Recent Submissions

  • Linked 3D modeling of megathrust earthquake-tsunami events: from subduction to tsunami run up

    Madden, Elizabeth; Bader, M; Behrens, J; van Dinther, Y; Gabriel, Alice-Agnes; Rannabauer, L; Ulrich, T; Uphoff, C; Vater, S; van Zelst, I (Geophysical Journal International, Oxford University Press (OUP), 2020-10-08) [Article]
    Summary How does megathrust earthquake rupture govern tsunami behavior? Recent modeling advances permit evaluation of the influence of 3D earthquake dynamics on tsunami genesis, propagation, and coastal inundation. Here, we present and explore a virtual laboratory in which the tsunami source arises from 3D coseismic seafloor displacements generated by a dynamic earthquake rupture model. This is achieved by linking open-source earthquake and tsunami computational models that follow discontinuous Galerkin schemes and are facilitated by highly optimized parallel algorithms and software. We present three scenarios demonstrating the flexibility and capabilities of linked modeling. In the first two scenarios, we use a dynamic earthquake source including time-dependent spontaneous failure along a 3D planar fault surrounded by homogeneous rock and depth-dependent, near-lithostatic stresses. We investigate how slip to the trench influences tsunami behavior by simulating one blind and one surface-breaching rupture. The blind rupture scenario exhibits distinct earthquake characteristics (lower slip, shorter rupture duration, lower stress drop, lower rupture speed), but the tsunami is similar to that from the surface-breaching rupture in run-up and length of impacted coastline. The higher tsunami-generating efficiency of the blind rupture may explain how there are differences in earthquake characteristics between the scenarios, but similarities in tsunami inundation patterns. However, the lower seafloor displacements in the blind rupture result in a smaller displaced volume of water leading to a narrower inundation corridor inland from the coast and a 15 % smaller inundation area overall. In the third scenario, the 3D earthquake model is initialized using a seismo-thermo-mechanical geodynamic model simulating both subduction dynamics and seismic cycles. This ensures that the curved fault geometry, heterogeneous stresses and strength, and material structure are consistent with each other and with millions of years of modeled deformation in the subduction channel. These conditions lead to a realistic rupture in terms of velocity and stress drop that is blind, but efficiently generates a tsunami. In all scenarios, comparison with the tsunamis sourced by the time-dependent seafloor displacements, using only the time-independent displacements alters tsunami temporal behavior, resulting in later tsunami arrival at the coast, but faster coastal inundation. In the scenarios with the surface-breaching and subduction-initialized earthquakes, using the time-independent displacements also over-predicts run-up. In the future, the here presented scenarios may be useful for comparison of alternative dynamic earthquake-tsunami modeling approaches or linking choices, and can be readily developed into more complex applications to study how earthquake source dynamics influence tsunami genesis, propagation and inundation.
  • Numerical Investigation of Traffic State Reconstruction and Control Using Connected Automated Vehicles

    Cicic, Mladen; Barreau, Matthieu; Johansson, Karl Henrik (arXiv, 2020-10-06) [Preprint]
    In this paper we present a numerical study on control and observation of traffic flow using Lagrangian measurements and actuators. We investigate the effect of some basic control and observation schemes using probe and actuated vehicles within the flow. The aim is to show the effect of the state reconstruction on the efficiency of the control, compared to the case using full information about the traffic. The effectiveness of the proposed state reconstruction and control algorithms is demonstrated in simulations. They show that control using the reconstructed state approaches the full-information control when the gap between the connected vehicles is not too large, reducing the delay by more than $60\%$ when the gap between the sensor vehicles is $1.25$~km on average, compared to a delay reduction of almost $80\%$ in the full-information control case. %It shows that the reconstruction is well achieved if the distance between two connected and autonomous vehicles is not too large (more than 1 vehicle per kilometer). %We also show that it is possible to further improve the control performance by employing a simple adaptive probe vehicle selection scheme. Moreover, we propose a simple scheme for selecting which vehicles to use as sensors, in order to reduce the communication burden. Numerical simulations demonstrate that %It also demonstrates that it is possible to reduce the communication burden using a triggering mechanism with with this triggering mechanism, the delay is reduced by around $65\%$, compared to a reduction of $72\%$ if all connected vehicles are communicating at all times.
  • Eulerian and Lagrangian Comparison of Primary and Secondary Wind Jets in the Tokar Gap Region

