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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

A methodology for modeling the mechanical interaction between a reaction wheel and a flexible structure

This paper presents a modeling methodology used to predict the performance of a flexible structure, such as a space telescope, in the presence of an on-board vibrational disturbance source, such as a reaction wheel assembly (RWA). Both decoupled and coupled analysis methods are presented. The decoupled method relies on blocked RWA disturbances, measured with the RWA hardmounted to a rigid surface. The coupled method corrects the blocked RWA disturbance boundary conditions using "force filters," which depend on estimates of the interface accelerances of the RWA and space-craft. Both methods were validated on the Micro-Precision Interferometer testbed at the Jet Propulsion Laboratory. Experimental results are encouraging, indicating that both methods provide sufficient accuracy compared to measured values; however, the coupled method provides the best results when the gyroscopic nature of the spinning RWA is captured in the RWA accelerance model. Additionally, the RWA disturbance cross spectral density terms are found to be influential.

vibration↗
NASA NTRS2024

x Thermal Straps

Thermal straps, also known as heat straps or flexible conductive links, offer design solutions for enhancing the thermal bond of two items that may need to be mechanically decoupled. The need for mechanical decoupling can be driven by requirements for things like vibration or load isolation, or simply by packaging constraints. A few examples include thermal straps used to mechanically isolate delicate spaceborne detectors from cryocooler vibrations, or thermal straps coupling a high-dissipation electronic component to a heat sink on an adjacent surface in a volume optimized electronics unit.

thermal, heat transfer, straps↗
DOE OSTI2018

Energy deposition validation results for the evaluated electron data library in FRENSIE - 25357

The Framework for Research in Nuclear Science and Engineering (FRENSIE) is a collection of packages written in C++ that are designed primarily to aid in methods development. A recent development in FRENSIE is the modeling of single scattering electron interactions using the data in the Evaluated Electron Data Library (EEDL) from Lawrence Livermore National Laboratory (LLNL). Preliminary verification and validation (V and V) results using the well-known Lockwood energy deposition experiment and a comparison with MCNP6.2 were performed using several bivariate grid policies (Unit-base, Correlated, Unit-base Correlated), interpolation schemes (lin-lin, log-log, lin-log), and physics options (Coupled and Decoupled Elastic Scattering). The results show an agreement to within 0.5% between MCNP6.2 and FRENSIE when using the same bivariate grid policy (Correlated) and interpolation scheme (log-log). When compared to the experimental results of the Lockwood experiment, it was found that a Unit-base bivariate grid policy, lin-lin interpolation scheme, and lin-log interpolation scheme did not produce accurate results for the energy deposition in test problems. The log-log Correlated and Unit-base Correlated results showed the greatest agreement with the Lockwood experiment. The total energy deposition matched the experimental data to within 3%. Both the Correlated and Unit-base Correlated results had a tendency to estimate a higher energy deposition near the peaks and a lower energy deposition near the tails. The differences between coupled elastic scattering and decoupled scattering models were shown to be more prominent at higher energies with the results of the coupled elastic scattering being more accurate for the peak and less accurate for the tail of the energy deposition profiles. (authors)

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2024

An Efficient Numerical Algorithm for Solving Coupled Time-Dependent Ginzburg-Landau Equation for Superconductivity and Elasticity

A decoupled finite element algorithm is developed for simulating the vortex dynamics on an elastic superconductor which couples the time-dependent Ginzburg- Landau equation with the complex-valued superconducting order parameter and the vector-valued magnetic potential, and the elasticity equation. We present an iterative algorithm for the decoupled system arising from the time and spatial discretization using a combination of preconditioner, algebraic multigrid method (AMG) and preconditioned conjugate gradient method (PCG). The iterative algorithm allows us to perform large-scale three-dimensional simulations of mesoscale pattern formation during superconducting phase transitions with arbitrary elastic boundary conditions. Here, the performance and efficiency of the algorithm are numerically verified by several benchmark problems, exhibiting up to two orders of magnitude improvement depending on the scale of discrete system compared to the exact solver.

Efficiency↗
DOE OSTI2026

WIMP-like Dark Matter Without Thermalization At Freeze-Out

In the standard thermal relic scenario, dark matter remains in chemical equilibrium with the Standard Model radiation bath until freeze-out occurs at $T \sim m_X/20$, where $m_X$ is the dark matter mass. In this familiar class of models, the observed relic density is obtained for annihilation cross sections of order $σv \sim 10^{-26}$ cm$^3$/s. We show that comparable cross sections can naturally be realized in hidden-sector models in which the dark matter and Standard Model sectors decouple at a very high temperature, $T \gg m_X$, and subsequently evolve with separate thermal histories. Despite this decoupling, the two sectors have similar temperatures during freeze-out, leading to the usual thermal relic abundance. As a consequence, the coupling between the Standard Model and hidden sectors can be extremely small, potentially placing direct detection and collider signals far below foreseeable sensitivities.

