Modeling of absorber pilot plant performance for CO2 capture with aqueous piperazine
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Zhang, Yue↗
SEARCH · Engineering Papers
Results for “Topic modeling”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Impact of Liquid-Vapor to Liquid-Liquid-Vapor Phase Transitions on Asphaltene-Rich Nanoaggregate Behavior in Athabasca Vacuum Residue + Pentane Mixtures
The bulk phase behavior of heavy oil + alkane mixtures and the behavior of the asphaltenes that they contain are topics of importance for the design and optimization of processes for petroleum production, transport, and refining and for performing routine saturates, aromatics, resins, and asphaltenes (SARA) analyses. In prior studies, partial phase diagrams and phase behavior models for Athabasca vacuum residue (AVR) comprising 32 wt % pentane asphaltenes + n-alkanes were reported. For mixtures with pentane, observed phase behaviors included single-phase liquid as well as liquid–liquid, liquid–liquid–vapor, and liquid–liquid–liquid–vapor regions. Dispersed solids were detected under some conditions as well but not quantified. In this work, small-angle X-ray scattering (SAXS) is used to study nanostructured materials in liquid phases present in AVR + n-pentane mixtures from 50 to 170 °C at mixture bubble pressure. The investigation focuses on the impact of the transition from a single AVR-rich liquid to co-existing pentane-rich and AVR-rich liquids on the nanostructure and the nanostructures most resistant to aggregation as the pentane composition axis is approached. Background scattering subtraction was performed using global mixture composition. The robustness of this assumption with respect to values obtained for coefficients appearing in a two level Beaucage unified equation fit is demonstrated. The nanostructured material is shown to arise at two length scales from 1 to 100 wt % AVR. Smaller nanostructures possess mean radii less than 50 Å, while the larger nanostructures possess mean radii greater than 250 Å. The addition of pentane to the AVR causes an increasingly large fraction of the large and small nanostructures to grow in size. Only nanostructures resistant to aggregation remain in the pentane-rich phase as the 0 wt % AVR axis is approached. Step changes in aggregation identified from changes in average radius of gyration, scattering coefficients, and surface/volume ratios arise at the liquid–vapor to liquid–liquid–vapor transition (~40 wt % pentane) and within the liquid–liquid–vapor region (~90 wt % pentane). The temperature is shown to have a limited effect on the mean size and structure of the nanostructured material present, irrespective of global composition.
Long, Bingwen↗
Controlled dynamic screening of excitonic complexes in 2D semiconductors
We report a combined theoretical/experimental study of dynamic screening of excitons in media with frequency-dependent dielectric functions. We develop an analytical model showing that interparticle interactions in an exciton are screened in the range of frequencies from zero to the characteristic binding energy depending on the symmetries and transition energies of that exciton. The problem of the dynamic screening is then reduced to simply solving the Schrodinger equation with an efectively frequency-independent potential. Quantitative predictions of the model are experimentally verifed using a test system: neutral, charged and defect-bound excitons in two-dimensional monolayer WS2, screened by metallic, liquid, and semiconducting environments. The screening-induced shifts of the excitonic peaks in photoluminescence spectra are in good agreement with our model.
36 MATERIALS SCIENCE↗
Variational multiscale reinforcement learning for discovering reduced order closure models of nonlinear spatiotemporal transport systems
Abstract A central challenge in the computational modeling and simulation of a multitude of science applications is to achieve robust and accurate closures for their coarse-grained representations due to underlying highly nonlinear multiscale interactions. These closure models are common in many nonlinear spatiotemporal systems to account for losses due to reduced order representations, including many transport phenomena in fluids. Previous data-driven closure modeling efforts have mostly focused on supervised learning approaches using high fidelity simulation data. On the other hand, reinforcement learning (RL) is a powerful yet relatively uncharted method in spatiotemporally extended systems. In this study, we put forth a modular dynamic closure modeling and discovery framework to stabilize the Galerkin projection based reduced order models that may arise in many nonlinear spatiotemporal dynamical systems with quadratic nonlinearity. However, a key element in creating a robust RL agent is to introduce a feasible reward function, which can be constituted of any difference metrics between the RL model and high fidelity simulation data. First, we introduce a multi-modal RL to discover mode-dependant closure policies that utilize the high fidelity data in rewarding our RL agent. We then formulate a variational multiscale RL (VMRL) approach to discover closure models without requiring access to the high fidelity data in designing the reward function. Specifically, our chief innovation is to leverage variational multiscale formalism to quantify the difference between modal interactions in Galerkin systems. Our results in simulating the viscous Burgers equation indicate that the proposed VMRL method leads to robust and accurate closure parameterizations, and it may potentially be used to discover scale-aware closure models for complex dynamical systems.