    Pratt, Larry; Albright, E. Jason; Rypina, Irina; Jiang, Houshuo (MDPI AG, 2020-10-01) [Preprint]
    The Lagrangian and Eulerian structure and dynamics of a strong wind event in the Tokar Gap region are described using a WRF model hindcast for 2008. Winds in the Tokar Gap reach 25 m s-1 and remain coherent as a jet far out over the Red Sea, whereas equally strong wind jets occurring in neighboring gaps are attenuated abruptly by a jump-like hydraulic transition that occur just offshore of the Sudan coast. The transition is made possible by the supercritical nature of the jets, which are fed by air that spills down from passes at relatively high elevation. By contrast, the spilling flow in the ravine-like Tokar Gap does not become substantially supercritical and therefore does not undergo a jump, and also carries more total horizontal momentum. The Tokar Wind Jet carries some air parcels across the Red Sea and into Saudi Arabia, whereas air parcel trajectories in the neighboring jets ascend as they cross through the jumps, then veer sharply to the southeast and do not cross the Red Sea. The mountain parameter Nh/U is estimated to lie in the rage 1.0-4.0 for the general region, a result roughly consistent with a primary gap jet having a long extension, and supercritical jets spilling down from higher elevation passes. The strong event is marked by the formation of a cyclonic cell near the upstream entrance to the Tokar Gap, a feature absent from the more moderate events that occur throughout the summer. The cell contains descending air parcels that are fed into the primary and secondary jets. An analysis of the Bernoulli function along air parcel trajectories reveals an approximate balance between the loss of potential energy and gain of internal energy and pressure, with surprisingly little contribution from kinetic energy, along the path of the descending flow. All jets attain the critical wind speed nominally required to loft dust into the atmosphere, though only the Tokar Gap has a broad, delta region with plentiful deposits of silt.
  • Oriented hydrocracking of naphthalene into high-value light aromatics over difunctional catalysts: the effect of hydrogen spillover and utilization of hydro-reaction characteristics for different active metals

    Cao, Zhengkai; Zhang, Xia; Guo, Rong; Ding, Sijia; Mei, Jinlin; Wang, Xilong; Zheng, Peng; Fan, Jiyuan; Xu, Chunming; Duan, Aijun (ACS Catalysis, American Chemical Society (ACS), 2020-09-29) [Article]
    Serial difunctional catalysts supported on γ-Al2O3 and HY zeolite were synthesized and characterized systemically. The characterization results disclosed that hydrogen spillover existed in the NiMo and CoMo catalysts, and decreasing Ni/Mo and Co/Mo ratios could reduce hydrogen spillover. Meanwhile, the naphthalene hydrocracking behaviors over different catalysts were investigated and compared. The higher yield of cyclane for CoMo/AY catalysts demonstrated that hydrogen spillover could deeply hydrogenate naphthalene into cyclane. The combined catalysts of Ni/Y@CoMo/A, Ni/Y@NiMo/A and Ni/Y@Mo/A showed relatively lower conversions of naphthalene but higher yields of valued <C10 aromatics. The combined catalyst Ni/Y@CoMo/A presented the highest yield of light aromatics due to the appropriate reduction of hydrogen spillover and rational utilization of hydro-reaction characteristics for different active metals. Moreover, the stability of CoMo catalyst was higher than NiMo catalyst. The catalysts containing Co and Mo active metals presented low content of carbon deposition.
  • Microkinetic Assessment of Electrocatalytic Oxygen Evolution Reaction over Iridium Oxide in Unbuffered Conditions

