10,305 research outputs found

    Ablation loading of barium ions into a surface electrode trap

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    Trapped-ion quantum information processing may benefit from qubits encoded in isotopes that are practically available in only small quantities, e.g. due to low natural abundance or radioactivity. Laser ablation provides a method of controllably liberating neutral atoms or ions from low-volume targets, but energetic ablation products can be difficult to confine in the small ion-electrode distance, micron-scale, microfabricated traps amenable to high-speed, high-fidelity manipulation of ion arrays. Here we investigate ablation-based ion loading into surface-electrode traps of different sizes to test a model describing ion loading probability as a function of effective trap volume and other trap parameters. We demonstrate loading of ablated and photoionized barium in two cryogenic surface-electrode traps with 730 μ\mum and 50 μ\mum ion-electrode distances. Our loading success probability agrees with a predictive analytical model, providing insight for the confinement of limited-quantity species of interest for quantum computing, simulation, and sensing

    Recent developments in 2D materials for energy harvesting applications

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    The ever-increasing demand for energy as a result of the growing interest in applications, such as the Internet of Things and wearable systems, etc, calls for the development of self-sustained energy harvesting solutions. In this regard, 2D materials have sparked enormous interest recently, due to their outstanding properties, such as ultra-thin geometry, high electromechanical coupling, large surface area to volume ratio, tunable band gap, transparency and flexibility. This has given rise to noteworthy advancements in energy harvesters such as triboelectric nanogenerators (TENGs), piezoelectric nanogenerators (PENGs) and photovoltaics based on 2D materials. This review introduces the properties of different 2D materials including graphene, transition metal dichalcogenides, MXenes, black phosphorus, hexagonal boron nitride, metal-organic frameworks and covalent-organic frameworks. A detailed discussion of recent developments in 2D materials-based PENG, TENG and photovoltaic devices is included. The review also considers the performance enhancement mechanism and importance of 2D materials in energy harvesting. Finally, the challenges and future perspectives are laid out to present future research directions for the further development and extension of 2D materials-based energy harvesters

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Miniature atomic beams and its application in quantum optics

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    The utilization of thermal atoms can enable further miniaturization and scalability of atomic devices and facilitate more applications of quantum information science in daily life. Thermal atomic beams can be easily generated and maintained compared with cold atoms. They also offer a longer coherence time and transverse Doppler-free interaction compared with thermal vapor. However, thermal atomic beams are rarely utilized in small-scale atomic devices. This thesis discussed novel approaches to generate miniature atomic beams and demonstrated their application in the field of quantum optics. The properties of our miniature atomic beam devices were characterized. Then, we studied the combination of our chip-scale atomic beams with nanophotonic resonators to achieve strong coupling in the cavity QED field. Master equation simulations were implemented to understand the dynamics, expected signal, and constraints of this platform. Efficient edge couple was demonstrated to couple free space laser beam to the chip. Besides the field of cavity QED, slow single atoms in our miniature atomic beams were isolated from our thermal atomic beam. Photon statistics from single atoms in our atomic beam were measured and studied theoretically. High values of the second-order and third-order correlation functions were found, which indicate its potential to be a source of photon pairs or triplets. Our observations showed the prospect of a bottom-up approach to building a thermal quantum system with trackable slow single atoms in an atomic beam.Ph.D

    Knowledge-based Modelling of Additive Manufacturing for Sustainability Performance Analysis and Decision Making

