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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

A Probable Approx. 2400 Year Solar Quasi-cycle in Atmospheric Delta C-14

A 2200 to 2600 year quasi-periodicity is present in atmospheric delta C-14 records after removal of long-term trends due to the geomagnetic dipole amplitude variation. This periodicity consists of both a long-term variation of the mean and a superposed, approximately recurring pattern of century-scale variations. The strongest of these latter variations occur near maxima of the approx. 2400 year delta C-14 cycles. The residual record can be modeled to first order as an amplitude modulation of a century-scale periodic forcing function by a approx. 2400 year periodic forcing function. During the last millennium, the largest century-scale variations (occurring near the most recent 2400 year delta C-14 maximum) are known to be mainly a consequence of the pronounced Maunder, Sporer, and Wolf solar activity minima, as verified by independent proxy solar activity records. Therefore, during this period, amplitude modulation has been occurring primarily in the sun and not in the terrestrial radiocarbon system. It is therefore inferred that the approx. 2400 year forcing function is mainly solar although some secondary terrestrial feedback into the delta C-14 record is likely. This conclusion has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor Holocene climatic variations.

Hood, L. L.↗
NASA NTRS1972

The measurement of pulsar periods.

The method used for determining the pulsar period is discussed. In connection with the computation of the time of arrival of a pulse the right ascension and declination of the earth relative to the barycenter, the center of mass of the solar system, are calculated. The data obtained together with the position of the pulsar are used to calculate what the time of arrival would have been had the antenna been at the barycenter. A matrix approach is used for series observations. Pulsar positions obtained are listed in a table. A graph is presented showing the rate of change of the period as a function of the period for several sources.

Downs, G. S.↗
NASA NTRS1974

Change in blood coagulation indices as a function of the incubation period of plasma in a constant magnetic field

The influence of a constant magnetic field (CMF) with a strength of 250 and 2500 oersteds on the recalcification reaction and the tolerance of plasma to heparin was studied as a function of the exposure time of the plasma to the CMF. The maximum and reliable change in the activation of the coagulatory system of the blood was observed after a 20-hour incubation of the plasma in a CMF. As the exposure time increased, the recalcification reaction changed insigificantly; the difference between the mean arithmetic of the experiment and control values was not statistically reliable. The tolerance of the plasma to heparin as a function of the exposure time to the CMF of the plasma was considerably modified, an was statistically reliable.

Yepishina, S. G.↗
NASA NTRS2021

A Functional Interpolation Approach to Compute Period Orbits in the Circular Restricted Three-body Problem

In this paper, we develop a method to solve for periodic orbits, i.e., Lyapunov and Halo orbits, using a functional interpolation scheme called the Theory of Func- tional Connections (TFC). Using this technique, a periodic constraint is analyti- cally embedded into the TFC constrained expression. By doing this, the system of differential equations governing the three-body problem is transformed into an unconstrained optimization problem where simple numerical schemes can be used to find a solution, e.g., nonlinear least-squares is used. This allows for a simpler numerical implementation with comparable accuracy and speed to the traditional differential corrector method.

Mortari, Daniele↗
DOE OSTI2025

A Computational Framework to design 3D stiffness gradient acoustic metamaterials for impedance matching

Acoustic waves play a crucial role in various applications, including medical imaging, non-destructive testing, and sonar systems. One of the significant challenges in these applications is impedance matching, which is essential for minimizing reflections and maximizing the transfer of acoustic energy between different media. Acoustic metamaterials offer a promising solution to this challenge. In addition to impedance control, gradient stiffness can enhance structural efficiency and enable spatial control of wave propagation, making it a valuable feature in acoustic metamaterial design. In this pa- per, we present our developed computational method to design 3D stiffness gradient acoustic metamaterials for impedance matching. The key steps in our approach include generating initial designs using a periodic covariance function to provide unit cells that are both periodic on the boundaries and randomly formed inside the unit cell. Furthermore, we integrated manufacturing constraints into the design process, ensuring that the structures are interconnected for fabrication. We propose two computational optimization algorithms: GenUnit, based on a non-dominated sorting genetic algorithm (NSGA-II), and MLMatch, which leverages differentiable machine learning. The two approaches are not separate contributions but complementary com- ponents of a unified framework. GenUnit requires no training data and directly interfaces with physics-based simulations, making it highly accurate but slower for large-scale exploration. In contrast, MLMatch is data-hungry during training but, once trained, enables near-instantaneous inference and broad design-space coverage. Together, they form a hybrid strategy: ML- Match rapidly explores the global design space, and GenUnit provides local refinement with high-fidelity accuracy. This balance between training cost, inference time, and precision is the motivation for including both methods in the same study. We applied this dual-algorithm framework to generate two metallic-based metamaterial designs that match the acoustic impedance of water while exhibiting a controlled gradient in stiffness (from stiff to soft). The stiffness gradient is particularly advantageous in applications where one side of the structure must interface with soft or sensitive surfaces, such as human tissue or delicate components. Here, this work paves the way for improved materials in various acoustic applications, particularly in ultrasound devices, by providing better impedance.

