40,896 research outputs found

    Strain and interfacial engineering of 2D materials

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    Deformable device technology with advanced functionalities spanning from wearable/personal electronics to flexible bio-implantable sensors, which require both static performance stability and dynamic sensitivity, has been ever-evolving with the substantial development in the field of two-dimensional (2D) materials. 2D materials are atomically thin, layered crystalline materials that possess strong intralayer (in-plane) covalent bond and weak interlayer (out-of-plane) van der Waals interaction resulting in extraordinary properties including high mechanical strength (in-plane) and extremely low bending stiffness (out-of-plane). Distinct from 3D bulk materials, the reduced dimensionality and the spatial confinement of 2D materials result in unique characteristics such as excellent electrical transport behavior, strong light-matter interaction, and vanishing flexural rigidity at the ultimate thickness limit, which will permit the achievement of next-generation flexible electronics beyond the capability of conventional semiconductor technology. Therefore, 2D materials have demanded substantial attention from the scientific community for both fundamental quantum physics/mechanics and device-level applications. Because of the exceptional mechanical strength and intrinsic flexibility, however, 2D materials can be strongly affected by external influences. Mechanical deformations, especially out-of-plane deformation, are commonly observed with 2D materials-based systems in the forms of intrinsic corrugation, wrinkles, delaminated buckles or crumples, and other non-linear complex deformations in an uncontrolled manner, which have been considered as inevitable topological defects. Furthermore, due to weak interlayer interactions of 2D materials via van der Waals interactions with surrounding environments, structural instability of delamination at the interfaces between 2D materials and substrate surfaces can occur. These mechanical instabilities are often considered as parameters deteriorating the mechanical integrity and functional performances of 2D materials-based systems. Contrary to such conventional wisdom, I have sought ways to leverage mechanical instabilities of 2D materials to advance functionalities of 2D materials-based systems including electrical sustainability, excitonic characteristics, energy generation, and novel optoelectronic phenomena by manipulating interfacial characteristics (interfacial engineering) and mechanical deformation (strain-engineering) of the constituent 2D material layers. First, I discussed a readily adaptable approach of inserting 2D materials to thin-film metal based flexible electrodes (2D-interfacial engineering) where we achieved several orders-of-magnitude enhanced strain resilient electrical functionality (which we termed ÔÇśelectrical ductilityÔÇÖ) by manipulating mechanical fracture behaviors of thin-film metals from rapid straight cracking to progressive tortuous cracking via a buckle-guided fracture mechanism induced by 2D materials at the interface. I demonstrated that our 2D-interfacial engineering is not limited to a certain combination of metals and 2D materials, which can be incorporated into the existing flexible/wearable electronics applications. Next, I demonstrated how the wrinkling deformation of artificially stacked 2D materials via strain engineering affects the optical characteristics of interlayer excitons in heterobilayer system where the effect of mechanical strain remains relatively uncharacterized. We observed highly strain-tunable interlayer excitons with non-monotonic photoluminescence characteristics in MoS2/WSe2 heterobilayer. I further provided an insight on the competition between in-plane strain and out-of-plane interlayer coupling effects on the photoluminescence characteristics, which can be an additional tuning knob to manipulate excitonic behaviors in 2D-multilayered systems. As an extension of the strain effect on the heterobilayer system, I explored how crumpling deformation of 2D materials affects both mechanical (the effective stiffness) and electromechanical (piezoelectricity) properties. Our results suggest that the effective elastic modulus can be reduced for the controlled crumpled heterostructure where the effective modulus decreased as the aspect ratio of formed crumples decreased. I further demonstrated that the crumpled MoS2/graphene heterostructures can be utilized as an effective active layer for mechanical-to-electrical energy conversion under both instantaneous and continuous strain-driven modes of stretching, bending, acoustic and mechanical vibrations. Finally, I introduced a strain-control platform to create freestanding wrinkled structures of monolayer 2D materials for the first time, offering exciting opportunities to further investigate the fundamental strain-tunability of various materials properties in 2D materials. In particular, I showed the spatial modulation of photo-induced force (near-field dipole-dipole interactions) in freestanding wrinkled 2D materials, which we attributed to a combination of the in-plane strain-induced piezoelectric effect and the out-of-plane strain gradient-induced flexoelectric effect. In conclusion, I demonstrated that controlling the mechanical deformation of 2D materials permits emergent functionalities ranging from the nanoscale to macroscale including electrical ductility, controllable excitonic behaviors, and even energy generation. Furthermore, since the deformation of 2D materials can directly manipulate bond length and angle in the atomic lattice, deformation can tune the electronic structure and interfacial characteristics. Thus, strain and interfacial engineering can serve as effective strategies to explore advanced functionalities of 2D materials. I believe our approaches to manipulate interfacial characteristics and deformation of 2D materials-based systems, as well as in a freestanding form, contribute to the larger research community by opening up exciting opportunities to study fundamental strain physics and to advance multifunctional deformable device technologies including robust flexible electronics, novel excitonic sensors, and self-powering wearable/implantable devices for health and structural monitoring.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Labor risk prevention in spanish flag vessels