Hooper, Dan [Wisconsin U., Madison] (ORCID:0009000↗
DOE OSTI2018

Mixed Spin (1, 5/2) Ising Ferromagnetic Blume-Capel Model Under Time-Dependent Sinusoidal Magnetic Field: an Effective-Field Theory Analysis

Non-equilibrium magnetic properties are studied in a two-dimensional mixed spin (1, 5/2) Blume-Capel Ising system under the influence sinusoidal magnetic fields using the effective-field theory based on a decoupling approximation. A dynamic equation of motion has been solved for a square lattice by utilizing a Glauber-type stochastic process. Dynamic phase diagrams are presented in the reduced magnetic field amplitude and reduced temperature plane (h,T) and reduced crystal-field and reduced temperature plane (Δ,T). We observe that the system exhibits dynamic tricritical behaviors. Phase diagrams contain the paramagnetic (p), ferrimagnetic (i), and coexistence or mixed-phase regions, namely the i,p, and i + p, which strongly depend on the crystal-field interaction parameter and oscillating magnetic field frequency. We have found that the system only exhibits a second-order transition line in the higher-frequency region. We have also compared our result with the mean-field prediction in order to indicate the effects of correlations and found that some of the dynamic first-order phase lines disappeared.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nanoscale plasmonic detector of wave intensity difference and uni-directional waveguide

In this paper, a new nanoscale plasmonic differential detector of wave intensities is proposed. This structure can be useful for calibration applications and for finding out if a wave intensity is high enough to pass a threshold level or not. Next, a nanoscale plasmonic uni-directional waveguide is presented. The distinction of this waveguide with similar cases is that the one-way wave-guiding is provided by adding a properly located controlling source, without employing any non-reciprocal material. This feature can be used in many applications that only uni-directional wave propagation is desirable. Both structures have been designed in metal–insulator–metal structure including cavity resonators. The operations are based on the coupling of the wave from input waveguides to the cavity resonators and decoupling to output waveguides in the cavity resonance wavelengths. The simulation results of performance of the structures, as elements applicable to photonic integrated circuits, have been obtained using the numerical method of the finite difference time domain.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Optimization of signal-to-noise ratio in the in vivo{sup 31}P magnetic resonance spectra of the human brain

The main problem in {sup 31}P magnetic resonance spectroscopy is a low signal-to-noise ratio (SNR) of spectra acquired with clinical magnetic resonance imaging (MRI) scanners. Using spin-spin phosphorus-proton ({sup 31}P-{sup 1}H) decoupling and heteronuclear Overhauser effect and taking into account the effect of the longitudinal relaxation time T{sub 1} on the SNR, the method for localization and excitation of the region of interest (Image Selected in vivo Spectroscopy pulse sequence) was optimized to increase the SNR in the {sup 31}P magnetic resonance spectra of the human brain to ~50% without increasing signal acquisition time.

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

Forest wind regimes and their implications on cross-canopy coupling

An analysis of wind regimes across forests of varying density and height is presented. The hockey stick-like dependence of the friction velocity on the mean advective wind speed is used to determine the threshold between the weak-wind and the strong-wind regime for the entire canopy. Such thresholds are compared across four different sites. The height dependence of thresholds within the canopy is inverted compared to the one above grassland sites. This can be understood by extending the accepted interpretation for weak-wind thresholds from grassland sites to forested sites. Even for large fluctuations above the canopy, the fluctuations of the vertical wind velocity in the subcanopy remain small during weak-wind situations. Correspondingly, in the strong-wind regime, turbulence in the subcanopy remains strong in spite of reduced above-canopy turbulence. This fact suggests that previously used methods for determining the degree of coupling across the canopy layer based upon the ratio of the vertical wind variance between the above-canopy and subcanopy may prove erroneous. Furthermore, it emphasizes the significance of mechanisms generating subcanopy turbulence other than above-canopy turbulent transport and shear. The transport of mass and energy between the subcanopy and above-canopy layers is significantly reduced during the weak-wind regime. In particular, the vertical turbulent transport is reduced by more than one order of magnitude. This suggests a decoupling of the subcanopy layer during weak-wind situations and allows for the accumulation of carbon dioxide originating from soil respiration in the subcanopy layer during the weak-wind regime.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Quantum dynamics of a small symmetry breaking measurement device

