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Results for “reversible computation”

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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Finite element methods in probabilistic mechanics

Probabilistic methods, synthesizing the power of finite element methods with second-order perturbation techniques, are formulated for linear and nonlinear problems. Random material, geometric properties and loads can be incorporated in these methods, in terms of their fundamental statistics. By construction, these methods are applicable when the scale of randomness is not too large and when the probabilistic density functions have decaying tails. By incorporating certain computational techniques, these methods are shown to be capable of handling large systems with many sources of uncertainties. Applications showing the effects of combined random fields and cyclic loading/stress reversal are studied and compared with Monte Carlo simulation results.

Liu, Wing Kam↗
NASA NTRS1993

General Aviation Task Force report

General aviation is officially defined as all aviation except scheduled airlines and the military. It is the only air transportation to many communities throughout the world. In order to reverse the recent decline in general aviation aircraft produced in the United States, the Task Force recommends that NASA provide the expertise and facilities such as wind tunnels and computer codes for aircraft design. General aviation manufacturers are receptive to NASA's innovations and technological leadership and are expected to be effective users of NASA-generated technologies.

Source record↗
NASA NTRS2006

Program Synthesizes UML Sequence Diagrams

A computer program called "Rational Sequence" generates Universal Modeling Language (UML) sequence diagrams of a target Java program running on a Java virtual machine (JVM). Rational Sequence thereby performs a reverse engineering function that aids in the design documentation of the target Java program. Whereas previously, the construction of sequence diagrams was a tedious manual process, Rational Sequence generates UML sequence diagrams automatically from the running Java code.

Barry, Matthew R.↗
NASA NTRSDate not supplied

Precision in Assembled Discrete Lattice Space Structures for Next-Generation ISAM Applications

Robust autonomous robotic assembly of large-scale space structures has been a long-term and challenging goal to enable higher quality in-space communication and science instrumentation. For optical observatory support structures and antenna structures, the challenge is the strict dimensional precision requirements (generally RMS surface error) driven by the operational radiation wavelength. Early theoretical work in the area linked RMS surface error of a reflector support truss plate to the natural passive dynamic mode frequencies of the structure, as well as to the error distribution in dimensions of constituent structural elements. Prior robotic truss assembly demonstrations focused on designing ultra-high precision structural elements, joints, and robotic actuators. Recently, an alternative space structure assembly strategy based on a programmable matter approach (NASA ARMADAS) was demonstrated. This approach uses lattice building blocks (voxels) that are reversibly, mechanically joined into a bulk lattice structure by robots that locomote in and on the structure itself. Such a system can achieve high-level autonomy with low computation, robustly assemble utilizing inexpensive and imprecise robots, and efficiently build structures several orders of magnitude larger than the assembly robots. However, for instrumentation support structure applications, the resulting precision of these building block-based lattice structures is not well studied. Since they are demonstrated with many more assembly units than prior art trusses, it is unclear whether the same precision design approaches apply. In this work, we study in simulation the effects of voxel geometry, error in distribution, assembly resolution (module size), and assembly geometry on the error of both beam and plate lattice structures. While average RMS error of a plate increases with plate size, increasing plate thickness quickly collapses RMS error towards a limit that is on the order of the error of the constituent parts. We validate our models against previously published precision measurements of built systems. Results from this study will guide manufacturing precision requirements, as well as designs, for future robotically assembled structural applications and establish feasibility for different applications.

Christine E Gregg↗
DOE OSTI2023

Finding a contaminant source in a volume of flowing fluid

A method includes: mapping a boundary of a volume of flowing fluid; partitioning the volume by a computational mesh; finding a contaminant location at a first sensor that is disposed within the volume; obtaining a measured velocity of the flowing fluid within the volume; generating a reversed velocity vector field within the mesh, in response to the measured velocity; time stepping the contaminant location from the first sensor along the reversed velocity vector field until the contaminant location intersects the boundary of the volume; and finding a contaminant source at the intersection of the time stepped contaminant location with the boundary of the volume.

