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Recent Submissions

  • The state of pore fluid pressure and 3D megathrust earthquake dynamics

    Madden, Elizabeth; Ulrich, Thomas; Gabriel, Alice-Agnes (California Digital Library (CDL), 2021-04-14) [Preprint]
    The importance of pore fluid pressure (Pf ) for fault strength, stress state and slip behavior holds promise for explaining spatio-temporal subduction zone megathrust be19 havior, but the coseismic state of Pf and its distribution with depth are poorly constrained. Here, we analyze fault stress states and 3D rupture dynamics of six scenarios based on the 2004 Mw 9.1 Sumatra-Andaman earthquake. We vary Pf from hydrostatic to litho22 static under two di↵erent gradients that result in depth-dependent versus constant ef23 fective normal stress on the seismogenic part of the megathrust. As Pf magnitude in24 creases, fault strength, moment magnitude, cumulative slip, peak slip rate, dynamic stress drop and rupture velocity decrease. When Pf follows the lithostatic gradient, depth-constant e↵ective normal stress results, as theoretically proposed. We find that such a near-lithostatic pore fluid pressure gradient shifts peak slip and peak slip rate up-dip
  • The presence of Superfund sites as a determinant of life expectancy in the United States

    Kiaghadi, Amin; Rifai, Hanadi S.; Dawson, Clint N. (Nature Communications, Springer Nature, 2021-04-13) [Article]
    AbstractSuperfund sites could affect life expectancy (LE) via increasing the likelihood of exposure to toxic chemicals. Here, we assess to what extent such presence could alter the LE independently and in the context of sociodemographic determinants. A nationwide geocoded statistical modeling at the census tract level was undertaken to estimate the magnitude of impact. Results showed a significant difference in LE among census tracts with at least one Superfund site and their neighboring tracts with no sites. The presence of a Superfund site could cause a decrease of −0.186 ± 0.027 years in LE. This adverse effect could be as high as −1.22 years in tracts with Superfund sites and high sociodemographic disadvantage. Specific characteristics of Superfund sites such as being prone to flooding and the absence of a cleanup strategy could amplify the adverse effect. Furthermore, the presence of Superfund sites amplifies the negative influence of sociodemographic factors at lower LEs.
  • Nonlinear valley phonon scattering under the strong coupling regime

    Liu, Xiaoze; Yi, Jun; Yang, Sui; Lin, Erh-Chen; Zhang, Yue-Jiao; Zhang, Peiyao; Li, Jian-Feng; Wang, Yuan; Lee, Yi-Hsien; Tian, Zhong-Qun; Zhang, Xiang (Nature Materials, Springer Nature, 2021-04-12) [Article]
    Research efforts of cavity quantum electrodynamics have focused on the manipulation of matter hybridized with photons under the strong coupling regime1,2,3. This has led to striking discoveries including polariton condensation2 and single-photon nonlinearity3, where the phonon scattering plays a critical role1,2,3,4,5,6,7,8,9. However, resolving the phonon scattering remains challenging for its non-radiative complexity. Here we demonstrate nonlinear phonon scattering in monolayer MoS2 that is strongly coupled to a plasmonic cavity mode. By hybridizing excitons and cavity photons, the phonon scattering is equipped with valley degree of freedom and boosted with superlinear enhancement to a stimulated regime, as revealed by Raman spectroscopy and our theoretical model. The valley polarization is drastically enhanced and sustained throughout the stimulated regime, suggesting a coherent scattering process enabled by the strong coupling. Our findings clarify the feasibility of valley–cavity-based systems for lighting, imaging, optical information processing and manipulating quantum correlations in cavity quantum electrodynamics2,3,10,11,12,13,14,15,16,17.
  • Overlooked Ecological Roles of Influent Wastewater Microflora in Improving Biological Phosphorus Removal in an Anoxic/Aerobic MBR Process

