Recent Submissions

  • Cu-α-diimine Compounds Encapsulated in Porous Materials as Catalysts for Electrophilic Amination of Aromatic C–H Bonds

    Van Emelen, Lisa; Lemmens, Vincent; Marquez, Carlos; Van Minnebruggen, Sam; Usoltsev, Oleg A.; Bugaev, Aram L.; Janssens, Kwinten; Cheung, Ka Yan; Van Velthoven, Niels; De Vos, Dirk E. (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2022-11-09) [Article]
    Electrophilic amination has emerged as a more environmentally benign approach to construct arene C–N bonds. However, heterogeneous catalysts remain largely unexplored in this area, even though their use could facilitate product purification and catalyst recovery. Here we investigate strategies to heterogenize a Cu(2,2′-bipyridine) catalyst for the amination of arenes lacking a directing group with hydroxylamine-O-sulfonic acid (HOSA). Besides immobilization of Cu on a metal–organic framework (MOF) or covalent organic framework (COF) with embedded 2,2′-bipyridines, a ship-in-a-bottle approach was followed in which the Cu complex is encapsulated in the pores of a zeolite. Recyclability and hot centrifugation tests show that zeolite Beta-entrapped CuII(2,2′-bipyridine) is superior in terms of stability. With N-methylmorpholine as a weakly coordinating, weak base, simple arenes, such as mesitylene, could be aminated with yields up to 59%, corresponding to a catalyst TON of 24. The zeolite could be used in three consecutive runs without a decrease in activity. Characterization of the catalyst by EPR and XAS showed that the active catalytic complex consisted of a site-isolated CuII species with one 2,2′-bipyridine ligand.
  • A spectral solver for solar inertial waves

    Bhattacharya, Jishnu; Hanasoge, Shravan M. (arXiv, 2022-11-07) [Preprint]
    Inertial waves, which are dominantly driven by the Coriolis force, likely play an important role in solar dynamics, and additionally, provide a window into the solar subsurface. The latter allows us to infer properties that are inaccessible to the traditional technique of acoustic-wave helioseismology. Thus, a full characterization of these normal modes holds promise in enabling the investigation of solar subsurface dynamics. In this work, we develop a spectral eigenvalue solver to model the spectrum of inertial waves in the Sun. We model the solar convection zone as an anelastic medium, and solve for the normal modes of the momentum and energy equations. We demonstrate that the solver can reproduce the observed mode frequencies and line-widths well, not only of sectoral Rossby modes, but also the recently observed high-frequency inertial modes. In addition, we believe that the spectral solver is a useful contribution to the numerical methods on modeling inertial modes on the Sun.
  • Gradient estimates for quasilinear elliptic Neumann problems with unbounded first-order terms

    Cirant, Marco; Goffi, Alessandro; Leonori, Tommaso (arXiv, 2022-11-07) [Preprint]
    This paper studies global a priori gradient estimates for divergence-type equations patterned over the p-Laplacian with first-order terms having polynomial growth with respect to the gradient, under suitable integrability assumptions on the source term of the equation. The results apply to elliptic problems with unbounded data in Lebesgue spaces complemented with Neumann boundary conditions posed on convex domains of the Euclidean space.
  • The spectral characterisation of reduced order models in chemical kinetic systems

    Valorani, Mauro; Malpica Galassi, Riccardo; Ciottoli, Pietro Paolo; Najm, Habib; Paolucci, Samuel (Combustion Theory and Modelling, Informa UK Limited, 2022-11-07) [Article]
    The size and complexity of multi-scale problems such as those arising in chemical kinetics mechanisms has stimulated the search for methods that reduce the number of species and chemical reactions but retain a desired degree of accuracy. The time-scale characterisation of the multi-scale problem can be carried out on the basis of local information such as the Jacobian matrix of the model problem and its related eigen-system evaluated at one point P of the system trajectory. While the original problem is usually described by ordinary differential equations (ODEs), the reduced order model is described by a reduced number of ODEs and a number of algebraic equations (AEs), that might express one or more physical conservation laws (mass, momentum, energy), or the fact that the long-term dynamics evolves within a so-called Slow Invariant Manifold (SIM). To fully exploit the benefits offered by a reduced order model, it is required that the time scale characterisation of the n-dimensional reduced order model returns an answer consistent and coherent with the time-scale characterisation of the N-dimensional original model. This manuscript discusses a procedure for obtaining the time-scale characterisation of the reduced order model in a manner that is consistent with that of the original problem. While a standard time scale characterisation of the (original) N-dimensional original model can be carried out by evaluating the eigen-system of the (N×N) Jacobian matrix of the vector field that defines the system dynamics, the time-scale characterisation of the n-dimensional reduced order model (with n<N) can be carried out by evaluating the eigen-system of a (n×n) constrained Jacobian matrix, JC, of the reduced vector field that accounts for the role of the constraints.
  • Hybrid Satellite–Terrestrial Networks toward 6G: Key Technologies and Open Issues

