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design and analysis of nanopatterned graphene-based structures for trapping applications

Physical Review B 2020年第8期102卷 085415-085415页

作者： Achiles F. da Mota Augusto Martins John Weiner Philippe Courteille Emiliano R. Martins Ben-Hur v. Borges Department of Electrical Engineering University of Brasília (UnB) Brasilia 70910-900 Brazil Department of Electrical and Computer Engineering University of São Paulo CEP 13566-590 São Carlos SP Brazil Physics Institute of São Carlos University of São Paulo CEP 13566-590 São Carlos SP Brazil

Trapping, levitating, and manipulating nanoscale objects with light forces shaped by patterned metamaterials continues to hold great interest for optical and condensed matter physics and engineering. Successful developments to date have concentrated on constraining movement only in one dimension, along the vertical axis to a material plane. Here we propose a realistic structure, consisting of alternating layers of graphene and dielectric, and periodically nanopatterned on the surface, that is capable of levitating and trapping nanoscale particles in two dimensions: one perpendicular and one parallel to the material plane. Repulsive forces arising from high- k modes of the metamaterial provide particle levitation along the vertical axis. At the point where this repulsive force balances the downward gravitational force, the particle is trapped at stable equilibrium. Periodic nanopatterning in the metamaterial surface furnishes the second, horizontal axis constraining particle motion. We show that the equilibrium position above the surface can be controlled by adjusting both the Fermi level and the number of graphene layers. Furthermore, to explicate the role of the high-k modes in generating the repulsive forces, we also propose a semianalytical method to calculate both the potential well and the forces generated by dipole radiation above the nanopatterned surface.

关键词： Metamaterials optical lattices & traps Photonics Graphene

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Artificial Neural Network based controller design for SMPS 3

Artificial Neural Network based controller design for SMPS

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3rd International Conference on Recent developments in Control, Automation and Power engineering (RDCAPE)

作者： Khan, Mohammad Ali Anand, Prashant Bhuvaneswari, G. IIT Delhi Fac Elect Engn Delhi India

ISBN: (纸本)9781728120683

This paper presents a novel approach to design a controller for a half-bridge converter based Switched Mode Power Supply of 150W rating. A half-bridge converter is designed for obtaining a stiffly regulated DC output voltage of 5v irrespective of load and supply voltage variations, with an artificial neural network (ANN) based controller. The duty ratio of the controller is determined by this ANN depending on the input voltage and the output load conditions. Data collection for training the ANN was done using a PID controller-based approach in which the transfer function for the SMPS was derived by performing the large signal and small signal analyses and appropriate parameter values for the PID controller were calculated. For different load and input supply voltage conditions, the output voltage was regulated by making use of the PID controller and appropriate duty ratios were arrived at. These 150 data points were used for the training the proposed ANN with four hidden layers. The trained neural network was further utilized in arriving at the duty ratio value directly by sensing the input voltage and load current and it is found to yield stiffly regulated voltage irrespective of supply voltage and load variations where the error is within 8%.

关键词： Neural networks

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Towards Studies of the Aubry-André Model with Ultracold Atoms in optical Lattices

Towards Studies of the Aubry-André Model with Ultracold Ato...

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作者： Pazmiño vélez, Arturo Gregorio State University of New York at Stony Brook

学位级别：Ph.D.

Atomic quantum gases in optical lattices allow for studies of ideal solid state-like systems with precisely controllable system parameters such as interactions, dimensionality and disorder. This thesis is devoted to the development of experimental capabilities, using ultracold rubidium-87 atoms in an optical lattice, to study transport and localization phenomena in one-dimensional lattice systems with weak and vanishing interactions. The first development is the design and implementation of a single-frequency diode laser system at 776 nm suitable for the creation of blue-detuned lattice tubes without residual axial confinement. The general suitability of the laser system for lattice experiments is demonstrated by implementing and studying a superfluid-to-Mott insulator transition. The second development concerns the control of the scattering length for rubidium-87 atoms through a narrow Feshbach resonance at 1007 G. For this purpose, a large portion of the magnetic field system of our apparatus was re-designed, including the coil assembly for magnetic trapping, its high-current switch configuration, and a precise magnetic field stabilization. The capabilities of the new system, in which the current of individual coils can be inverted, are demonstrated by accessing the Feshbach resonance through atom losses, with results that reproduce the state of the art in the field. Moreover, in quadrupole configuration, the new system allows for significant speedup of evaporative cooling. Based on these technical developments, we discuss the feasibility of experiments with incommensurate optical lattices that address properties of a mobility edge in the Aubry-André model, as well as of a method for stabilizing Bloch oscillations through a periodic modulation of interactions.