Highlights: • Ferromagnetic measurement device exploits symmetry breaking to measure a spin. • Quantum interaction results in loss of phase coherence of test object. • Dynamics lead to sizeable correlation with, and enhancement of, microscopic object. • No reliable registration of pointer readings is observed after decoupling spin. - Abstract: A quantum measuring instrument is constructed that utilises symmetry breaking to enhance a microscopic signal. The entire quantum system consists of a system–apparatus–environment triad that is composed of a small set of spin-1/2 particles. The apparatus is a ferromagnet that measures the z-component of a single spin. A full quantum many-body calculation allows for a careful examination of the loss of phase coherence, the formation and amplification of system–apparatus correlations, the irreversibility of registration, the fault tolerance, and the bias of the device.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Geodesic motion around hairy black holes

In a recent paper Ovalle et al. (2021) it has been obtained new static black hole solutions with primary hairs by the Gravitational Decoupling. In this work we either study the geodesic motion of massive and massless particles around those solutions and restrict the values of the primary hairs by observational data. In particular, we obtain the effective potential, the innermost stable circular orbits, the marginally bounded orbit, and the periastron advance for time-like geodesics. In order to restrict the values taken by the primary hairs we explore their relationship with the rotation parameter of the Kerr black hole giving the same innermost stable circular orbit radius and give the numerical values for the supermassive black holes at Ark 564 and NGC 1365. The photon sphere and the impact parameter associated to null geodesics are also discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Deforestation triggering irreversible transition in Amazon hydrological cycle

The Amazon is hypothesized to reach an irreversible ‘tipping point’ when deforestation slows the hydrological cycle sufficiently that tropical forest ecosystems cannot be sustained. However, inception of such a tipping point has not been supported by observations and the relevant links between deforestation and atmospheric moisture recycling are poorly understood. Here we show that reduction in evapotranspiration from 20 years of deforestation dried the atmosphere persistently and caused moisture decoupling, i.e. an opposite sign of moisture change between the lower and middle troposphere. Increased deforestation exacerbated the lower troposphere drying and caused it to penetrate deeper into the middle troposphere in the dry and transition seasons over monsoon forests and savannas. Deforestation induced warming-enhanced buoyant updrafts, elevated hot and dry air and thereby reduced downward mixing of water supplies from the tropical Atlantic that normally moisten the Amazon forests. The severe atmospheric desiccation in the southern and eastern Amazon cannot be compensated by enhanced water supplies from the Atlantic Ocean, demonstrating an irreversible transition in Amazon hydrological cycle exacerbated by rapid deforestation. The more recent drying through the seasons over rainforests and during the wet season over the transition zones from rainforests to monsoon forests and savannas, however, suggests a window of opportunity for preventing ecosystem collapse with forest conservation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Short-Depth QAOA circuits and Quantum Annealing on Higher-Order Ising Models (Rev.2)

The Quantum Alternating Operator Ansatz (QAOA) and Quantum Annealing (QA) are quantum algorithms that are both based on the adiabatic theorem and both have the goal of sampling the optimal solution(s) of combinatorial optimization problems. Quantum annealing has been physically instantiated on D-Wave devices using superconducting flux qubits, and QAOA can be programmed on digital gate-model quantum computers such as the programmable superconducting transmon qubits devices of the IBMQ series, for instance ibm washington. QAOA and QA address the same types of problems, but it is unclear how they will scale to large problem sizes and to larger and higher-fidelity quantum computers. In this article, we present a direct comparison between QAOA, one and two rounds, run on all 127 qubits of ibm washington and QA run on D-Wave Advantage system4.1 and Advantage system6.1. The problems which allow for this comparison are random Ising model problems whose connectivity matches the heavy hexagonal lattice topology of ibm washington and the Pegasus graph connectivity of the two D-Wave devices. We create two classes of problem instances for this comparison: one with higher order terms (ZZZ variable interactions), linear terms, and quadratic terms, and a separate problem type with only linear and quadratic terms. Our QAOA circuits are novel and extremely short depth, with a CNOT depth of 6 per round, which allows whole chip usage of ibm washington’s heavy hexagonal lattice and can be applied to future heavy-hex chips. We also test the effectiveness of the error suppression technique digital dynamical decoupling on the QAOA circuits. The QAOA circuits compiled to ibm washington are composed of several thousand circuit instructions, approximately 3, 000 depending on the details of the circuit, making these some the largest quantum circuits ever executed on a digital quantum processor. QAOA and QA are compared against the classical heuristic algorithm of simulated annealing and all problem instances are exactly solved using CPLEX in order to evaluate which samplers, if any, correctly found the ground state solution(s) of the problem instances. We find that (i) QA outperforms QAOA on all problem instances, (ii) QAOA samples the problems better than random sampling, and (iii) QAOA angle computation exhibits clear parameter concentration across the ensemble of Ising models.