    Tirmizi, Syed Bilal Raza; Chen, Yunfei; Lakshminarayana, Subhash; Feng, Wei; Khuwaja, Aziz A. (Sensors, MDPI AG, 2022-11-06) [Article]
    Future wireless networks will be required to provide more wireless services at higher data rates and with global coverage. However, existing homogeneous wireless networks, such as cellular and satellite networks, may not be able to meet such requirements individually, especially in remote terrain, including seas and mountains. One possible solution is to use diversified wireless networks that can exploit the inter-connectivity between satellites, aerial base stations (BSs), and terrestrial BSs over inter-connected space, ground, and aerial networks. Hence, enabling wireless communication in one integrated network has attracted both the industry and the research fraternities. In this work, we provide a comprehensive survey of the most recent work on hybrid satellite–terrestrial networks (HSTNs), focusing on system architecture, performance analysis, design optimization, and secure communication schemes for different cooperative and cognitive HSTN network architectures. Different key technologies are compared. Based on this comparison, several open issues for future research are discussed.
  • The Richtmyer–Meshkov instability of thermal, isotope and species interfaces in a five-moment multi-fluid plasma

    Tapinou, K.C.; Wheatley, V.; Bond, D.; Jahn, Ingo (Journal of Fluid Mechanics, Cambridge University Press (CUP), 2022-11-03) [Article]
    The Richtmyer–Meshkov instability (RMI) results from the impulsive acceleration of a density interface where either it or the acceleration is perturbed. Density interfaces may arise due to a change in gas species, isotope, temperature or a combination of these. We computationally investigate the effect of interface type on the plasma RMI, which is relevant for a range of applications, including inertial confinement fusion. We simulate the evolution of single-mode perturbed thermal, species and isotope interfaces in an ideal ion–electron plasma using the multi-fluid plasma (MFP) model. We find that, in the MFP model, the evolution of different types of interface differs significantly, in contrast to single-fluid models where they behave similarly if the Atwood number is matched. The thermal and species interfaces produce the most severe response to shock acceleration, experiencing the secondary instabilities and enhanced primary mode growth. The isotope interface evolution is restrained in comparison with the former cases, resembling the response predicted by single-fluid models. The determining factor in the severity of the MFP RMI is the density ratio across the initial interface in the electron fluid, which is unity for an isotope interface. We observe that, as the density ratio across the electron interface decreases, so do the magnitudes of the self-generated fields and consequently the severity of the growth amplification. Generally, the evolution of the RMI with different types of interface becomes more similar as the level of coupling between the ion and electron fluids is increased, characterised by reducing the plasma non-dimensional skin depth.
  • Examining Different Regimes of Ionization-Induced Damage in GaN Through Atomistic Simulations

