Publications Acknowledging KAUST Support: Recent submissions
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Photosymbiosis in Late Triassic scleractinian corals from the Italian Dolomites(PeerJ, PeerJ, 20210316) [Article]During the Carnian, oligotrophic shallowwater regions of the western Tethys were occupied by small, coralrich patch reefs. Scleractinian corals, which already contributed to the formation of the reef structure, owed their position most probably to the symbiosis with dinoflagellate algae (zooxanthellae). Using microstructural (regularity of growth increments) and geochemical (oxygen and carbon stable isotopes) criteria of zooxanthellae symbiosis, we investigated whether this partnership was widespread among Carnian scleractinians from the Italian Dolomites (locality Alpe di Specie). Although corals from this locality are renowned from excellent mineralogical preservation (aragonite), their skeletons were rigorously tested against traces of diagenesis Irrespective of their growth forms, well preserved skeletons of corals from the Dolomites, most frequently revealed regular growth bands (low values of coefficient of variation) typical of modern zooxanthellate corals. Paradoxically, some Carnian taxa (Thamnasteriomorpha frechi and Thamnasteriomorphasp.)with highly integrated thamnasterioid colonies which today are formed exclusively by zooxanthellate corals, showed irregular finescale growth bands (coefficient of variation of 40% and 41% respectively) that could suggest their asymbiotic status. However, similar irregular skeletal banding is known also in some modern agariciids (Leptoseris fragilis) which are symbiotic with zooxanthellae. This may point to a similar ecological adaptation of Triassic taxa with thamnasterioid colonies. Contrary to occasionally ambiguous interpretation of growth banding, all examined Carnian corals exhibited lack of distinct correlation between carbon (δ$^{13}$C range between 0.81‰ and 5.81‰) and oxygen (δ$^{18}$O values range between −4.21‰ and −1.06‰) isotope composition of the skeleton which is consistent with similar pattern in modern zooxanthellates. It is therefore highly likely, that Carnian scleractinian corals exhibited analogous ecological adaptations as modern symbiotic corals and that coralalgal symbiosis that spread across various clades of Scleractinia preceded the reef bloom at the end of the Triassic.

A unified firstorder hyperbolic model for nonlinear dynamic rupture processes in diffuse fracture zones(Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, The Royal Society, 20210315) [Article]Earthquake fault zones are more complex, both geometrically and rheologically, than an idealized infinitely thin plane embedded in linear elastic material. To incorporate nonlinear material behaviour, natural complexities and multiphysics coupling within and outside of fault zones, here we present a firstorder hyperbolic and thermodynamically compatible mathematical model for a continuum in a gravitational field which provides a unified description of nonlinear elastoplasticity, material damage and of viscous Newtonian flows with phase transition between solid and liquid phases. The fault geometry and secondary cracks are described via a scalar function ξ ∈ [0, 1] that indicates the local level of material damage. The model also permits the representation of arbitrarily complex geometries via a diffuse interface approach based on the solid volume fraction function α ∈ [0, 1]. Neither of the two scalar fields ξ and α needs to be meshaligned, allowing thus faults and cracks with complex topology and the use of adaptive Cartesian meshes (AMR). The model shares common features with phasefield approaches, but substantially extends them. We show a wide range of numerical applications that are relevant for dynamic earthquake rupture in fault zones, including the coseismic generation of secondary offfault shear cracks, tensile rock fracture in the Brazilian disc test, as well as a natural convection problem in molten rocklike material. This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.

SubstrateIndependent LaserInduced Graphene Electrodes for Microfluidic Electroanalytical Systems(ACS Applied Nano Materials, American Chemical Society (ACS), 20210311) [Article]Laserinduced graphene’s (LIG) inherent graphenelike and highly porous characteristics and its simple, scalable, and inexpensive fabrication render it a desirable electrode material for bio and chemosensors. The best LIG electrodes are made in polyimide foils using a CO2 laser scriber, which unfortunately limits their integration into more sophisticated analytical devices due to polyimide’s inertness. The transfer of LIG electrodes onto standard polymer substrates used in microfluidic systems and their use in microfluidic assays were therefore studied and the resulting electrodes characterized morphologically, chemically, and electroanalytically. It was found that a direct pressuredriven transfer produces highly functional transferLIG (tLIG) electrodes. tLIG differed from LIG electrodes with respect to a much smoother surface and hence a lower active surface area, a loss of the graphene characteristic Raman 2D peak, and a slight decrease in electron transfer rates. However, their performance in amperometric detection strategies were comparable also when used in adhesivetapeenabled microfluidic channels for the detection of paminophenol. tLIG outperformed LIG electrodes in their ability to be integrated into more advanced microfluidic channel systems made of an allpolymethyl methacrylate (PMMA) substrate for the biosensing detection of alkaline phosphatase, commonly used as a biomarker and as a biosensor amplification system. LIG and tLIG have hence the potential to change electroanalytical sensing in diagnostic systems as their fabrication requires minimal resources, is highly scalable, and allows their integration into simple and, as tLIG, also sophisticated analytical systems.