    Xu, Ronghua; Fan, Fuqiang; Lin, Qining; Yuan, Shasha; Meng, Fangang (Environmental Science & Technology, American Chemical Society (ACS), 2021-04-08) [Article]
    The ecological roles of influent microflora in activated sludge communities have not been well investigated. Herein, parallel lab-scale anoxic/aerobic (A/O) membrane bioreactors (MBRs), which were fed with raw (MBR-C) and sterilized (MBR-T) municipal wastewater, were operated. The MBRs showed comparable nitrogen removal but superior phosphorus removal in MBR-C than MBR-T over the long-term operation. The MBR-C sludge community had higher diversity and deterministic assembly than the MBR-T sludge community as revealed by 16S rRNA gene sequencing and null model analysis. Moreover, the MBR-C sludge community had higher abundance of polyphosphate accumulating organisms (PAOs) and hydrolytic/fermentative bacteria (HFB) but lower abundance of glycogen-accumulating organisms (GAOs), in comparison with MBR-T sludge. Intriguingly, the results of both the net growth rate and Sloan’s neutral model demonstrated that HFB in the sludge community were generally slow-growing or nongrowing and their consistent presence in activated sludge was primarily attributed to the HFB immigration from influent microflora. Positive correlations between PAOs and HFB and potential competitions between HFB and GAOs were observed, as revealed by the putative species–species associations in the ecological networks. Taken together, this work deciphers the positive ecological roles of influent microflora, particularly HFB, in system functioning and highlights the necessity of incorporating influent microbiota for the design and modeling of A/O MBR plants.
  • Cryogenic Carbon Capture™ (CCC) Status Report

    Baxter, Larry; Hoeger, Christopher; Stitt, Kyler; Burt, Stephanie; Baxter, Andrew (SSRN Electronic Journal, Elsevier BV, 2021-04-07) [Article]
    The Cryogenic Carbon Capture™ (CCC) process separates CO2 from light gases in essentially any continuous process. CCC cools the gases to the frost or desublimation point of CO2 (−100 to −135 °C), separates and pressurizes the solids, and warms all streams to produce a CO2-depleted stream at ambient pressure and a pure (99+%) pressurized liquid CO2 stream typically to about 150 bar, both at ambient temperature. The process also recovers all gas moisture and most gas impurities less volatile than CO2 (NOx, SOx, Hg, PM, UHC, CCC, etc.) in separable streams. CCC nearly eliminates refrigeration energy for sensible temperature changes through heat integration. CCC does require energy to change the CO2 phase from a mixed vapor to a pressurized fluid, which represents the minimum energy required of any process for this separation. CCC uses additional energy for turbomachinery inefficiencies, heat losses, moisture removal and overall process pressure drop. Aside from these real-world energy demands, CCC operates near the minimum energy required to perform this gas separation by minimizing stream recycling. CCC compresses CO2 as a liquid, which is one of several reasons it costs about about half as much and consumes about half as much energy as an amine process when using flue gases with about 15% CO2. The process also has several major additional advantages, including (a) it is a bolt-on retrofit technology that does not need steam or any modification of existing equipment, (b) it recovers water and nearly all pollutants in addition to CO2 from the flue gas, (c) it enables highly efficient and cost effective energy storage at grid scale and on time scales of minutes, (d) it enables NG storage if the energy storage option is used, and (d) it has a small footprint and is minimally disruptive to existing plants, requiring only electrical power and a gas source to operate. Sustainable Energy Solutions (SES) has scaled this technology through several levels, the largest of which captures nominally 1 tonne of CO2/day and is called the skid system. Skid system field tests include utility-scale power plants, cement plants, heating plants, and other utility or industrial sites that burn natural gas, biomass, coal, shredded tires, municipal waste, and combinations of these fuels. These field tests produced 95-99% CO2 capture with CO2 purities of 99+% and initial CO2 contents that range from 4 to 28%. SES currently seeks to scale the system to merchant scale (10-80 tonnes of CO2 per day). In the process of doing so, SES has demonstrated the potential for CCC to contribute to energy storage and direct air capture in innovative and cost-effective ways.
  • Damage-free substrate removal technique: Wet undercut etching of semipolar (20-21) laser structures by incorporation of un/relaxed sacrificial layer single quantum well

    Abbas, Arwa Saud; Alyamani, Ahmed; Nakamura, Shuji; DenBaars, Steven P. (Japanese Journal of Applied Physics, IOP Publishing, 2021-03-30) [Article]
    We applied a damage-free substrate removal technique using photoelectrochemical etching (PECE) by incorporating sacrificial layer In0.12Ga0.88N single quantum well (SL-SQW) types in semipolar (202 ̅1) flip-chip laser diode (FC-LD) structures. Although 40-nm type I promoted the development of high-quality green active region (AR) devices in terms of managing strain relaxation, processing was required under low-temperature KOH. However, 10-nm type II exhibited a smooth n-type GaN surface with room-temperature KOH, thereby promoting the applicability of the proposed technique for either a short light emitter or a combination with type I. The temperature-dependent PECE of SL-SQW types is important in realizing advanced FC-LDs.
  • Physics-informed Learning for Identification and State Reconstruction of Traffic Density