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    RESUMEN. Los accidentes laborales muchas veces ocurren por desconocimiento de las normativas y de los riesgos asociados al puesto de trabajo, otras tantas veces por descuidos y en algunos casos por la falta de orden y limpieza en el ├írea designada para las labores. Con esta motivaci├│n a trav├ęs de la presente investigaci├│n se pretendi├│ detectar y prevenir los riesgos laborales a los que est├ín expuestos el personal de cubierta que cumple sus funciones en buques de pabell├│n espa├▒ol, a fin reducir las posibles enfermedades ocupacionales asociadas a los mismos. Para ello se emple├│ una investigaci├│n de tipo descriptiva, a trav├ęs de la cual se lograron determinar los peligros potenciales y latentes para el personal de cubierta en funci├│n a las labores realizadas, posteriormente se evaluaron los riesgos asociados en base a la probabilidad y severidad de los mismos y finalmente se formul├│ la propuesta de las medidas preventivas apropiadas para el control de los riesgos laborales, permitiendo concluir que entre los riegos m├ís importantes a los que est├ín expuestos los trabajadores del departamento de cabina destacan los f├şsicos, mec├ínicos, qu├şmicos, el├ęctricos, entre otros y est├ín asociados al uso de los equipos de visualizaci├│n, vibraciones, ruido, soldadura, manipulaci├│n de herramientas manuales y pesadas, riesgos por operaciones de embarque de carga rodada espec├şficamente tr├ífico de veh├şculos de carga rodada, el cual fue valorado como medio para el caso del Capit├ín lo que indica, que se deben implantar medidas para reducir el mismo y en el caso de trincaje de la carga se califica como intrascendente, por lo que no requerir├í medidas espec├şficas puesto que la posibilidad de que ocurra es baja y los resultados o lesiones producidas son leves o poco da├▒inas.ABSTRACT. Occupational accidents often occur due to ignorance of the regulations and the risks associated with the job, as many times due to carelessness and in some cases due to the lack of order and cleanliness in the area designated for work. With this motivation, through this research, it was intended to detect and prevent the occupational risks to which deck personnel who perform their duties on Spanish-flagged ships are exposed, in order to reduce the possible occupational diseases associated with them. For this, a descriptive investigation was used, through which it was possible to determine the potential and latent dangers for the deck personnel based on the work carried out, subsequently the associated risks were evaluated based on the probability and severity of the themselves and finally the proposal of appropriate preventive measures for the control of occupational risks was formulated, allowing to conclude that among the most important risks to which workers in the cabin department are exposed, physical, mechanical, chemical, electrical, among others and are associated with the use of visualization equipment, vibrations, noise, welding, manipulation of manual and heavy tools, risks from ro-ro shipping operations specifically ro-ro vehicle traffic, which was valued as a means for the case of the Master which indicates that measures should be implemented to reduce it and in the case Lashing of the load is classified as inconsequential, so it will not require specific measures since the possibility of it happening is low and the results or injuries produced are slight or little harmful.Grado en Ingenier├şa N├íutica y Transporte Mar├ştim

    Acoustic intensity technique applied to monitor planetary gears

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    Condition monitoring of gear trains by classic techniques based on vibrations and/or extensometry measurements requires the preparation of the sensor contact surfaces and the cables installation. In the case of planetary gear trains, this task is more difficult due to their compactness and the complexity of the relative movements among their different elements. As an alternative, the authors studied the possibility of using acoustic measurements for the planetary gear-set characterisation, as well as for predictive maintenance of this mechanical system. In order to perform this study, a suitable measurement equipment was selected and a bespoke software was developed to control it, to process the data, as well as to represent the results. This informatic tool was used to perform the acoustic characterisation, in which acoustic pressure and intensity measurements were combined with advanced algorithms, such as sincronous-average technique. In this study, two different failures were experimentally recreated in a commercial gearbox, representing the results by frequency and order spectra and intensity maps. The obtained results were compared with those obtained in the box without defect.This work has been supported by project DPI2017-85390-P funded by the Spanish Ministry of Economy, Industry and Competitiveness