High Thermal Effusivity Nanocarbon Materials for Resonant Thermal Energy Harvesting(Small, Wiley, 20210306) [Article]Carbon nanomaterials have extraordinary thermal properties, such as high conductivity and stability. Nanocarbon combined with phase change materials (PCMs) can yield exceptionally high thermal effusivity composites optimal for thermal energy harvesting. The progress in synthesis and processing of high effusivity materials, and their application in resonant energy harvesting from temperature variations is reviewed.

Assessing MarginWide Rupture Behaviors along the Cascadia Megathrust with 3D Dynamic Rupture Simulations(California Digital Library (CDL), 20210305) [Preprint]

A unified first order hyperbolic model for nonlinear dynamic rupture processes in diffuse fracture zones(Copernicus GmbH, 20210304) [Presentation]Earthquake fault zones are more complex, both geometrically and rheologically, than an idealised infinitely thin plane embedded in linear elastic material. To incorporate nonlinear material behaviour, natural complexities and multiphysics coupling within and outside of fault zones, here we present a first order hyperbolic and thermodynamically compatible mathematical model for a continuum in a gravitational field which provides a unified description of nonlinear elastoplasticity, material damage and of viscous Newtonian flows with phase transition between solid and liquid phases. The fault geometry and secondary cracks are described via a scalar function $\xi \in [0,1]$ that indicates the local level of material damage. The model also permits the representation of arbitrarily complex geometries via a diffuse interface approach based on the solid volume fraction function $\alpha \in [0,1]$. Neither of the two scalar fields $\xi$ and $\alpha$ needs to be meshaligned, allowing thus faults and cracks with complex topology and the use of adaptive Cartesian meshes (AMR). The model shares common features with phasefield approaches, but substantially extends them. We show a wide range of numerical applications that are relevant for dynamic earthquake rupture in fault zones, including the coseismic generation of secondary offfault shear cracks, tensile rock fracture in the Brazilian disc test, as well as a natural convection problem in molten rocklike material.

Designing optimal experiments: an application to proton Compton scattering(The European Physical Journal A, Springer Nature, 20210227) [Article]Interpreting measurements requires a physical theory, but the theory’s accuracy may vary across the experimental domain. To optimize experimental design, and so to ensure that the substantial resources necessary for modern experiments are focused on acquiring the most valuable data, both the theory uncertainty and the expected pattern of experimental errors must be considered. We develop a Bayesian approach to this problem, and apply it to the example of proton Compton scattering. Chiral Effective Field Theory (χEFT) predicts the functional form of the scattering amplitude for this reaction, so that the electromagnetic polarizabilities of the nucleon can be inferred from data. With increasing photon energy, both experimental rates and sensitivities to polarizabilities increase, but the accuracy of χEFT decreases. Our physicsbased model of χEFT truncation errors is combined with present knowledge of the polarizabilities and reasonable assumptions about experimental capabilities at HIγS and MAMI to assess the information gain from measuring specific observables at specific kinematics, i.e. to determine the relative amount by which new data are apt to shrink uncertainties. The strongest gains would likely come from new data on the spin observables Σ 2x and Σ2x′ at ω≃ 140 to 200 MeV and 40 ∘ to 120 ∘. These would tightly constrain γE1E1 γE1M2. New data on the differential cross section between 100 and 200 MeV and over a wide angle range will substantially improve constraints on αE1 βM1, γπ and γM1M1 γM1E2. Good signals also exist around 160 MeV for Σ 3 and Σ2z′. Such data will be pivotal in the continuing quest to pin down the scalar polarizabilities and refine understanding of the spin polarizabilities.

