compression is possible for a density of 25%. It was studied also the response of gyroid lattice structures in the impact absorption when used as core pattern in sandwich-like panels. The absorbed impact energy increased as the infill density increased while the gyroid was not damaged but was detached from the impacted skin. Non-destructive inspection (NDI) highlighted that the extent of the detachment increased with the impact energy. However, further investigation for the optimization and characterization of sandwich panels is necessary.
The results presented in this thesis work pave the way towards a turning point in the engineering and manufacturing of molds, tools and end-use products for aeronautics
Family-governed businesses and successful equity crowdfunding: The moderating role of sustainability orientation
No full textCrowdfunding has arisen as a prominent alternative to more traditional forms of financing, with equity crowdfunding (EC) becoming increasingly significant for its economic relevance and unique dynamics. While previous research has explored various factors contributing to EC campaign success, the role of firm governance, particularly family governance – i.e., the involvement in management and/or ownership of members of the same family - remains underexplored. Therefore, this study tackles this gap by examining the influence of family governance on EC success. Family-governed businesses, known for their long-term orientation and more conservative risk behavior, may inspire greater trust from investors, hence enhancing their campaign success. Additionally, the growing importance of business and campaign sustainability orientation in investors’ decision-making suggests it could further strengthen the positive relationship between family-governed businesses and EC success. Using data collected on 500 EC campaigns from leading Italian platforms, we find support for our hypotheses. This study contributes to the EC literature and family business research and has important implications for family-governed businesses seeking to optimize their EC campaigns
Development of a predictive method of the response to shock loads of a spacecraft's structure
Get PDFThis thesis addresses one of the most pressing challenges in satellite development:
accurately predicting shock loads during launch to optimize structural design and
reduce the need for costly and time-consuming testing. As satellites are exposed
to severe dynamic loads from rocket stage separations and pyrotechnic events, en-
suring resilience against these forces is crucial for mission success. Traditional em-
pirical methods for shock load prediction often rely on conservative assumptions,
leading to over-design and added costs. This research, conducted in collaboration
with SITAEL SpA and supported by insights and tools from the European Space
Agency (ESA), introduces a novel methodology for more precise shock load predic-
tion. The proposed model, based on modal decomposition and transfer function
analysis, enables engineers to calculate shock transmissibility from low to high fre-
quency spectrum, overcoming the limitations of empirical methods. The method-
ology was initially validated through simulations on simple 2-DOF systems and
subsequently applied to the complex ShockSat case study, an open-source satel-
lite project by NASA. Simulations carried out during a research period at ESA
provided critical industry insights and further refined the model’s accuracy and
practical relevance. These simulations revealed the model’s capability to predict
shock responses in real satellite structures, offering potential design optimizations
to mitigate shock effects. While experimental validation remains a future goal, this
thesis establishes a robust foundation for advancing shock analysis in aerospace
engineering. By shifting away from conservative assumptions toward more accu-
rate prediction, the research holds promise for reducing dependency on extensive
physical testing, ultimately leading to more efficient and sustainable satellite de-
velopment. As the space industry places greater emphasis on cost-effectiveness and
reliability, this predictive shock model meets the needs of today’s market, opening
up new possibilities for building more resilient spacecraft and making the design
process more efficient