Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “point”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Reconfigurable Pointing Control for High Resolution Space Spectroscopy

In this paper, a pointing control performance criteria is established to suppport high resolution space spectroscopy. Results indicate that these pointing control requirements are very stringent, and would typically be difficult to meet using standard 3-axis spacecraft control. To resolve this difficulty, it is shown that performance can be significantly improved using a reconfigurable control architecture that switches among a small bankof detuned Kalman filters. The effectiveness of the control reconfiguration approach is demonstrated by example on the Space Infra-Red Telescope Facility (SIRTF) pointing system, in support of the InfraRed Spectrograph (IRS) payload.

spectroscophy spacecraft pointing spacecraft contr↗
NASA NTRS2010

Normalized Point Source Sensitivity for Off-Axis Optical Performance Evaluation of the Thirty Meter Telescope

The Normalized Point Source Sensitivity (PSSN) has previously been defined and analyzed as an On-Axis seeing-limited telescope performance metric. In this paper, we expand the scope of the PSSN definition to include Off-Axis field of view (FoV) points and apply this generalized metric for performance evaluation of the Thirty Meter Telescope (TMT). We first propose various possible choices for the PSSN definition and select one as our baseline. We show that our baseline metric has useful properties including the multiplicative feature even when considering Off-Axis FoV points, which has proven to be useful for optimizing the telescope error budget. Various TMT optical errors are considered for the performance evaluation including segment alignment and phasing, segment surface figures, temperature, and gravity, whose On-Axis PSSN values have previously been published by our group.

optical performance metric↗
NASA NTRS2019

Challenges and Solutions for Precision Solar Pointing on the ISS for the TSIS Instrument

The International Space Station offers an attractive platform for external payloads in many regards, but its large, complex structure is challenging for payloads that require precise, unobstructed pointing. As an instrument that measures solar irradiance on a continual basis, the TSIS payload was designed to robustly account for these ISS challenges and is now performing its mission on the ISS with great success.This paper first describes how TSIS was able to measure the ISS background jitter using High-rate Fine Sun Sensor data that was taken during passive solar transits through its field of view. The measurements showed that ISS jitter at the TSIS location on ELC-3 Site 5 is relatively benign with less than 4 arcseconds 1 at frequencies less than 0.5 Hz. This value is lower than previous estimates but agrees well with recent measurements from other external payloads, including OPALS and SAGE III. Because TSIS was designed to be robust to base motion jitter, it has achieved less than 4 arcseconds 1 of pointing error, which provides an extremely precise pointing platform for the solar irradiance measurements. The other challenging ISS characteristic is its large, complex structure that obscures solar viewing at sunrise and sunset from the zenith-facing location of TSIS. Although TSIS was able to predict solar viewing durations during the design phase with relatively high accuracy, the exact timing and causes of obscuration were difficult to predict and understand after TSIS began operating on the ISS. To aid in the understanding of blockage by ISS structure, detailed obscuration maps were created using HFSS measurements that clearly show the exact gimbal angles where blockage occurs and the specific structural features of the ISS that cause the blockage. These maps have helped TSIS to maximize its solar tracking durations each orbit, which has supported the mission in meeting its science objectives.

background jitter↗
NASA NTRSDate not supplied

Dew Point Simulation and Analysis of the Heat Melt Compactor Gas Effluent

The effluent gases and water vapor of the Trash Compaction and Processing System (TCPS) can be vented through the Vacuum Exhaust System (VES) if requirements are met. One of the constraints in this venting scenario is the dew point of the exhaust gases disposed into the VES must be less than 15.5 °C. With simulations using Aspen Plus and the effluent gas sample results of the Heat Melt Compactor (HMC), flash calculations were conducted in the modeling study to calculate the feed temperature and dew point at fixed pressures. Saturated vapor curves were produced and provided a preliminary result on optimal feed conditions that satisfy the dew point and vapor-phase only requirements after flashing across the throttle valve towards the VES.

