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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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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Lateral-Directional Parameter Estimation on the X-48B Aircraft Using an Abstracted, Multi-Objective Effector Model

The problem of parameter estimation on hybrid-wing-body aircraft is complicated by the fact that many design candidates for such aircraft involve a large number of aerodynamic control effectors that act in coplanar motion. This adds to the complexity already present in the parameter estimation problem for any aircraft with a closed-loop control system. Decorrelation of flight and simulation data must be performed in order to ascertain individual surface derivatives with any sort of mathematical confidence. Non-standard control surface configurations, such as clamshell surfaces and drag-rudder modes, further complicate the modeling task. In this paper, time-decorrelation techniques are applied to a model structure selected through stepwise regression for simulated and flight-generated lateral-directional parameter estimation data. A virtual effector model that uses mathematical abstractions to describe the multi-axis effects of clamshell surfaces is developed and applied. Comparisons are made between time history reconstructions and observed data in order to assess the accuracy of the regression model. The Cram r-Rao lower bounds of the estimated parameters are used to assess the uncertainty of the regression model relative to alternative models. Stepwise regression was found to be a useful technique for lateral-directional model design for hybrid-wing-body aircraft, as suggested by available flight data. Based on the results of this study, linear regression parameter estimation methods using abstracted effectors are expected to perform well for hybrid-wing-body aircraft properly equipped for the task.

Ratnayake, Nalin A.↗
DOE OSTI2014

Automatic identification of abstract online groups

Online abstract groups, in which members aren't explicitly connected, can be automatically identified by computer-implemented methods. The methods involve harvesting records from social media and extracting content-based and structure-based features from each record. Each record includes a social-media posting and is associated with one or more entities. Each feature is stored on a data storage device and includes a computer-readable representation of an attribute of one or more records. The methods further involve grouping records into record groups according to the features of each record. Further still the methods involve calculating an n-dimensional surface representing each record group and defining an outlier as a record having feature-based distances measured from every n-dimensional surface that exceed a threshold value. Each of the n-dimensional surfaces is described by a footprint that characterizes the respective record group as an online abstract group.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

System and method for identifying and comparing code by semantic abstractions

Certain embodiments of the present invention are configured to facilitate analyzing computer code more efficiently. For example, by conducting a first level abstraction (e.g., symbolic interpretation and algebraic simplification) and a second level abstraction (e.g., generalization) of the computer code, the analysis may more accurately account for variations in the code that may occur as a result of register renaming, instruction reordering, choice of instructions, etc. while minimizing the cost of computations required to perform the analysis.

Lakhotia, Arun↗
DOE OSTI2025

2024-03U-JWS01 - Initial Abstract

Abstract for recently approved CRADA joint work statement 2024-03U-JWS01 with University of Nevada Reno. Publication of abstract at time of approval satisfies requirements of DOE O 483.1B.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Hydrogen-Abstraction/Acetylene-Addition Exposed

Polycyclic aromatic hydrocarbons (PAHs) are omnipresent in the interstellar medium (ISM) and also in carbonaceous meteorites (CM) such as Murchison. However, the basic reaction routes leading to the formation of even the simplest PAH—naphthalene (C 10 H 8 )—via the hydrogen-abstraction/acetylene-addition (HACA) mechanism still remain ambiguous. By revealing the uncharted fundamental chemistry of the styrenyl (C 8 H 7 ) and the ortho-vinylphenyl radicals (C 8 H 7 )—key transient species of the HACA mechanism—with acetylene (C 2 H 2 ), we provide the first solid experimental evidence on the facile formation of naphthalene in a simulated combustion environment validating the previously postulated HACA mechanism for these two radicals. This study highlights, at the molecular level spanning combustion and astrochemistry, the importance of the HACA mechanism to the formation of the prototype PAH naphthalene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

A Scale-Dynamic Network Abstraction Approach for Traffic Analysis

The necessary trade-off between accuracy and efficiency of various traffic simulation tools depends on the resolution of the roadway network. While a detailed high-resolution road network could better represent connectivity of real-world road network and ensure an accurate simulation result, a low-resolution network omitting trivial details could reduce computational burden and improve the computational efficiency of traffic simulation. This study focuses on dynamically adjusting the roadway network resolution during the process of simulation-based dynamic traffic assignment (SBDTA) with the objective to expedite both the simulation and the assignment within SBDTA. We propose to divide the whole time horizon into several periods dynamically and to Abstract the network for each period separately. The result showed that half of the CPU time for both the simulation and the assignment is saved, while the network performance remains consistent or near consistent compared with the scenario using the most detailed network.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2018

GPU code optimization using abstract kernel emulation and sensitivity analysis

In this paper, we develop a novel approach to GPU kernel optimization by focusing on identification of bottleneck resources and determining optimization parameters that can alleviate the bottleneck. Performance modeling for GPUs is done by abstract kernel emulation along with latency/gap modeling of resources. Sensitivity analysis with respect to resource latency/gap parameters is used to predict the bottleneck resource for a given kernel's execution. Here, the utility of the bottleneck analysis is demonstrated in two contexts: 1) Enhancing the OpenTuner auto-tuner with the new bottleneck-driven optimization strategy. Experimental results on all kernels from the Rodinia suite and GPU tensor contraction kernels from the NWChem computational chemistry suite demonstrate effectiveness. 2) Manual code optimization: two case studies illustrate the use of the bottleneck analysis to iteratively improve performance of code from state-of-the-art DSL code generators.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2001

Using abstraction in multi-rover scheduling

r describes how an iterative repair planner/scheduler can reason about the activities of multiple spacecraft at abstract levels in order to greatly improve the scheduling of their use of shared resources.

abstraction planning rovers multiple agents↗
NASA NTRS2001

Reasoning abstractly about resources

r describes a way to schedule high level activities before distributing them across multiple rovers in order to coordinate the resultant use of shared resources regardless of how each rover decides how to perform its activities. We present an algorithm for summarizing the metric resource requirements of an abstract activity based n the resource usages of its potential refinements.

abstraction planning rovers multiple agents↗