97 MATHEMATICS AND COMPUTING↗
Three-block model of the kinetics of vibrationally excited I{sub 2}(X) molecules in the active media of oxygen - iodine lasers
A three-block model of the kinetics of vibrationally excited I{sub 2}(X) molecules in the active media of chemical oxygen - iodine lasers is developed. Instead of the system of equations describing a change in the concentrations of I{sub 2}(X, u) (u=0 - 47) molecules, this model uses equations for the total concentrations of iodine molecules belonging to the blocks of vibrational levels with u {<=} 10, u = 11 - 24, and u {>=} 25. Effective deactivation rate constants of I{sub 2}(X, 11 {<=} u {<=} 24) molecules are found for laser media of different compositions. The results of calculations performed using the proposed model agree with experimental data and are close to the parameters calculated previously by using the total system of equations for populations of individual vibrational levels of I{sub 2}(X, u). (laser applications and other topics in quantum electronics)
74 ATOMIC AND MOLECULAR PHYSICS↗
Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate
Changes in the Atlantic Meridional Overturning Circulation (AMOC) are moderate in most climate model projections under increasing greenhouse gas forcing. This intermodel consensus may be an artifact of common model biases that favor a stable AMOC. Observationally based freshwater budget analyses suggest that the AMOC is in an unstable regime susceptible for large changes in response to perturbations. By correcting the model biases, we show that the AMOC collapses 300 years after the atmospheric CO2 concentration is abruptly doubled from the 1990 level. Compared to an uncorrected model, the AMOC collapse brings about large, markedly different climate responses: a prominent cooling over the northern North Atlantic and neighboring areas, sea ice increases over the Greenland-Iceland-Norwegian seas and to the south of Greenland, and a significant southward rain-belt migration over the tropical Atlantic. Our results highlight the need to develop dynamical metrics to constrain models and the importance of reducing model biases in long-term climate projection.
54 ENVIRONMENTAL SCIENCES↗
Position Papers for the ASCR Workshop on the Management and Storage of Scientific Data
The purpose of this workshop is to identify priority research directions in the area of data management for high-performance and scientific computing above and beyond HPC’s traditional "the parallel file system is the data-management system" model. Supporting the breadth of the DOE mission, including the explosion of AI uses and the growing needs of experimental and observational science, motivates revisiting our assumptions about data management. There are many facets of this topic to explore including: (1) Interfaces for accessing data that resides on traditional persistent storage as well as memory devices; (2) Storage-system architecture design that supports scientific workflows on varied hierarchical storage and networking devices; (3) Devising metadata management infrastructure to support FAIR principles (Findability, Accessibility, Interoperability, and Reusability); (4) Capturing provenance information about scientific data; (5) Utilizing AI to learn I/O patterns of emerging workloads for efficient data management; (6) Providing data management support for AI and complex workflows; and (7) Understanding the overlap between traditional storage systems and I/O (SSIO) efforts and data management. While the program committee has identified these topics as important areas for discussion, we welcome position papers from the community that propose additional topics of interest for discussion at the workshop. The workshop agenda will include breakout sessions for discussing these and selected topic areas to inform priority research directions for data management for high-performance and scientific computing.
