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Articles de revues sur le sujet "Graphene based 2-dimensional systems"
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Dolina, Ekaterina S., Pavel A. Kulyamin, Anastasiya A. Grekova, Alexey I. Kochaev, Mikhail M. Maslov et Konstantin P. Katin. « Thermal Stability and Vibrational Properties of the 6,6,12-Graphyne-Based Isolated Molecules and Two-Dimensional Crystal ». Materials 16, no 5 (27 février 2023) : 1964. http://dx.doi.org/10.3390/ma16051964.
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We report the geometry, kinetic energy, and some optical properties of the 6,6,12-graphyne-based systems. We obtained the values of their binding energies and structural characteristics such as bond lengths and valence angles. Moreover, using nonorthogonal tight-binding molecular dynamics, we carried out a comparative analysis of the thermal stability of 6,6,12-graphyne-based isolated fragments (oligomer) and two-dimensional crystals constructed on its basis in a wide temperature range from 2500 to 4000 K. We found the temperature dependence of the lifetime for the finite graphyne-based oligomer as well as for the 6,6,12-graphyne crystal using a numerical experiment. From these temperature dependencies, we obtained the activation energies and frequency factors in the Arrhenius equation that determine the thermal stability of the considered systems. The calculated activation energies are fairly high: 1.64 eV for the 6,6,12-graphyne-based oligomer and 2.79 eV for the crystal. It was confirmed that the thermal stability of the 6,6,12-graphyne crystal concedes only to traditional graphene. At the same time, it is more stable than graphene derivatives such as graphane and graphone. In addition, we present data on the Raman and IR spectra of the 6,6,12-graphyne, which will help distinguish it from the other carbon low-dimensional allotropes in the experiment.
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KAN, ERJUN, ZHENYU LI et JINLONG YANG. « MAGNETISM IN GRAPHENE SYSTEMS ». Nano 03, no 06 (décembre 2008) : 433–42. http://dx.doi.org/10.1142/s1793292008001350.
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Graphene has attracted great interest in materials science, owing to its novel electronic structures. Recently, magnetism discovered in graphene-based systems has opened up the possibility of their spintronics application. This paper provides a comprehensive review of the magnetic behaviors and electronic structures of graphene systems, including two-dimensional graphene, one-dimensional graphene nanoribbons, and zero-dimensional graphene nanoclusters. Theoretical research suggests that such metal-free magnetism mainly comes from the localized states or edges states. By applying an external electric field, or by chemical modification, we can turn the zigzag nanoribbon systems into half metal, thus obtaining a perfect spin filter.
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Marchenko, D., D. V. Evtushinsky, E. Golias, A. Varykhalov, Th Seyller et O. Rader. « Extremely flat band in bilayer graphene ». Science Advances 4, no 11 (novembre 2018) : eaau0059. http://dx.doi.org/10.1126/sciadv.aau0059.
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We propose a novel mechanism of flat band formation based on the relative biasing of only one sublattice against other sublattices in a honeycomb lattice bilayer. The mechanism allows modification of the band dispersion from parabolic to “Mexican hat”–like through the formation of a flattened band. The mechanism is well applicable for bilayer graphene—both doped and undoped. By angle-resolved photoemission from bilayer graphene on SiC, we demonstrate the possibility of realizing this extremely flattened band (< 2-meV dispersion), which extends two-dimensionally in a k-space area around the K¯ point and results in a disk-like constant energy cut. We argue that our two-dimensional flat band model and the experimental results have the potential to contribute to achieving superconductivity of graphene- or graphite-based systems at elevated temperatures.
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Knoll, T., G. Jenke, A. Brenner, H. Schuck, A. Schultz, R. Warmers, A. Zumbülte et al. « Zweifarben-Druckanlage für die Sensorherstellung/Two-colour printing machine for sensor production - Rotary printing of foil-based graphene sensors ». wt Werkstattstechnik online 107, no 11-12 (2017) : 827–33. http://dx.doi.org/10.37544/1436-4980-2017-11-12-51.
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Der Fachartikel stellt eine kompakte Zweifarben-Druckanlage für die Fertigung folienbasierter Sensoren aus Graphen vor. Mithilfe einer Graphentinte sowie eines rotativen Tiefdruckverfahrens lassen sich zweidimensionale Elektrodenstrukturen beliebiger Geometrie in hohen Stückzahlen fertigen. Beschrieben werden die Druckanlage, die Herstellung der Tiefdruckzylinder und der graphenbasierten Tinte sowie die bisher beim Drucken von Elektroden für zellbasierte Sensoren erzielten Ergebnisse. The article presents a compact two-colour printing system for the production of foil-based sensors made of graphene. Graphene is a suitable material for electrodes of cell-based sensors. If graphene is used as a printable ink, two-dimensional electrode structures of any geometry can be produced. The article describes the printing system, the production of the gravure cylinders and the graphene-based ink as well as the results of printing experiments achieved so far.
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Barlas, Yafis, Kun Yang et A. H. MacDonald. « Quantum Hall effects in graphene-based two-dimensional electron systems ». Nanotechnology 23, no 5 (11 janvier 2012) : 052001. http://dx.doi.org/10.1088/0957-4484/23/5/052001.
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Chen, Yiwen, Habibullah, Guanghui Xia, Chaonan Jin, Yao Wang, Yigang Yan, Yungui Chen, Xiufang Gong, Yuqiu Lai et Chaoling Wu. « Palladium-Phosphide-Modified Three-Dimensional Phospho-Doped Graphene Materials for Hydrogen Storage ». Materials 16, no 12 (7 juin 2023) : 4219. http://dx.doi.org/10.3390/ma16124219.
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The development of efficient hydrogen storage materials is crucial for advancing hydrogen-based energy systems. In this study, we prepared a highly innovative palladium-phosphide-modified P-doped graphene hydrogen storage material with a three-dimensional configuration (3D Pd3P0.95/P-rGO) using a hydrothermal method followed by calcination. This 3D network hindering the stacking of graphene sheets provided channels for hydrogen diffusion to improve the hydrogen adsorption kinetics. Importantly, the construction of the three-dimensional palladium-phosphide-modified P-doped graphene hydrogen storage material improved the hydrogen absorption kinetics and mass transfer process. Furthermore, while acknowledging the limitations of primitive graphene as a medium in hydrogen storage, this study addressed the need for improved graphene-based materials and highlighted the significance of our research in exploring three-dimensional configurations. The hydrogen absorption rate of the material increased obviously in the first 2 h compared with two-dimensional sheets of Pd3P/P-rGO. Meanwhile, the corresponding 3D Pd3P0.95/P-rGO-500 sample, which was calcinated at 500 °C, achieved the optimal hydrogen storage capacity of 3.79 wt% at 298 K/4 MPa. According to molecular dynamics, the structure was thermodynamically stable, and the calculated adsorption energy of a single H2 molecule was −0.59 eV/H2, which was in the ideal range of hydrogen ad/desorption. These findings pave the way for the development of efficient hydrogen storage systems and advance the progress of hydrogen-based energy technologies.