关键词： Physics

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A series of selenium-containing non-fullerene acceptors with side chain engineering for organic solar cells

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DYES AND PIGMENTS 2022年 207卷

作者： Oh, Juhui Park, Hye Yeon Kim, Ju-Hyeon Chen, Shuhao Lee, Sanseong Kim, Jaeyoung Song, Xuyao Kang, Hongkyu Jang, Soo-Young Kwon, Soon-Ki Kim, Yun-Hi Lee, Kwanghee Gwangju Inst Sci & Technol Sch Mat Sci & Engn Heeger Ctr Adv Mat HCAM Res Inst Solar & Sustainable Energies RISE Gwangju 61005 South Korea Gyeongsang Natl Univ Dept Mat Engn & Convergence Technol Jinju 52828 South Korea Gyeongsang Natl Univ ERI Jinju 52828 South Korea Gyeongsang Natl Univ Dept Chem Jinju 52828 South Korea Gyeongsang Natl Univ RINS Jinju 52828 South Korea Gwangju Inst Sci & Technol Ctr Res Innovat Gwangju South Korea Gwangju Inst Sci & Technol Res Inst Solar & Sustainable Energies Gwangju 61005 South Korea

Non-fullerene acceptors (NFAs) have been crucial in improving the efficiency of organic solar cells (OSCs) due to their attractive properties, such as strong light-harvesting ability, easily tunable energy levels, and high crys-tallinity. Nevertheless, general NFAs have limited light absorption, and studies on the design of NFAs that can absorb a broad range of the solar spectrum and that offer complementary absorption to that of donors should be conducted. Because selenium, a chalcogen element, can induce strong intermolecular SeMIDLINE HORIZONTAL ELLIPSISSe interactions, planarity, and extended effective conjugated length in OSC materials, NFAs with selenium usually exhibit redshifted absorption. Here, we synthesized a series of selenium-containing non-fullerene acceptors with different inner alkyl chain lengths, named Se-Y6-BO (2,2'-((2Z, 2 ' Z)-((12,13-bis(2-butyloctyl)-3,9-dinonyl-12,13-dihydroselenopheno[2 '',3":4 ',5']thieno[2 ',3':4,5]pyrrolo[3,2-g]selenopheno[2 ',3':4,5]thieno [3,23,2-b] [1,2,5] thiadiazolo [3,43,4-e]indole-2,10-diyl)bis(methanylylidene))bis(5,6-dichloro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) and Se-Y6-HD (2,2'-((2Z, 2 ' Z)-((12,13-bis(2-hexyldecyl)-3,9-dinonyl-12,13-dihy-droselenopheno[2 '',3":4 ',5']thieno[2 ',3':4,5]pyrrolo[3,2-g]selenopheno[2 ',3':4,5]thieno [3,23,2-b] [1,2,5]thia-diazolo [3,43,4-e]indole-2,10-diyl)bis(methanylylidene))bis(5,6-dichloro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile). The optical absorption of two selenium-containing NFAs was redshifted compared with that of Y6 due to the effect of selenium atoms in the backbone. The PM6:Se-Y6-BO-based devices achieved a power conversion efficiency (PCE) of 13.8% with an open-circuit voltage (vOC) of 0.81 v, short-circuit current density (JSC) of 24.4 mA cm-2, and a fill factor of 0.70. Similarly, the OSCs based on PM6:Se-Y6-HD achieved a PCE of 13.6% and a JSC of 23.7 mA cm-2.

关键词： Organic solar cells Non-fullerene acceptors Selenium Side -chain engineering Thermal stability

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Study of the influence of molten pool behaviour on the microstructure and chracteristics of additive manufactured TI-6AL-4v alloy

Study of the influence of molten pool behaviour on the micro...

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作者： Naidoo, Lester Caleb University of Johannesburg

学位级别：硕士

Titanium and its alloys are utilised in a wide range of diversified engineering applications. Its properties of low density, good corrosion resistance and high specific strength make it one of the most favourable materials in industrial applications. However, its applications are limited, due to its low hardness and poor tribological characteristics, which consequently reduce its life service. The surface integrity may be improved by surface modification, to extend its availability for more diverse industrial applications. Additive manufacturing is a commercially competitive manufacturing technique, with the possibility of altering the entire perception of design and fabrication. It offers suitable capabilities for the building and repairing applications in the aerospace industry, which usually requires high levels of accuracy and customisation of parts that generally use materials known to pose difficulties in fabrication, such as Titanium and its alloys. However, this process is currently at its pioneer stage; and very little is known about the fundamental physics of the process. currently, the major problems faced in additive manufacturing include the evolution of residual stresses, leading to deformed parts and the formation of defects, such as pores and cracks. The presence of these unwanted artefacts on additively-manufactured parts depends on what happens in the melt pool during melting, cooling, and solidification. Direct laser metal deposition is employed to fabricate the specimens and microstructural characterisation of the as-received samples; this was conducted by means of Scanning Electron Microscopy (SEM) / Electron Dispersive Spectroscopy (EDS), optical Microscopy (OPM) and X-ray Diffraction (XRD). The microhardness and corrosion behaviour were measured by using a vicker's hardness tester and a DY2300 Series Potentiostat, respectively. The results were compared to the current state of knowledge in the literature for confirmation and validation. The la

