1,358,420 research outputs found
Electromechanical behavior of carbon nanotubes under traction, bending, torsion and misalignment of the two ends
No full textCarbon nanotubes (CNTs) can be metallic or semiconductors depending simply on geometric characteristics [e.g., 1]. This peculiar electronic behavior, combined with high mechanical strength, make them potential building blocks of a new nano-electronic technology. Most discussions of the electronic structure of CNTs assume perfect cylindrical symmetry, but this is somewhat of an oversimplification. High resolution images of CNTs often disclose structural deformations such as bent, twisted, or collapsed tubes. These deformations may develop during growth, deposition, and processing, or upon interaction with other CNTs, and with surfaces and surface features such as electrodes. Deformations break the tube symmetry, and a change in their electronic properties should result.
A computationally effective mixed finite element-tight-binding approach [2-7] able to simulate the electromechanical behavior of single and multiwall nanotubes used in nano-electronic devices is presented. The finite element (FE) computes the evolution of atomic coordinates with deformation and provides these coordinates to a tight-binding (TB) code, enabling computation and updating of the electrical conductivity. The TB code is engineered to realize dramatic computational savings in calculating deformation-induced changes in electrical transport properties of the nanotubes. The FE-TB computational approach is successfully validated in a simulation of laboratory experiments which had measured the changes in electrical conductivity of a multiwall carbon nanotube during mechanical deformation.
References
[1]. J. Bernholc et al, Annu. Rev. Mat. Res. 32 , 347 (2002)
[2]. A. Pantano et al, Phys. Rev. Lett. 91, 145504 (2003)
[3]. A. Pantano et al, J. Mech. Phys. Solids 52, 789 (2004)
[4]. A. Pantano et al, J. of Eng. Materials and Technology Trans. ASME 126, 279-284 (2004)
[5]. A. Pantano et al, J. of Applied Physics 92, 6756-6760 (2004)
[6]. A. Pantano et al, ACS Nano 3, 3266–3272 (2009)
[7]. A. Pantano. Chapter of the book “Trends in Computational Nanomechanics: Transcending Length and Time Scales”. Springer , pp. 335-365. ISBN: 978-1-4020-9784-3
Mechanical properties of carbon nanotube reinforced nanocomposites
No full textOne way to take advantage of the marvelous properties of the carbon nanotubes consists in incorporating them into a matrix to build composite materials. The best candidates for this task are undoubtedly polymers thanks to their strength, toughness, low weight, and easy processing.
A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. A three-dimensional model, using a single CNT immersed in an infinite matrix, allows us to numerically evaluate the concentration tensor by evaluating the average nanotube strain. The Mori-Tanaka model uses this tensor to predict the effective elastic modulus of composites with CNTs randomly oriented. This hybrid approach represents an appreciable evolution over the micromechanical modeling [1] and can be applied to every nanostructured composites. To simulate the mechanical behavior of CNTs, a structural non linear model, previously developed [2], has been adopted; this model is a modified version of a known methodology [3-4]. To simulate the nanotube-matrix interface, interactions have been implemented.
The new methodology has been validated by comparison with the results of laboratory tests performed on epoxy resin-CNTs composites.
References
[1] A. Pantano, G. Modica, F. Cappello: Mat. Sci. and Eng. A, 486, 222-227, 2008.
[2] M. Garg, A. Pantano, M.C. Boyce: J. of Eng. Mat. and Tech., 129, 431-439, 2007.
[3] A. Pantano, M.C. Boyce, D.M. Parks: J. Mech. Phys. Solids, 52, 789-821, 2004.