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Wang, Xiunan, Yi Liu, Jingcheng Xu, Shengjuan Li, Fada Zhang, Qian Ye, Xiao Zhai et Xinluo Zhao. « Molecular Dynamics Study of Stability and Diffusion of Graphene-Based Drug Delivery Systems ». Journal of Nanomaterials 2015 (2015) : 1–14. http://dx.doi.org/10.1155/2015/872079.
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Graphene, a two-dimensional nanomaterial with unique biomedical properties, has attracted great attention due to its potential applications in graphene-based drug delivery systems (DDS). In this work graphene sheets with various sizes and graphene oxide functionalized with polyethylene glycol (GO-PEG) are utilized as nanocarriers to load anticancer drug molecules including CE6, DOX, MTX, and SN38. We carried out molecular dynamics calculations to explore the energetic stabilities and diffusion behaviors of the complex systems with focuses on the effects of the sizes and functionalization of graphene sheets as well as the number and types of drug molecules. Our study shows that the binding of graphene-drug complex is favorable when the drug molecules and finite graphene sheets become comparable in sizes. The boundaries of finite sized graphene sheets restrict the movement of drug molecules. The double-side loading often slows down the diffusion of drug molecules compared with the single-side loading. The drug molecules bind more strongly with GO-PEG than with pristine graphene sheets, demonstrating the advantages of functionalization in improving the stability and biocompatibility of graphene-based DDS.
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Jana, Susmita, Arka Bandyopadhyay, Sujoy Datta, Debaprem Bhattacharya et Debnarayan Jana. « Emerging properties of carbon based 2D material beyond graphene ». Journal of Physics : Condensed Matter 34, no 5 (10 novembre 2021) : 053001. http://dx.doi.org/10.1088/1361-648x/ac3075.
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Abstract Graphene turns out to be the pioneering material for setting up boulevard to a new zoo of recently proposed carbon based novel two dimensional (2D) analogues. It is evident that their electronic, optical and other related properties are utterly different from that of graphene because of the distinct intriguing morphology. For instance, the revolutionary emergence of Dirac cones in graphene is particularly hard to find in most of the other 2D materials. As a consequence the crystal symmetries indeed act as a major role for predicting electronic band structure. Since tight binding calculations have become an indispensable tool in electronic band structure calculation, we indicate the implication of such method in graphene’s allotropes beyond hexagonal symmetry. It is to be noted that some of these graphene allotropes successfully overcome the inherent drawback of the zero band gap nature of graphene. As a result, these 2D nanomaterials exhibit great potential in a broad spectrum of applications, viz nanoelectronics, nanooptics, gas sensors, gas storages, catalysis, and other specific applications. The miniaturization of high performance graphene allotrope based gas sensors to microscopic or even nanosized range has also been critically discussed. In addition, various optical properties like the dielectric functions, optical conductivity, electron energy loss spectra reveal that these systems can be used in opto-electronic devices. Nonetheless, the honeycomb lattice of graphene is not superconducting. However, it is proposed that the tetragonal form of graphene can be intruded to form new hybrid 2D materials to achieve novel superconducting device at attainable conditions. These dynamic experimental prospects demand further functionalization of these systems to enhance the efficiency and the field of multifunctionality. This topical review aims to highlight the latest advances in carbon based 2D materials beyond graphene from the basic theoretical as well as future application perspectives.
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Koppens, F. H. L., T. Mueller, Ph Avouris, A. C. Ferrari, M. S. Vitiello et M. Polini. « Photodetectors based on graphene, other two-dimensional materials and hybrid systems ». Nature Nanotechnology 9, no 10 (octobre 2014) : 780–93. http://dx.doi.org/10.1038/nnano.2014.215.
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Si, Wei, Chang Chen, Gensheng Wu, Qianyi Sun, Meng Yu, Yu Qiao et Jingjie Sha. « High Efficient Seawater Desalination Based on Parallel Nanopore Systems ». Nano 16, no 07 (21 juin 2021) : 2150077. http://dx.doi.org/10.1142/s1793292021500776.
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Graphene is one of the most attractive two-dimensional materials that can be used for efficient desalination due to its ideal physical properties and high performance in ion selectivity and salt rejection. Here, in this paper, molecular dynamics simulations were applied to investigate the possibility of using a parallel nanopore system to pump ions so that the ions of both cation and anion species in the middle compartment could be evacuated at an extremely rapid rate. By building hexagonal parallel single-layer graphene films with spacing of 3.0 nm and changing the pore numbers and surface charge densities of the nanopores, the efficiency of desalination could be well controlled. It is found that the ion concentration decreases exponentially with time. The more the number of nanopore is, the stronger the surface charge density of nanopore is, the evacuation of ions in the middle compartment is more obvious, offering a new means for controlling the desalination efficiency. The simulations performed here provide theoretical insights for designing and fabricating high efficient and less energy consumption graphene desalination devices in the future.
Thèses sur le sujet "Graphene based 2-dimensional systems"
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OMICIUOLO, LUCA. « Graphene-based low dimensional systems : growth processes and characterization ». Doctoral thesis, Università degli Studi di Trieste, 2016. http://hdl.handle.net/11368/2908086.
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Questo lavoro di tesi si occupa di sistemi a bassa dimensionalità basati su grafene, dalla caratterizzazione delle procedure di crescita fino alla produzione di eterostrutture per la possibile integrazione in dispostivi elettronici di nuova generazione. La prima parte del lavoro è dedicata alla caratterizzazione, mediante tecniche sperimentali e simulazioni teoriche, del processo di crescita di grafene su metalli di transizione e allo studio dei meccanismi di interazione tra il grafene e il substrato di crescita. Nella seconda parte, due approcci sono proposti per la sintesi di interfacce grafene/ossido di alta qualità e per il gating chimico del grafene. La terza parte è invece focalizzata sulla sintesi di altri sistemi a bassa dimensionalità legati al grafene, come il nitruro di boro esagonale e i nanoflakes di grafene. Nella parte finale del lavoro viene descritta nel dettaglio una macchina per la produzione di cluster selezionati in massa attualmente in costruzione presso il Laboratorio di Scienza delle Superfici dell’Università di Trieste e alla cui costruzione e progettazione ho attivamente partecipato durante il periodo di attività dottorale.This thesis work is focused on the characterization of graphene-related low-dimensional systems, from the synthesis to the production of heterostructures for possible integration in new-generation electronic devices. The first part of the work is devoted to the characterization, by means of a combination of experimental techniques and theoretical simulations, of the growth processes of graphene and to the study of the interaction mechanism with transition metal substrates. In the second part two different approaches for the production of high-quality graphene/oxide interfaces and for the chemical gating of graphene are presented. The third part is focused on the synthesis of graphene-related systems like hexagonal boron nitride and graphene nanoflakes. Finally, the last part introduces the mass selected cluster source that is currently under development at the Surface Science Laboratory of the University of Trieste, and in whose design and development I was involved during the PhD activity.