    Dynamic analysis of fatigue in-situ loading device for material testing inside a CT scanner

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    Kompoziti oja─Źani vlaknima, zbog mogu─çnosti modifikacije mehani─Źkih svojstava, preuzimaju ulogu konvencionalnih materijala te svoju primjenu pronalaze ponajprije u zrakoplovstvu i automobilskoj industriji. Mehani─Źka svojstva kompozita ovise ponajvi┼íe o heterogenoj strukturi, raspodjeli i udjelu konstituenata, izme─Ĺu kojih se mogu pojaviti razli─Źiti mehanizmi o┼íte─çenja. Za odre─Ĺivanje mehani─Źkih svojstava navedenih materijala potrebno je koristiti napredne metode ispitivanja koje pru┼żaju uvid u fenomene koji se javljaju unutar ispitnog uzorka tijekom optere─çivanja. Ra─Źunalna tomografija (eng. Computed Tomography-CT) omogu─çuje trodimenzijski prikaz vanjskog i unutarnjeg stanja skeniranog objekta bez da ga o┼íteti. Mehani─Źka ispitivanja mogu se provoditi ex-situ ili in-situ unutar CT skenera. Prilikom ex-situ ispitivanja optere─çivanje uzorka provodi se izvan CT skenera te se potom uzorak skenira u rastere─çenom stanju. Me─Ĺutim, kod in-situ ispitivanja, uzorak se istovremeno optere─çuje i skenira. Iako in-situ ispitivanja daju potpuni uvid u promjene unutar uzorka u odnosu na ex-situ ispitivanja, njihovo provo─Ĺenje je kompleksnije i zahtjeva uporabu specifi─Źnih ispitnih ure─Ĺaja koji stanu unutar CT skenera. Iz tog je razloga razvijena in-situ cikli─Źka kidalica za potrebe projekta FULLINSPECT, koji se bavi promatranjem inicijacije i propagacije pukotina te identifikacijom mehanizama loma unutar kompozita oja─Źanim vlaknima uslijed cikli─Źkih optere─çenja. Prilikom rada takve kidalice javljaju se vibracije koje mogu o┼ítetiti rotacijski stol CT skener ili utjecati na kvalitetu zabilje┼żenih 3D slika. Stoga je u ovom radu izra─Ĺen pojednostavljeni model kidalice te je prou─Źavan najkonzervativniji slu─Źaj optere─çivanja pri maksimalnoj amplitudi pomaka ispitnog uzorka od 1 mm. Primjenom metode kona─Źnih elemenata odre─Ĺene su glavne forme vibriranja kidalice i izra─Źunate su sile koje djeluju na rotacijski stol tomografa u frekvencijskom rasponu od 0 do 100 Hz.Fiber-reinforced composites, due to possibility of modifying the mechanical properties, take on the role of conventional materials and find their application primarily in the aviation and automotive industries. The mechanical properties of composites depend mainly on the heterogeneous structure, distribution and fraction of constituents, between which various damages can occur. To determine the mechanical properties, it is necessary to use advanced test methods that provide insight into the phenomena that occur within the test specimen during loading. Computed Tomography (CT) allows a three-dimensional view of the external and internal state of a scanned object without damaging it. Mechanical tests can be performed ex-situ or in-situ inside the CT scanner. In ex-situ testing, the sample is loaded outside the CT scanner and then the sample is scanned in the unloaded state. However, in in-situ testing, the sample is loaded and scanned at the same time. Although in-situ tests provide a more complete insight into changes within the sample compared to ex-situ tests, their implementation is more complex and requires the use of specific test devices that fit inside the CT scanner. For this reason, developed in-situ cyclic fatigue machine for the project FULLINSPECT, which deals with the observation of the initiation and propagation of cracks, and identification of mechanisms of fracture within the fiber-reinforced composites during cyclic loading. During the operation of such a fatigue machine, vibrations occur which can damage the rotary table of CT scanner or affect the quality of recorded 3D images. Hence, in this thesis, a simplified model of the fatigue machine was developed and the most conservative case of loading at the maximum displacement amplitude of the test specimen of 1 mm was studied. Using the finite element method, the main vibration shapes were determined and the forces acting on the rotary table of the tomograph in the frequency range from 0 to 100 Hz were calculated