97 MATHEMATICS AND COMPUTING↗
Report for the ASCR Workshop on the Management and Storage of Scientific Data
The purpose of this workshop is to identify priority research directions in the area of data management for high-performance and scientific computing above and beyond HPC’s traditional "the parallel file system is the data-management system" model. Supporting the breadth of the DOE mission, including the explosion of AI uses and the growing needs of experimental and observational science, motivates revisiting our assumptions about data management. There are many facets of this topic to explore including: (1) Interfaces for accessing data that resides on traditional persistent storage as well as memory devices; (2) Storage-system architecture design that supports scientific workflows on varied hierarchical storage and networking devices; (3) Devising metadata management infrastructure to support FAIR principles (Findability, Accessibility, Interoperability, and Reusability); (4) Capturing provenance information about scientific data; (5) Utilizing AI to learn I/O patterns of emerging workloads for efficient data management; (6) Providing data management support for AI and complex workflows; and (7) Understanding the overlap between traditional storage systems and I/O (SSIO) efforts and data management. While the program committee has identified these topics as important areas for discussion, we welcome position papers from the community that propose additional topics of interest for discussion at the workshop. The workshop agenda will include breakout sessions for discussing these and selected topic areas to inform priority research directions for data management for high-performance and scientific computing.
97 MATHEMATICS AND COMPUTING↗
Temperature Dependence of Structural Relaxation in Glass-Forming Liquids and Polymers
Understanding the microscopic mechanism of the transition of glass remains one of the most challenging topics in Condensed Matter Physics. What controls the sharp slowing down of molecular motion upon approaching the glass transition temperature T g , whether there is an underlying thermodynamic transition at some finite temperature below T g , what the role of cooperativity and heterogeneity are, and many other questions continue to be topics of active discussions. This review focuses on the mechanisms that control the steepness of the temperature dependence of structural relaxation (fragility) in glass-forming liquids. We present a brief overview of the basic theoretical models and their experimental tests, analyzing their predictions for fragility and emphasizing the successes and failures of the models. Special attention is focused on the connection of fast dynamics on picosecond time scales to the behavior of structural relaxation on much longer time scales. A separate section discusses the specific case of polymeric glass-forming liquids, which usually have extremely high fragility. We emphasize the apparent difference between the glass transitions in polymers and small molecules. We also discuss the possible role of quantum effects in the glass transition of light molecules and highlight the recent discovery of the unusually low fragility of water. At the end, we formulate the major challenges and questions remaining in this field.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Datasets for "Excessive rainfall leads to maize yield loss of a comparable magnitude to extreme drought in the United States"
Updated on 2021/07/01 Add python codes for data processing of the NASS yield data, PRISM climate data, RMA insurance data, agmip yield simulation data, and related geospatial analysis-------------------This repository is for the datasets and codes for “Excessive rainfall leads to maize yield loss of a comparable magnitude to extreme drought in the United States” (Li et al. 2019 GCB). The datasets include maize yield, climate data, maize yield loss from crop insurance data in the US, etc. The datasets can reproduce the results of the paper and they can also be reused to explore other topics. Please cite Li et al (2019) or acknowledge this dataset (DOI: 10.6084/m9.figshare.7581473) when using it.
Agricultural spatial analysis and modelling↗
The CORDEX-CORE EXP-I Initiative: Description and Highlight Results from the Initial Analysis
Here we describe the first effort within the Coordinated Regional Climate Downscaling Experiment–Coordinated Output for Regional Evaluation, or CORDEX-CORE EXP-I. It consists of a set of twenty-first-century projections with two regional climate models (RCMs) downscaling three global climate model (GCM) simulations from the CMIP5 program, for two greenhouse gas concentration pathways (RCP8.5 and RCP2.6), over nine CORDEX domains at ~25-km grid spacing. Illustrative examples from the initial analysis of this ensemble are presented, covering a wide range of topics, such as added value of RCM nesting, extreme indices, tropical and extratropical storms, monsoons, ENSO, severe storm environments, emergence of change signals, and energy production. They show that the CORDEX-CORE EXP-I ensemble can provide downscaled information of unprecedented comprehensiveness to increase understanding of processes relevant for regional climate change and impacts, and to assess the added value of RCMs. The CORDEX-CORE EXP-I dataset, which will be incrementally augmented with new simulations, is intended to be a public resource available to the scientific and end-user communities for application to process studies, impacts on different socioeconomic sectors, and climate service activities. The future of the CORDEX-CORE initiative is also discussed.