    Barreau, Matthieu; Aguiar, Miguel; Liu, John; Johansson, Karl Henrik (arXiv, 2021-03-25) [Preprint]
    This paper deals with traffic density reconstruction using measurements from Probe Vehicles (PVs). The main difficulty arises when considering a low penetration rate, meaning that the number of PVs is small compared to the total number of vehicles on the road. Moreover, the formulation assumes noisy measurements and a partially unknown first-order model. All these considerations make the use of machine learning to reconstruct the state the only applicable solution. We first investigate how the identification and reconstruction processes can be merged and how a sparse dataset can still enable a good identification. Secondly, we propose a pre-training procedure that helps the hyperparameter tuning, preventing the gradient descent algorithm from getting stuck at saddle points. Examples using numerical simulations and the SUMO traffic simulator show that the reconstructions are close to the real density in all cases.
  • Effective strain manipulation of the antiferromagnetic state of polycrystalline NiO

    Barra, A.; Ross, A.; Gomonay, O.; Baldrati, L.; Chavez, A.; Lebrun, R.; Schneider, J. D.; Shirazi, P.; Wang, Q.; Sinova, J.; Carman, G. P.; Kläui, M. (arXiv, 2021-03-24) [Preprint]
    As a candidate material for applications such as magnetic memory, polycrystalline antiferromagnets offer the same robustness to external magnetic fields, THz spin dynamics, and lack of stray field as their single crystalline counterparts, but without the limitation of epitaxial growth and lattice matched substrates. Here, we first report the detection of the average Neel vector orientiation in polycrystalline NiO via spin Hall magnetoresistance (SMR). Secondly, by applying strain through a piezo-electric substrate, we reduce the critical magnetic field required to reach a saturation of the SMR signal, indicating a change of the anisotropy. Our results are consistent with polycrystalline NiO exhibiting a positive sign of the in-plane magnetostriction. This method of anisotropy-tuning offers an energy efficient, on-chip alternative to manipulate a polycrystalline antiferromagnets magnetic state.
  • Automated Applications of Acoustics for Stored Product Insect Detection, Monitoring, and Management

    Mankin, Richard; Hagstrum, David; Guo, Min; Eliopoulos, Panagiotis; Njoroge, Anastasia (Insects, MDPI AG, 2021-03-19) [Article]
    Acoustic technology provides information difficult to obtain about stored insect behavior, physiology, abundance, and distribution. For example, acoustic detection of immature insects feeding hidden within grain is helpful for accurate monitoring because they can be more abundant than adults and be present in samples without adults. Modern engineering and acoustics have been incorporated into decision support systems for stored product insect management, but with somewhat limited use due to device costs and the skills needed to interpret the data collected. However, inexpensive modern tools may facilitate further incorporation of acoustic technology into the mainstream of pest management and precision agriculture. One such system was tested herein to describe Sitophilus oryzae (Coleoptera: Curculionidae) adult and larval movement and feeding in stored grain. Development of improved methods to identify sounds of targeted pest insects, distinguishing them from each other and from background noise, is an active area of current research. The most powerful of the new methods may be machine learning. The methods have different strengths and weaknesses depending on the types of background noise and the signal characteristic of target insect sounds. It is likely that they will facilitate automation of detection and decrease costs of managing stored product insects in the future.
  • Catalytic Mechanism of Interfacial Water in the Cycloaddition of Quadricyclane and Diethyl Azodicarboxylate

    Nguyen, Duy; Casillas, Sarah; Vang, Hnubci; Garcia, Anthony; Mizuno, Hikaru; Riffe, Erika J.; Saykally, Richard J.; Nguyen, Son C. (The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2021-03-18) [Article]
    “On-water” catalysis, the unusual activity of water molecules at the organic solvent–water interface, has been demonstrated in many organic reactions. However, the catalytic mechanism has remained unclear, largely because of the irreproducibility of the organic–water interface under the common stirring condition. Here, the interfacial area was controlled by employing adsorbed water on mesoporous silica nanoparticles as the catalyst. Reliable kinetics of the cycloaddition reaction of quadricyclane and diethyl azodicarboxylate (DEAD) at the toluene–water interface within the nanoparticle pores were measured. Data reveal an Eley–Rideal mechanism, wherein DEAD adsorbs at the toluene–water interface via hydrogen bonds formed with interfacial water, which lower the activation energy of the cycloaddition reaction. The mechanistic insights gained and preparation of surface water in silica pores described herein may facilitate the future design of improved “on-water” catalysts.
  • Photosymbiosis in Late Triassic scleractinian corals from the Italian Dolomites