    The passage of time and top-down causation

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    It is often claimed that the fundamental laws of physics are deterministic and time-symmetric and that therefore our experience of the passage of time is an illusion. This paper will critically discuss these claims and show that they are based on the misconception that the laws of physics are an exact and complete description of nature. I will argue that all supposedly fundamental deterministic and time-symmetric laws have their limitations and are supplemented by stochastic and irreversible elements. In fact, a deterministic description of a system is valid only as long as interactions with the rest of the world can be ignored. The most famous example is the quantum measurement process that occurs when a quantum system interacts with a macroscopic environment such as a measurement apparatus. This environment determines in a top-down way the possible outcomes of the measurement and their probabilities. I will argue that more generally the possible events that can occur in a system and their probabilities are the result of top-down influences from the wider context. In this way the microscopic level of a system is causally open to influences from the macroscopic environment. In conclusion, indeterminism and irreversibility are the result of a system being embedded in a wider context.Comment: This paper is based on a talk given at the MG16 conference in July 2021, and it appeared this year in the proceedings of this conference (online, open access, and print

    Quantum Mechanics Lecture Notes. Selected Chapters

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    These are extended lecture notes of the quantum mechanics course which I am teaching in the Weizmann Institute of Science graduate physics program. They cover the topics listed below. The first four chapter are posted here. Their content is detailed on the next page. The other chapters are planned to be added in the coming months. 1. Motion in External Electromagnetic Field. Gauge Fields in Quantum Mechanics. 2. Quantum Mechanics of Electromagnetic Field 3. Photon-Matter Interactions 4. Quantization of the Schr\"odinger Field (The Second Quantization) 5. Open Systems. Density Matrix 6. Adiabatic Theory. The Berry Phase. The Born-Oppenheimer Approximation 7. Mean Field Approaches for Many Body Systems -- Fermions and Boson

    A family of total Lagrangian Petrov-Galerkin Cosserat rod finite element formulations

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    The standard in rod finite element formulations is the Bubnov-Galerkin projection method, where the test functions arise from a consistent variation of the ansatz functions. This approach becomes increasingly complex when highly nonlinear ansatz functions are chosen to approximate the rod's centerline and cross-section orientations. Using a Petrov-Galerkin projection method, we propose a whole family of rod finite element formulations where the nodal generalized virtual displacements and generalized velocities are interpolated instead of using the consistent variations and time derivatives of the ansatz functions. This approach leads to a significant simplification of the expressions in the discrete virtual work functionals. In addition, independent strategies can be chosen for interpolating the nodal centerline points and cross-section orientations. We discuss three objective interpolation strategies and give an in-depth analysis concerning locking and convergence behavior for the whole family of rod finite element formulations.Comment: arXiv admin note: text overlap with arXiv:2301.0559

    Cavity-Catalyzed Hydrogen Transfer Dynamics in an Entangled Molecular Ensemble under Vibrational Strong Coupling

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    Microcavities have been shown to influence the reactivity of molecular ensembles by strong coupling of molecular vibrations to quantized cavity modes. In quantum mechanical treatments of such scenarios, frequently idealized models with single molecules and scaled, effective molecule-cavity interactions or alternatively ensemble models with simplified model Hamiltonians are used. In this work, we go beyond these models by applying an ensemble variant of the Pauli-Fierz Hamiltonian for vibro-polaritonic chemistry and numerically solve the underlying time-dependent Schr\"odinger equation to study the cavity-induced quantum dynamics in an ensemble of thioacetylacetone (TAA) molecules undergoing hydrogen transfer under vibrational strong coupling (VSC) conditions. Beginning with a single molecule coupled to a single cavity mode, we show that the cavity indeed enforces hydrogen transfer from an enol to an enethiol configuration with transfer rates significantly increasing with light-matter interaction strength. This positive effect of the cavity on reaction rates is different from several other systems studied so far, where a retarding effect of the cavity on rates was found. It is argued that the cavity ``catalyzes'' the reaction by transfer of virtual photons to the molecule. The same concept applies to ensembles with up to N=20N=20 TAA molecules coupled to a single cavity mode, where an additional, significant, ensemble-induced collective isomerization rate enhancement is found. The latter is traced back to complex entanglement dynamics of the ensemble, which we quantify by means of von Neumann-entropies. A non-trivial dependence of the dynamics on ensemble size is found, clearly beyond scaled single-molecule models, which we interpret as transition from a multi-mode Rabi to a system-bath-type regime as NN increases.Comment: Manuscript 9 pages, 5 figures (minor changes in v2). Supplementary Information 7 pages, 5 figures (Section III rewritten in v2 after peer-review