54 ENVIRONMENTAL SCIENCES↗
Is it possible to establish the photon horizon in the waveguide model of a black hole outside the field of gravity?
On the basis of the fundamental provision of general relativity about the equality of inertial and gravitational masses and the equivalence of kinematic and gravitational acceleration, a negative answer is given to the question posed in the title. (laser applications and other topics in quantum electronics)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Genetically-modified bone mesenchymal stem cells with TGF-β3 improve wound healing and reduce scar tissue formation in a rabbit model
Highlights: • BMSCs displayed a highly efficient and long lasting expression of TGF-β{sub 3} after transferred with Ad-TGF-β{sub 3}/GFP. • High protein levels of TGF-β{sub 1} and type I collagen, and lower protein levels of TGF-β{sub 3} and type III collagen were detected in the skin scarring tissue. • BMSCs expressing TGF-β{sub 3} significantly reduced scar depth and density as well as a reduced ratio of collagen type I to type III. • A combination stem cell-gene therapy with BMSCs{sup TGF-β3} improved skin wound healing and prevention of scaring formation. Extensive scar tissue formation often occurs after severe burn injury, trauma, or as one of complications after surgical intervention. Despite significant therapeutic advances, it is still a significant challenge to manage massive scar tissue formation while also promoting normal wound healing. The goal of this study was to investigate the therapeutic effect of bone mesenchymal stem cells (BMSCs) that were genetically modified to overexpress transforming growth factor-beta 3 (TGF-β{sub 3}), an inhibitor of myofibroblast proliferation and collagen type I deposition, on full-thickness cutaneous wound healing in a rabbit model. Twenty-four rabbits with surgically-induced full-thickness cutaneous wounds created on the external ear (1.5 × 1.5 cm, two wounds/ear) were randomized into four groups: (G1), wounds with no special treatment but common serum-free culture medium as negative controls; (G2), topically-applied recombinant adenovirus, expressing TGF-β{sub 3}/GFP; (G3), topically-applied BMSCs alone; (G4), topically-applied BMSCs transfected with Ad-TGF-β{sub 3}/GFP (BMSCs{sup TGF-β3}); and (G5), an additional normal control (n = 2) with neither wound nor treatment on the external ear skin. The sizes of wounds on the ear tissues were grossly examined, and the scar depth and density of wounds were histologically evaluated 21, 45, and 90 days after surgical wound creation. Our results demonstrated that G4 significantly reduced the wound scar depth and density, compared to G1~3. Numbers of cells expressing GFP significantly increased in G4, compared to G2. The protein expression of TGF-β{sub 3} and type III collagen in G4 significantly increased, while the ratio of type I to type III collagen was also significantly reduced, which is similar to the tissue architecture found in G5, as compared the other treatment groups. In conclusion, transplantation of BMSCs{sup TGF-β3} remarkably improves wound healing and reduces skin scar tissue formation in an animal model, which may potentially provide an alternative in the treatment of extensive scar tissue formation after soft tissue injury.
60 APPLIED LIFE SCIENCES↗
RF Sheath-Enhanced Plasma Surface Interaction Studies using Beryllium Optical Emission Spectroscopy in JET ITER-Like Wall
A dedicated study on JET-ILW, deploying two types of ICRH antennas and spectroscopic observation spots at two outboard, beryllium limiters, has provided insight on long-range (up to 6m) RFenhanced plasma-surface interactions (RF-PSI) due to near-antenna electric fields. To aid in the interpretation of optical emission measurements of these effects, the antenna near-fields are computed using the TOPICA code, specifically run for the ITER-like antenna (ILA); similar modelling already existed for the standard JET antennas (A2). In the experiment, both antennas were operated in current drive mode, as RF-PSI tends to be higher in this phasing and at similar power (~0.5 MW). When sweeping the edge magnetic field pitch angle, peaked RF-PSI effects, in the form of 2-4 fold increase in the local Be source,are consistently measured with the observation spots magnetically connect to regions of TOPICAL-calculated high near-fields, particularly at the near-antenna limiters. It is also found that similar RF-PSI effects are produced by the two types of antenna on similarly distant limiters. Although this mapping of calculated near-fields to enhanced RF-PSI gives only qualitative interpretion of the data, the present dataset is expected to provide a sound experimental basis for emerging RF sheath simulation model validation.