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MATRECANO, RICCARDO. « On AdS4 Holography - Towards applications to 2+1 dimensional graphene-like systems ». Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2967030.
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Janson, Oleg. « DFT-based microscopic magnetic modeling for low-dimensional spin systems ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-91976.
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In the vast realm of inorganic materials, the Cu2+-containing cuprates form one of the richest classes. Due to the combined effect of crystal-field, covalency and strong correlations, all undoped cuprates are magnetic insulators with well-localized spins S=1/2, whereas the charge and orbital degrees of freedom are frozen out. The combination of the spin-only nature of their magnetism with the unique structural diversity renders cuprates as excellent model systems. The experimental studies, boosted by the discovery of high-temperature superconductivity in doped La2CuO4, revealed a fascinating variety of magnetic behaviors observed in cuprates. A digest of prominent examples should include the spin-Peierls transition in CuGeO3, the Bose-Einstein condensation of magnons in BaCuSi2O6, and the quantum critical behavior of Li2ZrCuO4. The magnetism of cuprates originates from short-range (typically, well below 1 nm) exchange interactions between pairs of spins Si and Sj, localized on Cu atoms i and j. Especially in low-dimensional compounds, these interactions are strongly anisotropic: even for similar interatomic distances |Rij|, the respective magnetic couplings Jij can vary by several orders of magnitude. On the other hand, there is an empirical evidence for the isotropic nature of this interaction in the spin space: different components of Si are coupled equally strong. Thus, the magnetism of cuprates is mostly described by a Heisenberg model, comprised of Jij(Si*Sj) terms. Although the applicability of this approach to cuprates is settled, the model parameters Jij are specific to a certain material, or more precisely, to a particular arrangement of the constituent atoms, i.e. the crystal structure. Typically, among the infinite number of Jij terms, only several are physically relevant. These leading exchange couplings constitute the (minimal) microscopic magnetic model. Already at the early stages of real material studies, it became gradually evident that the assignment of model parameters is a highly nontrivial task. In general, the problem can be solved experimentally, using elaborate measurements, such as inelastic neutron scattering on large single crystals, yielding the magnetic excitation spectrum. The measured dispersion is fitted using theoretical models, and in this way, the model parameters are refined.
Despite excellent accuracy of this method, the measurements require high-quality samples and can be carried out only at special large-scale facilities. Therefore, less demanding (especially, regarding the sample requirements), yet reliable and accurate procedures are desirable. An alternative way to conjecture a magnetic model is the empirical approach, which typically relies on the Goodenough-Kanamori rules. This approach links the magnetic exchange couplings to the relevant structural parameters, such as bond angles. Despite the unbeatable performance of this approach, it is not universally applicable. Moreover, in certain cases the resulting tentative models are erroneous. The recent developments of computational facilities and techniques, especially for strongly correlated systems, turned density-functional theory (DFT) band structure calculations into an appealing alternative, complementary to the experiment. At present, the state-of-the-art computational methods yield accurate numerical estimates for the leading microscopic exchange couplings Jij (error bars typically do not exceed 10-15%).
Although this computational approach is often regarded as ab initio, the actual procedure is not parameter-free. Moreover, the numerical results are dependent on the parameterization of the exchange and correlation potential, the type of the double-counting correction, the Hubbard repulsion U etc., thus an accurate choice of these crucial parameters is a prerequisite. In this work, the optimal parameters for cuprates are carefully evaluated based on extensive band structure calculations and subsequent model simulations.
Considering the diversity of crystal structures, and consequently, magnetic behaviors, the evaluation of a microscopic model should be carried out in a systematic way. To this end, a multi-step computational approach is developed. The starting point of this procedure is a consideration of the experimental structural data, used as an input for DFT calculations. Next, a minimal DFT-based microscopic magnetic model is evaluated. This part of the study comprises band structure calculations, the analysis of the relevant bands, supercell calculations, and finally, the evaluation of a microscopic magnetic model. The ground state and the magnetic excitation spectrum of the evaluated model are analyzed using various simulation techniques, such as quantum Monte Carlo, exact diagonalization and density-matrix renormalization groups, while the choice of a particular technique is governed by the dimensionality of the model, and the presence or absence of magnetic frustration.
To illustrate the performance of the approach and tune the free parameters, the computational scheme is applied to cuprates featuring rather simple, yet diverse magnetic behaviors: spin chains in CuSe2O5, [NO]Cu(NO3)3, and CaCu2(SeO3)2Cl2; quasi-two-dimensional lattices with dimer-like couplings in alpha-Cu2P2O7 and CdCu2(BO3)2, as well as the 3D magnetic model with pronounced 1D correlations in Cu6Si6O18*6H2O. Finally, the approach is applied to spin liquid candidates --- intricate materials featuring kagome-lattice arrangement of the constituent spins. Based on the DFT calculations, microscopic magnetic models are evaluated for herbertsmithite Cu3(Zn0.85Cu0.15)(OH)6Cl2, kapellasite Cu3Zn(OH)6Cl2 and haydeeite Cu3Mg(OH)6Cl2, as well as for volborthite Cu3[V2O7](OH)2*2H2O. The results of the DFT calculations and model simulations are compared to and challenged with the available experimental data.
The advantages of the developed approach should be briefly discussed. First, it allows to distinguish between different microscopic models that yield similar macroscopic behavior. One of the most remarkable example is volborthite Cu3[V2O7](OH)2*2H2O, initially described as an anisotropic kagome lattice. The DFT calculations reveal that this compound features strongly coupled frustrated spin chains, thus a completely different type of magnetic frustration is realized.
Second, the developed approach is capable of providing accurate estimates for the leading magnetic couplings, and consequently, reliably parameterize the microscopic Hamiltonian. Dioptase Cu6Si6O18*6H2O is an instructive example showing that the microscopic theoretical approach eliminates possible ambiguity and reliably yields the correct parameterization.