    Causes of downhole equipment failures in production wells equipped with a sucker rod pumping system : master's thesis

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    Primjena dubinskih klipnih sisaljki s klipnim ┼íipkama najstariji je i naj─Źe┼í─çe kori┼íten sustav za prinudno podizanje kapljevine. Na─Źin rada sustava podrazumijeva prijenos energije i pogona od pogonskog motora na povr┼íini do niza klipnih ┼íipki i dalje do dubinske klipne sisaljke. Podizanje fluida posti┼że se cikli─Źnim kretanjem klipa prema gore i prema dolje. Tijekom rada u bu┼íotini, dubinska oprema izlo┼żena je razli─Źitim tipovima optere─çenja, i vibracijama, uz druge bitne elemente kao ┼íto su utjecaj tlaka i temperature te korozivnosti le┼żi┼ínog fluida. Posljedi─Źno, nastaju zna─Źajna o┼íte─çenja i kvarovi povezani uglavnom s nizovima klipnih ┼íipki i uzlaznih cijevi. Naj─Źe┼í─çe prisutni kvarovi su mehani─Źko tro┼íenje spojnica klipnih ┼íipki i propu┼ítanje uzlaznih cijevi. Ostali primjetni kvarovi odnose se na dubinsku klipnu sisaljku i uklju─Źuju ─Źepljenje sisaljke, propu┼ítanje miruju─çeg i putuju─çeg ventila te ispadanje klipa iz cilindra. Ovaj ─çe rad donijeti pregled mogu─çih kvarova dubinske opreme u eksploatacijskim bu┼íotinama koje su opremljene dubinskim sisaljkama s klipnim ┼íipkama. Definirat ─çe uzroke spomenutih kvarova uz rje┼íenja i metode kori┼ítene s ciljem smanjenja njihove u─Źestalosti. Nakon teorijskog obja┼ínjenja, prikazat ─çe o┼íte─çenja dubinske opreme na primjeru jednog hrvatskog naftnog polja.Sucker rod pumping is the oldest and most utilized artificial lifting system. The working principle of a system implies energy and power transportation from a surface power source to the sucker rod string and then to the sucker rod pump. Fluid lifting is achieved by a cyclic upward and downward movement of a plunger. During its stay in a well, downhole equipment is exposed to different types of load and vibrations along with other important elements like pressure and temperature influence or corrosiveness of a reservoir fluid. As a consequence, significant damages and failures occur, connected mostly with rod and tubing strings. The most frequent failures are rod string couplings mechanical wear and tubing leakage. The other notable failures refer to the sucker rod pump and include pump plugging, standing and travelling valve leakage and plunger dropping out of the cylinder. This thesis will present a review of potential downhole equipment failures in production wells equipped with a sucker rod pumping system. It will also define causes of the mentioned failures along with solutions and methods being utilized to reduce the frequency of their occurence . After theoretical explanation, an example of one Croatian oil field with downhole equipment failures will be given

    Mechanical behaviour of rubber blocks

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    This study investigates the behaviour of rubber blocks bonded between two plates under combined compression and shear loading, using experimental and numerical analyses, and also approximate analytical theories. First, experimental data from a series of compression and shear tests of rubber blocks with different aspect ratios are presented. Next, numerical simulations are carried out with three-dimensional finite element (FE) models, allowing insight to be gained into the stress and strain fields within the blocks. Existing analytical theories for blocks under compression and combined compressive and shear loading are then reviewed, and their accuracy is evaluated against test and numerical results. The study shows that those theories accounting for the effect of the axial shortening of the blocks provide a better description of the combined compression and shear behaviour, compared to theories, developed for laminated structural bearings with many thin rubber layers, that ignore this effect. An improved theory is also proposed, which better describes the effects of the bulging of the compressed blocks on their shear and flexural parameters and provides a better fit to experimental and numerical results
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