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Effect of Gd-doped ceria infiltration into Ni-YSZ on reversible solid oxide cell operation
Gadolinium doped ceria (GDC) infiltration into Ni-(Y 2 O 3 ) 0•08 (ZrO 2 ) 0.92 (Ni-YSZ) fuel electrodes has been shown to significantly improve solid oxide electrolysis cell performance and stability. However, the effects of GDC infiltration on cells operated reversibly between fuel cell and electrolysis modes have not been reported previously. Here we present reversible solid oxide cell life test results for different GDC infiltration loadings into Ni-YSZ electrodes in two types of fuel-electrode-supported solid oxide cells. Electrochemical impedance spectroscopy reveals that GDC infiltrant lowers the initial cell area specific resistance (ASR) and limits the degradation – for example, the GDC-infiltrated electrode ASR increased by 0.1 Ω cm 2 over 1000 h of reversible operation at ±0.5 A cm –2 and 800 °C, compared to 0.19 Ω cm 2 for non-infiltrated cells. Cell voltage degradation rates were reduced by infiltration during operation at a current density of ±0.5 A cm –2 at 800 °C, and during at 700 °C at ±0.75 A cm –2 . Furthermore, scanning electron microscopy observations show that the infiltrated GDC nanoparticles mitigate Ni particle coarsening in the Ni-YSZ electrode, possibly explaining the enhanced cell stability.
Mitigation of turbophoresis in particle-laden turbulent channel flows by using incident electric fields
It is known that the dynamics of particles dispersed in turbulent flows can be significantly altered by electric charges and external electric fields. The next step therefore involves the investigation of whether these electric interactions can be exploited in engineering applications to control processes involving the transport of particles in turbulence. In this study, direct numerical simulations of incompressible turbulent channel flows laden with a positively isocharged suspension of monodisperse small inertial particles are employed to investigate the effect of electric charges carried by the particles on their dispersion, and to illustrate the intentional abatement of turbophoretic effects using incident electric fields. An Eulerian-Lagrangian formulation is employed along with a fast multipole method for the electric potential conveniently corrected with wall boundary conditions. Finally, operating conditions are identified in terms of characteristic dimensionless parameters where an AC electric field applied across the channel walls decreases the time-averaged concentration of particles near the walls by up to two orders of magnitude.
Investigation of fast timing capabilities of silicon sensors for the CMS high granularity calorimeter at HL-LHC
The High Granularity Calorimeter (HGCAL) is the technology choice of the CMS collaboration for the endcap calorimetry upgrade planned to cope with the harsh radiation and unprecedented in-time event pileup projected at the High Luminosity-LHC era. In this context, profiting from fast-timing information with a resolution of a few tens of picoseconds embedded in the calorimeter would represent a unique capability for resolving information from individual collisions at the HL-LHC. This will enhance the reconstruction and physics capabilities of the CMS detector in terms of pileup mitigation and particle identification. The HGCAL is realized as a sampling calorimeter that uses silicon sensors as its active elements. Prototype sensors were tested with high-energy electron beams at the CERN SPS, and at the FNAL FTBF test beam facilities. We present the motivation for this studies including the concept and use of fast-timing in the HGCAL, and the measured intrinsic timing capabilities of silicon sensors for electromagnetic showers and minimum-ionizing particles.
Detectors and diagnostics for multiprobe radiography using high-energy short-pulse lasers
Multiprobe radiography requires the following diagnostic capabilities at minimum: radiographic source diagnostics, spectroscopy, imaging, and tomography diagnostics. Depending on the repetition rate of the radiation sources, the diagnostics may be a single-shot diagnostic, such as photographic (radiochromic and X-ray films for high energy photons) films, or a multiple-shot diagnostic for repetitive source operations, such as a high-speed framing camera. Due to the drastically different detector physics of electrons, photons at different energies (keV to 10s of MeV in the radiography context), heavy ions such as protons, alphas, and neutrons, see, for example, Ref. [1, 2] for an overview, different types or configurations of detectors and constructions may be required for multiprobe radiography applications. Some of the common detector metricsinclude, independent of the particle/photon species, sensitivities or efficiency, energy resolution, spatial or temporal resolutions and others. Some unique detection scenarios arise in a multiprobe radiography setting, for example, crosstalk mitigation and particle identification (ID) when X-ray and higher energy photons, relativistic electrons, neutrons, other hadrons, and heavy particles coexist at the detector location.