trash↗
NASA NTRSDate not supplied

Unsupervised Change Detection for Space Habitats Using 3D Point Clouds

This work presents an algorithm for scene change detection from point clouds to enable autonomous robotic caretaking in future space habitats. Autonomous robotic systems will help maintain future deep-space habitats, such as the Gateway space station, which will be uncrewed for extended periods. Existing scene analysis software used on the International Space Station (ISS) relies on manually-labeled images for detecting changes. In contrast, the algorithm presented in this work uses raw, unlabeled point clouds as inputs. The algorithm first applies modified Expectation-Maximization Gaussian Mixture Model (GMM) clustering to two input point clouds. It then performs change detection by comparing the GMMs using the Earth Mover’s Distance. The algorithm is validated quantitatively and qualitatively using a test dataset collected by an Astrobee robot in the NASA Ames Granite Lab comprising single frame depth images taken directly by Astrobee and full-scene reconstructed maps built with RGB-D and pose data from Astrobee. The runtimes of the approach are also analyzed in depth. The source code is publicly released to promote further development.

robotics↗
DOE OSTI2025

On the Recoverability of Reactor Dynamics from Point Kinetics Data using SINDYc

Data driven models for reactor dynamics tend to face a few notable challenges. First, the broad range of timescales present across the various feedback mechanisms. Next, high standards for safety and importance of model performance in all operational domains. Finally, the correlations between state variables observed in most transients leads to difficulties when methods attempt to attribute certain dynamic phenomena to a particular cause. The current paper seeks to support efforts towards incorporating physics knowledge into one particular data-driven method for finding reactor dynamics called ``Sparse Identification of Nonlinear Dynamics with Control (SINDYc). The incorporation of physical knowledge into SINDYc will help address the challenges listed above by giving the model an initial understanding of the system being modeled. The demonstration of an exact representation of a set of point reactor dynamics equations in SINDYc is provided. Then, this allows for further discussion with mathematical justification as to why SINDYc, and other data-driven methods, may be difficult to apply to nuclear reactor dynamics due to correlations in the state variables. A particularly useful result of this work is the set of candidate functions required in SINDYc to exactly represent the reactor dynamics under a point approximation. In the future, SINDYc can be integrated with point models for reactor dynamics before being applied to the physical system to yield higher accuracy.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

First‐Principles Calculations of Quantum Efficiency for Point Defects in Semiconductors: The Example of Yellow Luminance by GaN: C N +O N and GaN:C N

Abstract Point defects play an important role in the photoelectrical properties of semiconductor materials, and they can be luminescence centers. However, the relationships among the observed luminescence wavelengths, intensities, and the microscopic processes are in most cases unknown, or depend heavily on parameter fitting. In this work, the light‐emitting quantum efficiencies for point defects using ab initio density functional theory are calculated. The study of radiation recombination for electrons and nonradiation recombination for holes is reported here. The results show that the defect C N transition between “−” and “0” charged levels and the defect C N +O N transition between “0” and “+” charged levels both may be responsible for the yellow luminescence (YL) which is observed in experiment. Moreover, the calculation shows significant thermal quenching of the YL starting at 480 K due to re‐excitation of hole into the valence band from the point defects, which is in relatively good agreement with the experimentally observed value. This work shows that it is possible to use ab initio calculations to understand the microscopic mechanisms and the competitions among different channels for the light emissions caused by defects.

Zhang, Hai‐Shan↗
DOE OSTI2016

Emerging Diluted Ferromagnetism in High- T c Superconductors Driven by Point Defect Clusters

Here, defects in ceramic materials are generally seen as detrimental to their functionality and applicability. Yet, in some complex oxides, defects present an opportunity to enhance some of their properties or even lead to the discovery of exciting physics, particularly in the presence of strong correlations. A paradigmatic case is the high–temperature superconductor YBa 2 Cu 3 O 7–δ (Y123), in which nanoscale defects play an important role as they can immobilize quantized magnetic flux vortices. Here previously unforeseen point defects buried in Y123 thin films that lead to the formation of ferromagnetic clusters embedded within the superconductor are unveiled. Aberration–corrected scanning transmission microscopy has been used for exploring, on a single unit–cell level, the structure and chemistry resulting from these complex point defects, along with density functional theory calculations, for providing new insights about their nature including an unexpected defect–driven ferromagnetism, and X–ray magnetic circular dichroism for bearing evidence of Cu magnetic moments that align ferromagnetically even below the superconducting critical temperature to form a dilute system of magnetic clusters associated with the point defects.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The φ-relation and a simple method to predict how many data points are needed for relevant steady-state detection

Steady–state detection is of vital importance for experiments and simulations in chemical engineering, as well as also other fields of science, engineering, and finance—particularly when the full timescale of interest cannot be measured or simulated. We present a breakthrough for estimating the number of data points required before successful steady–state detection is feasible. Using an initial window of data, the method enables predicting the prerequisites for steady state detection (ppSSD), given as a number of data points. The method is shown to be accurate for data with realistic distributions (uniform, normal, and sine–wave), and data from actual kinetic Monte Carlo simulations. In conclusion, users need only to use the algebraic equations derived and provided in this work to estimate the required number of data points for relevant steady–state detection.