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    Additiivista valmistusta on pidetty käyttökelpoisena monimutkaisissa geometrioissa, topologisesti optimoiduissa kappaleissa ja kappaleissa joita on muuten vaikea valmistaa perinteisillä valmistusprosesseilla. Eduista huolimatta, yksi additiivisen valmistuksen vallitsevista haasteista on ollut heikko kyky tuottaa toimivia osia kilpailukykyisillä tuotantomäärillä perinteisen valmistuksen kanssa. Mallintaminen ja simulointi ovat tehokkaita työkaluja, jotka voivat auttaa lyhentämään suunnittelun, rakentamisen ja testauksen sykliä mahdollistamalla erilaisten tuotesuunnitelmien ja prosessiskenaarioiden nopean analyysin. Perinteisten ja edistyneiden valmistusteknologioiden mahdollisuudet ja rajoitukset määrittelevät kuitenkin rajat uusille tuotekehityksille. Siksi on tärkeää, että suunnittelijoilla on käytettävissään menetelmät ja työkalut, joiden avulla he voivat mallintaa ja simuloida tuotteen suorituskykyä ja siihen liittyvän valmistusprosessin suorituskykyä, toimivien korkea arvoisten tuotteiden toteuttamiseksi. Motivaation tämän väitöstutkimuksen tekemiselle on, meneillään oleva kehitystyö uudenlaisen korkean lämpötilan suprajohtavan (high temperature superconducting (HTS)) magneettikokoonpanon kehittämisessä, joka toimii kryogeenisissä lämpötiloissa. Sen monimutkaisuus edellyttää monitieteisen asiantuntemuksen lähentymistä suunnittelun ja prototyyppien valmistuksen aikana. Tutkimus hyödyntää tietopohjaista mallinnusta valmistusprosessin analysoinnin ja päätöksenteon apuna HTS-magneettien mekaanisten komponenttien suunnittelussa. Tämän lisäksi, tutkimus etsii mahdollisuuksia additiivisen valmistuksen toteutettavuuteen HTS-magneettikokoonpanon tuotannossa. Kehitetty lähestymistapa käyttää fysikaalisiin kokeisiin perustuvaa tuote-prosessi-integroitua mallinnusta tuottamaan kvantitatiivista ja laadullista tietoa, joka määrittelee prosessi-rakenne-ominaisuus-suorituskyky-vuorovaikutuksia tietyille materiaali-prosessi-yhdistelmille. Tuloksina saadut vuorovaikutukset integroidaan kaaviopohjaiseen malliin, joka voi auttaa suunnittelutilan tutkimisessa ja täten auttaa varhaisessa suunnittelu- ja valmistuspäätöksenteossa. Tätä varten testikomponentit valmistetaan käyttämällä kahta metallin additiivista valmistus prosessia: lankakaarihitsaus additiivista valmistusta (wire arc additive manufacturing) ja selektiivistä lasersulatusta (selective laser melting). Rakenteellisissa sovelluksissa yleisesti käytetyistä metalliseoksista (ruostumaton teräs, pehmeä teräs, luja niukkaseosteinen teräs, alumiini ja kupariseokset) testataan niiden mekaaniset, lämpö- ja sähköiset ominaisuudet. Lisäksi tehdään metalliseosten mikrorakenteen karakterisointi, jotta voidaan ymmärtää paremmin valmistusprosessin parametrien vaikutusta materiaalin ominaisuuksiin. Integroitu mallinnustapa yhdistää kerätyn kokeellisen tiedon, olemassa olevat analyyttiset ja empiiriset vuorovaikutus suhteet, sekä muut tietopohjaiset mallit (esim. elementtimallit, koneoppimismallit) päätöksenteon tukijärjestelmän muodossa, joka mahdollistaa optimaalisen materiaalin, valmistustekniikan, prosessiparametrien ja muitten ohjausmuuttujien valinnan, lopullisen 3d-tulosteun komponentin halutun rakenteen, ominaisuuksien ja suorituskyvyn saavuttamiseksi. Valmistuspäätöksenteko tapahtuu todennäköisyysmallin, eli Bayesin verkkomallin toteuttamisen kautta, joka on vankka, modulaarinen ja sovellettavissa muihin valmistusjärjestelmiin ja tuotesuunnitelmiin. Väitöstyössä esitetyn mallin kyky parantaa additiivisien valmistusprosessien suorituskykyä ja laatua, täten edistää kestävän tuotannon tavoitteita.Additive manufacturing (AM) has been considered viable for complex geometries, topology optimized parts, and parts that are otherwise difficult to produce using conventional manufacturing processes. Despite the advantages, one of the prevalent challenges in AM has been the poor capability of producing functional parts at production volumes that are competitive with traditional manufacturing. Modelling and simulation are powerful tools that can help shorten the design-build-test cycle by enabling rapid analysis of various product designs and process scenarios. Nevertheless, the capabilities and limitations of traditional and advanced manufacturing technologies do define the bounds for new product development. Thus, it is important that the designers have access to methods and tools that enable them to model and simulate product performance and associated manufacturing process performance to realize functional high value products. The motivation for this dissertation research stems from ongoing development of a novel high temperature superconducting (HTS) magnet assembly, which operates in cryogenic environment. Its complexity requires the convergence of multidisciplinary expertise during design and prototyping. The research applies knowledge-based modelling to aid manufacturing process analysis and decision making in the design of mechanical components of the HTS magnet. Further, it explores the feasibility of using AM in the production of the HTS magnet assembly. The developed approach uses product-process integrated modelling based on physical experiments to generate quantitative and qualitative information that define process-structure-property-performance interactions for given material-process combinations. The resulting interactions are then integrated into a graph-based model that can aid in design space exploration to assist early design and manufacturing decision-making. To do so, test components are fabricated using two metal AM processes: wire and arc additive manufacturing and selective laser melting. Metal alloys (stainless steel, mild steel, high-strength low-alloyed steel, aluminium, and copper alloys) commonly used in structural applications are tested for their mechanical-, thermal-, and electrical properties. In addition, microstructural characterization of the alloys is performed to further understand the impact of manufacturing process parameters on material properties. The integrated modelling approach combines the collected experimental data, existing analytical and empirical relationships, and other data-driven models (e.g., finite element models, machine learning models) in the form of a decision support system that enables optimal selection of material, manufacturing technology, process parameters, and other control variables for attaining desired structure, property, and performance characteristics of the final printed component. The manufacturing decision making is performed through implementation of a probabilistic model i.e., a Bayesian network model, which is robust, modular, and can be adapted for other manufacturing systems and product designs. The ability of the model to improve throughput and quality of additive manufacturing processes will boost sustainable manufacturing goals