    Nishimoto, Takeshi; Shinagawa, Tatsuya; Naito, Takahiro; Takanabe, Kazuhiro (Journal of Catalysis, Elsevier BV, 2020-09-17) [Article]
    Water electrolysis driven by electrical power generated from renewable energy sources will play a pivotal role in future sustainable societies, which requires adaptation of various reaction conditions as well as electrolyte identities. Regardless, the anodic half-reaction of the oxygen evolution reaction (OER) is considered a kinetic bottleneck. This study provides quantitative description of the OER kinetics based on rigorous microkinetic analyses including Tafel analysis, isotope effects and temperature dependence using an IrOx electrocatalyst in unbuffered solution at varying pH levels. The diffusional constraints of H+/OH− determine three distinctive kinetic regimes in the pH-potential-current relationships: below pH 5, between pH 5 and 10, and above pH 10 at appreciable current densities on the order of 1 mA cm−2. When shifting from alkaline to acidic solution, the complete consumption of local OH− near the electrode surface switches the OER proceeding as the oxidation of OH− to that of the water molecule at pH ∼11 irrespective of the electrode identity. At pH 5-10, the diffusional constraints of H+ generated via oxidation reaction yield an environment with pH ∼4 near the electrode surface even prior to the OER, resulting in a bulk pH-independent region for the OER performance. Under this unbuffered near-neutral-pH condition, the isotope effect was diminished for the OER catalysis, which is consistent with the rate-determining step (rds) being the sole electron-transfer step via the formation of O-O bonds, decoupled from proton transfer. This reaction mechanism is distinct from that under more acidic conditions (pH < 4), although the water molecule is the same reactant. Under acidic conditions, noticeable isotope effects were observable, which is consistent with the formation of O-O bonds being the rds on uncoordinated bare Ir sites as the most abundant surface species. This study provides a quantitative description of the reactant- and mechanistic-switching that points to concurrent optimization of both electrode materials and electrolyte for improved OER performance at near-neutral pH levels.
  • Thermal Properties of Copper Particles-filled Polypropylene Composites

    Alghanmi, Ashraf; Thomas, Selvin P.; Gopanna, Aravinthan; Alrefae, Majed A. (IEEE, 2020-09-10) [Conference Paper]
    Current trends of decreasing the size of electronic devices accompanied by raising their energy density imply the search for alternative thermal management materials. Reinforcing polymers with thermally conductive metallic materials is considered as one of the feasible solutions to overcome the thermal management issues for modern electronic devices. In this work, we report the thermal properties of composite materials made of polypropylene (PP) with copper (Cu) particles in different weight percentages; 0, 3, 6 and 10%. The effective thermal conductivity of the Cu/PP composites is measured by the Armfield Linear Heat Conduction experimental setup. Results show that the effective thermal conductivity of the polymer matrix increases slightly with the addition of Cu particles. This effect can be attributed to the higher thermal conductivity of the metal particles compared to the polymer as well as the effective reinforcement in the polymer matrix. In addition, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques were utilized to characterize the Cu/PP composites. The addition of 10 weight% of Cu particles improves the temperature stability of the composites by approximately 12%. However, the melting point and the crystallization temperatures remain almost unchanged, with values of approximately 161°C and 114°C, respectively. These preliminary experiments are intended to deliberate on the influences of metal particles in polymers to enhance their thermal properties without affecting their durability and mechanical properties. Such composites will be essential components in electronic packaging to spread thermal energy efficiently.
  • Surface morphology and inner fractal cutoff scale of spherical turbulent premixed flames in decaying isotropic turbulence