    Frankowiak, Katarzyna; Roniewicz, Ewa; Stolarski, Jarosław (PeerJ, PeerJ, 2021-03-16) [Article]
    During the Carnian, oligotrophic shallow-water regions of the western Tethys were occupied by small, coral-rich 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 fine-scale 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 coral-algal symbiosis that spread across various clades of Scleractinia preceded the reef bloom at the end of the Triassic.
  • A unified first-order hyperbolic model for nonlinear dynamic rupture processes in diffuse fracture zones

    Gabriel, Alice-Agnes; Li, D.; Chiocchetti, S.; Tavelli, M.; Peshkov, I.; Romenski, E.; Dumbser, M. (Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, The Royal Society, 2021-03-15) [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 multi-physics 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 elasto-plasticity, 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 mesh-aligned, allowing thus faults and cracks with complex topology and the use of adaptive Cartesian meshes (AMR). The model shares common features with phase-field 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 co-seismic generation of secondary off-fault shear cracks, tensile rock fracture in the Brazilian disc test, as well as a natural convection problem in molten rock-like material. This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.
  • Substrate-Independent Laser-Induced Graphene Electrodes for Microfluidic Electroanalytical Systems

    Griesche, Christian; Hoecherl, Kilian; Baeumner, Antje J. (ACS Applied Nano Materials, American Chemical Society (ACS), 2021-03-11) [Article]
    Laser-induced graphene’s (LIG) inherent graphene-like 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 pressure-driven transfer produces highly functional transfer-LIG (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 adhesive-tape-enabled microfluidic channels for the detection of p-aminophenol. tLIG outperformed LIG electrodes in their ability to be integrated into more advanced microfluidic channel systems made of an all-polymethyl 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

    Zhang, Ge; Koman, Volodymyr B.; Shikdar, Tafsia; Oliver, Ronald J.; Perez-Lodeiro, Natalia; Strano, Michael S. (Small, Wiley, 2021-03-06) [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 Margin-Wide Rupture Behaviors along the Cascadia Megathrust with 3-D Dynamic Rupture Simulations

    Ramos, Marlon; Huang, Yihe; Ulrich, Thomas; Li, D.; Gabriel, Alice-Agnes; Thomas, Amanda (California Digital Library (CDL), 2021-03-05) [Preprint]
  • A unified first order hyperbolic model for nonlinear dynamic rupture processes in diffuse fracture zones

    Gabriel, Alice-Agnes; Li, Duo; Chiocchetti, Simone; Tavelli, Maurizio; Peshkov, Ilya; Romenski, Evgeniy; Dumbser, Michael (Copernicus GmbH, 2021-03-04) [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 multi-physics 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 elasto-plasticity, 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 mesh-aligned, allowing thus faults and cracks with complex topology and the use of adaptive Cartesian meshes (AMR). The model shares common features with phase-field 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 co-seismic generation of secondary off-fault shear cracks, tensile rock fracture in the Brazilian disc test, as well as a natural convection problem in molten rock-like material.
  • Designing optimal experiments: an application to proton Compton scattering

    Melendez, J. A.; Furnstahl, R. J.; Grießhammer, H. W.; McGovern, J. A.; Phillips, D. R.; Pratola, M. T. (The European Physical Journal A, Springer Nature, 2021-02-27) [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 physics-based 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 one-sided Lipschitz condition in the follow-the-leader approximation of scalar conservation laws

    Francesco, Marco Di; Stivaletta, Graziano (arXiv, 2021-02-26) [Preprint]
    We consider the follow-the-leader 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 one-sided 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 Oleinik-Hoff one-sided 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 many-particle limit, which was never proven before. Second, we prove that in case $f(\rho)=\rho(A-\rho^\gamma)$ the one-sided Lipschitz condition can be improved to a discrete version of the classical (and sharp) Oleinik-Hoff condition. In order to make the paper self-contained, 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 

    Yuan, Ning; Gudmundsson, Arnar; Gustafson, Karl P. J.; Oschmann, Michael; Tai, Cheuk-Wai; Persson, Ingmar; Zou, Xiaodong; Verho, Oscar; Bajnóczi, Éva G.; Bäckvall, Jan-E. (ACS Catalysis, American Chemical Society (ACS), 2021-02-22) [Article]
    A well-studied 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 X-ray 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 triethylamine-promoted 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 COVID-19 spatial-temporal spreading in London

    Zheng, J.; Wu, X.; Fang, F.; Li, J.; Wang, Z.; Xiao, H.; Zhu, J.; Pain, C. C.; Linden, P. F.; Xiang, B. (arXiv, 2021-02-19) [Preprint]
    Recent study reported that an aerosolised virus (COVID-19) 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 COVID-19 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 COVID-19. 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.

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