Lopez-Marrero, Vanessa↗
DOE OSTI2025

Electric Field Control of Magnetic Skyrmion Helicity in a Centrosymmetric 2D van der Waals Magnet

Two-dimensional van der Waals magnets hosting topological magnetic textures, such as skyrmions, show promise for spintronics and quantum computing. Electrical control of these topological spin textures is crucial for enhancing operational performance and functionality. Here, using electron microscopy combined with in situ electric and magnetic biasing, we show that the skyrmion helicity in insulating Cr 2 Ge 2 Te 6 can be controlled by the direction of the external electric field applied during the field cooling process. The electric field-tuned helicity remains stable at low temperature, even amid variations in magnetic and electric fields. Our theoretical investigation reveals that nonzero Dzyaloshinskii-Moriya interactions between nearest neighbors, induced by the electric field, change their sign upon reversing the electric field direction, thereby facilitating helicity selection. The electrical control of magnetic helicity demonstrated in this study can be extended to other centrosymmetric skyrmion-hosting magnets, paving the way for future device designs in topological spintronics and quantum computing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Proton Tunable Analog Transistor for Low Power Computing

This project was broadly motivated by the need for new hardware that can process information such as images and sounds right at the point of where the information is sensed (e.g. edge computing). The project was further motivated by recent discoveries by group demonstrating that while certain organic polymer blends can be used to fabricate elements of such hardware, the need to mix ionic and electronic conducting phases imposed limits on performance, dimensional scalability and the degree of fundamental understanding of how such devices operated. As an alternative to blended polymers containing distinct ionic and electronic conducting phases, in this LDRD project we have discovered that a family of mixed valence coordination compounds called Prussian blue analogue (PBAs), with an open framework structure and ability to conduct both ionic and electronic charge, can be used for inkjet-printed flexible artificial synapses that reversibly switch conductance by more than four orders of magnitude based on electrochemically tunable oxidation state. Retention of programmed states is improved by nearly two orders of magnitude compared to the extensively studied organic polymers, thus enabling in-memory compute and avoiding energy costly off-chip access during training. We demonstrate dopamine detection using PBA synapses and biocompatibility with living neurons, evoking prospective application for brain - computer interfacing. By application of electron transfer theory to in-situ spectroscopic probing of intervalence charge transfer, we elucidate a switching mechanism whereby the degree of mixed valency between N-coordinated Ru sites controls the carrier concentration and mobility, as supported by density functional theory (DFT) .

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Stepped pressure equilibrium with relaxed flow and applications in reversed-field pinch plasmas

The multi-region relaxed magnetohydrodynamics (MRxMHD) has been successful in the construction of equilibria in three-dimensional (3D) configurations. In MRxMHD, the plasma is sliced into sub-volumes separated by ideal interfaces, each undergoing relaxation, allowing the formation of islands and chaos. The resulting equilibrium has a stepped pressure profile across sub-volumes. The stepped pressure equilibrium code (SPEC) was developed to calculate MRxMHD equilibria numerically. In this work, we have extended the SPEC code to compute MRxMHD equilibria with field-aligned flow and rotation, following the theoretical development to incorporate cross-helicity and angular momentum constraints. The code has been verified for convergence and compared to a Grad–Shafranov solver in 2D. We apply our new tool to study the flow profile change before and after the sawtooth crash of a reversed-field pinch discharge, in which data of the parallel flow is available. We find the promising result that under the constraints of cross-helicity and angular momentum, the parallel flow profile in post-crash SPEC equilibrium is flat in the plasma core and the amplitude of the flow matches experimental observations. Lastly, we provide an example equilibrium with a 3D helical field structure as the favored lower energy state. This will be the first 3D numerical equilibrium in which the flow effects are self-consistently calculated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2006

Unsteady Flow Simulation of High-speed Turbopumps

Computation of high-speed hydrodynamics requires high-fidelity simulation to resolve flow features involving transient flow, cavitation, tip vortex and multiple scales of unsteady fluctuations. One example of this type in aerospace is related to liquid-fueled rocket turbopump. Rocket turbopumps operate under severe conditions at very high rotational speeds typically at thousands of rpm. For example, the Shuttle orbiter low-pressure-fuel-turbopump creates transient flow features associated with reverse flows, tip clearance effects, secondary flows, vortex shedding, junction flows, and cavitation effects. Flow unsteadiness originating from the orbiter Low-Pressure-Fuel-Turbopump (LPFTP) inducer is one of the major contributors to the high frequency cyclic loading that results in high cycle fatigue damage to the flow liners just upstream of the LPFTP. The reverse flow generated at the tip of the inducer blades travels upstream and interacts with the bellows cavity. Simulation procedure for this type high-speed hydrodynamic problems requires a method for quantifying multi-scale and multi-phase flow as well as an efficient high-end computing strategy. The current paper presents a high-fidelity computational procedure for unsteady hydrodynamic problems using a high-speed liquid-fueled rocket turbopump.