    Kulkarni, Tejas; Bisetti, Fabrizio (Proceedings of the Combustion Institute, Elsevier BV, 2020-09-03) [Article]
    The surface of turbulent premixed flames is fractal within a finite range of scales and the fractal dimension and inner cutoff scale are key components of fractal turbulent combustion closures. In such closures, the estimate for the surface area is sensitive to the value of the inner fractal cutoff scale, whose modeling remains unclear and for which both experimental and numerical contradictory evidence exists. In this work, we analyze data from six direct numerical simulations of spherically expanding turbulent premixed flames at varying Reynolds and Karlovitz numbers. The flames propagate in decaying isotropic turbulence and fall in the flamelet regime. Past an initial transient, we find that the fractal dimension reaches an asymptotic value between 2.3 and 2.4 in good agreement with previous results at similar conditions. A minor dependence of the fractal dimension on the Reynolds and Karlovitz numbers is observed and explained by the relatively low values of the Reynolds number and narrow inertial and fractal ranges. The inner fractal cutoff scale Δ* is found to scale as where l is the integral scale of turbulence and Reλ is the Reynolds number based on the Taylor micro-scale computed in the turbulence on the reactants’ side. The scaling is robust and insensitive to the Karlovitz number over the range of values considered in this study. An important implication is that the ratio Δ*/η grows with Reynolds number (η is the Kolmogorov scale), albeit at a rather slow rate that may explain the widespread observation that 4 ≤ Δ*/η ≤ 10. This suggests that Δ*, although smaller than λ, is not a dissipative length scale for the flame surface and scaled solely by η. Finally, a dissipative threshold scale that remains constant once normalized by η is identified.
  • Oxidative desulfurization of heavy gas oil over Ti-TUD-1 supported Keggin-type molybdenum heteropolyacid

    Vedachalam, Sundaramurthy; Boahene, Philip E.; Dalai, Ajay K. (Energy & Fuels, American Chemical Society (ACS), 2020-08-20) [Article]
    Catalytic oxidative desulfurization (ODS) is emerging as a potential alternative to deep hydroprocessing due to its milder operating conditions and no hydrogen requirements. In this study, ODS catalysts based on mesoporous TUD-1 support were developed to overcome the diffusion limitation of zeolite-based catalysts in oxidizing large-size organosulfur compounds present in real petroleum feedstocks. Different mesoporous oxidation catalysts were formed by substituting Ti in the TUD-1 framework and impregnating Keggin molybdenum heteropoly acid (HPA) on TUD-1 support. The mesoporosity of TUD-1, and the presence of Ti (IV) and Mo Keggin units in the prepared catalysts were confirmed from the characterization results of XRD, XPS, XANES, and BET-N2. The ODS performance of catalysts was studied using a mild hydrotreated bitumen derived heavy gas oil feedstock. The HPA dispersed Ti-TUD-1 catalyst was found to be most active for desulfurizing the heavy gas oil feedstock due to a strong synergy effect of Ti and Mo Keggin ions on catalyzing oxygen transfer from an oxidant to a substrate. Oxidants such as hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, and molecular oxygen were screened in this study. The first two oxidants were better than others and equally efficient. The HPA /Ti-TUD-1 catalyst was found to be suitable for oxidative desulfurization and oxidative denitrogenation (ODN) both in the batch stirred tank reactor and continuous fixed-bed reactor systems.
  • Identification of Néel vector orientation in antiferromagnetic domains switched by currents in NiO/Pt thin films

    Schmitt, Christin; Baldrati, Lorenzo; Sanchez-Tejerina, Luis; Schreiber, Felix; Ross, Andrew; Filianina, Mariia; Ding, Shilei; Fuhrmann, Felix; Ramos, Rafael; Maccherozzi, Francesco; Backes, Dirk; Saitoh, Eiji; Finocchio, Giovanni; Kläui, Mathias (arXiv, 2020-08-19) [Preprint]
    Understanding the electrical manipulation of antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequency. Focusing on collinear insulating antiferromagnetic NiO/Pt thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the N\'eel vector direction changes. We demonstrate electrical switching between different T-domains by current pulses, finding that the N\'eel vector orientation in these domains is along $[\pm1\ \pm1\ 3.8]$, different compared to the bulk $$ directions. The final state of the N\'eel vector $\textbf{n}$ switching after current pulses $\textbf{j}$ along the $[1\ \pm1\ 0]$ directions is $\textbf{n}\parallel \textbf{j}$. By comparing the observed N\'eel vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as $b_{0}+2b_{1}=3*10^7 J\ m^{-3}$ . This information is key for the understanding of current-induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices.
  • Deep Geometric Functional Maps: Robust Feature Learning for Shape Correspondence