    Sequeira, Miguel C.; Djurabekova, Flyura; Nordlund, Kai; Mattei, Jean-Gabriel; Monnet, Isabelle; Grygiel, Clara; Alves, Eduardo; Lorenz, Katharina (Small, Wiley, 2022-10-30) [Article]
    The widespread adoption of gGaN in radiation-hard semiconductor devices relies on a comprehensive understanding of its response to strongly ionizing radiation. Despite being widely acclaimed for its high radiation resistance, the exact effects induced by ionization are still hard to predict due to the complex phase-transition diagrams and defect creation-annihilation dynamics associated with group-III nitrides. Here, the Two-Temperature Model, Molecular Dynamics simulations and Transmission Electron Microscopy, are employed to study the interaction of Swift Heavy Ions with GaN at the atomic level. The simulations reveal a high propensity of GaN to recrystallize the region melted by the impinging ion leading to high thresholds for permanent track formation. Although the effect exists in all studied electronic energy loss regimes, its efficiency is reduced with increasing electronic energy loss, in particular when there is dissociation of the material and subsequent formation of N2 bubbles. The recrystallization is also hampered near the surface where voids and pits are prominent. The exceptional agreement between the simulated and experimental results establishes the applicability of the model to examine the entire electronic energy loss spectrum. Furthermore, the model supports an empirical relation between the interaction cross sections (namely for melting and amorphization) and the electronic energy loss.
  • Linear analysis of magnetohydrodynamic Richtmyer-Meshkov instability in cylindrical geometry for double interfaces in the presence of an azimuthal magnetic field

    Bakhsh, Abeer (Physics of Fluids, AIP Publishing, 2022-10-29) [Article]
    Richtmyer-Meshkov instability (RMI) occurs when a shock wave impulsively accelerates a perturbed density interface between different fluids. The present work investigates the suppression of RMI of double interfaces in terms of linear analysis in cylindrical geometry. An exponential increase/decrease in a growth rate is related to the Rayleigh-Taylor instability (RTI) that occurs without a magnetic field as the lighter fluid penetrates the heavier one. The research program of inertial confinement fusion (ICF) is one of the advanced applications where fluid mixing is the main mechanize of producing energy. The investigations represent the effects of different Atwood numbers or magnetic strengths on the suppression of the instabilities. Three different cases are considered with the hydrodynamics (HD) and magnetohydrodynamics (MHD). In MHD case, the instability's growth rate reduces proportion to the Atwood ratios or the strength of the magnetic field. Two waves are interfering and running parallel and anti-parallel to the interfaces and transport the generated vorticity at the interfaces, causing the perturbed interfaces' growth rate to oscillate in time, which is the essential suppression mechanism.
  • Harnessing phenological traits of wild ancestor Chenopodium hircinum to improve climate adaptation of quinoa

    Curti, Ramiro N.; Ortega-Baes, Pablo; Ratto, Santiago; Bertero, Daniel (CROP & PASTURE SCIENCE, CSIRO Publishing, 2022-10-27) [Article]
    Context: Cultivation of quinoa (Chenopodium quinoa Willd.) is rapidly expanding worldwide. Characterisation of populations of Chenopodium hircinum Schard., its wild ancestor, which thrives in some of the hottest environments in South America, may provide adaptations to new environments. Aims: This study evaluated the developmental patterns of populations of C. hircinum collected from a range of agroecological environments in Argentina, in order to quantify variability among sites of origin and to explore the association between climatic data from environments of provenance and variation in development. Methods: Thirty-three populations of C. hircinum from contrasting sites of origin in Argentina were multiplied in a common-garden experiment under non-limiting conditions of water and nutrient availability. Plants were sampled once or twice weekly (according to parameter) for estimation of the duration of developmental phases, leaf number, and dates of initiation of branching on the main stem. Key results: Significant variation was detected for all phenological traits, and populations were categorised into six groups based on similarity of patterns of variation. We found positive association of the duration of development phases and the number of leaves on the main-stem with maximum temperature during the growing season, and negative association with altitude of origin, consistent with variation in growing-season duration. Conclusions: The finding that late-flowering populations are associated with warmest climates reveals that longer vegetative growth is an adaptive strategy to cope with heat stress in Chenopodium spp. Implications: Time to flowering should be considered in attempts to improve quinoa performance under heat-stress conditions. Further work is needed to understand the genetic basis controlling this response in wild populations of C. hircinum.
  • Using charge collection narrowing to tune from broadband to narrowband all-polymer photodetectors