An electrostatic Particle-In-Cell code on multi-block structured meshes
We present an electrostatic Particle-In-Cell (PIC) code on multi-block, locally structured, curvilinear meshes called Curvilinear PIC (CPIC). Multi-block meshes are essential to capture complex geometries accurately and with good mesh quality, something that would not be possible with single-block structured meshes that are often used in PIC and for which CPIC was initially developed. In spite of the structured nature of the individual blocks, multi-block meshes resemble unstructured meshes in a global sense and introduce several new challenges, such as the presence of discontinuities in the mesh properties and coordinate orientation changes across adjacent blocks, and polyjunction points where an arbitrary number of blocks meet. In CPIC, these challenges have been met by an approach that features: (1) a curvilinear formulation of the PIC method: each mesh block is mapped from the physical space, where the mesh is curvilinear and arbitrarily distorted, to the logical space, where the mesh is uniform and Cartesian on the unit cube; (2) a mimetic discretization of Poisson's equation suitable for multi-block meshes; and (3) a hybrid (logical-space position/physical-space velocity), asynchronous particle mover that mitigates the performance degradation created by the necessity to track particles as they move across blocks. The numerical accuracy of CPIC was verified using two standard plasma–material interaction tests, which demonstrate good agreement with the corresponding analytic solutions. And compared to PIC codes on unstructured meshes, which have also been used for their flexibility in handling complex geometries but whose performance suffers from issues associated with data locality and indirect data access patterns, PIC codes on multi-block structured meshes may offer the best compromise for capturing complex geometries while also maintaining solution accuracy and computational efficiency.
Synergistic effect of polyaniline on stabilizing Pt nanoparticles in PEMFCs†
The stability of Pt nanoparticles on a carbon support is crucial for the lifespan of polymer electrolyte membrane fuel cells as well as other electrocatalysis systems such as electrolyzers. Here we took the approach of utilizing the covalently grafted polyaniline on carbon to stabilize Pt nanoparticles by simultaneously alleviating the particle migration and mitigating the Ostwald ripening, which are two major mechanisms for loss of the catalyst stability. A comprehensive investigation of the stability and performance of Pt catalyst nanoparticles on these supports reveals that the polyaniline can shift the Pt L edge binding energy and the Pt 4f peak energy, leading to the increased redox potential of the Pt nanoparticles and making them more resistant to oxidation. Interestingly, the highest polyaniline density (50 wt%) does not show the best catalyst stability, rather, the second (33 wt%) demonstrates the best catalyst stability among these catalysts. Combining the XPS, XAS and fuel cell stability studies, we concluded that the locations of the Pt nanoparticles over the polyaniline layer on the carbon surface depend on the surface density of the polyaniline over the carbon surface. The Pt nanoparticles in the 50 wt% polyaniline catalyst are wrapped by the polyaniline polymer but do not sit directly on the carbon surface, while Pt nanoparticles in the 33 wt% polyaniline catalyst sit on the carbon surface and are densely surrounded by the polyaniline polymer. The results show that the mass activity loss is 12.5% while the ECSA (electrochemically active surface area) loss is 37.1% after 30k cycles of accelerating stress test for the 33 wt% polyaniline catalyst, far exceeding the DOE 2020 target for MEA (i.e., mass activity loss < 50%, and ECSA loss < 40%). Overall, the polyaniline has a synergistic effect on mitigating the surface migration and slowing down the Ostwald ripening to stabilize the Pt nanoparticles in fuel cells. The novel strategy to stabilize Pt nanoparticles using polyaniline opens a new pathway in the development of highly stable catalysts: relying on the functionalization group on the carbon support, instead of just focusing on the catalyst itself.