    Donati, Nicolas; Sharma, Abhishek; Ovsjanikov, Maks (IEEE, 2020-08-05) [Conference Paper]
    We present a novel learning-based approach for computing correspondences between non-rigid 3D shapes. Unlike previous methods that either require extensive training data or operate on handcrafted input descriptors and thus generalize poorly across diverse datasets, our approach is both accurate and robust to changes in shape structure. Key to our method is a feature-extraction network that learns directly from raw shape geometry, combined with a novel regularized map extraction layer and loss, based on the functional map representation. We demonstrate through extensive experiments in challenging shape matching scenarios that our method can learn from less training data than existing supervised approaches and generalizes significantly better than current descriptor-based learning methods. Our source code is available at:
  • Printable 3D Carbon Nanofiber Networks with Embedded Metal Nanocatalysts

    Simsek, Marcel; Hoecherl, Kilian; Schlosser, Marc; Baeumner, Antje J; Wongkaew, Nongnoot (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2020-08-04) [Article]
    Carbon nanofiber (CNF)-nanocatalyst hybrids hold great promise in fields such as energy storage, synthetic chemistry and sensors. Current strategies to generate such hybrids are laborious and utterly incompatible with miniaturization and large-scale production. Instead, this work demonstrates that Ni-nanoparticles embedded in 3D CNFs of any shape and design can be easily prepared using electrospinning followed by laser carbonization under ambient conditions. Specifically, a solution of Ni(acac)2/Polyimide is electrospun and subsequently a design is printed via CO2 laser (Ni-LCNFs). This creates uniformly distributed small Ni nanoparticles (~ 8nm) very tightly adhered to the CNF network. Morphological and performance characteristics can be directly influenced by metal content and lasing power and hence adapted towards desired performance. Here, Ni-LCNFs are optimized for non-enzymatic electrochemical sensing of glucose with a great sensitivity of 2092 µA mM-1 cm-2 and a detection limit down to 0.3 µM. Its selectivity for glucose versus interfering species (ascorbic and uric acid) is essentially governed by the Ni content. Most importantly, this strategy can be adapted to a whole range of metal precursors and hence provide opportunities for such 3D CNFs nanocatalyst hybrids in point-of-care applications where high performance but also sustainable and low-cost fabrication are of utmost importance.
  • Stress, rigidity and sediment strength control megathrust earthquake and tsunami dynamics

    Ulrich, Thomas; Gabriel, Alice-Agnes; Madden, Elizabeth (Center for Open Science, 2020-07-31) [Preprint]
    Megathrust faults host the largest earthquakes on Earth which can trigger cascading hazards such as devastating tsunamis.Determining characteristics that control subduction zone earthquake and tsunami dynamics is critical to mitigate megathrust hazards, but is impeded by structural complexity, large spatio-temporal scales, and scarce or asymmetric instrumental coverage.Here we show that tsunamigenesis and earthquake dynamics are controlled by along-arc variability in regional tectonic stresses together with depth-dependent variations in rigidity and yield strength of near-fault sediments. We aim to identify dominant regional factors controlling megathrust hazards. To this end, we demonstrate how to unify and verify the required initial conditions for geometrically complex, multi-physics earthquake-tsunami modeling from interdisciplinary geophysical observations. We present large-scale computational models of the 2004 Sumatra-Andaman earthquake and Indian Ocean tsunami that reconcile near- and far-field seismic, geodetic, geological, and tsunami observations and reveal tsunamigenic trade-offs between slip to the trench, splay faulting, and bulk yielding of the accretionary wedge.Our computational capabilities render possible the incorporation of present and emerging high-resolution observations into dynamic-rupture-tsunami models. Our findings highlight the importance of regional-scale structural heterogeneity to decipher megathrust hazards.
  • Dynamic Topological Data Analysis for Functional Brain Signals