The onesided Lipschitz condition in the followtheleader approximation of scalar conservation laws(arXiv, 20210226) [Preprint]We consider the followtheleader particle approximation scheme for a $1d$ scalar conservation law with nonnegative $L^\infty_c$ initial datum and with a $C^1$ concave flux, which is known to provide convergence towards the entropy solution $\rho$ to the corresponding Cauchy problem. We provide two novel contributions to this theory. First, we prove that the onesided Lipschitz condition satisfied by the approximating density $\rho^n$ is a discrete version of an entropy condition; more precisely, under fairly general assumptions on $f$ (which imply concavity of $f$) we prove that the continuum version $\left(f(\rho)/\rho\right)_x\leq 1/t$ of said condition allows to select a unique weak solution, despite $\left(f(\rho)/\rho\right)_x\leq 1/t$ is apparently weaker than the classical OleinikHoff onesided Lipschitz condition $f'(\rho)_x\leq 1/t$. Said result relies on an improved version of Hoff's uniqueness proof. A byproduct of it is that the entropy condition is encoded in the particle scheme prior to the manyparticle limit, which was never proven before. Second, we prove that in case $f(\rho)=\rho(A\rho^\gamma)$ the onesided Lipschitz condition can be improved to a discrete version of the classical (and sharp) OleinikHoff condition. In order to make the paper selfcontained, we provide proofs (in some cases alternative ones) of all steps of the convergence of the particle scheme.

Investigation of the Deactivation and Reactivation Mechanism of a Heterogeneous Palladium(II) Catalyst in the Cycloisomerization of Acetylenic Acids by In Situ XAS(ACS Catalysis, American Chemical Society (ACS), 20210222) [Article]A wellstudied heterogeneous palladium(II) catalyst used for the cycloisomerization of acetylenic acids is known to be susceptible to deactivation through reduction. To gain a deeper understanding of this deactivation process and to enable the design of a reactivation strategy, in situ Xray absorption spectroscopy (XAS) was used. With this technique, changes in the palladium oxidation state and coordination environment could be studied in close detail, which provided experimental evidence that the deactivation was primarily caused by triethylaminepromoted reduction of palladium(II) to metallic palladium nanoparticles. Furthermore, it was observed that the choice of the acetylenic acid substrate influenced the distribution between palladium(II) and palladium(0) species in the heterogeneous catalyst after the reaction. From the mechanistic insight gained through XAS, an improved catalytic protocol was developed that did not suffer from deactivation and allowed for more efficient recycling of the catalyst.

Numerical study of COVID19 spatialtemporal spreading in London(arXiv, 20210219) [Preprint]Recent study reported that an aerosolised virus (COVID19) can survive in the air for a few hours. It is highly possible that people get infected with the disease by breathing and contact with items contaminated by the aerosolised virus. However, the aerosolised virus transmission and trajectories in various meteorological environments remain unclear. This paper has investigated the movement of aerosolised viruses from a high concentration source across a dense urban area. The case study looks at the highly air polluted areas of London: University College Hospital (UCH) and King Cross and St Pancras International Station (KCSPI). We explored the spread and decay of COVID19 released from the hospital and railway stations with the prescribed meteorological conditions. The study has three key findings: the primary result is that it is possible for the virus to travel from meters up to hundred meters from the source location. The secondary finding shows viruses released into the atmosphere from entry and exit points at KCSPI remain trapped within a small radial distance of < 50m. This strengthens the case for the use of face coverings to reduce the infection rate. The final finding shows that there are different levels of risk at various door locations for UCH, depending on which door is used there can be a higher concentration of COVID19. Although our results are based on London, since the fundamental knowledge processes are the same, our study can be further extended to other locations (especially the highly air polluted areas) in the world.

FluxPMU  A Maker's Guide of a DIY Synchronized Phasor Measurement Unit(Institute of Electrical and Electronics Engineers (IEEE), 20210216) [Conference Paper]Synchrophasor technology is transforming the way the power grid is being monitored thanks to the benefits provided by synchronized Phasor Measurement Units (PMUs). To exploit these benefits, future power engineers need better understanding of how PMUs work at all levels, from hardware components to phasor estimation methods implemented in software. However, handson experiences with these technologies allowing students to “tinker” with a PMU are limited. The FluxPMU project aims to enable students to explore and build an open source, low cost PMU. Building from the legacy of OpenPMU V1, FluxPMU provides a DoitYourself (DIY) guide with all documentation and software sources required to build the FluxPMU, which can be found in the following Github repository: https://github.com/alsetlab/fluxpmu. This paper summarizes the authors’ efforts in creating this Maker’s Guide.

A nonunitary metasurface enables continuous control of quantum photon–photon interactions from bosonic to fermionic(Nature Photonics, Springer Nature, 20210211) [Article]Photonic quantum information processing, one of the leading platforms for quantum technologies1–5, critically relies on optical quantum interference to produce an indispensable effective photon–photon interaction. However, such an effective interaction is fundamentally limited to bunching6 due to the bosonic nature of photons7 and the restricted phase response from conventional unitary optical elements8,9. Here we propose and experimentally demonstrate a new degree of freedom in the optical quantum interference enabled by a nonunitary metasurface. Due to the unique anisotropic phase response that creates two extreme eigenoperations, we show dynamical and continuous control over the effective interaction of two single photons such that they show bosonic bunching, fermionic antibunching or arbitrarily intermediate behaviour, beyond their intrinsic bosonic nature. This quantum operation opens the door to both fundamental quantum light–matter interaction and innovative photonic quantum devices for quantum communication, quantum simulation and quantum computing.