    Wang, Xiao; Fang, Yuan; Jin, Hui; Jiang, Wei; Gao, Mile; Burn, Paul L.; Shaw, Paul E. (Physica Scripta, IOP Publishing, 2022-10-25) [Article]
    We report an all-polymer photodiode comprising a new electron-transporting polymer, PNNTH, that contains naphthalene diimide and thiazole moieties. PNNTH has strong absorption at around 670 nm and an electron mobility of ≈10−4 cm2 V−1 s−1. Bulk heterojunction films composed of PNNTH blended with the donor polymer, PBDTT-FTTE, in a weight ratio of 1:2 were found to have electron and hole mobilities of ≈10−5 cm2 V−1 s−1 and ≈10−4 cm2 V−1 s−1, respectively. The photoresponse of conventional and inverted organic photodiodes containing the blend could be tuned from broadband (400–800 nm) to narrowband (50 nm full-width-at-half-maximum) simply by changing the thickness of the all-polymer blend. The narrowband response was achieved using the charge collection narrowing mechanism, which was enhanced by the unbalanced charge mobility. Transfer matrix-based optical modelling confirmed the wavelength dependence of the photoresponse. For both the broadband and narrowband photodiodes, the specific detectivity was greater than 1011 Jones.
  • Hybrid Indirect Evaporative Cooling-Mechanical Vapor Compression System: A Mini-Review

    Chen, Qian; Burhan, Muhammad; Ja, M Kum; Shahzad, Muhammad; Ybyraiymkul, Doskhan; Zheng, Hongfei; Cui, Xin; Ng, Kim Choon (Energies, MDPI AG, 2022-10-21) [Article]
    The hybrid indirect evaporative cooling-mechanical vapor compression (IEC-MVC) process is deemed a promising cooling system for hot and humid areas. It possesses the merits of high energy efficiency and strong capability of temperature and humidity control. Herein, we provide an overview of the state-of-the-art investigations over different aspects of the hybrid IEC-MVC process. Firstly, we evaluate the potential of IEC as a pre-cooler and heat-recovery device. Then, we compare the energy efficiency of IEC-MVC with standalone MVC and summarize its long-term energy-saving potential under specific weather conditions. Subsequently, we discuss the economic viability and water consumption of the hybrid process. These studies form a solid foundation for the future installation of the IEC-MVC system.
  • All-Optical Switching of Antiferromagnetic NiO thin films

    Meer, Hendrik; Wust, Stephan; Schmitt, Christin; Herrgen, Paul; Fuhrmann, Felix; Hirtle, Steffen; Bednarz, Beatrice; Rajan, Adithya; Ramos, Rafael; Niño, Miguel Angel; Foerster, Michael; Kronast, Florian; Kleibert, Armin; Rethfeld, Baerbel; Saitoh, Eiji; Stadtmüller, Benjamin; Aeschlimann, Martin; Kläui, Mathias (arXiv, 2022-10-20) [Preprint]
    We demonstrate how the antiferromagnetic order in heterostructures of NiO/Pt thin films can be modified by optical pulses. We irradiate our samples with laser light and identify an optically induced switching of the antiferromagnetic order by imaging the created domain structure utilizing the X-ray magnetic linear dichroism effect. We study the effect of different laser polarizations on the switching and identify a polarization-independent creation of 180{\deg} domain walls and domains with 180{\deg} different N\'eel vector orientation. By varying the irradiation parameters, we determine the switching mechanism to be thermally induced and demonstrate the reversibility. We thus demonstrate experimentally the possibility to optically create antiferromagnetic domains, an important step towards future functionalization of all optical switching mechanisms in antiferromagnets.
  • Viologen Hydrothermal Synthesis and Structure-Property Relationships for Redox Flow Battery Optimization