    Songdechakraiwut, Tananun; Chung, Moo K. (IEEE, 2020-07-31) [Conference Paper]
    We propose a novel dynamic topological data analysis (TDA) framework that builds persistent homology over a time series of 3D functional brain images. The proposed method encodes the time series as a time-ordered sequence of Vietoris-Rips complexes and their corresponding barcodes in studying dynamically changing topological patterns. The method is applied to the resting-state functional magnetic resonance imaging (fMRI) of the human brain. We demonstrate that the dynamic-TDA can capture the topological patterns that are consistently observed across different time points in the resting-state fMRI.
  • Evolution and scaling of the peak flame surface density in spherical turbulent premixed flames subjected to decaying isotropic turbulence

    Kulkarni, Tejas; Bisetti, Fabrizio (Proceedings of the Combustion Institute, Elsevier BV, 2020-07-25) [Article]
    The peak flame surface density within the turbulent flame brush is central to turbulent premixed combustion models in the flamelet regime. This work investigates the evolution of the peak surface density in spherically expanding turbulent premixed flames with the help of direct numerical simulations at various values of the Reynolds and Karlovitz number. The flames propagate in decaying isotropic turbulence inside a closed vessel. The effects of turbulent transport, transport due to mean velocity gradient, and flame stretch on the peak surface density are identified and characterized with an analysis based on the transport equation for the flame surface density function. The three mechanisms are governed by distinct flow time scales; turbulent transport by the eddy turnover time, mean transport by a time scale related to the pressure rise in the closed chamber, and flame stretch by the Kolmogorov time scale. Appropriate scaling of the terms is proposed and shown to collapse the data despite variations in the dimensionless groups. Overall, the transport terms lead to a reduction in the peak value of the surface density, while flame stretch has the opposite effect. In the present configuration, a small imbalance between the two leads to an exponential decay of the peak surface density in time. The dimensionless decay rate is found to be consistent with the evolution of the wrinkling scale as defined in the Bray-Moss-Libby model.
  • All-optical density downramp injection in electron-driven plasma wakefield accelerators

    Ullmann, D.; Scherkl, P.; Knetsch, A.; Heinemann, T.; Sutherland, A.; Habib, A. F.; Karger, O. S.; Beaton, A.; Manahan, G. G.; Deng, A.; Andonian, G.; Litos, M. D.; OShea, B. D.; Bruhwiler, D. L.; Cary, J. R.; Hogan, M. J.; Yakimenko, V.; Rosenzweig, J. B.; Hidding, B. (arXiv, 2020-07-24) [Preprint]
    Injection of well-defined, high-quality electron populations into plasma waves is a key challenge of plasma wakefield accelerators. Here, we report on the first experimental demonstration of plasma density downramp injection in an electron-driven plasma wakefield accelerator, which can be controlled and tuned in all-optical fashion by mJ-level laser pulses. The laser pulse is directed across the path of the plasma wave before its arrival, where it generates a local plasma density spike in addition to the background plasma by tunnelling ionization of a high ionization threshold gas component. This density spike distorts the plasma wave during the density downramp, causing plasma electrons to be injected into the plasma wave. By tuning the laser pulse energy and shape, highly flexible plasma density spike profiles can be designed, enabling dark current free, versatile production of high-quality electron beams. This in turn permits creation of unique injected beam configurations such as counter-oscillating twin beamlets.
  • Grayscale stencil lithography for patterning multispectral color filters