Demonstration of Wide Area Radiological Decontamination and Mitigation Technologies for Building Structures and Vehicles - 16508
Researchers at the U.S. Environmental Protection Agency in collaboration with the Department of Homeland Security conducted the 'Wide-Area Urban Radiological Contaminant, Mitigation, and Clean-Up Technology Demonstration' in Columbus, Ohio on June 22-25, 2015. EPA's National Homeland Security Research Center (NHSRC) demonstrated five wide-area radiological decontamination technologies (including strippable coatings, gels, and chemical foam technologies) on an urban building. Decontamination technologies were applied to remove the contaminants from the building's surfaces by physical, chemical, or other methods, which in practice could reduce radiation exposure level. In addition, NHSRC teamed with the Department of Homeland Security (DHS) to demonstrate several radiological contaminant mitigation technologies including building and vehicle wash technologies, as well as several approaches to contain wash water and radioactive particles. 'Radiological contaminant mitigation' technologies are measures taken to reduce adverse impacts of radiological contamination on people and the environment, and facilitate such purposes as restoration of first responder services and critical infrastructure. Radiological contaminant mitigation technologies are designed for containing and removing radiological contamination on the surface in the first hours or days following a radiological event (early phase response). Such technologies include 'radiological particle containment', which is design to prevent the spread of particles which might result from vehicle or foot traffic. Radiological particle containment technologies are applicable for early phase response to contain the radionuclides and to reduce radiation dose to responders and the public. Mitigation also includes 'gross decontamination' technologies, which perform a type of decontamination that is conducted with the goal of reducing contamination levels. This reduction may not meet final cleanup levels, but may be useful to mitigate some public hazard or contain contamination. The purpose of the demonstrations was to educate potential end-users and stakeholders of this technology about a 'Toolbox of Options' for radiological decontamination, as well as radiological contaminant mitigation. Both demonstrations were conducted using a 75-year old brick building and the surrounding area (including parking lots) in Columbus, OH. No radioactive contaminants were applied during either demonstration, as the objective was to duplicate and implement realistic operational conditions for these technologies. Surrogate contaminants such as particle tracers were used in several demonstrations. The decontamination technologies were used in a scaled-up setting with application to the building. Contaminant mitigation technologies were demonstrated on the building as well as on vehicles. Example technology application techniques/accessories included an articulating boom lift, repelling boatswain chair, stand-alone surface material structures, high-volume foam applicators, fire truck foam applicator, a vehicle wash tent for vehicles, particle tracers to simulate radiological contaminants, and high- and low-technology liquid containment approaches. Results and stakeholder observations from the demonstration are now publically in a report entitled 'Technical Report for the Demonstration of Radiological Decontamination and Mitigation Technologies for Building Structures and Vehicles' available at http://www.epa.gov/hsresearch Example information that was obtained included decontamination rate, contaminant mitigation and containment capacity, user friendliness of each technology, the required utilities (electric, water, etc.) for each technology, skill of worker required, and the cost. The condition (color, texture, integrity, etc.) of each building material present on the structure along with all structural components such as gutters, windows, doors, etc. were carefully examined and documented. All demonstrations were open to individuals, organizations, and local, state, federal, tribal, and international governments who may be involved with implementing or planning radiological incident response. (authors)
New insights into the role of fly ash in mitigating alkali-silica reaction (ASR) in concrete
Alkali-silica reaction (ASR) mitigation mechanisms of fly ash in concrete are still being debated and remain an interesting research topic. This study provides new insights into the role of aluminum oxide (Al{sub 2}O{sub 3}) in fly ash particles on ASR mitigation. A comprehensive test program was conducted and included expansion measurements, dissolution model experiments of exposed and embedded borosilicate glass elements, analyses of pore and immersion solutions, quantification of Ca(OH){sub 2} content, and microstructural analyses. It was found that in addition to the traditionally accepted mitigation mechanisms such as alkali binding, diffusion control and reduction in available Ca(OH){sub 2}, dissolution control of reactive aggregates by aluminum discharged from fly ash particles also contributed to the ASR mitigation. Re-introducing alkalis to fly ash-incorporated concrete prisms which exhibited undeleterious expansion under a long-term ASR exposure triggered and significantly increased the subsequent expansion.
