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Recent Submissions

  • Analysis of interface mode localization in disordered photonic crystal structure

    Goyal, Amit Kumar; Husain, Mudassir; Massoud, Yehia Mahmoud (Journal of Nanophotonics, SPIE-Intl Soc Optical Eng, 2022-12-06) [Article]
    A disordered photonic crystal (D-PhC) structure is analyzed to study the interface mode localization characteristics. The design comprises a bilayer-disordered PhC structure, where layers are arranged in Thue–Morse sequence (TMS). The impact of local symmetric substructures on eigenstates coupling is also considered over a wider wavelength range. The mode hybridization study is carried out for varying refractive index contrast values of TMS structures at an operating wavelength of 550, 632.8, and 750 nm, respectively. The dispersion analysis confirms the localization of bulk guided, and edge-guided modes for different incidence angles at the structural local resonators. Further, increasing the RI contrast value leads to generation of hybrid interface modes of very high electric field intensity. Thus, showing its potential applications in both sensing and light guiding applications. Moreover, because of the higher surface electric field intensity this structure can also be used for fluorescence-based detection and surface-enhanced Raman spectroscopy as well.
  • Continuous and discrete data assimilation with noisy observations for the Rayleigh-Bénard convection: a computational study

    Hammoud, Mohamad Abed El Rahman; Le Maître, Olivier; Titi, Edriss S.; Hoteit, Ibrahim; Knio, Omar (Computational Geosciences, Springer Science and Business Media LLC, 2022-12-05) [Article]
    Obtaining accurate high-resolution representations of model outputs is essential to describe the system dynamics. In general, however, only spatially- and temporally-coarse observations of the system states are available. These observations can also be corrupted by noise. Downscaling is a process/scheme in which one uses coarse scale observations to reconstruct the high-resolution solution of the system states. Continuous Data Assimilation (CDA) is a recently introduced downscaling algorithm that constructs an increasingly accurate representation of the system states by continuously nudging the large scales using the coarse observations. We introduce a Discrete Data Assimilation (DDA) algorithm as a downscaling algorithm based on CDA with discrete-in-time nudging. We then investigate the performance of the CDA and DDA algorithms for downscaling noisy observations of the Rayleigh-Bénard convection system in the chaotic regime. In this computational study, a set of noisy observations was generated by perturbing a reference solution with Gaussian noise before downscaling them. The downscaled fields are then assessed using various error- and ensemble-based skill scores. The CDA solution was shown to converge towards the reference solution faster than that of DDA but at the cost of a higher asymptotic error. The numerical results also suggest a quadratic relationship between the ℓ2 error and the noise level for both CDA and DDA. Cubic and quadratic dependences of the DDA and CDA expected errors on the spatial resolution of the observations were obtained, respectively.
  • Correct estimation of permeability using experiment and simulation

    Khirevich, Siarhei; Yutkin, Maxim; Patzek, Tadeusz (Physics of Fluids, AIP Publishing, 2022-12-05) [Article]
    Estimation of permeability of porous media dates back to Henry Darcy [H. Darcy, Les Fontaines Publiques de la Ville de Dijon (Victor Dalmont, 1856)], and its knowledge is essential in many scientific and engineering endeavors. Despite apparent simplicity of permeability measurements, the literature data are scattered, and this scatter not always can be attributed to the precision of experiment or simulation or to sample variability. Here, we demonstrate an excellent agreement (<1%) between experiments and simulations, where experimental results are extensive and stable, while flow is simulated from first principles, directly on three-dimensional images of the sample, and without fitting parameters. Analyzing when experiments and simulations agree reveals a major flaw affecting many experimental measurements with the out-of-sample placement of pressure ports, including industry standards. The flaw originates from (1) incorrect calculation of the applied pressure gradient, (2) omitting virtual part of the measured system, and (3) pressure loss at the sample–tube contact. Contrary to common wisdom, the relative magnitude of (3) is defined by the sample–tube diameter ratio and is independent of the size of sample pores. Our findings are applicable to a wide range of permeability measurements, including geological-sample-type (Hassler cell) and membrane-type. The reported pressure loss (3) also affects two-phase flow measurements, such as capillary pressure estimation. Removing or taking the flaw into account advances the understanding and control of flow-related processes in complex geometries.
  • Impact of layer thickness on the operating characteristics of In2O3/ZnO heterojunction thin-film transistors featured