42 ENGINEERING↗
DOE OSTI2021

Biogeochemical control points of connectivity between a tidal creek and its floodplain

As global climates shift, coastal systems experience changes that alter function within the tidal zone. However, it remains uncertain how changes in tidal extent and magnitude will alter coastal biogeochemical cycling. We present high-frequency data collected in-situ along two transects across a tidal creek and floodplain to capture how changes in vertical and lateral connectivity act as biogeochemical control points. Using wavelet analysis, we identified short periods of strong vertical connectivity during spring tides followed by extended periods of floodplain isolation from tides. During a drier period, neap tides were linked to lateral creek-floodplain connectivity, detected by discharge of saline, oxygen-depleted groundwater to the creek on ebb tides. We estimate up to half of creek water throughout the tidal cycle was associated with floodplain drainage. From point measurements of carbon, nitrogen, and greenhouse gases along the creek-floodplain transect, we infer that lateral connectivity functions as a biogeochemically significant control point.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Lagrangian–Eulerian multidensity topology optimization with the material point method

Abstract In this paper, a hybrid Lagrangian–Eulerian topology optimization (LETO) method is proposed to solve the elastic force equilibrium with the Material Point Method (MPM). LETO transfers density information from freely movable Lagrangian carrier particles to a fixed set of Eulerian quadrature points. This transfer is based on a smooth radial kernel involved in the compliance objective to avoid the artificial checkerboard pattern. The quadrature points act as MPM particles embedded in a lower‐resolution grid and enable a subcell multidensity resolution of intricate structures with a reduced computational cost. A quadrature‐level connectivity graph‐based method is adopted to avoid the artificial checkerboard issues commonly existing in multiresolution topology optimization methods. Numerical experiments are provided to demonstrate the efficacy of the proposed approach.

Li, Yue↗
DOE OSTI2021

A three-point form factor through five loops

We bootstrap the three-point form factor of the chiral part of the stress­tensor supermultiplet in planar $\mathcal{N}$ = 4 super-Yang-Mills theory, obtaining new results at three, four, and five loops. Our construction employs known conditions on the first, second, and final entries of the symbol, combined with new multiple-final-entry conditions, “extended-Steinmann-like” conditions, and near-collinear data from the recently-developed form factor operator product expansion. Our results are expected to give the maximally transcendental parts of the gg → Hg and H → ggg amplitudes in the heavy-top limit of QCD. At two loops, the extended-Steinmann-like space of functions we describe contains all transcendental functions required for four-point amplitudes with one massive and three massless external legs, and all massless internal lines, including processes such as gg → Hg and γ * → $q\overline{q}g$. We expect the extended-Steinmann-like space to contain these amplitudes at higher loops as well, although not to arbitrarily high loop order. We present evidence that the planar $\mathcal{N}$ = 4 three-point form factor can be placed in an even smaller space of functions, with no independent ζ values at weights two and three.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Fishnet four-point integrals: integrable representations and thermodynamic limits

In this work, we consider four-point integrals arising in the planar limit of the conformal “fishnet” theory in four dimensions. They define a two-parameter family of higher-loop Feynman integrals, which extend the series of ladder integrals and were argued, based on integrability and analyticity, to admit matrix-model-like integral and determinantal representations. In this paper, we prove the equivalence of all these representations using exact summation and integration techniques. We then analyze the large-order behaviour, corresponding to the thermodynamic limit of a large fishnet graph. The saddle-point equations are found to match known two-cut singular equations arising in matrix models, enabling us to obtain a concise parametric expression for the free-energy density in terms of complete elliptic integrals. Interestingly, the latter depends non-trivially on the fishnet aspect ratio and differs from a scaling formula due to Zamolodchikov for large periodic fishnets, suggesting a strong sensitivity to the boundary conditions. We also find an intriguing connection between the saddle-point equation and the equation describing the Frolov-Tseytlin spinning string in AdS 3 × S 1 , in a generalized scaling combining the thermodynamic and short-distance limits.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Six-point functions and collisions in the black hole interior