Third, DFT calculations yield even better accuracy for the ratios of magnetic exchange couplings. This holds also for small interchain or interplane couplings that can be substantially smaller than the leading exchange. Hence, band structure calculations provide a unique possibility to address the interchain or interplane coupling regime, essential for the magnetic ground state, but hardly perceptible in the experiment due to the different energy scales.
Finally, an important advantage specific to magnetically frustrated systems should be mentioned. Numerous theoretical and numerical studies evidence that low-dimensionality and frustration effects are typically entwined, and their disentanglement in the experiment is at best challenging. In contrast, the computational procedure allows to distinguish between these two effects, as demonstrated by studying the long-range magnetic ordering transition in quasi-1D spin chain systems.
The computational approach presented in the thesis is a powerful tool that can be directly applied to numerous S=1/2 Heisenberg materials. Moreover, with minor modifications, it can be largely extended to other metallates with higher value of spin. Besides the excellent performance of the computational approach, its relevance should be underscored: for all the systems investigated in this work, the DFT-based studies not only reproduced the experimental data, but instead delivered new valuable information on the magnetic properties for each particular compound.
Beyond any doubt, further computational studies will yield new surprising results for known as well as for new, yet unexplored compounds. Such "surprising" outcomes can involve the ferromagnetic nature of the couplings that were previously considered antiferromagnetic, unexpected long-range couplings, or the subtle balance of antiferromagnetic and ferromagnetic contributions that "switches off" the respective magnetic exchange. In this way, dozens of potentially interesting systems can acquire quantitative microscopic magnetic models.
The results of this work evidence that elaborate experimental methods and the DFT-based modeling are of comparable reliability and complement each other. In this way, the advantageous combination of theory and experiment can largely advance the research in the field of low-dimensional quantum magnetism. For practical applications, the excellent predictive power of the computational approach can largely alleviate designing materials with specific properties.
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Fekih, Hassen Wiem. « A ubiquitous navigation service on smartphones ». Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI006.
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La navigation pédestre est un domaine de recherche en pleine croissance qui vise à développer des services assurant le positionnement et la navigation en continu des personnes à l'extérieur comme à l'intérieur de bâtiments. Dans cette thèse, nous proposons un prototype de service pour la navigation pédestre ubiquitaire qui tient compte des préférences de l'utilisateur et de la technologie de positionnement optimale disponible. Notre objectif principal est d'estimer, d'une façon continue, la position d'un piéton muni d'un smartphone. En premier lieu, nous proposons un nouvel algorithme, nommé UCOSA, qui permet de sélectionner la technologie de positionnement à adopter à tout moment le long du processus de navigation. L'algorithme UCOSA commence par inférer la nécessité de déclencher un processus de "handover" (changement de technologie) entre les technologies de positionnement détectées (i.e. quand les zones de couvertures se chevauchent) en utilisant la technique de la logique floue. Ensuite, il sélectionne la technologie optimale à l'aide d'une fonction qui calcule un score pour chaque technologie disponible et qui se compose de deux parties. La première partie représente les poids, calculés en utilisant la méthode d'analyse hiérarchique (AHP). Tandis que, la deuxième partie fournit les valeurs normalisées des paramètres considérés. L'algorithme UCOSA intègre aussi la technique de positionnement à l'estime appelé PDR afin d'améliorer le calcul de la position du smartphone. En second lieu, nous portons l'intérêt à la technique de positionnement par empreintes RSS dont le principe consiste à calculer la position du smartphone en comparant les valeurs RSSs enregistrées, en temps réel, avec les valeurs RSSs stockées dans une base de données (radiomap). La majorité des radiomaps sont représentées sous forme de grilles composées de points de référence (PR). Nous proposons une nouvelle conception de radiomap qui ajoute d'autres PRs au centre de gravité de chaque carré de la grille. En troisième lieu, nous abordons le problème de la construction du graphe modélisant un bâtiment multi-étages. Nous proposons un algorithme qui crée tout d'abord un graphe plan pour chaque étage, séparément, et qui relie ensuite les différents étages par des liens verticaux. En dernier lieu, nous étudions un nouvel algorithme nommé SIONA qui calcule et qui affiche d'une manière continue le chemin entre deux points situés à l'intérieur ou à l'extérieur d'un bâtiment. Plusieurs expériences réelles ont été réalisées pour évaluer les performances des algorithmes proposés avec des résultats prometteurs en termes de continuité et de précision (de l'ordre de 1.8 m) du service de navigationPedestrian navigation is a growing research field, which aims at developing services and applications that ensure the continuous positioning and navigation of people inside and outside covered areas (e.g. buildings). In this thesis, we propose a ubiquitous pedestrian navigation service based on user preferences and the most suitable efficient available positioning technology (e.g. WiFi, GNSS). Our main objective is to estimate continuously the position of a pedestrian carrying a smartphone equipped with a variety of technologies and sensors. First, we propose a novel positioning technology selection algorithm, called UCOSA for the complete ubiquitous navigation service in indoor and outdoor environments. UCOSA algorithm starts by inferring the need of a handover between the available positioning technologies on the overlapped coverage areas using fuzzy logic technique. If a handover process is required, a score is calculated for each captured Radio Frequency (RF) positioning technology. The score function consists of two parts: the first part represents the user preferences weights computed based on the Analytic Hierarchy Process (AHP). Whereas, the second part provides the user requirements (normalized values). UCOSA algorithm also integrates the Pedestrian Dead Reckoning (PDR) positioning technique through the navigation process to enhance the estimation of the smartphone's position. Second, we focus on the RSS fingerprinting positioning technique as it is the most widely used technique, which principle is to return the smartphone's position by comparing the real time recorded RSS values with the radiomap (i.e. a database of previous stored RSS values). Most of radiomap are organized in a grid, formed or Reference Point (RP): we propose a new design of radiomap which complements the grid with other RPs located at the center of gravity of each grid square. Third, we address the challenge of constructing a graph for a multi-floor building. We propose an algorithm that starts by creating the horizontal graph of each floor, separately, and then, adds vertical links between the different floors. Finally, we implement a novel algorithm, called SIONA that calculates and displays in a continuous manner the pathway between two distinct points being located indoor or outdoor. We conduct several real experiments inside the campus of the University of Passau in Germany to evaluate the performance of the proposed algorithms. They yield promising results in terms of continuity and accuracy (around 1.8 m indoor) of navigation service
Livres sur le sujet "Graphene based 2-dimensional systems"
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Enoki, Toshiaki, Morinobu Endo et Masatsugu Suzuki. Graphite Intercalation Compounds and Applications. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195128277.001.0001.