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模拟雷击导电体过程中脉冲电弧光-电联合诊断和损伤机制分析

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强度与环境 2022年第5期49卷 1-11页

作者：付继伟洪蓓隗功正李琛韩若愚北京宇航系统工程研究所北京100076 首都航天机械有限公司北京100076 北京理工大学机电动态控制重点实验室北京100081

雷电放电伴随短时间内高功率、大库伦量的电荷转移,可在电-磁-热-力等效应下造成结构壳体烧蚀甚至穿孔。由于雷电主放电阶段存在强烈的光辐射和电磁辐射,且耦合激波和等离子体现象,在模型描述和实验诊断方面难度大。放电过程物理机制研... 详细信息

雷电放电伴随短时间内高功率、大库伦量的电荷转移,可在电-磁-热-力等效应下造成结构壳体烧蚀甚至穿孔。由于雷电主放电阶段存在强烈的光辐射和电磁辐射,且耦合激波和等离子体现象,在模型描述和实验诊断方面难度大。放电过程物理机制研究的不深入,制约了结构防护设计优化。本文基于棒(高压)-板(接地)间隙大电流脉冲放电系统,研究了对壳体雷击的主放电过程的物理模拟和诊断技术,对放电过程的电物理参数、光辐射参数进行联合测量,实现了强光辐射下的自辐射和阴影法高速摄影,从多空间角度获取了放电等离子体的时空演化细节,建立了放电电磁过程和等离子体动力学行为之间的关联性。实验发现,雷电流破坏效应主要来源于接触点附近的传热过程以及面电流集肤效应导致的焦耳加热现象,激波则主要来源于电爆炸等离子体早期膨胀过程。最后从损伤来源角度为雷电防护设计提供一定建议。

关键词：雷电防护脉冲电流热等离子体激波/冲击波高速摄影

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High performance metalenses: numerical aperture, aberrations, chromaticity, and trade-offs

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OPTICA 2019年第12期6卷 1461-1470页

作者： Liang, Haowen Martins, Augusto Borges, Ben-Hur v. Zhou, Jianying Martins, Emiliano R. Li, Juntao Krauss, Thomas F. Sun Yat Sen Univ Sch Phys State Key Lab Optoelect Mat & Technol Guangzhou 510275 Guangdong Peoples R China Univ Sao Paulo Dept Elect & Comp Engn Sao Carlos Sch Engn BR-13566590 Sao Paulo Brazil Univ York Dept Phys York YO10 5DD N Yorkshire England

Metalenses consist of nanostructures that locally control the optical phase. They offer many degrees of freedom for manipulating a wavefront, which gives a number of advantages over bulk lenses, such as the straightforward elimination of spherical aberrations and an ultrathin dimension. Here, we compare the phase profiles of metalenses made of different dielectric materials and note the advantage of high refractive index materials. Higher refractive index materials such as silicon afford more degrees of freedom in terms of design and fabrication and are the basis for high-performance metalenses, even in the visible. Nevertheless, the imaging performance of single-element metalenses is still limited by coma and chromatic aberrations. This limitation is exacerbated by high numerical apertures and large areas. We review the challenges and trade-offs between numerical aperture, field of view, coma, chromatic aberration, and size. We also evaluate different phase engineering approaches to address these problems. We believe this review will help guide future developments in high-performance metalenses toward wide-field and high-resolution imaging, enabling scientific high-end miniature imaging systems. (c) 2019 optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Chromatic aberrations Confocal laser scanning microscopy Imaging systems optical systems optical testing Refractive index

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Study of the Influence of Molten Pool Behaviour on the Microstructure and Chracteristics of Additive Manufactured TI-6AL-4v Alloy

Study of the Influence of Molten Pool Behaviour on the Micro...