    Alghamdi, Wejdan S.; Fakieh, Aiman; Faber, Hendrik; Lin, Yen-Hung; Lin, Wei-Zhi; Lu, Po-Yu; Liu, Chien-Hao; Salama, Khaled N.; Anthopoulos, Thomas D. (Applied Physics Letters, AIP Publishing, 2022-12-05) [Article]
    Combining low-dimensional layers of dissimilar metal oxide materials to form a heterojunction structure offers a potent strategy to improve the performance and stability of thin-film transistors (TFTs). Here, we study the impact of channel layer thicknesses on the operating characteristics of In2O3/ZnO heterojunction TFTs prepared via sputtering. The conduction band offset present at the In2O3/ZnO heterointerface affects the device's operating characteristics, as is the thickness of the individual oxide layers. The latter is investigated using a variety of experimental and computational modeling techniques. An average field-effect mobility (μFE) of >50 cm2 V−1 s−1, accompanied by a low threshold voltage and a high on/off ratio (∼108), is achieved using an optimal channel configuration. The high μFE in these TFTs is found to correlate with the presence of a quasi-two-dimensional electron gas at the In2O3/ZnO interface. This work provides important insight into the operating principles of heterojunction metal oxide TFTs, which can aid further developments.
  • Complex systems engineering theory is a scientific theory

    Feron, Eric (2022-12-05) [Technical Report]
    The proper design of complex engineering systems is what allows corporations and nations to distinguish themselves in a global competition for technical excellence and economic well-being. After quickly reviewing the central elements of systems engineering, we map all of them onto concepts of mathematics such as theorems and proofs, and onto scientific theories. This mapping allows the protagonists of complex systems engineering and design to map existing techniques from one field to the others; it provides a surprising number of suggestions for improving system design, especially system architecture, by leveraging advanced mathematical and / or scientific concepts in a productive way. In return, mathematicians and computer scientists can benefit from this bridge by bringing to bear many of their automated theorem provers to help with the design of complex systems. Clear classifications of what is "hard" and what is "easy" in mathematical proofs can instantaneously map onto similar appreciations for system design and its reliance on engineers’ creativity. Last, understanding system design from the mathematical-scientific viewpoint can help the system engineer think more maturely about organizing the multitude of tasks required by systems engineering.
  • Bayesian survival analysis with INLA

    Alvares, Danilo; Rustand, Denis; Krainski, Elias Teixeira; Niekerk, Janet van; Rue, Haavard (arXiv, 2022-12-04) [Preprint]
    This tutorial uses the conjunction of INLA and INLAjoint R-packages to show how various Bayesian survival models can be fitted using the integrated nested Laplace approximation in a clear, legible, and comprehensible manner. Such models include accelerated failure time, proportional hazards, mixture cure, competing risks, multi-state, frailty, and joint models of longitudinal and survival data, originally presented in the article "Bayesian survival analysis with BUGS" (Alvares et al., 2021). In addition, we illustrate the implementation of a new joint model for a longitudinal semicontinuous marker, recurrent events, and a terminal event. Our proposal aims to provide the reader with syntax examples for implementing survival models using a fast and accurate Bayesian inferential approach.
  • On the Performance of Non-Terrestrial Networks to Support the Internet of Things