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Graphite intercalation compounds are a new class of electronic materials that are classified as graphite-based host guest systems. They have specific structural features based on the alternating stacking of graphite and guest intercalate sheets. The electronic structures show two-dimensional metallic properties with a large variety of features including superconductivity. They are also interesting from the point of two-dimensional magnetic systems. This book presents the synthesis, crystal structures, phase transitions, lattice dynamics, electronic structures, electron transport properties, magnetic properties, surface phenomena, and applications of graphite intercalation compounds. The applications covered include batteries, highly conductive graphite fibers, exfoliated graphite and intercalated fullerenes and nanotubes.
Chapitres de livres sur le sujet "Graphene based 2-dimensional systems"
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Medvedeva, Elena, et Ekaterina Kurbatova. « Image Segmentation Based on Two-Dimensional Markov Chains ». Dans Computer Vision in Control Systems-2, 277–95. Cham : Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-11430-9_11.
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Ghosh, Mili, Debarka Mukhopadhyay et Paramartha Dutta. « 2-Dimensional 2-Dot 1-Electron Quantum Cellular Automata-Based Dynamic Memory Design ». Dans Advances in Intelligent Systems and Computing, 357–65. New Delhi : Springer India, 2015. http://dx.doi.org/10.1007/978-81-322-2695-6_30.
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Vytovtov, K., E. Barabanova et V. M. Vishnevskiy. « Accurate Mathematical Model of Two-Dimensional Parametric Systems Based on $$2\times 2$$ Matrix ». Dans Communications in Computer and Information Science, 199–211. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-36625-4_17.
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Vytovtov, K., et E. Barabanova. « Mathematical Model of Four-Dimensional Parametric Systems Based on Block Diagonal Matrix with $$2\times 2$$ Blocks ». Dans Communications in Computer and Information Science, 139–51. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-36625-4_12.
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Xiong, Mei, Longwei Chen, Chaochao Li et Juan Wang. « Exact Solutions for $$(2+1)$$ –Dimensional Nonlinear Schrödinger Schrodinger Equation Based on Modified Extended tanh Method ». Dans Advances in Natural Computation, Fuzzy Systems and Knowledge Discovery, 224–31. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-32456-8_24.
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Fischer, P., et M. Medarde. « Magnetic 2-D and 3-D Ordering Phenomena in Rare-Earth Based Copper-Oxide Superconductors and Related Systems ». Dans Physics and Chemistry of Materials with Low-Dimensional Structures, 261–301. Dordrecht : Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-015-1284-8_7.
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Zhang, Q., C. Zheng, K. Sagoe-Crentsil et W. Duan. « Transfer and Substrate Effects on 2D Materials for Their Sensing and Energy Applications in Civil Engineering ». Dans Lecture Notes in Civil Engineering, 409–19. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-3330-3_42.
Texte intégralRésumé :
AbstractThe recent emergence of two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs) of the family (Mo, W)(S, Se)2 has attracted interest from a broad range of engineering applications, including advanced sensing and energy harvesting and conservation, because of their distinctive properties. However, it is critical important to achieve intact delamination and transfer of these atomically thin materials, as well as to understand the effects of the target substrates on their optical and electronic properties. Therefore, we developed and compared techniques for transferring as-grown WS2 crystals to arbitrary substrates. Polystyrene-assisted wet transfer can realize improved preservation of monolayer WS2 crystals than the commonly used poly(methyl methacrylate) (PMMA)-assisted wet transfer method, due to minimal chemical etching involved in the 2D material delamination process. The intercalation of alkali ions in the PMMA-based transfer method induces chemical doping over the transferred 2D crystals, leading to the formation of trions. Moreover, the edges of the crystals on hydrophilic substrates, such as sapphire or SiO2/Si, are subject to ambient water intercalation, which locally affects the photoluminescence behavior of the monolayer WS2 by doping and changing of the dielectric environment. This non-uniform optical behavior is absent when the crystal is transferred onto a hydrophobic substrate through which ambient water cannot penetrate. These results have important implications for the choice of target substrate and transfer method adopted for 2D TMD-based applications such as next-generation strain sensing, photodetectors, gas sensing, bio sensing, solar energy harvesting and radiative cooling in which uniform behavior of the channel material is required.
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Vin, Eric, Shun Kashiwa, Matthew Rhea, Daniel J. Fremont, Edward Kim, Tommaso Dreossi, Shromona Ghosh, Xiangyu Yue, Alberto L. Sangiovanni-Vincentelli et Sanjit A. Seshia. « 3D Environment Modeling for Falsification and Beyond with Scenic 3.0 ». Dans Computer Aided Verification, 253–65. Cham : Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-37706-8_13.
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AbstractWe present a major new version of Scenic, a probabilistic programming language for writing formal models of the environments of cyber-physical systems. Scenic has been successfully used for the design and analysis of CPS in a variety of domains, but earlier versions are limited to environments that are essentially two-dimensional. In this paper, we extend Scenic with native support for 3D geometry, introducing new syntax that provides expressive ways to describe 3D configurations while preserving the simplicity and readability of the language. We replace Scenic’s simplistic representation of objects as boxes with precise modeling of complex shapes, including a ray tracing-based visibility system that accounts for object occlusion. We also extend the language to support arbitrary temporal requirements expressed in LTL, and build an extensible Scenic parser generated from a formal grammar of the language. Finally, we illustrate the new application domains these features enable with case studies that would have been impossible to accurately model in Scenic 2.
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Zhao, Dangjun, Zhiwei Zhang et Mingzhen Gui. « Birkhoff Pseudospectral Method and Convex Programming for Trajectory Optimization ». Dans Autonomous Trajectory Planning and Guidance Control for Launch Vehicles, 99–127. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-0613-0_4.
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AbstractTrajectory optimization, an optimal control problem (OCP) in essence, is an important issue in many engineering applications including space missions, such as orbit insertion of launchers, orbit rescue, formation flying, etc. There exist two kinds of solving methods for OCP, i.e., indirect and direct methods. For some simple OCPs, using the indirect methods can result in analytic solutions, which are not easy to be obtained for complicated systems. Direct methods transcribe an OCPs into a finite-dimensional nonlinear programming (NLP) problem via discretizing the states and the controls at a set of mesh points, which should be carefully designed via compromising the computational burden and the solution accuracy. In general, the larger number of mesh points, the more accurate solution as well as the larger computational cost including CPU time and memory [1]. There are many numerical methods have been developed for the transcription of OCPs, and the most common method is by using Pseudospectral (PS) collocation scheme [2], which is an optimal choice of mesh points in the reason of well-established rules of approximation theory [3]. Actually, there have several mature optimal control toolkits based PS methods, such as DIDO [4], GPOPS [5]. The resulting NLP problem can be solved by the well-known algorithm packages, such as IPOPT [6] or SNOPT [7]. However, these algorithms cannot obtain a solution in polynomial-time, and the resulting solution is locally optimal. Moreover, a good initial guess solution should be provided for complicated problems.