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作者： Naidoo, Lester Caleb University of Johannesburg (South Africa)

学位级别：M.Eng., Master of Engineering

Titanium and its alloys are utilised in a wide range of diversified engineering applications. Its properties of low density, good corrosion resistance and high specific strength make it one of the most favourable materials in industrial applications. However, its applications are limited, due to its low hardness and poor tribological characteristics, which consequently reduce its life service. The surface integrity may be improved by surface modification, to extend its availability for more diverse industrial applications. Additive manufacturing is a commercially competitive manufacturing technique, with the possibility of altering the entire perception of design and fabrication. It offers suitable capabilities for the building and repairing applications in the aerospace industry, which usually requires high levels of accuracy and customisation of parts that generally use materials known to pose difficulties in fabrication, such as Titanium and its alloys. However, this process is currently at its pioneer stage; and very little is known about the fundamental physics of the process. currently, the major problems faced in additive manufacturing include the evolution of residual stresses, leading to deformed parts and the formation of defects, such as pores and cracks. The presence of these unwanted artefacts on additively-manufactured parts depends on what happens in the melt pool during melting, cooling, and solidification. Direct laser metal deposition is employed to fabricate the specimens and microstructural characterisation of the as-received samples; this was conducted by means of Scanning Electron Microscopy (SEM) / Electron Dispersive Spectroscopy (EDS), optical Microscopy (OPM) and X-ray Diffraction (XRD). The microhardness and corrosion behaviour were measured by using a vicker’s hardness tester and a DY2300 Series Potentiostat, respectively. The results were compared to the current state of knowledge in the literature for confirmation and validation. The la

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Machine learning assisted global optimization of photonic devices

arXiv

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arXiv 2020年

作者： Kudyshev, Zhaxylyk A. Kildishev, Alexander v. Shalaev, vladimir M. Boltasseva, Alexandra School of Electrical and Computer Engineering Birck Nanotechnology Center Purdue Quantum Science and Engineering Institute Purdue University West LafayetteIN47906 United States

Over the past decade, artificially engineered optical materials and nanostructured thin films have revolutionized the area of photonics by employing novel concepts of metamaterials and metasurfaces where spatially varying structures yield tailorable, "by design" effective electromagnetic properties. The current state-of-the-art approach to designing and optimizing such structures relies heavily on simplistic, intuitive shapes for their unit cells or meta-atoms. Such approach can not provide the global solution to a complex optimization problem where both meta-atoms shape, in-plane geometry, out-of-plane architecture, and constituent materials have to be properly chosen to yield the maximum performance. In this work, we present a novel machine-learning-assisted global optimization framework for photonic metadevices design. We demonstrate that using an adversarial autoencoder coupled with a metaheuristic optimization framework significantly enhances the optimization search efficiency of the meta-devices configurations with complex topologies. We showcase the concept of physics-driven compressed design space engineering that introduces advanced regularization into the compressed space of adversarial autoencoder based on the optical responses of the devices. Beyond the significant advancement of the global optimization schemes, our approach can assist in gaining comprehensive design "intuition" by revealing the underlying physics of the optical performance of meta-devices with complex topologies and material compositions. Copyright © 2020, The Authors. All rights reserved.

关键词： Global optimization

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optical-RF dual relay communication system for 1000-Au interstellar mission 70

Optical-RF dual relay communication system for 1000-Au inter...

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70th International Astronautical Congress, IAC 2019

作者： Kufahl, Katelyn M. Boone, Bradley G. Beck, Adam L. Space Exploration Sector Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd LaurelMD20755 United States Whiting School of Engineering Johns Hopkins University BaltimoreMD21218 United States

The goal of a realistic interstellar mission to the nearest star, recently announced by NASA as a new space exploration objective targeted for circa 2069, presents an exciting prospect for creating a pragmatic but visionary mission design. In light of such a long-term mission goal, potential technological developments that might be mission enablers are a matter of speculation at best, but the basic physical principles underlying telecommunications subsystem conceptual design are well within our grasp. For example, the range required of a communications link to the Alpha Centauri system is prohibitively large due to current and foreseeable engineering limits in pointing capability, receiver sensitivity, and power transmission in both RF and optical domains. However, realistic design specifications can be identified if the mission concept is broadened in two ways: launch a precursor mission to a distance of 1000 AU, and implement the precursor mission not as a single spacecraft but as a fleet of several spacecraft launched in periodic succession. In doing so, the communications subsystem can take the form of a relay chain for which the spacing is determined by the upper limits of downlink transmission capability at the time of launch. By reducing the required link range to within achievable limits, link analysis can be further constrained by examination of tradeoffs in transmitter output power, data rate, bit error rate, antenna sizes, pointing loss, path attenuation, turbulence effects, and link availability at both optical and radio frequencies. The proposed subsystem is dual-channel: an optical link to achieve the minimum required downlink data rates, and an RF link to minimize pointing loss for spacecraft emergency recovery. Through the implementation of a relay-based dual-channel design, the subsystem can yield effective and reliable downlink data transmission over communication distances of unprecedented vastness. Copyright © 2019 by the International Astronauti

关键词： optical communication

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