In the eternal AdS black hole geometry, we consider two signals sent from the boundaries into the black hole interior shared between the two asymptotic regions. We compute three different out-of-time-order six-point functions to quantify various properties of the collision of these signals behind the horizons: (i) We diagnose the strength of the collision by probing the two-signal state on a late time slice with boundary operators. (ii) We quantify two-sided operator growth, which provides a dual description of the signals meeting in the black hole interior, in terms of the quantum butterfly effect and quantum circuits. (iii) We consider an explicit coupling between the left and right CFTs to make the wormhole traversable and extract information about the collision product from behind the horizon. At a technical level, our results rely on the method of eikonal resummation to obtain the relevant gravitational contributions to Lorentzian six-point functions at all orders in the GN-expansion. We observe that such correlation functions display an intriguing factorization property. We corroborate these results with geodesic computations of six-point functions in two- and three-dimensional gravity.

2D Gravity↗
DOE OSTI2022

Accumulation-point amplitudes in string theory

We point out some common qualitative features of the Coon amplitude — a family of deformations of the Veneziano amplitude with logarithmic Regge trajectories — and the open string scattering amplitude for strings ending on a D-brane in AdS. Both reduce to the Veneziano amplitude at relatively low energies. Both systems have an accumulation point in their spectrum, with an infinite number of states below a certain energy. The approach to this point is very similar. Both have the same high-energy fixed-angle behavior. Nevertheless, we find some differences in the spectrum of states with highest angular momentum. These similarities suggest that there may exist a string background that realizes the Coon amplitude.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

A magnetically induced quantum critical point in holography

Here, we investigate quantum critical points in a 2+1 dimensional gauge theory at finite chemical potential χ and magnetic field B. The gravity dual is based on 4D N = 2 Fayet-Iliopoulos gauged supergravity and the solutions we consider — that are constructed analytically — are extremal, dyonic, asymptotically AdS 4 black-branes with a nontrivial radial profile for the scalar field. We discover a line of second order fixed points at B = B c (χ) between the dyonic black brane and an extremal “thermal gas” solution with a singularity of good-type, according to the acceptability criteria of Gubser. The dual field theory is a strongly coupled nonconformal field theory at finite charge and magnetic field, related to the ABJM theory deformed by a triple trace operator Φ 3 . This line of fixed points might be useful in studying the various strongly interacting quantum critical phenomena such as the ones proposed to underlie the cuprate superconductors. We also find curious similarities between the behaviour of the VeV <Φ> under B and that of the quark condensate in 2+1 dimensional NJL models.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

The convolutional double copy: a case study with a point

The double copy relates scattering amplitudes in gauge and gravity theories. It has also been extended to classical solutions, and a number of approaches have been developed for doing so. One of these involves expressing fields in a variety of (super-)gravity theories in terms of convolutions of gauge fields, including also BRST ghost degrees of freedom that map neatly to their corresponding counterparts in gravity. In this paper, we spell out how to use the convolutional double copy to map gauge and gravity solutions in the manifest Lorenz and de Donder gauges respectively. We then apply this to a particular example, namely the point charge in pure gauge theory. As well as clarifying how to use the convolutional approach, our results provide an alternative point of view on a recent discussion concerning whether point charges map to the Schwarzschild solution, or the more general two-parameter JNW solution, which includes a dilaton field. We confirm the latter.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Kinematic focus point method for particle mass measurements in missing energy events

We investigate the solvability of the event kinematics in missing energy events at hadron colliders, as a function of the particle mass ansatz. To be specific, we reconstruct the neutrino momenta in dilepton tt¯-like events, without assuming any prior knowledge of the mass spectrum. We identify a class of events, which we call extreme events, with the property that the kinematic boundary of their allowed region in mass parameter space passes through the true mass point. We develop techniques for recognizing extreme events in the data and demonstrate that they are abundant in a realistic data sample, due to expected singularities in phase space. We propose a new method for mass measurement whereby we obtain the true values of the mass parameters as the focus point of the kinematic boundaries for all events in the data sample. Since the masses are determined from a relatively sharp peak structure (the density of kinematic boundary curves), the method avoids some of the systematic errors associated with other techniques. We show that this new approach is complementary to previously considered methods in the literature where one studies the solvability of the kinematic constraints throughout the mass parameter space. In particular, we identify a problematic direction in mass space of nearly 100% solvability, and then show that the focus point method is effective in lifting the degeneracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