Agarici, G.↗
Influence of Gaussian disorder and exponential traps on charge carriers transport and recombination in single layer polymer light-emitting diodes based on PFO as emitting layer
In this paper, we study the transport and recombination mechanisms of charge carriers in a single layer PLED device based on PFO as emitting layer with considering Gaussian disorder, exponential distribution of traps, Poole–Frankel type field dependent hopping mobility and field independent effective transport hopping energy models. For this purpose, we use the one-dimensional and time-independent drift–diffusion model for simulation of electrical and optical characteristics of the PFO based PLED devices such as current density–luminance–voltage (J–L–V), recombination rate and singlet exciton density profile in steady-state and room temperature conditions. Also, we study the influence of the characteristic temperature and density of electron traps on the performance of devices at different voltages. Another topic is analyzing the current density–voltage characteristics of uni-polar devices (hole only or electron only) by using the well known expressions for trap-limited current and space charge-limited current and comparing them with simulation results.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
A mechanism of wave drag reduction in the thermal energy deposition experiments
Many experimental studies report reduced wave drag when thermal energy is deposited in the supersonic flow upstream of a body. Though a large amount of research on this topic has been accumulated, the exact mechanism of the drag reduction is still unknown. This paper is to fill the gap in the understanding connecting multiple stages of the observed phenomena with a single mechanism. The proposed model provides an insight on the origin of the chain of subsequent transformations in the flow leading to the reduction in wave drag, such as typical deformations of the front, changes in the gas pressure and density in front of the body, the odd shapes of the deflection signals, and the shock wave extinction in the plasma area. The results of numerical simulation based on the model are presented for three types of plasma parameter distribution. The spherical and cylindrical geometry has been used to match the data with the experimental observations. The results demonstrate full ability of the model to exactly explain all the features observed in the drag reduction experiments. Analytical expressions used in the model allow separating out a number of adjustment parameters that can be used to optimize thermal energy input and thus achieve fundamentally lower drag values than that of conventional approaches.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Toward adaptive decision support for assessing infrastructure system resilience using hidden performance measures
The understanding of resilience is an emerging topic within the study of risks affecting distributed transportation infrastructure systems. Although recent studies have explored the quantification of system resilience, there has been limited research aimed at understanding the role of multiple performance measures, geographies, and modeling uncertainties within the assessment of resilience and associated decision-making. Under real-world conditions, there is an increased burden on analysts for translating observed system data (from human and electronic sensor observations) into the estimation of system performance that may not be directly observable. This paper addresses these issues using a scenario-based risk modeling approach to understand: 1) resilience of complex systems, often in cases of hidden (not readily observable) measures of performance, 2) resilience sensitivity to modeling uncertainties in event and system characteristics, and 3) resilience sensitivity to the measurement of performance across multiple dimensions. The methods in this paper integrate uncertainty-driven risk and probabilistic modeling within a multi-state Markov approach. This study contributes to the state-of-the-art by developing methodologies for assessing community perceptions of infrastructure system resilience using observable factors and inferring possibly hidden performance measures for facilitating adaptive decision-support. The methods are demonstrated with hypothetical spatiotemporal data for the Washington, District of Columbia and Baltimore, Maryland urban regions in the United States against evacuation-causing and shelter-in-place disruptive scenarios across multiple system performance dimensions. The analysis results may be useful for risk managers, supply chain analysts, emergency decision-makers, and the general public.
Infrastructure System Resilience, Risk Management,↗