127 Qubits↗
DOE OSTI2018

Temporal Coupling of Subsurface and Surface Soil CO 2 Fluxes: Insights From a Nonsteady State Model and Cross-Wavelet Coherence Analysis

Inferences about subsurface CO 2 fluxes often rely on surface soil respiration (R soil ) estimates because directly measuring subsurface microbial and root respiration (collectively, CO 2 production, S Total ), is difficult. To evaluate how well R soil serves as a proxy for S Total , we applied the nonsteady state DEconvolution of Temporally varying Ecosystem Carbon componenTs model (0.01-m vertical resolution), using 6-hourly data from a Wyoming grassland, in six simulations that cross three soil types (clay, sandy loam, and sandy) with two depth distributions of subsurface biota. We used cross-wavelet coherence analysis to examine temporal coherence (localized linear correlation) and offsets (lags) between S Total and R soil and fluxes and drivers (e.g., soil temperature and moisture). Cross-wavelet coherence revealed higher coherence between fluxes and drivers than linear regressions between concurrent variables. Soil texture and moisture exerted the strongest controls over coherence between CO 2 fluxes. Coherence between CO 2 fluxes in all soil types was strong at short (~1 day) and long periods (>8 days), but soil type controlled lags, and rainfall events decoupled the fluxes at periods of 1–8 days for several days in sandy soil, up to 1 week in sandy loam, and for a month or more in clay soil. Concentrating root and microbial biomass nearer the surface decreased lags in all soil types and increased coherence up to 10% in clay soil. The assumption of high temporal coherence between R soil and S Total is likely valid in dry, sandy soil, but may lead to underestimates of short-term STotal in semiarid grasslands with fine-grained and/or wet soil.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

The Unified Electrochemical Band Diagram Framework: Understanding the Driving Forces of Materials Electrochemistry

Recent work that establishes a picture of the driving forces that govern material transformations and degradation in electrochemical environments to enable the ab initio design of electrochemical materials is highlighted. Select prototype systems are used to describe how the interplay between materials properties such as crystal field splitting, band edge energies, surface termination, material length scale, dielectric constant, and isoelectric point, and electrolyte properties such as pH and ion type, impacts electrochemical behavior - i.e., redox potentials, reaction enthalpies, reactivity, and decoupled ionic/electronic processes. Ab initio modeling of charged defects and intercalants within the grand canonical unified electrochemical band-diagram (UEB) framework is shown to enable the quantitative prediction of electrochemical materials behavior. UEB combines electrochemical theory, charged defect theory, and band diagram descriptions and can be used both for materials discovery and development. First, a pedagogical description of the UEB framework is presented, and then the application of this framework to reveal mechanisms for high rate electronic charge storage in cation incorporated α.-MnO 2 and λ-MnO 2 , high desalination efficiency of thin-film NaMn 4 O 8 , and the flat charge/discharge profile of FePO 4 is reviewed. Finally, new prospects for the application of the UEB framework to electrolyte design, interfacial engineering, and catalysis are suggested.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Metallo‐Hydrogel‐Assisted Synthesis and Direct Writing of Transition Metal Dichalcogenides

Abstract Two dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted interest for their compelling nanoscale new properties and numerous potential applications including fast optoelectronic devices, ultrathin photovoltaics, and high‐performance catalysts. Large‐scale growth of uniform TMDC materials is essential for investigating their physics and for their integration into devices. However, the wafer scale deposition of TMDCs on arbitrary nonselective substrates is still beyond the current state‐of‐the‐art. In this article, a method to synthesize layered TMDCs (MoS 2 and WS 2 ) at the wafer‐scale by sulfurization of transition metal ions (Mo 5+ and W 6+ ) in a gelatin template (metallo‐hydrogel) is reported. This process is adaptable to versatile substrates, including amorphous silicon oxide, high‐temperature quartz, and silicon. Although the products are nominally few layer materials, direct band photoluminescent (≈1.8 eV), similar to single‐ or decoupled multilayer MoS 2 is observed. Finally, the solution‐based deposition enables contact printing of TMDC channels to be useable for device applications including thin film transistors with printed silver contacts using the same process.

Zang, Xining↗