    Li, Xinhao; Tan, Zheng Jie; Fang, Nicholas X. (Optica, The Optical Society, 2020-07-22) [Article]
    Flat optics for spatially resolved amplitude and phase modulation usually rely on 2D patterning of layered structures with spatial thickness variation. For example, Fabry–Perot-type multilayer structures have been applied widely as spectral filter arrays. However, it is challenging to efficiently fabricate large-scale multilayer structures with spatially variable thicknesses. Conventional photo/eBeam-lithography-based approaches suffer from either low-efficiency and high-cost iterative processes or limitations on materials for spectral tunability. In this work, an efficient and cost-effective grayscale stencil lithography method is demonstrated to achieve material deposition with spatial thickness variation. The design of stencil shadow masks and deposition strategy offers arbitrarily 2D thickness patterning with low surface roughness. The method is applied to fabricate multispectral reflective filter arrays based on lossy Fabry–Perot-type optical stacks with dielectric layers of variable thickness, which generate a wide color spectrum with high customizability. Grayscale stencil lithography offers a feasible and efficient solution to overcome the thickness-step and material limitations in fabricating spatially thickness-varying structures. The principles of this method can find applications in micro-fabrication for optical sensing, imaging, and computing.
  • Dynamic Traffic Reconstruction using Probe Vehicles

    Barreau, Matthieu; Selivanov, Anton; Johansson, Karl Henrik (arXiv, 2020-07-20) [Preprint]
    This article deals with the observation problem in traffic flow theory. The model used is the semilinear viscous Burgers equation. Instead of using the traditional fixed sensors to estimate the state of the traffic at given points, the measurements here are obtained from Probe Vehicles (PVs). We propose then a moving dynamic boundary observer whose boundaries are defined by the trajectories of the PVs. The main result of this article is the exponential convergence of the observation error, and, in some cases, its finite-time convergence. Finally, numerical simulations show that it is possible to observe the traffic in the congested, free-flow, and mixed regimes provided that the number of PVs is large enough.
  • Evolving Graphical Planner: Contextual Global Planning for Vision-and-Language Navigation

    Deng, Zhiwei; Narasimhan, Karthik; Russakovsky, Olga (arXiv, 2020-07-11) [Preprint]
    The ability to perform effective planning is crucial for building an instruction-following agent. When navigating through a new environment, an agent is challenged with (1) connecting the natural language instructions with its progressively growing knowledge of the world; and (2) performing long-range planning and decision making in the form of effective exploration and error correction. Current methods are still limited on both fronts despite extensive efforts. In this paper, we introduce the Evolving Graphical Planner (EGP), a model that performs global planning for navigation based on raw sensory input. The model dynamically constructs a graphical representation, generalizes the action space to allow for more flexible decision making, and performs efficient planning on a proxy graph representation. We evaluate our model on a challenging Vision-and-Language Navigation (VLN) task with photorealistic images and achieve superior performance compared to previous navigation architectures. For instance, we achieve a 53% success rate on the test split of the Room-to-Room navigation task through pure imitation learning, outperforming previous navigation architectures by up to 5%.
  • 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 (arXiv, 2020-07-02) [Preprint]
    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.
  • Multi-Level Nanoimprint Lithography for Large-Area Thin Film Transistor Backplane Manufacturing

    Dogan, Tamer; de Riet, Joris; Bel, Thijs; Verbeek, Roy; Katsouras, Ilias; Meulenkamp, Eric; Gelinck, Gerwin; Jisk Kronemeijer, Auke (Journal of Photopolymer Science and Technology, Technical Association of Photopolymers, Japan, 2020-06-30) [Article]
    Thin film transistors (TFTs) are the basis for current AMOLED display arrays. For next- generation displays, higher resolution and cost-effective manufacturing of panels is adamant. The current benchmark patterning method in the display industry is photolithography. Here, we propose the use of a hybrid approach of nanoimprint lithography and conventional FPD processing for the realization of high-resolution display backplanes. We demonstrate the realization of sub-micron amorphous oxide semiconductor TFTs with multi-level nanoimprint lithography in order to decrease the number of patterning steps in display manufacturing. Top-gate self-aligned a-IGZO TFTs are realized with performance comparable to benchmark photolithography-based TFTs.

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