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Ryzhii, V., A. Satou et T. Otsuji. « Plasma Waves in Two-Dimensional Electron-Hole System in Gated Graphene Heterostructures * ». Dans Graphene-Based Terahertz Electronics and Plasmonics, 3–15. Jenny Stanford Publishing, 2020. http://dx.doi.org/10.1201/9780429328398-2.
Texte intégralActes de conférences sur le sujet "Graphene based 2-dimensional systems"
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Bin, Jonghoon, William S. Oates et Kunihiko Taira. « Thermoacoustic Modeling of a Graphene-Based Actuator ». Dans ASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/smasis2014-7600.
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A model for two-dimensional graphene-based thermoacoutic membranes is investigated analytically and validated numerically in this study. In one-dimension, the temperature and the pressure variables are analytically determined by decoupling the two variables in the governing equations due to the large disparity between length scales. We further extend the one-dimensional findings to three dimensions. The three-dimensional pressure fluctuation produced by the surface temperature variation is determined with the aid of the acoustic piston model. Through the one and three-dimensional model analysis, the dependence of acoustic pressure as a function of frequency is studied and the acoustic response with respect to the frequency shows different characteristics when assuming Dirichlet (temperature) or Neumann (heat flux) boundary conditions. The general thermoacoustic model is then applied to a graphene-on-paper sound device. Probabilistic Bayesian method coupled with Monte Carlo Markov Chain (MCMC) algorithms is used to optimize model parameters and to analyze model parameter uncertainty. Excellent correlations of thermoacoustic behavior is predicted by the model which provides insight into heat transport mechanisms associated with generating sound from thermally cycling graphene at high frequencies.
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Ghanekar, Alok, Jiahui Wang, Cheng Guo, Shanhui Fan et Michelle L. Povinelli. « Nonreciprocal Thermal Emission based on Space-Time Modulation of Graphene ». Dans CLEO : Fundamental Science. Washington, D.C. : Optica Publishing Group, 2023. http://dx.doi.org/10.1364/cleo_fs.2023.fth3m.2.
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We present a non-reciprocal thermal emitter based on the dynamic space-time modulation of graphene. Compound symmetry in the system gives rise to a new dimension of tunable thermal emission in non-reciprocal systems.
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Jiang, Zhangfan, Osman E. Ozbulut et Devin K. Harris. « Graphene Nanoplatelets-Based Self-Sensing Cementitious Composites ». Dans ASME 2016 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/smasis2016-9188.
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Over the past two decades, numerous research studies have been conducted to explore behavior of self-sensing cementitious composites with different functional fillers. Most of these studies investigated the use of fillers such as carbon nanofiber (CNF), carbon black, and carbon nanotubes (CNTs) in cement composites to develop a multifunctional material. Since its discovery in 2004, graphene has also raised significant attention as 2D nanoscale reinforcement for composite materials. The planar structure of graphene sheets provides more contact area with the host material. However, high cost and dispersion difficulties are among the drawbacks of graphene. More recently, graphene nanoplatelets (GNPs), which have very thin but wide aspect ratio, are drawing the graphene market due to their advantages such as ease of processing and excellent material properties at a very low cost. The application of two-dimensional graphene nanoplatelets in cementitious composites has yet to gain widespread attention. This paper investigates the self-sensing capabilities of GNP-reinforced hydraulic Portland cement composites. In particular, the effects of GNP content on the electrical properties and piezoresistive characteristics of mortar specimens are explored. In addition, a simple fabrication method that does not require special treating procedures such as ultrasonication and chemical (covalent) treatments for the dispersion of GNPs is pursued. The GNPs used in this study have an average thickness of 8 nanometers and a diameter of 25 microns. Standard prismatic mortar specimens containing different GNP concentrations are prepared using three different mixing procedures. The resistivity of the specimens is measured using a four-point probe method. The piezoresistive response of GNP-reinforced cement composites is evaluated under cyclic compressive loads.
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Wang, Max Zenghui. « Nanoelectromechanical systems based on low dimensional nanomaterials : Beyond carbon nanotube and graphene nanomechanical resonators—a brief review ». Dans 2016 IEEE 16th International Conference on Nanotechnology (IEEE-NANO). IEEE, 2016. http://dx.doi.org/10.1109/nano.2016.7751567.
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Ohnishi, Masato, Yusuke Suzuki, Yusuke Ohashi, Ken Suzuki et Hideo Miura. « Change of the Electronic Conductivity of Carbon Nanotube and Graphene Sheets Caused by a Three-Dimensional Strain Field ». Dans ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems. ASMEDC, 2011. http://dx.doi.org/10.1115/ipack2011-52057.
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In this study, the change of the resistivity of carbon nanotubes and graphene sheets under strain was analyzed by applying a quantum chemical molecular dynamics analysis and the first principle calculation. Various combinations of double-walled carbon nanotube structures were modeled for the analysis. The change of the band structure was calculated by changing the amplitude of the applied strain. It was found in some cases that the band structure changes drastically from metallic band structure to semiconductive one, and this result clearly indicated that the electronic conductivity of the MWCNT decreased significantly in a three-dimensional strain field. It was also found that there is a critical strain at which the electronic band structure changes from metallic to semiconductive and vice versa. This result indicated that the metallic CNT changes a semiconductive CNT depending on the applied strain field. The effect of the diameter of the zigzag type CNT on the critical strain of buckling deformation was analyzed under uni-axial strain. In this analysis, the aspect ratio of each structure was fixed at 10. It was found that the critical strain decreased monotonically with the decrease of the diameter. This was because that the flexural rigidity of a cylinder decreased with the decrease of its diameter when the thickness of the wall of the cylinder was fixed. It was found that the critical strain decreased drastically from about 5% to 0.5% when the aspect ratio was changed from 10 to 30. Since the typical aspect ratio of CNTs often exceeds 1000, most CNTs should show buckling deformation when an axial compressive strain is applied to the CNTs. Finally, the shape of a six-membered ring of the CNT was found to be the dominant factor that determines the electronic band structure of a CNT. The change of the band structure of a grapheme sheet was analyzed by applying the abinitio calculation based on density functional theory. It was found that the fluctuation of the atomic distance among the six-membered ring is the most dominant factor of the electronic band structure. When the fluctuation exceeded about 10%, band gap appeared in the deformed six-membered ring, and thus, the electronic conductivity of the grapheme sheet change from metallic one to semiconductive one. It is therefore, possible to predict the change of the electronic conductivity of a CNT by considering the local shape of a six-membered ring in the deformed CNT.