Particle damage sources for fused silica optics and their mitigation on high energy laser systems
High energy laser systems are ultimately limited by laser-induced damage to their critical components. This is especially true of damage to critical fused silica optics, which grows rapidly upon exposure to additional laser pulses. Much progress has been made in eliminating damage precursors in as-processed fused silica optics (the advanced mitigation process, AMP3), and very high damage resistance has been demonstrated in laboratory studies. However, the full potential of these improvements has not yet been realized in actual laser systems. In this work, we explore the importance of additional damage sources–in particular, particle contamination–for fused silica optics fielded in a high-performance laser environment, the National Ignition Facility (NIF) laser system. We demonstrate that the most dangerous sources of particle contamination in a system-level environment are laser-driven particle sources. In the specific case of the NIF laser, we have identified the two important particle sources which account for nearly all the damage observed on AMP3 optics during full laser operation and present mitigations for these particle sources. Finally, with the elimination of these laser-driven particle sources, we demonstrate essentially damage free operation of AMP3 fused silica for ten large optics (a total of 12,000 cm 2 of beam area) for shots from 8.6 J/cm 2 to 9.5 J/cm 2 of 351 nm light (3 ns Gaussian pulse shapes). Potentially many other pulsed high energy laser systems have similar particle sources, and given the insight provided by this study, their identification and elimination should be possible. The mitigations demonstrated here are currently being employed for all large UV silica optics on the National Ignition Facility
Prospect of Studying Nonperturbative QED with Beam-Beam Collisions
We demonstrate the experimental feasibility of probing the fully nonperturbative regime of quantum electrodynamics with a 100 GeV-class particle collider. By using tightly compressed and focused electron beams, beamstrahlung radiation losses can be mitigated, allowing the particles to experience extreme electromagnetic fields. Three-dimensional particle-in-cell simulations confirm the viability of this approach. The experimental forefront envisaged has the potential to establish a novel research field and to stimulate the development of a new theoretical methodology for this yet unexplored regime of strong-field quantum electrodynamics.
Modelling of Ablatant Deposition from Electromagnetically Driven Radiative Pellets for Disruption Mitigation Studies
The Electromagnetic Particle Injector (EPI) concept is advanced through the simulation of ablatant deposition into ITER H-mode discharges with calculations showing penetration past the H-mode pedestal for a range of injection velocities and granule sizes concurrent with the requirements of disruption mitigation. As discharge stored energy increases in future fusion devices such as ITER, control and handling of disruption events becomes a critical issue. An unmitigated disruption could lead to failure of the plasma facing components resulting in financially and politically costly repairs. Methods to facilitate the quench of an unstable high current discharge are required. With the onset warning time for some ITER disruption events estimated to be less than 10 ms, a disruption mitigation system needs to be considered which operates at injection speeds greater than gaseous sound speeds. Such an actuator could then serve as a means to augment presently planned pneumatic injection systems. The EPI uses a rail gun concept whereby a radiative payload is delivered into the discharge by means of the JxB forces generated by an external current pulse, allowing for injection velocities in excess of 1 km/s. The present status of the EPI project is outlined, including the addition of boost magnetic coils. These coils augment the self-generated rail gun magnetic field and thus provide a more efficient acceleration of the payload. The coils and the holder designed to constrain them have been modelled with the ANSYS code to ensure structural integrity through the range of operational coil cu
Pile-up mitigation using attention
Abstract Particle production from secondary proton-proton collisions, commonly referred to as pile-up, impair the sensitivity of both new physics searches and precision measurements at large hadron collider (LHC) experiments. We propose a novel algorithm, Puma , for modeling pile-up with the help of deep neural networks based on sparse transformers. These attention mechanisms were developed for natural language processing but have become popular in other applications. In a realistic detector simulation, our method outperforms classical benchmark algorithms for pile-up mitigation in key observables. It provides a perspective for mitigating the effects of pile-up in the high luminosity era of the LHC, where up to 200 proton-proton collisions are expected to occur simultaneously.
Predicting the impact of particle-particle collisions on turbophoresis with a reduced number of computational particles
A common feature of wall-bounded turbulent particle-laden flows is enhanced particle concentrations in a thin layer near the wall due to a phenomenon known as turbophoresis. Even at relatively low bulk volume fractions, particle-particle collisions regulate turbophoresis in a critical way, making simulations sensitive to collisional effects. Lagrangian tracking of every particle in the flow can become computationally expensive when the physical number of particles in the system is large. Artificially reducing the number of particles in the simulation can mitigate the computational cost. When particle-particle collisions are an important aspect determining the simulation outcome, as in the case when turbophoresis plays an active role, simply reducing the number of particles in the simulation significantly alters the computed particle statistics. This paper introduces a computational particle treatment for particle-particle collisions which reproduces the results of a full simulation with a reduced number of particles. This is accomplished by artificially enhancing the particle collision radius based on scaling laws for the collision rates. The proposed method retains the use of deterministic collision models and is applicable for both low and high Stokes number regimes.