    Sullivan, Patrick; Liu, Honghao; Lv, Xiu-Liang; Jin, Song; Li, Wenjie; Feng, Dawei (American Chemical Society (ACS), 2022-10-19) [Preprint]
    Aqueous organic redox flow batteries (AORFBs) are an emerging grid energy storage technology for fire safe grid energy storage systems with sustainable material feedstocks. Yet, designing organic redox molecules with the desired solubility, viscosity, permeability, formal potential, kinetics, and stability while remaining synthetically scalable is challenging. Herein, we demonstrate the adaptability of a single-step, high-yield hydrothermal reaction for viologen chloride salts, which have shown promise for pH neutral AORFB. Nine viologens, including five symmetric and four asymmetric, were synthesized in high purity for physiochemical and electrochemical characterization. New empirical insights are gleaned into fundamental structure-property relationships for multi-objective optimization. Ultimately, a new Dex-DiOH-Vi derivative showcased record viologen concentration of 2.5 M in an anolyte-limiting AORFB with 14-days of stable cycling performance. This work highlights the importance of designing efficient synthetic approaches of organic redox species for molecular engineering high-performance and sustainable flow battery electrolytes.
  • Organic Planar Heterojunction Solar Cells and Photodetectors Tailored to the Exciton Diffusion Length Scale of a Non-Fullerene Acceptor

    Lee, Tack Ho; Dong, Yifan; Pacalaj, Richard A.; Park, Song Yi; Xu, Weidong; Kim, Ji-Seon; Durrant, James R. (ADVANCED FUNCTIONAL MATERIALS, Wiley, 2022-10-18) [Article]
    While non-fullerene acceptors (NFAs) have recently been demonstrated to exhibit long-range exciton diffusion, most organic photovoltaic and photodetector studies still focus on blended polymer: NFA systems. Herein, a 40 nm exciton diffusion length for IT4F excitons is determined, and it is demonstrated that sharp interface, planar heterojunction (PHJ) IT4F/PM6 devices with the IT4F layer thickness matched to this diffusion length yield optimized photovoltaic and photodetector performance. The PHJ devices yield an enhanced device open-circuit voltage relative to bulk heterojunction (BHJ) devices, associated with suppressed bimolecular recombination losses. The PHJ architecture also results in a ≈100-fold increase in electroluminescence (EL) quantum efficiency relative to the BHJ device, correlated with a shift from charge transfer state EL for the BHJ to IT4F exciton dominated EL for the PHJ, attributed to significant hole injection from PM6 into IT4F. Of particular note, the PHJ architecture is shown to suppress dark leakage current, resulting in 83 times higher photodetector detectivity at −2 V bias than the equivalent BHJ device.
  • Anisotropic long-range spin transport in canted antiferromagnetic orthoferrite YFeO3

    Das, Shubhankar; Ross, A.; Ma, X X; Becker, S.; Schmitt, C; van Duijn, F; Galindez-Ruales, E F; Fuhrmann, F; Syskaki, M-A; Ebels, U; Baltz, V; Barra, A-L; Chen, H Y; Jakob, G.; Cao, S X; Sinova, J; Gomonay, Olena; Lebrun, R.; Kläui, M (Nature communications, Springer Science and Business Media LLC, 2022-10-17) [Article]
    In antiferromagnets, the efficient transport of spin-waves has until now only been observed in the insulating antiferromagnet hematite, where circularly (or a superposition of pairs of linearly) polarized spin-waves diffuse over long distances. Here, we report long-distance spin-transport in the antiferromagnetic orthoferrite YFeO3, where a different transport mechanism is enabled by the combined presence of the Dzyaloshinskii-Moriya interaction and externally applied fields. The magnon decay length is shown to exceed hundreds of nanometers, in line with resonance measurements that highlight the low magnetic damping. We observe a strong anisotropy in the magnon decay lengths that we can attribute to the role of the magnon group velocity in the transport of spin-waves in antiferromagnets. This unique mode of transport identified in YFeO3 opens up the possibility of a large and technologically relevant class of materials, i.e., canted antiferromagnets, for long-distance spin transport.
  • Vecchia Approximations and Optimization for Multivariate Matérn Models

    Fahmy, Youssef; Guinness, Joseph (arXiv, 2022-10-17) [Preprint]
    We describe our implementation of the multivariate Mat\'ern model for multivariate spatial datasets, using Vecchia's approximation and a Fisher scoring optimization algorithm. We consider various pararameterizations for the multivariate Mat\'ern that have been proposed in the literature for ensuring model validity, as well as an unconstrained model. A strength of our study is that the code is tested on many real-world multivariate spatial datasets. We use it to study the effect of ordering and conditioning in Vecchia's approximation and the restrictions imposed by the various parameterizations. We also consider a model in which co-located nuggets are correlated across components and find that forcing this cross-component nugget correlation to be zero can have a serious impact on the other model parameters, so we suggest allowing cross-component correlation in co-located nugget terms.
  • Host-cell recognition of SARS-CoV-2 spike receptor binding domain from different variants