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Neumann, Laurie. « Synthesis of 5,15-A2BC-Type Porphyrins to Modify a Field-Effect Transistor for Detection of Gram-Negative Bacteria ». Dans SurfCoat Korea and Graphene Korea 2021 International Joint Virtual Conferences. Setcor Conferences and Events, 2021. http://dx.doi.org/10.26799/cp-surfcoat-graphene-korea-2021/2.
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Current biological sensing technologies of bacteria are time consuming, labor intensive and thus expensive. Furthermore, their accuracy and reproducibility could be improved. Conventional electrical measurement methods might combine high sensitive sensing systems with biological requirements. A promising approach is the trapping of bacteria on the surface of the gate-electrode of a modified field-effect transistor (FET) using porphyin based self-assembled monolayers (SAMs). 5,15-A2BC-type porphyrins were synthesized originating from a 5,15-diphenylporphyrin with the functionality to connect to a gold surface. The SAM formation on the surface of the gold electrode was proven by well-established analytical methods. In this work a synthesis route is presented for a linker which is attached to a peptide or cysteine group for trapping of Gram-negative bacteria. Fluorescence lifetime imaging microscopy (FLIM) measurements of porphyrin-stained bacteria were performed to verify the linkage ability.
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Khan, Muhammad Omer, Ellen Chan, Siu N. Leung, Hani Naguib, Francis Dawson et Vincent Adinkrah. « Multifunctional Liquid Crystal Polymeric Composites Embedded With Graphene Nano Platelets ». Dans ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2011. http://dx.doi.org/10.1115/smasis2011-5123.
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This paper studies the development of new multifunctional liquid crystal polymeric composites filled with graphene nano platelets (GNPs) for electronic packaging applications. A series of parametric studies were conducted to study the effect of GNP content on the thermal conductivity of LCP-based nanocomposites. Graphene, ranging from 10 wt. % to 50 wt. %, were melt-compounded with LCP using a twin-screw compounder. The extrudates were ground and compression molded into small disc-shaped specimens. The thermal conductivity of LCP matrix was observed to have increased by more than 1000% where as the electrical conductivity increased by 13 orders of magnitude with the presence of 50 wt% GNP fillers. The morphology of the composites was analyzed using SEM micrographs to observe the dispersion of filler within the matrix. These thermally conductive composites represent potential cost-effective materials to injection mold three-dimensional, net-shape microelectronic enclosures with superior heat dissipation performance.
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Cassiano, Tiago de Sousa Araújo, Fábio Ferreira Monteiro et Pedro Henrique de Oliveira Neto. « Unveiling the Dynamics of Quasiparticles in Cove-type Graphene Nanoribbons ». Dans VIII Simpósio de Estrutura Eletrônica e Dinâmica Molecular. Universidade de Brasília, 2020. http://dx.doi.org/10.21826/viiiseedmol202074.
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Since its isolation in 2004, graphene has attracted the attention of many scientists due to its excellent transport and mechanical features. However, the use of this material in optoelectronics is limited since it has no bandgap. One can detour it by cutting a graphene sheet laterally. The new carbon nanostructure that emerges from this procedure is known as graphene nanoribbon (GNR). Nowadays, a quest to develop a viable production of these materials drives many researchers. Narita et al.[2] successfully synthesized a candidate using a bottom-up solution procedure, known as cove-type GNR. Despite all the promising attributes, the electronic transport mechanism of this material is so far unexplored. In this work, we investigated through computational simulations the electronic transport of the cove-type GNR. We did so by employing an extended two-dimensional SSH model [3] with a tight-binding effect (electron-phonon coupling). A self-consistent field method generates stationary states, while time evolution is conducted based on the Ehrenfest theorem. Results reveal the formation of two polarized regions after photoionization: a polaron and a bipolaron. These quasiparticles are mobile by the application of a uniform electric field, unveiling its role as a charge transporter. Finally, a semi-classical algorithm evaluates their mobility and effective mass. Calculations indicate that both structures have a low effective mass along with intrinsic mobility. Hence, the cove-type GNRs may be suitable to perform as highly efficient semiconductors in future applications. This study contributes as well to the theoretical understanding of confined quantum systems.
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Ghosh, Dipannita, Md Ashiqur Rahman, Ali Ashraf et Nazmul Islam. « Hydrogel and Graphene Embedded Piezoresistive Microcantilever Sensor for Solvent and Gas Flow Detection ». Dans ASME 2022 17th International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/msec2022-85544.
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Abstract Piezoresistive microcantilever sensor is widely used in sensing applications including liquid and gas flow detection. Microcantilevers can function as an embedded system if they are coated with polymers or nanomaterials to improve sensing performance. In this paper, we investigated the performance of piezoresistive microcantilevers (PMC) with and without additional coating. We studied the sensitivity of the PMC sensor after coating it with a three-dimensional porous hydrogel and piezoresistive graphene oxide layer. Hydrogel embedded piezoresistive microcantilever (EPM) showed better results than PMC during solvent sensing application. The resistance change for hydrogel embedded PMC was higher compared to bare PMC by 430% (3.2% to 17%) while detecting isopropyl alcohol (IPA), by approximately 1.5 orders of magnitude (0.19% to 5.7%) while detecting the presence of deionized water. Graphene Oxide coated PMC showed a wider detection range by 30 milliliter/min and 24% better sensitivity than bare PMC during the gas detection experiment. Additionally, we compared the experiment result with COMSOL simulation to develop a model for our embedded PMC sensing. Simulation shows significantly higher deflection of the EPM compared to the bare PMC (66.67% higher while detecting IPA, consistent with the trend observed during the experiment). The facile drop casting-based embedded microcantilever fabrication technique can lead to improved performance in different sensing applications. Our future work will focus on detecting biomolecules by using our constructed embedded systems.
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Lei, Nan, Pengfei Li, Wei Xue et Jie Xu. « Gate-Free Graphene-Based Sensor for pH Monitoring ». Dans ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65166.