Kiris, Cetin C.↗
DOE OSTI2017

Revealing the Conversion Mechanism of Transition Metal Oxide Electrodes during Lithiation from First-Principles

Transition metal oxides such as Co3O4 and NiO are of significant interest as conversion anode materials for lithium-ion batteries (LIBs), due to their remarkably high theoretical capacities and low cost. While many previous experiments have found that the charge/discharge reactions of Co3O4 and NiO can be highly reversible, detailed information about the mechanisms of these reactions, such as the origin of the voltage hysteresis (>1.0 V) between the charge/discharge cycles, is still poorly understood. In this work, we develop and utilize a new computational mechanistic approach that helps elucidate the hysteresis and nonequilibrium reaction pathways associated with these conversion materials. We apply this methodology to investigate a variety of lithiation reaction pathways of Co3O4 and NiO by systematically exploring the energetics of a large number of equilibrium and nonequilibrium LixCo3O4 (0 ≤ x ≤ 8) and LixNiO (0 ≤ x ≤ 2) structural configurations using first-principles calculations. The overall value of the voltages from our nonequilibrium pathway is in much better agreement with experimental lithiation than the calculated equilibrium voltage while the overall value of the latter reasonably agrees with experimental delithiation. Hence, we propose the charge and discharge processes proceed through equilibrium and nonequilibrium reaction paths, respectively, which contribute significantly to the experimentally observed voltage hysteresis in Co3O4 and NiO. Additionally, we find a low-energy, lithiated intermediate phase (Li3Co3O4) with an oxygen framework equal to that of the initial Co3O4 spinel phase. This intermediate phase represents the capacity threshold below which limited volume expansion and better reversibility can be realized and above which reactions lead to structural degradation and huge expansion.

Yao, Zhenpeng↗
DOE OSTI2018

Memristive Ion Channel-Doped Biomembranes as Synaptic Mimics

Solid-state neuromorphic systems based on transistors or memristors have yet to achieve the interconnectivity, performance, and energy efficiency of the brain due to excessive noise, undesirable material properties, and nonbiological switching mechanisms. Here in this work, we demonstrate that an alamethicin-doped, synthetic biomembrane exhibits memristive behavior, emulates key synaptic functions including paired-pulse facilitation and depression, and enables learning and computing. Unlike state-of-the-art devices, our two-terminal, biomolecular memristor features similar structure (biomembrane), switching mechanism (ion channels), and ionic transport modality as biological synapses while operating at considerably lower power. The reversible and volatile voltage-driven insertion of alamethicin peptides into an insulating lipid bilayer creates conductive pathways that exhibit pinched current–voltage hysteresis at potentials above their insertion threshold. Moreover, the synapse-like dynamic properties of the biomolecular memristor allow for simplified learning circuit implementations. Finally, low-power memristive devices based on stimuli-responsive biomolecules represent a major advance toward implementation of full synaptic functionality in neuromorphic hardware.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Target–decoy false discovery rate estimation using Crema

Assigning statistical confidence estimates to discoveries produced by a tandem mass spectrometry proteomics experiment is critical to enabling principled interpretation of the results and assessing the cost/benefit ratio of experimental follow-up. The most common technique for computing such estimates is to use target-decoy competition (TDC), in which observed spectra are searched against a database of real (target) peptides and a database of shuffled or reversed (decoy) peptides. TDC procedures for estimating the false discovery rate (FDR) at a given score threshold have been developed for application at the level of spectra, peptides, or proteins. Although these techniques are relatively straightforward to implement, it is common in the literature to skip over the implementation details or even to make mistakes in how the TDC procedures are applied in practice. Here we present Crema, an open-source Python tool that implements several TDC methods of spectrum-, peptide- and protein-level FDR estimation. Crema is compatible with a variety of existing database search tools and provides a straightforward way to obtain robust FDR estimates.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Acceleration and Stabilization of Electron Transfer Products with Improved Quantum Yields upon Cation Binding to a Fused Bis-Zinc Porphyrin-Quinone Donor–Acceptor Conjugate

The role of metal ions in promoting electron transfer processes in biological coenzymes is of great significance not only to understand their mechanistic details but also due to their direct utilization in a number of chemical and biochemical processes. Here, we demonstrate an increased rate of forward electron transfer with improved reaction quantum yield, and an enhanced lifetime of electron transfer products upon cation binding to the acceptor entity in a donor-acceptor conjugate. Selective binding of cations such as Mg 2+ or Sc 3+ to the electron acceptor, quinone, in a fused, bis-zinc porphyrin-quinone donor-acceptor conjugate leads to facile reduction of the quinone making the electron transfer process thermodynamically highly feasible. Furthermore, the binding of metal ions to the electron transfer product, quinone anion, decelerates the reverse electron transfer process due to ion-pairing interactions, resulting in improving both the lifetime and quantum yields of the electron transfer products. Furthermore, systematic studies including spectral, electrochemical, computational, spectroelectrochemical, and transient absorption techniques, coupled with data analysis by Global Target Analysis (GloTarAn), are performed to demonstrate these novel findings that are relevant to further our understanding of electron transfer processes occurring in biological coenzymes and pertinent energy harvesting schemes.