[4] A. Pantano, M.C. Boyce, D.M. Parks: J. of Eng. Mat. and Tech., Trans. ASME, 126, 279-284, 2004
Ubiquitous computing, contactless points, and distributed stores: a new place for shopping
No full textNowadays, retailing is subjected to constant changes due to the continuous advancements in technology (Pantano, 2014). In fact, the increasing computing capabilities, the mobile and wireless
technologies improvements, as well as the development of flexible software architectures and automatic identification technologies support the ubiquitous access to data for both consumers
and firms. As a consequence, these new systems modify the interface between clients and vendor, by providing new consumer-oriented services (Ngo and O’Cass, 2013; Pantano, 2014), as well
as the customer behavior and corporate approach to retail process, by changing both the way customers access and consume the information, and the way firms and organizations reach clients and
deliver the service (Kim, et al., 2009; Demirkan and Spohrer, 2014)
Electrical conduction in carbon nanotubes under mechanical deformations
No full textThe enormous potential of carbon nanotubes (CNTs) as primary components in electronic devices and NEMS necessitates the understanding and predicting of the effects of mechanical deformation on electron transport in CNTs. In principle, detailed atomic/electronic calculations can provide both the deformed configuration and the resulting electrical transport behavior of the CNT. However, the computational expense of these simulations limits the size of the CNTs that can be studied with this technique and a direct analysis of CNTs of the dimension used in nano-electronic devices, particularly multi-wall CNTs (MWNTs), seems prohibitive at the present. Here a computationally effective mixed finite element/tight-binding (to be referred to as FE-TB) approach able to simulate the electromechanical behavior of CNTs devices is presented. The FE-based structural procedure computes the mechanical deformation of the CNTs and provides a tight-binding (TB) code with the atomic coordinates in the deformed configuration. The TB code is carefully designed to realize orders-of-magnitude reduction in computational time in calculating deformation-induced changes in electrical transport properties of the nanotubes. The FE-TB computational approach is validated in a simulation of laboratory experiments on a multiwall CNT and then used to demonstrate the role of the multiwall structure in providing robustness to conductivity in the event of imposed mechanical deformations
ELEMENTO D’INTERFACCIA PER LA SIMULAZIONE DI PROCESSI DI DANNEGGIAMENTO IN MODO MISTO I/II NEI MATERIALI COMPOSITI E NELLE GIUNZIONI ADESIVE
No full textE’ stato sviluppato un elemento coesivo in grado di connettere e simulare la crescita delle cricche tra sottodomini di elementi finiti modellati in modo indipendente con mesh incompatibili. L'approccio si basa su funzioni di penalità e presenta numerosi vantaggi rispetto alle tecniche FEM convenzionali nelle simulazioni di delaminazione. Il più importante è la possibilità di rilasciare una porzione dell'interfaccia più piccola della lunghezza degli elementi finiti locali. Pertanto la delaminazione non avanza solamente rilasciando i nodi del modello FEM, una limitazione comune a molti metodi trovati in letteratura. È stato anche sviluppato un nuovo approccio per modellare la crescita delle cricche in modalità mista I+II. Questa formulazione porta ad un approccio computazionale molto efficiente che è completamente compatibile con i software commerciali esistenti. La tecnica è validata tramite simulazione di test DCB, ENF e MMB.A cohesive element able to connect and simulate crack growth between independently modeled finite element subdomains with non-matching meshes is proposed and validated. The approach is based on penalty constraints and has several advantages over conventional FE techniques in disconnecting two regions of a model during crack growth. The most important is the ability to release portion of the interface that are smaller than the local finite element length. Thus, the growth of delamination is not limited to advancing by releasing nodes of the FE model, which is a limitation common to the methods found in the literature. A novel approach for modeling the crack growth in mixed mode I+II conditions has been developed. This formulation leads to a very efficient computational approach that is completely compatible with existing commercial software. The growth of the delamination is simulated for the DCB, ENF and MMB tests and the results are compared with the experimental data
The Pantano Longarini shipwreck: a reanalysis