Texte intégralRésumé :
Graphene, as an ideal two-dimensional material, holds great potential for building high-performance sensors. Traditional microfabrication processes, such as lithography and etching, often require multiple complex steps including masking and aligning. Moreover, the graphene is often configured as the semiconducting material in transistors, which add complexity to the system. In this paper, we report the fabrication and characterization of a simple gate-free graphene device. The graphene sheets are made by mechanical exfoliation from bulk graphite and then placed onto a silicon wafer with a thermal oxidization layer. Platinum contact electrodes are fabricated with a mask-free process using focused ion beam, and then expanded by silver paint. An annealing process is used to improve the electrical contact. During the experiment, the fabricated graphene device is used to sense different pH values in the surrounding liquid environment. The results show that the conductance of the graphene increases quadratically with the increasing pH values, which makes the device a high-sensitivity pH sensor. In the end, the possible sensing mechanisms of our graphene device are discussed.
Rapports d'organisations sur le sujet "Graphene based 2-dimensional systems"
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Mani, Ramesh G. Final Report : Magnetotransport studies of low dimensional electron systems based on GaAs/AlGaAs heterostructures and graphene. Office of Scientific and Technical Information (OSTI), février 2019. http://dx.doi.org/10.2172/1494586.
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Yan, Yujie, et Jerome F. Hajjar. Automated Damage Assessment and Structural Modeling of Bridges with Visual Sensing Technology. Northeastern University, mai 2021. http://dx.doi.org/10.17760/d20410114.
Texte intégralRésumé :
Recent advances in visual sensing technology have gained much attention in the field of bridge inspection and management. Coupled with advanced robotic systems, state-of-the-art visual sensors can be used to obtain accurate documentation of bridges without the need for any special equipment or traffic closure. The captured visual sensor data can be post-processed to gather meaningful information for the bridge structures and hence to support bridge inspection and management. However, state-of-the-practice data postprocessing approaches require substantial manual operations, which can be time-consuming and expensive. The main objective of this study is to develop methods and algorithms to automate the post-processing of the visual sensor data towards the extraction of three main categories of information: 1) object information such as object identity, shapes, and spatial relationships - a novel heuristic-based method is proposed to automate the detection and recognition of main structural elements of steel girder bridges in both terrestrial and unmanned aerial vehicle (UAV)-based laser scanning data. Domain knowledge on the geometric and topological constraints of the structural elements is modeled and utilized as heuristics to guide the search as well as to reject erroneous detection results. 2) structural damage information, such as damage locations and quantities - to support the assessment of damage associated with small deformations, an advanced crack assessment method is proposed to enable automated detection and quantification of concrete cracks in critical structural elements based on UAV-based visual sensor data. In terms of damage associated with large deformations, based on the surface normal-based method proposed in Guldur et al. (2014), a new algorithm is developed to enhance the robustness of damage assessment for structural elements with curved surfaces. 3) three-dimensional volumetric models - the object information extracted from the laser scanning data is exploited to create a complete geometric representation for each structural element. In addition, mesh generation algorithms are developed to automatically convert the geometric representations into conformal all-hexahedron finite element meshes, which can be finally assembled to create a finite element model of the entire bridge. To validate the effectiveness of the developed methods and algorithms, several field data collections have been conducted to collect both the visual sensor data and the physical measurements from experimental specimens and in-service bridges. The data were collected using both terrestrial laser scanners combined with images, and laser scanners and cameras mounted to unmanned aerial vehicles.
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Shmulevich, Itzhak, Shrini Upadhyaya, Dror Rubinstein, Zvika Asaf et Jeffrey P. Mitchell. Developing Simulation Tool for the Prediction of Cohesive Behavior Agricultural Materials Using Discrete Element Modeling. United States Department of Agriculture, octobre 2011. http://dx.doi.org/10.32747/2011.7697108.bard.
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The underlying similarity between soils, grains, fertilizers, concentrated animal feed, pellets, and mixtures is that they are all granular materials used in agriculture. Modeling such materials is a complex process due to the spatial variability of such media, the origin of the material (natural or biological), the nonlinearity of these materials, the contact phenomenon and flow that occur at the interface zone and between these granular materials, as well as the dynamic effect of the interaction process. The lack of a tool for studying such materials has limited the understanding of the phenomena relevant to them, which in turn has led to energy loss and poor quality products. The objective of this study was to develop a reliable prediction simulation tool for cohesive agricultural particle materials using Discrete Element Modeling (DEM). The specific objectives of this study were (1) to develop and verify a 3D cohesionless agricultural soil-tillage tool interaction model that enables the prediction of displacement and flow in the soil media, as well as forces acting on various tillage tools, using the discrete element method; (2) to develop a micro model for the DEM formulation by creating a cohesive contact model based on liquid bridge forces for various agriculture materials; (3) to extend the model to include both plastic and cohesive behavior of various materials, such as grain and soil structures (e.g., compaction level), textures (e.g., clay, loam, several grains), and moisture contents; (4) to develop a method to obtain the parameters for the cohesion contact model to represent specific materials. A DEM model was developed that can represent both plastic and cohesive behavior of soil. Soil cohesive behavior was achieved by considering tensile force between elements. The developed DEM model well represented the effect of wedge shape on soil behavior and reaction force. Laboratory test results showed that wedge penetration resistance in highly compacted soil was two times greater than that in low compacted soil, whereas DEM simulation with parameters obtained from the test of low compacted soil could not simply be extended to that of high compacted soil. The modified model took into account soil failure strength that could be changed with soil compaction. A three dimensional representation composed of normal displacement, shear failure strength and tensile failure strength was proposed to design mechanical properties between elements. The model based on the liquid bridge theory. An inter particle tension force measurement tool was developed and calibrated A comprehensive study of the parameters of the contact model for the DEM taking into account the cohesive/water-bridge was performed on various agricultural grains using this measurement tool. The modified DEM model was compared and validated against the test results. With the newly developed model and procedure for determination of DEM parameters, we could reproduce the high compacted soil behavior and reaction forces both qualitatively and quantitatively for the soil conditions and wedge shapes used in this study. Moreover, the effect of wedge shape on soil behavior and reaction force was well represented with the same parameters. During the research we made use of the commercial PFC3D to analyze soil tillage implements. An investigation was made of three different head drillers. A comparison of three commonly used soil tillage systems was completed, such as moldboard plow, disc plow and chisel plow. It can be concluded that the soil condition after plowing by the specific implement can be predicted by the DEM model. The chisel plow is the most economic tool for increasing soil porosity. The moldboard is the best tool for soil manipulation. It can be concluded that the discrete element simulation can be used as a reliable engineering tool for soil-implement interaction quantitatively and qualitatively.