Synthesis of nickel and cobalt oxide nanoparticles by pulsed underwater spark discharges(Journal of Applied Physics, AIP Publishing, 20210210) [Article]Electrical discharges in liquids are considered an efficient and ecological technique of nanoparticle synthesis via controlled erosion of electrodes. Herein, we use spark discharges between Co–Co, Ni–Ni, Co–Ni, or Ni–Co electrodes immersed in distilled water to synthesize Co and/or Ni nanoparticles, as well as their oxides. When mixed electrodes are used (Co–Ni or Ni–Co), both Co and Ni nanoparticles are produced, and the major species is dictated by the nature of the anode pin. The characteristics of nanoparticles synthesized under varying conditions of pulse width (100 and 500 ns) and voltage amplitude (5 and 20 kV) are analyzed by transmission electron microscopy. Within the investigated discharge conditions, it is not possible to produce Co–Ni nanoalloys; however, core–shell nanoparticles are observed among the Ni and Co nanoparticles. Finally, the direct optical bandgaps of the nanomaterials are determined using UVvisible absorption spectroscopy.

Seismic source tracking with six degreeoffreedom ground motion observations(Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), 20210204) [Article]Back azimuth information can be determined from combined measurements of rotations and translations at a single site. Such six degreeoffreedom (6DoF) measurements are reasonably stable in delivering similar information compared to a smallscale array of threecomponent seismometers. Here we investigate whether a 6DoF approach is applicable to tracking seismic sources. While common approaches determining the timing and location of energy sources generating seismic waves rely on the information of Pwaves, here we use Swaves. We track back azimuths of directly arriving SHwaves in the 2D case, Pconverted SVwaves, direct SV and direct SHwaves in the 3D case. For data analysis, we compare a crosscorrelation approach using a gridsearch optimization algorithm with a polarization analysis method. We successfully recover the rupture path and rupture velocity with only one station, under the assumption of an approximately known fault location. Using more than one station, rupture imaging in space and time is possible without a priori assumptions. We discuss the effects of rupture directivity, supershear rupture velocity, sourcereceiver geometry, wavefield interference, and noise. We verify our approach with the analysis of moving traffic noise sources using 6DoF observations. The collocated classic seismometer and newlybuilt ring laser gyroscope ROMY near Munich, Germany, allow us to record highfidelity, broadband 6DoF (particle velocity and rotational rate) ground motions. We successfully track vehicles and estimate their speed while traveling along a nearby highway using the estimated BAz as a function of time of a single station observation.

DFT insights into hydrogen activation on the doping Ni2P surfaces under the hydrodesulfurization condition(Applied Surface Science, Elsevier BV, 202102) [Article]Hydrogen activation on the different Ni2P surfaces were explored under the traditional hydrodesulfurization conditions using density function theory (DFT) calculations. Firstly, the H2 dissociative adsorption phase diagrams were calculated and compared on the Ni(I) and Ni(II)exposed surfaces. The H2 dissociative adsorption on the Ni(I)exposed surface had high activity below 4 H2 coverage, and the H2 dissociative adsorption on the Ni(II)exposed surface was preferable below 2 H2 coverage. By contrast, the Ni(I)exposed surface exhibited higher H2 activation activity than that on the Ni(II)exposed surface. Moreover, the dissociative H atoms on Ni(II)exposed surface would lead the rearrangement of surface Ni atoms to form the quasi tetrahedral coordination structure, which was similar to that of Ni(I)exposed surface. Secondly, the surface phase diagrams were discussed on the different transition metals (Cr, Fe, Co, Cu or Mo) doping Ni(I)exposed surfaces. The results revealed that H2 activation ability followed the order: Fe > Co > Mo > Cr > Ni > Cu. Furthermore, the difference charge densities and bader charge analysis were calculated to provide the additional information for understanding the phenomenon clearly, and the results indicated that the difficulty sequence of charge transfer between transition metals atom and H atoms was completely consistent with the above research.