Metamaterial↗
NASA NTRS2017

Kepler Planet Detection Metrics: Window and One-Sigma Depth Functions for Data Release 25

This document describes the window and one-sigma depth functions relevant to the Transiting Planet Search (TPS) algorithm in the Kepler pipeline (Jenkins 2002; Jenkins et al. 2017). The window function specifies the fraction of unique orbital ephemeris epochs over which three transits are observable as a function of orbital period. In this context, the epoch and orbital period, together, comprise the ephemeris of an orbiting companion, and ephemerides with the same period are considered equivalent if their epochs differ by an integer multiple of the period. The one-sigma depth function specifies the depth of a signal (in ppm) for a given light curve that results in a one-sigma detection of a transit signature as a function of orbital period when averaged over all unique orbital ephemerides. These planet detection metrics quantify the ability of TPS to detect a transiting planet signature on a star-by-star basis. They are uniquely applicable to a specific Kepler data release, since they are dependent on the details of the light curves searched and the functionality of the TPS algorithm used to perform the search. This document describes the window and one-sigma depth functions relevant to Kepler Data Release 25 (DR25), where the data were processed (Thompson et al. 2016) and searched (Twicken et al. 2016) with the SOC 9.3 pipeline. In Section 4, we describe significant differences from those reported in Kepler Data Release 24 (Burke Seader 2016) and document our verification method.

Planet Detection Metrics↗
NASA NTRS1974

Experiments with a four-bladed cyclic pitch stirring model rotor, part 3

The experimental work with the 2-bladed 16-inch diameter model rotor has been continued with a 4-bladed 16.5 inch diameter rotor capable of progressing and regressing cyclic pitch excitation (cyclic pitch stirring). Advance ratios of 0, .19 and .38 were tested at rotor speeds corresponding to non-dimensional blade natural frequencies of 1:14 and 1.19. The results are presented in the form of the first 5 Fourier components of the periodic response modulating function which for a periodic system takes the place of the complex response amplitude ratio of a constant system. In addition, the first and second harmonics of the trim response are presented. The test data are compared to analytical data without rotor wake and to the test data obtained earlier with the two-bladed rotor model of half the blade solidity ratio.

Hohenemser, K. H.↗
NASA NTRS1992

Description of the SSF PMAD dc testbed control system data acquisition function

A functional description of the various levels of the SSF power management and distribution dc test-bed control system architecture is presented, and the data acquisition function and the status of its implementation are described. The data requirements for the test-bed control system are dictated by the functionality being implemented at each level of the architecture. The test-bed control system hierarchy data acquisition function is distributed among its various levels. Fast-acting control functions that require time critical data are implemented at the lowest level. These functions require periodic data sampling to assure safe system operation and performance. Slower response control functions are implemented at the higher levels and require data to be reported at least every second. The present data acquisition function meets the requirements for a hierarchical and distributed power management and control system.

Baez, Anastacio N.↗
NASA NTRS1992

Resolution properties of the Fourier method for discontinuous waves

In this paper we discuss the wave-resolution properties of the Fourier approximations of a wave function with discontinuities. It is well known that a minimum of two points per wave is needed to resolve a periodic wave function using Fourier expansions. For Chebyshev approximations of a wave function, a minimum of pi points per wave is needed. Here we obtain an estimate for the minimum number of points per wave to resolve a discontinuous wave based on its Fourier coefficients. In our recent work on overcoming the Gibbs phenomenon, we have shown that the Fourier coefficients of a discontinuous function contain enough information to reconstruct with exponential accuracy the coefficient of a rapidly converging Gegenbauer expansion. We therefore study the resolution properties of a Gegenbauer expansion where both the number of terms and the order increase.

Gottlieb, David↗
DOE OSTI2024

Approaching periodic systems in ensemble density functional theory via finite one-dimensional models

Ensemble density functional theory (EDFT) is a generalization of ground-state DFT, which is based on an exact formal theory of finite collections of a system's ground and excited states. EDFT in various forms has been shown to improve the accuracy of calculated energy level differences in isolated model systems, atoms, and molecules, but it is not yet clear how EDFT could be used to calculate band gaps for periodic systems. We extend the application of EDFT toward periodic systems by estimating the thermodynamic limit with increasingly large finite one-dimensional 'particle in a box' systems, which approach the uniform electron gas (UEG). Using ensemble-generalized Hartree and local spin density approximation exchange-correlation functionals, we find that corrections go to zero in the infinite limit, as expected for a metallic system. However, there is a correction to the effective mass, with results comparable to other calculations on 1D, 2D, and 3D UEGs, which indicates promise for non-trivial results from EDFT on periodic systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1997

United States Control Module Guidance, Navigation, and Control Subsystem Design Concept

Should the Russian Space Agency (RSA) not participate in the International Space Station (ISS) program, then the United States (U.S.) National Aeronautics and Space Administration (NASA) may choose to execute the ISS mission. However, in order to do this, NASA must build two new space vehicles, which must perform the functions that the Russian vehicles and hardware were to perform. These functions include periodic ISS orbit reboost, initial ISS attitude control, and U.S. On-Orbit Segment (USOS) control Moment gyroscope (CMG) momentum desaturation. The two new NASA vehicles that must perform these functions are called the U.S. control module (USCM) and the U.S. resupply module. This paper presents a design concept for the USCM GN&C subsystem, which must play a major role in ISS orbit reboost and initial attitude control, plus USOS CMG momentum desaturation. The proposed concept is structured similar to the USOS GN&C subsystem, by design. It is very robust, in that it allows the USCM to assume a variety of vehicle attitudes and stay power-positive. It has a storage/safe mode that places the USCM in a gravity-gradient orientation and keeps it there for extended periods of time without consuming a great deal of propellant. Simulation results are presented and discussed that show the soundness of the design approach. An equipment list is included that gives detailed information on the baselined GN&C components.

Polites, M. E.↗