Hydrate Formation in an Unsaturated System - Impacts of Fine Particles and Water Content
Parametric study of hydrate saturation dependent properties of hydrate-bearing sediments requires a large amount of uniform and representative specimens. Expedited synthetization of hydrate-bearing sediments in the laboratory usually uses an unsaturated system due to low methane solubility in water. This study experimentally investigates how various factors affect the distribution of formed hydrate in the sediments via X-ray computed tomography. Results show that the pressure-temperature history is the most critical factor influencing water migration during hydrate formation. Hydrate formed by cooling-pressurization method tends to lead to preferred hydrate formation at core boundaries where exothermic heat can be easily dissipated. The presence of fine-grained particles fails to mitigate this phenomenon, but can effectively suppress water migration even when hydrate is formed using the pressurization-cooling method or the freezing-pressurization-thawing method. Fine-grained particles reduce water activity which further reduce the amount of hydrate formed in the system. The mixing sequence of sand-clay-water mixture affects the final morphology and distribution of each phase and eventually affects hydrate distribution in the sediments. A small amount of clay in sands can suppress water preferentially residing at grain contacts and combine with water acting as a pore filling component. This potentially helps synthesize non-cementing hydrate-bearing sediments in the laboratory more efficiently.
Beam halo formation with different cathode distributions
Beam halo refers to the low-density distribution of particles extending beyond the beam core, and its generation and mitigation are important topics in particle accelerator design. Effective mitigation of beam halo is essential for the cooler design based on Energy Recovery Linac (ERL), which must deliver an electron beam with average beam current of 100 mA and a charge 1 nC per bunch. In the ERL injector and booster linacs, space charge effects are stronger due to relatively low beam energy (6 MeV). Additionally, the longer bunch length of approximately 100 ps in this regime vs the RF period of 5.08 ns makes the formation of beam halos more likely. Therefore, effective collimation of beam halo is critical to maintaining the required beam parameters. To design an effective collimation scheme, several halo distributions were generated at the cathode and used to study halo formation within the injector-merger. This paper presents different halo distributions and halo formation, providing insights on halo collimation strategy.
Prototype tests of the electromagnetic particle injector-2 for fast time response disruption mitigation in tokamaks
Predicting and controlling disruptions is an important and urgent issue for ITER. Some disruptions with a short warning time may be unavoidable. For these cases, a fast time response disruption mitigation method is essential. Experimental tests on a prototype system of a novel, rapid time-response disruption mitigation system being developed for tokamak-based reactors and as a backup option for ITER, referred to as the electromagnetic particle injector (EPI), have been able to verify the primary advantages of the concept. These are its ability to meet short warning time scales of <10 ms while attaining the projected high velocities for deep radiative payload penetration in reactor-scale plasmas. The EPI relies on an electromagnetic propulsion system. A metallic sabot is accelerated electromagnetically to the required velocities (>1 km s -1 ) within 2 ms, at which point it releases a radiative payload consisting of a shell pellet or well-defined microspheres. Initial experimental tests from the prototype system show attainment of over 600 m s -1 in about 1 ms. Finally, essential aspects of payload separation from the sabot and sabot capture have also been demonstrated at 200 m s -1 , and the method can be extended to over 2 km s -1 .
Pileup per particle identification
We propose a new method for pileup mitigation by implementing “pileup per particle identification” (PUPPI). For each particle we first define a local shape α which probes the collinear versus soft diffuse structure in the neighborhood of the particle. The former is indicative of particles originating from the hard scatter and the latter of particles originating from pileup interactions. The distribution of α for charged pileup, assumed as a proxy for all pileup, is used on an event-by-event basis to calculate a weight for each particle. The weights describe the degree to which particles are pileup-like and are used to rescale their four-momenta, superseding the need for jet-based corrections. Furthermore, the algorithm flexibly allows combination with other, possibly experimental, probabilistic information associated with particles such as vertexing and timing performance. We demonstrate the algorithm improves over existing methods by looking at jet p T and jet mass. As a result, we also find an improvement on non-jet quantities like missing transverse energy.