    Wang, Dengke; Traspadini, Alessandro; Giordani, Marco; Alouini, Mohamed-Slim; Zorzi, Michele (arXiv, 2022-12-03) [Preprint]
    The advent of the Internet of Things (IoT) era, where billions of devices and sensors are becoming more and more connected and ubiquitous, is putting a strain on traditional terrestrial networks, that may no longer be able to fulfill service requirements efficiently. This issue is further complicated in rural and remote areas with scarce and low-quality cellular coverage. To fill this gap, the research community is focusing on non-terrestrial networks (NTNs), where Unmanned Aerial Vehicles (UAVs), High Altitude Platforms (HAPs) and satellites can serve as aerial/space gateways to aggregate, process, and relay the IoT traffic. In this paper we demonstrate this paradigm, and evaluate how common Low-Power Wide Area Network (LPWAN) technologies, designed and developed to operate for IoT systems, work in NTNs. We then formalize an optimization problem to decide whether and how IoT traffic can be offloaded to LEO satellites to reduce the burden on terrestrial gateways.
  • Computing with B-series

    Ketcheson, David I.; Ranocha, Hendrik (ACM Transactions on Mathematical Software, Association for Computing Machinery (ACM), 2022-12-02) [Article]
    We present BSeries.jl, a Julia package for the computation and manipulation of B-series, which are a versatile theoretical tool for understanding and designing discretizations of differential equations. We give a short introduction to the theory of B-series and associated concepts and provide examples of their use, including method composition and backward error analysis. The associated software is highly performant and makes it possible to work with B-series of high order.
  • Performance Improvement of InGaN-Based LEDs via a Current-Blocking Region Prepared via Hydrogen Passivation

    Kirilenko, Pavel; Altinkaya, Cesur; Iida, Daisuke; Ohkawa, Kazuhiro (Crystals, MDPI AG, 2022-12-01) [Article]
    We report p-GaN passivation via hydrogen plasma used to create current blocking regions (CBRs) in InGaN-based green LEDs with standard dimensions of 280 × 650 μm2. The CBRs are created before mesa etching in two variants: underneath the opaque metal p-pad and both underneath the p-pad and along the device’s mesa perimeter. The peak EQE increased by 13% and 23% in the first and the second cases, respectively, in comparison to the reference LED with no CBR. With a high injection current of 50 A/cm2, the EQE value increased by 2% in the case of CBRs underneath the p-pad as well as by 14% in the case of CBRs both underneath the p-pad and along the mesa perimeter (relative to the reference sample with no CBR).
  • Hybrid FSO/THz-based Backhaul Network for mmWave Terrestrial Communication

    Singya, Praveen Kumar; Makki, Behrooz; D'Errico, Antonio; Alouini, Mohamed-Slim (IEEE Transactions on Wireless Communications, Institute of Electrical and Electronics Engineers (IEEE), 2022-12-01) [Article]
    In this work, a hybrid free-space optics (FSO)/ teraHertz (THz) based backhaul network is considered to provide high-data-rate reliable communication to the terrestrial mobile users (MUs) operating at millimeter-wave (mmWave) bands. The FSO link is affected by atmospheric turbulence and pointing error impairments. At the FSO receiver, both intensity-modulated direct detection and heterodyne detection techniques are considered. The multi-antenna THz link suffers from high path-loss, small-scale fading, and misalignment error. To minimize the effect of back-and-forth switching, soft switching method is introduced at the access point (AP) to select the signal coming through the hybrid FSO/THz link, and a comparison with hard switching method is presented. Selective decode-and-forward relaying is considered at the AP. In this context, we derive closed-form expressions of the individual link’s outage probability, end-to-end (E2E) outage probability, asymptotic outage probability, ergodic capacity, and generalized average bit-error-rate. Finally, we study the effect of different parameters such as atmospheric turbulence, pointing/misalignment errors, link distance, atmospheric attenuation/path-loss, fading parameters of the THz and access links, and number of antennas on the network performance. Our results indicate that, with a proper switching method, the joint implementation of FSO/THz links improves the rate/reliability of the backhaul links with limited switching overhead.
  • Mitigation of Cyberattacks through Battery Storage for Stable Microgrid Operation