Charge transfer↗
DOE OSTI2020

Ca Cobaltites as Potential Cathode Materials for Rechargeable Ca-Ion Batteries: Theory and Experiment

Rechargeable Ca-based batteries can potentially achieve higher energy capacity than Li-ion batteries. The development of Ca-ion batteries, however, remains in its infancy, especially due to the challenge of finding cathode materials with high reversible capacity. In this work, we investigate properties of Ca cobaltites as Ca-ion intercalation cathodes, by means of density functional theory calculations validated by synthesis and electrochemical measurements. Computationally, we accessed thermodynamic, diffusion properties, energy capacity, and the voltage profiles for four Ca cobaltite compounds of different stoichiometry and Co oxidation states: Ca 3 Co 2 O 6 , CaCo 2 O 4 , Ca 2 Co 2 O 5 , and [Ca 2 CoO 3 ][CoO 2 ] 1.62 . We found good stability and relatively low migration barriers of some Ca cobaltites during cycling with the layered CaCo 2 O 4 having the lowest Ca migration barrier of 0.7 eV and the highest theoretical capacity. To validate our calculations, we synthesized Ca 3 Co 2 O 6 , CaCo 2 O 4 , and [Ca 2 CoO 3 ][CoO 2 ] 1.62 with the Pechini method and, subsequently, to test the electrochemical extraction of Ca.

25 ENERGY STORAGE↗
DOE OSTI2014

How to Chemically Tailor Metal-Porphyrin-Like Active Sites on Carbon Nanotubes and Graphene for Minimal Overpotential in the Electrochemical Oxygen Evolution and Oxygen Reduction Reactions

Density functional theory calculations are used to study the energetics of the electrochemical oxygen evolution reaction (OER) of water and the reverse oxygen reduction reaction (ORR) on metal-porphyrin-like centers incorporated into graphene layers or single-walled carbon nanotubes (SWCNTs). The objective is to explore the reductions in computational thermodynamic overpotential that can be achieved relative to catalysis on metal oxide surfaces (OER) or platinum (ORR) by varying the metal center and axial ligand. This permits a degree of simultaneous control over the free energy gap between the lowest energy OH and highest energy OOH intermediates, and the position of the oxo (O) intermediate in this gap. Optimal choice of metal toward the right of the first transition series largely controls the gap. Given a suitable metal such as Fe, the overpotential for OER can be tuned over a range greater than 0.35 V by choice of the axial ligand. For OER occurring within the SWCNTs, a minimum predicted overpotential of 0.35 V is found, very close to the gap-imposed limit of 0.30 V for this system. Similarly, the overpotential of ORR can be tuned over a range more than 0.30 V by selection of the axial ligand. While the calculations necessarily have limited accuracy, the principles should provide a transferable path toward overpotential optimization for the OER and ORR.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Direct in situ measurement of specific capacitance, monolayer tension, and bilayer tension in a droplet interface bilayer

In this study, thickness and tension are important physical parameters of model cell membranes. However, traditional methods to measure these quantities require multiple experiments using separate equipment. This work introduces a new multi-step procedure for directly accessing in situ multiple physical properties of droplet interface bilayers (DIB), including specific capacitance (related to thickness), lipid monolayer tension in the Plateau-Gibbs border, and bilayer tension. The procedure employs a combination of mechanical manipulation of bilayer area followed by electrowetting of the capacitive interface to examine the sensitivities of bilayer capacitance to area and contact angle to voltage, respectively. These data allow for determining the specific capacitance of the membrane and surface tension of the lipid monolayer, which are then used to compute bilayer thickness and tension, respectively. The use of DIBs affords accurate optical imaging of the connected droplets in addition to electrical measurements of bilayer capacitance, and it allows for reversibly varying bilayer area. After validating the accuracy of the technique with diphytanoyl phosphatidylcholine (DPhPC) DIBs in hexadecane, the method is applied herein to quantify separately the effects on membrane thickness and tension caused by varying the solvent in which the DIB is formed and introducing cholesterol into the bilayer. Because the technique relies only on capacitance measurements and optical images to determine both thickness and tension, this approach is specifically well-suited for studying the effects of peptides, biomolecules, natural and synthetic nanoparticles, and other species that accumulate within membranes without altering bilayer conductance.

59 BASIC BIOLOGICAL SCIENCES↗