    Concepts in low-cost and flow NMR

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    Challenge and Research Trends of Solar Concentrators

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    Primary and secondary solar concentrators are of vital importance for advanced solar energy and solar laser researches. Some of the most recent developments in primary and secondary solar concentrators were firstly presented. A novel three-dimensional elliptical-shaped Fresnel lens analytical model was put forward to maximize the solar concentration ratio of Fresnel-lens-based solar concentrators. By combining a Fresnel lens with a modified parabolic mirror, significant improvement in solar laser efficiency was numerically calculated. A fixed fiber light guide system using concave outlet concentrators was proposed. The absence of a solar tracking structure highlights this research. By shaping a luminescent solar concentrators in the form of an elliptic array, its emission losses was drastically reduced. Simple conical secondary concentrator was effective for thermal applications. New progresses in solar-pumped lasers by NOVA University of Lisbon were presented. By adopting a rectangular fused silica light guide, 40 W maximum solar laser power was emitted from a single Ce:Nd:YAG rod. An aspheric fused silica secondary concentrator and a small diameter Ce:Nd:YAG rod were essential for attaining 4.5 % record solar-to-laser power conversion efficiency. A novel solar concentrator design for the efficient production of doughnut-shaped and top-hat solar laser beams were also reported. More importantly, a novel solar concentrator approach for the emission of 5 kW-class TEM00 mode solar laser beams from one megawatt solar furnace was put forward at the end of this book, revealing promising future for solar-pumped lasers

    Measurement of the Environmental Impact of Materials

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    Throughout their life cycles—from production, usage, through to disposal—materials and products interact with the environment (water, soil, and air). At the same time, they are exposed to environmental influences and, through their emissions, have an impact on the environment, people, and health. Accelerated experimental testing processes can be used to predict the long-term environmental consequences of innovative products before these actually enter the environment. We are living in a material world. Building materials, geosynthetics, wooden toys, soil, nanomaterials, composites, wastes and more are research subjects examined by the authors of this book. The interactions of materials with the environment are manifold. Therefore, it is important to assess the environmental impact of these interactions. Some answers to how this task can be achieved are given in this Special Issue

    Recent progress in piezotronic sensors based on one-dimensional zinc oxide nanostructures and its regularly ordered arrays: from design to application

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    Piezotronic sensors and self-powered gadgets are highly sought-after for flexible, wearable, and intelligent electronics for their applications in cutting-edge healthcare and human-machine interfaces. With the advantages of a well-known piezoelectric effect, excellent mechanical properties, and emerging nanotechnology applications, one-dimensional (1D) ZnO nanostructures organized in the form of a regular array have been regarded as one of the most promising inorganic active materials for piezotronics. This report intends to review the recent developments of 1D ZnO nanostructure arrays for multifunctional piezotronic sensors. Prior to discussing rational design and fabrication approaches for piezotronic devices in precisely controlled dimensions, well-established synthesis methods for high-quality and well-controlled 1D ZnO nanostructures are addressed. The challenges associated with the well-aligned, site-specific synthesis of 1D ZnO nanostructures, development trends of piezotronic devices, advantages of an ordered array of 1D ZnO in device performances, exploring new sensing mechanisms, incorporating new functionalities by constructing heterostructures, the development of novel flexible device integration technology, the deployment of novel synergistic strategies in piezotronic device performances, and potential multifunctional applications are covered. A brief evaluation of the end products, such as small-scale miniaturized unconventional power sources in sensors, high-resolution image sensors, and personalized healthcare medical devices, is also included. The paper is summarized towards the conclusion by outlining the present difficulties and promising future directions. This study will provide guidance for future research directions in 1D ZnO nanostructure-based piezotronics, which will hasten the development of multifunctional devices, sensors, chips for human-machine interfaces, displays, and self-powered systems
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