    Zografopoulos, Ioannis; Karamichailidis, Panagiotis; Procopiou, Andreas T.; Teng, Fei; Konstantopoulos, George C.; Konstantinou, Charalambos (IEEE, 2022-12-01) [Conference Paper]
    In this paper, we present a mitigation methodology that leverages battery energy storage system (BESS) resources in coordination with microgrid (MG) ancillary services to maintain power system operations during cyberattacks. The control of MG agents is achieved in a distributed fashion, and once a misbehaving agent is detected, the MG , ′s mode supervisory controller (MSC) isolates the compromised agent and initiates self-healing procedures to support the power demand and restore the compromised agent. Our results demonstrate the practicality of the proposed attack mitigation strategy and how grid resilience can be improved using BESS synergies. Simulations are performed on a modified version of the Canadian urban benchmark distribution model.
  • Diffractive lensless imaging with optimized Voronoi-Fresnel phase

    Fu, Qiang; Yan, Dong-Ming; Heidrich, Wolfgang (Optics Express, Optica Publishing Group, 2022-12-01) [Article]
    Lensless cameras are a class of imaging devices that shrink the physical dimensions to the very close vicinity of the image sensor by replacing conventional compound lenses with integrated flat optics and computational algorithms. Here we report a diffractive lensless camera with spatially-coded Voronoi-Fresnel phase to achieve superior image quality. We propose a design principle of maximizing the acquired information in optics to facilitate the computational reconstruction. By introducing an easy-to-optimize Fourier domain metric, Modulation Transfer Function volume (MTFv), which is related to the Strehl ratio, we devise an optimization framework to guide the optimization of the diffractive optical element. The resulting Voronoi-Fresnel phase features an irregular array of quasi-Centroidal Voronoi cells containing a base first-order Fresnel phase function. We demonstrate and verify the imaging performance for photography applications with a prototype Voronoi-Fresnel lensless camera on a 1.6-megapixel image sensor in various illumination conditions. Results show that the proposed design outperforms existing lensless cameras, and could benefit the development of compact imaging systems that work in extreme physical conditions.
  • ODPP: A Unified Algorithm Framework for Unsupervised Option Discovery based on Determinantal Point Process

    Chen, Jiayu; Aggarwal, Vaneet; Lan, Tian (arXiv, 2022-12-01) [Preprint]
    Learning rich skills through temporal abstractions without supervision of external rewards is at the frontier of Reinforcement Learning research. Existing works mainly fall into two distinctive categories: variational and Laplacian-based option discovery. The former maximizes the diversity of the discovered options through a mutual information loss but overlooks coverage of the state space, while the latter focuses on improving the coverage of options by increasing connectivity during exploration, but does not consider diversity. In this paper, we propose a unified framework that quantifies diversity and coverage through a novel use of the Determinantal Point Process (DPP) and enables unsupervised option discovery explicitly optimizing both objectives. Specifically, we define the DPP kernel matrix with the Laplacian spectrum of the state transition graph and use the expected mode number in the trajectories as the objective to capture and enhance both diversity and coverage of the learned options. The proposed option discovery algorithm is extensively evaluated using challenging tasks built with Mujoco and Atari, demonstrating that our proposed algorithm substantially outperforms SOTA baselines from both diversity- and coverage-driven categories.
  • Enhanced Selectivity in the Electroproduction of H2O2 via F/S Dual-Doping in Metal-Free Nanofibers