    Elfiky, Abdo A.; Ibrahim, Ibrahim M; Ibrahim, Mohamed N; Elshemey, Wael M (The Journal of infection, Elsevier BV, 2022-10-09) [Article]
  • On monotonicity conditions for Mean Field Games

    Graber, P. Jameson; Mészáros, Alpár R. (arXiv, 2022-10-05) [Preprint]
    In this paper we propose two new monotonicity conditions that could serve as sufficient conditions for uniqueness of Nash equilibria in mean field games. In this study we aim for unconditional uniqueness that is independent of the length of the time horizon, the regularity of the starting distribution of the agents, or the regularization effect of a non-degenerate idiosyncratic noise. Through a rich class of simple examples we show that these new conditions are not only in dichotomy with each other, but also with the two widely studied monotonicity conditions in the literature, the Lasry-Lions monotonicity and displacement monotonicity conditions.
  • Identifying Conservation Priorities for a Widespread Dugong Population in the red sea: Megaherbivore Grazing Patterns Inform Management Planning

    Khamis, Abdulqader; Alcoverro, Teresa; D'Souza, Elrika; Arthur, Rohan; Pagès, Jordi F.; Shah, Junid; Al-Qahtani, Tareq; Eweida, Ameer Abdulla (Marine Environmental Research, Elsevier BV, 2022-10-02) [Article]
    Extensive home ranges of marine megafauna present a challenge for systematic conservation planning because they exceed spatial scales of conventional management. For elusive species like dugongs, their management is additionally hampered by a paucity of basic distributional information across much of their range. The Red Sea is home to a wide-spread, globally important but data-poor population of dugongs. We surveyed the north-eastern Red Sea in the waters of NEOM, Kingdom of Saudi Arabia, to locate feeding sites and determine priority areas for dugong conservation. We conducted large-scale in-water surveys of dugong feeding trails across 27 seagrass meadows that span 0.7 degree of latitude and recorded nine seagrass species and 13 dugong feeding sites. Spread over ∼4‚061 km2 of nearshore and offshore waters, many of these sites clustered around five main core feeding areas. Dugong feeding trails were mostly recorded at sites dominated by the fast-growing pioneer seagrasses Halodule uninervis, Halophila ovalis and/or H. stipulacea. Multispecific meadows with pioneer seagrasses tended to be sheltered and shallow, reflecting a similar spatial pattern to the identified dugong feeding sites. Often close to hotels and fishing harbours, these high-use dugong areas are subject to high boat traffic, fishing, and coastal development which places considerable pressures on this vulnerable mammal and its seagrass habitat. The rapidly accelerating coastal development in the northern Red Sea directly threatens the future of its dugong population. Although our sampling focuses on feeding signs in early successional seagrasses, the results are valuable to spatial conservation planning as they will trigger overdue conservation interventions for a globally threatened species in a data-poor area. Urgent dugong conservation management actions in the northern Red Sea should focus on shallow waters sheltered by coastal lagoons, bays and the lee of large islands.
  • The taxicab sampler: MCMC for discrete spaces with application to tree models

    Geels, Vincent; Pratola, Matthew T.; Herbei, Radu (Journal of Statistical Computation and Simulation, Informa UK Limited, 2022-09-29) [Article]
    Motivated by the problem of exploring discrete but very complex state spaces in Bayesian models, we propose a novel Markov Chain Monte Carlo search algorithm: the taxicab sampler. We describe the construction of this sampler and discuss how its interpretation and usage differs from that of standard Metropolis-Hastings as well as the related Hamming ball sampler. The proposed sampling algorithm is then shown to demonstrate substantial improvement in computation time without any loss of efficiency relative to a naïve Metropolis–Hastings search in a motivating Bayesian regression tree count model, in which we leverage the discrete state space assumption to construct a novel likelihood function that allows for flexibly describing different mean-variance relationships while preserving parameter interpretability compared to existing likelihood functions for count data.

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