Get PDFA late antique shipwreck was excavated in the Pantano Longarini marsh in the southeastern corner of Sicily in the 1960s. Despite its excellent preservation, problematic circumstances surrounding its excavation and publication have resulted in scholars ignoring or misinterpreting it. The majority of the data, including original field notes and documentation, are lost, and the drawings, plans, and photographs that remain are sometimes inconsistent and incomplete. My research reanalyzes the remains of this ship to determine how the Sicilians adapted to their marine and economic conditions within the turbulent socio-economic and political climate of late antiquity. The Pantano Longarini shipwreck demonstrates early stages in a shift from the tradition of plank-based construction to the modern system of reliance on an internal framework for structural support. Contemporary wrecks provide parallels, but unique elements distinguish this ship from those typically studied. Extremely thick timbers, a relatively flat bottom and bow and stern ramps argue that the Pantano Longarini ship was designed to carry bulk loads. Although the ship was originally reported as an extremely advanced ship, the present analysis points to a different type of watercraft: a coastal barge. Correctly identifying the Pantano Longarini ship allows us to gather information about the needs of its builders, as well as extends our knowledge of shipping and ship construction in the seventh century
Simulation of laser generated ultrasound with application to defect detection
No full textLaser generated ultrasound holds substantial promise for use as a tool for defect detection in remote inspection thanks to its ability to produce frequencies in the MHz range, enabling fine spatial resolution of defects. Despite the potential impact of laser generated ultrasound in many areas of science and industry, robust tools for studying the phenomenon are lacking and thus limit the design and optimization of non-destructive testing and evaluation techniques. The laser generated ultrasound propagation in complex structures is an intricate phenomenon and is extremely hard to analyze. Only simple geometries can be studied analytically. Numerical techniques found in the literature have proved to be limited in their applicability, by the frequencies in the MHz range and very short wavelengths. The objective of this research is to prove that by using an explicit integration rule together with diagonal element mass matrices, instead of the almost universally adopted implicit integration rule to integrate the equations of motion in a dynamic analysis, it is possible to efficiently and accurately solve ultrasound wave propagation problems with frequencies in the MHz range travelling in relatively large bodies. Presented results on NDE testing of rails demonstrate that the proposed FE technique can provide a valuable tool for studying the laser generated ultrasound propagation
FUCILE DA PESCA SUBACQUEO A DUE FUSTI ORIZZONTALI CON ASTA SINGOLA O DOPPIA
No full textIl brevetto ha per oggetto un fucile subacqueo caratterizzato da due aste, o arpioni, indipendenti che possono essere sparate separatamente. Un’altra variante dell’invenzione prevede una singola asta.
Il brevetto presenta numerosi innovazioni che si traducono in significativi vantaggi funzionali rispetto ai fucili subacquei ad elastico attualmente sul mercato. Oltre ai numerosi benefici derivanti dalla possibilità del doppio sparo, lo schema costruttivo azzera le deformazioni dovute al carico esercitato dagli elastici in tensione di cui soffrono i tradizionali fucili subacquei ad elastico, ne consegue una elevata precisione del tiro anche con fusti di piccolo diametro, molto idrodinamici, realizzati in materiale economico come l’alluminio. La particolare configurazione del fucile consente, anche in presenza della doppia asta, una ubicazione funzionale e quindi una vantaggiosa gestione del filo utilizzato per consentire il recupero del pesce colpito. L’operazione di caricamento dei tradizionali fucili ad elastico non si presenta mai come una operazione facile a causa degli elevatissimi sforzi richiesti alla muscolatura del subacqueo e alla scomoda presa che si ha sugli elastici. Grazie al design del fucile, è possibile realizzare una variante costruttiva opzionale del fucile dove, in alternativa alle tecniche di caricamento tradizionali, sia presente una asta in grado di guidare un componente meccanico avente lo scopo di consentire un agevole caricamento degli elastici. E’ importante sottolineare che l’idrodinamica dell’arma in configurazione a doppia asta è ottimizzata soprattutto rispetto agli spostamenti di brandeggio laterali che sono quelli più frequenti nella normale attività di pesca. Il brandeggio verticale, pur non essendo ottimizzato come nel caso di quello orizzontale, risulterà di pari livello rispetto ad un fucile tradizionale. Il vantaggio della doppia asta coniugato ad una precisione di tiro impareggiabile e ad un basso costo costruttivo potrebbe consentire al fucile di affermarsi con successo sul mercato nazionale e internazionale. La variante ad asta singola, pur non avvantaggiandosi della possibilità del doppio colpo, mantiene una precisione di tiro impareggiabile in relazione al costo costruttivo molto basso
Correction to: Resting-state functional MRI in multicenter studies on multiple sclerosis: a report on raw data quality and functional connectivity features from the Italian Neuroimaging Network Initiative (Journal of Neurology, (2023), 270, 2, (1047-1066), 10.1007/s00415-022-11479-z)
No full textThe original version of this article unfortunately contained a mistake. The second affiliation for author "Patrizia Pantano” was missing. The second affiliation should be IRCCS Neuromed, Pozzilli (IS), Italy
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