    Xiang, Fei; Zhao, Xuhong; Yang, Jian; Li, Ning; Gong, Wenxiao; Liu, Yizhen; Burguete-Lopez, A.; Li, Yulan; Niu, Xiaobin; Fratalocchi, Andrea (Advanced Materials, Wiley, 2022-11-30) [Article]
    Electrocatalytic two-electron oxygen reduction (2e- ORR) to hydrogen peroxide (H2 O2 ) is attracting broad interest in diversified areas including paper manufacturing, wastewater treatment, production of liquid fuels, and public sanitation. Current efforts focus on researching low-cost, large-scale, and sustainable electrocatalysts with high activity and selectivity. Here we engineer large-scale H2 O2 electrocatalysts based on metal-free carbon fibers with a fluorine and sulfur dual-doping strategy. Optimized samples yield with a high onset potential of 0.814 V versus reversible hydrogen electrode (RHE), an almost an ideal 2e- pathway selectivity of 99.1%, outperforming most of the recent reported carbon-based or metal-based electrocatalysts. First principle theoretical computations and experiments demonstrate that the intermolecular charge transfer coupled with electron spin redistribution from fluorine and sulfur dual-doping is the crucial factor contributing to the enhanced performances in 2e- ORR. This work opens the door to the design and implementation of scalable, earth-abundant, highly selective electrocatalysts for H2 O2 production and other catalytic fields of industrial interest.
  • On Secure CDRT with NOMA and Physical-Layer Network Coding

    Lei, Hongjiang; She, Xusheng; Park, Kihong; Ansari, Imran Shafique; Shi, Zheng; Jiang, Jing; Alouini, Mohamed-Slim (IEEE Transactions on Communications, Institute of Electrical and Electronics Engineers (IEEE), 2022-11-30) [Article]
    This paper proposes a new scheme to enhance the secrecy performance of non-orthogonal multiple access (NOMA)-based coordinated direct relay transmission (CDRT) systems with an untrusted relay. The physical-layer network coding (PNC) and the NOMA schemes are combined to improve spectrum efficiency. Furthermore, inter-user interference and friendly jamming signals are utilized to suppress the eavesdropping ability of the untrusted relay without compromising the acceptance quality of legitimate users. Specifically, the far user in the first slot and the near user in the second slot act as jammers that generate jamming signals to ensure secure transmissions of confidential messages. We investigate the secrecy performance of the NOMA-based CDRT systems with the PNC scheme and derive the closed-form expression for the ergodic secrecy sum rate. The asymptotic analysis at a high signal-to-noise ratio is performed to obtain more insights. Finally, simulation results are presented to demonstrate the proposed scheme’s effectiveness and the theoretical analysis’s correctness.
  • Submarine optical fiber communication provides an unrealized deep-sea observation network

    Ashry, Islam; Guo, Yujian; Marin, Juan; Trichili, Abderrahmen; Havlik, Michelle Nicole; Ng, Tien Khee; Duarte, Carlos M.; Ooi, Boon S. (Research Square Platform LLC, 2022-11-30) [Preprint]
    The ocean is key to human survival, providing natural resources, most of the global oxygen supply, and economic development through mineral, gas, and oil deposits. Although the sea is primarily considered a silent world, it is abundant with the natural sounds of marine life communication and geological processes. Human activities, especially active sonars, shipping traffic, and underwater vehicles, have significantly affected underwater soundscapes and reduced natural sounds. We report on a joint optical fiber-based communication and sensing technology to minimize noise pollution in the ocean while achieving data transmission and ocean environment monitoring and exploration. The proposed multifunctional communication and sensing fiber system enables two-way data transfer while a) monitoring marine life and ship movement near the deployed fiber at the sea bottom and b) sensing temperature. The same fiber is simultaneously used to transfer energy that can be harvested by devices in the internet of underwater things. The proposed approach dramatically reduces the costs and effects of monitoring marine ecosystems while transferring data, monitoring oceans, and charging submerged devices in the internet of underwater things.
  • New Type High-Frequency Transformer Isolated Cascaded AC-AC Converter for DVR to Compensate Sag or Swell in Voltage