DFT insights into the hydrodesulfurization mechanisms of different sulfurcontaining compounds over CoMoS active phase: Effect of the brim and CUS sites(Chemical Engineering Science, Elsevier BV, 202102) [Article]Density functional theory calculations are performed to investigate the hydrodesulfurization (HDS) mechanisms of different sulfurcontaining compounds, such as thiophene, benzothiophene, dibenzothiophene (DBT) and 4,6dimethyldibenzothiophene (4,6DMDBT) on the brim and CUS sites. Based on the systematic calculations, the dominant reaction pathway of different molecules are explored, and the structureactivity relationship of brim and CUS sites is mainly discussed under the real reaction conditions (p(H2) = 4 MPa, T = 650 K). According to the DFT calculation results, brim site is more favorable for the HDS reactions of thiophene and benzothiophene. However, both brim and CUS sites are considered to participate in the DBT and 4.6DMDBT HDS processes. The brim site provides the hydrogenation active sites, and the CUS site promotes the removal of sulfur atoms. The proposed mechanism strongly supports that the brim and CUS sites act in synergistic effect for the HDS reaction of the highly refractory organic sulfides.

Deep distribution regression(Computational Statistics & Data Analysis, Elsevier BV, 202102) [Article]Due to their flexibility and predictive performance, machinelearning based regression methods have become an important tool for predictive modeling and forecasting. However, most methods focus on estimating the conditional mean or specific quantiles of the target quantity and do not provide the full conditional distribution, which contains uncertainty information that might be crucial for decision making. A general solution consists of transforming a conditional distribution estimation problem into a constrained multiclass classification problem, in which tools such as deep neural networks can be applied. A novel joint binary crossentropy loss function is proposed to accomplish this goal. Its performance is compared to current stateoftheart methods via simulation. The approach also shows improved accuracy in a probabilistic solar energy forecasting problem.

On the Performance of LargeScale Wireless Networks in the Finite BlockLength Regime(arXiv, 20210128) [Preprint]UltraReliable LowLatency Communications have stringent delay constraints, and hence use codes with small block length (short codewords). In these cases, classical models that provide good approximations to systems with infinitely long codewords become imprecise. To remedy this, in this paper, an average coding rate expression is derived for a large scale network with short codewords using stochastic geometry and the theory of coding in the finite blocklength regime. The average coding rate and upper and lower bounds on the outage probability of the largescale network are derived, and a tight approximation of the outage probability is presented. Then, simulations are presented to study the effect of network parameters on the average coding rate and the outage probability of the network, which demonstrate that results in the literature derived for the infinite blocklength regime overestimate the network performance, whereas the results in this paper provide a more realistic performance evaluation.

Aircraft Acoustic Signal Modeled as Oscillatory AlmostCyclostationary Process(Institute of Electrical and Electronics Engineers (IEEE), 20210124) [Conference Paper]The acoustic almostcyclostationary signal emitted by a moving aircraft is modeled as an oscillatory almostcyclostationary process when it is received by a stationary listener. Its autocorrelation function is constituted by the superposition of anglemodulated sinewaves, where the angle modulation is consequence of the timevarying delay due to the relative motion between aircraft and listener. Conditions under which the source almostcyclostationary signal can be recovered by the received signal by time dewarping are established. Thus, cyclic features of the source signal carrying information on aircraft parameters are estimated by classical cyclic spectral analysis.

Experimental and Theoretical Investigation of the Synergy Effect of Zr and Ce on the Catalytic Efficiency of NiMoS Grafted on SBA15 for Oil Hydrodesulfurization(Energy & Fuels, American Chemical Society (ACS), 20210120) [Article]In this study, the synergy effect of biheteroatoms (ZrOx and CeOy) and a Ni promoter on the catalytic performance of MoS2 crystallites grafted on SBA15 silica for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) in diesel was investigated. The pyridineFourier transform infrared (pyFTIR) spectroscopy, ammonia temperatureprogrammed desorption (NH3TPD), and Xray photoelectron spectroscopy (XPS) analyses revealed that the surface acidity, number of active sites, and the dispersion of MoS2 crystallites increased significantly with the incorporation of ZrOx and CeOy on SBA15 than other supported catalysts evaluated. The ZrOx–CeOy–SBA15supported NiMo catalyst could remove 59% of DBT in diesel spiked with 1000 ppm of DBT after 1 h of reaction and up to 96% of DBT after 5 h of reaction. Density functional theory (DFT) simulations further gave interesting insights; a thinfilm model of SBA15 decorated with Zr and Ce indicates that the metal sites induced a strong hydrogen bond network leading to higher surface stability. Furthermore, Ce grafted on SBA15 enhanced the adsorption of water molecules that increases the Bro̷nsted acid sites and subsequently improved its catalytic efficiency. DFT simulation of thiophene HDS showed a stepwise rupture of thiophene C–S bonds with the second C–S bond breaking as the plausible ratedetermining step.