    Khan, Ashraf Ali; Khan, Usman Ali; Ahmed, Hafiz Furqan; Ahmad, Shehab (IEEE, 2022-11-30) [Conference Paper]
    In this paper, a high-frequency transformer-isolated cascaded ac-ac converter is proposed. By cascading N-unit cells, the proposed converter can generate output ac voltage with a maximum peak of NVin , where Vin is the peak of the input ac voltage, and N is the number of cascaded units. Unlike most of the conventional cascaded ac-ac converters, the proposed converter does not require a separate ac source for each unit cell. In addition, the proposed converter can provide higher ac output voltages using low-voltage rating devices. The proposed converter can be utilized for ac voltage regulation and as a dynamic voltage restorer (DVR) for grid voltage regulation, with the following features: No need for an external dc source, separate ac sources, and a line-frequency voltage injection transformer. The basic operation is given in this digest with experimental results using a 2-kW scale-down laboratory prototype.
  • Novel Common-Ground Dual-Buck Inverter for Photovoltaic Applications with No Leakage Current Issues

    Khan, Ashraf Ali; Khan, Usman Ali; Khan, Shahnawaz; Ahmad, Shehab (IEEE, 2022-11-30) [Conference Paper]
    This paper proposes a novel common-ground dual- buck inverter for photovoltaic (PV) applications. The proposed inverter remarkably reduces the leakage current due to a direct connection between the input and output. As a result, the proposed inverter can be used in grid-connected PV applications without leakage current issues. It has a bidirectional power flow and can work with any power factor. In the operation, at a time only two switches work at high frequency thus reducing the overall power losses and enhancing the power transfer efficiency. The proposed inverter is extremely reliable because it is free of short-circuit issues. Moreover, the reverse recovery loss of the body diodes of the MOSFETs can be eliminated. The experiments have been conducted with an 800 W laboratory prototype at a 50 kHz switching frequency for the output voltage of 110 Vrms/60.
  • Detection and Separation of Faults in Permanent Magnet Synchronous Machines using Hybrid Fault-Signatures

    Ullah, Zia; Im, JunHyuk; Ahmed, Shehab (IEEE, 2022-11-30) [Conference Paper]
    As digitalization in electric motors accelerates, online condition monitoring systems are becoming more popular, allowing unplanned downtime to be detected at its initial stage. Individual faults in motors are effectively diagnosed. However, due to identical signatures, fault separation and/or identification remain a challenge. This study presents the detection and separation of inter-turn short, demagnetization, static eccentricity, bearing, and the combination of these faults in permanent magnet synchronous machines. Hybrid fault signatures are used by monitoring the frequency spectrum of stator current, vibration, and induced voltage in the airgap. A planer-shaped airgap search coil (PASC) is employed to extract the induced voltage of each stator tooth. Faults-related anomalies in the induced-voltage, vibration, and the stator current caused are monitored. Any deviation in either signal is considered as generic fault indicator. Furthermore, specific fault features in all signals are used to classify these faults with improved accuracy. The PASC used in this study can also identify the location of the inter-turn short fault and the severity of demagnetization fault. The proposed method is verified using the finite element method simulation and experiments.
  • Demagnetization Risk Assessment in a Dual Stator Permanent Magnet Vernier Machines

    Ullah, Zia; Siddiqi, Mudassir Raza; Ahmed, Shehab (IEEE, 2022-11-30) [Conference Paper]
    As the topologies of permanent magnet vernier machines (PMVM) is getting more complex such as dual rotor and its variants. The thermal, mechanical, and especially demagnetization concern increasing. In this paper, the demagnetization risk evaluation of three similar topologies of dual stator radial type PMVM is presented. Three recently published topologies: dual winding with rotor-yoke, dual winding without rotor-yoke, and single winding without yoke are selected. This design highly improved the torque density and reduced the overall volume. However, the permanent magnets (PMs) in these topologies are at huge risk of irreversible demagnetization. Furthermore, the overall performance of PM-type machines is incomprehensible without a detailed demagnetization analysis. Therefore, a comprehensive mechanical, thermal, and demagnetization analysis considering various operating points and temperatures is conducted to evaluate the risk of demagnetization in these topologies. Finally, some modification are made to optimize of these designs. All analyses are carried out using finite element analysis and co-simulation in ANSYS maxwell and mechanical.

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