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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 145 records · Page 8

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NASA NTRS1984

A numerical analysis of transient planetary waves and the vertical structure in a meso-strato-troposphere model, part 1.4A

The structure of unstable planetary waves is computed by a quasi-geostrophic model extending from the surface up to 80 km by means of eigenvalue-eigenfunction techniques in spherical coordinates. Three kinds of unstable modes of distinct phase speeds and vertical structures are identified in the winter climate state: (1) the deep Green mode with its maximum amplitude in the stratosphere; (2) the deep Charney mode with its maximum amplitude in the troposphere: and (3) the shallow Charney mode which is largely confined to the troposphere. Both the Green mode and the deep Charney mode are characterized by very slow phase speeds. They are mainly supported by upward wave energy fluxes, but the local baroclinic energy conversion within the stratosphere also contributes in supporting these deep modes. The mesosphere and the troposphere are dynamically independent in the summer season decoupled by the deep stratospheric easterly. The summer mesosphere supports the easterly unstable waves 1-4. Waves 3 and 4 are identified with the observed mesospheric 2-day wave and 1.7-day wave, respectively.

Zhang, K. S.↗

NASA NTRS2020

The Dynamics, Destruction, and Survival of Supernova-Formed Dust Grains

Observations have demonstrated that supernovae efficiently produce dust. This is consistent with the hypothesis that supernovae and asymptotic giant branch stars are the primary producers of dust in the universe. However, there has been a longstanding question of how much of the dust detected in the interiors of young supernova remnants can escape into the interstellar medium. We present new hydrodynamical calculations of the evolution of dust grains that were formed in dense ejecta clumps within a Cas A–like remnant. We follow the dynamics of the grains as they decouple from the gas after their clump is hit by the reverse shock. They are subsequently subject to destruction by thermal and kinetic sputtering as they traverse the remnant. Grains that are large enough (∼0.25 μm for silicates and ∼0.1 μm for carbonaceous grains) escape into the interstellar medium while smaller grains get trapped and destroyed. However, grains that reach the interstellar medium still have high velocities, and are subject to further destruction as they are slowed down. We find that for initial grain size distributions that include large (∼0.25–0.5 μm) grains, 10%–20% of silicate grains can survive, while 30–50% of carbonaceous grains survive even when the initial size distribution cuts off at smaller (0.25 μm) sizes. For a 19 Mꙩ star similar to the progenitor of Cas A, up to 0.1 Mꙩ of dust can survive if the dust grains formed are large. Thus we show that supernovae under the right conditions can be significant sources of interstellar dust.

Jonathan D. Slavin↗

DOE OSTI2026

Temporal entanglement transitions in the periodically driven Ising chain

Periodically driven quantum systems can host non-equilibrium phenomena without static analogs, including in their entanglement dynamics. Here, we discover (TET) in a Floquet spin chain, which correspond to a quantum phase transition in the spectrum of the entanglement Hamiltonian and are signaled by dynamical spontaneous symmetry breaking. We identify the symmetry principles underlying these transitions: they appear when the driven Hamiltonian preserves global symmetry (here, ℤ2), the initial state respects this symmetry, and the reduced density matrix carries weight in both subsystem-parity sectors, with TET occurring precisely when the sector weights become equal (given the previous two conditions are also satisfied). Intriguingly, we find these transitions across a broad range of driving frequencies (from adiabatic to high-frequency regime) and independently of drive details, where they manifest as periodic, sharp entanglement spectrum reorganizations marked by the Schmidt-gap closure, a vanishing entanglement echo, and symmetry-quantum-number flips, while remaining invisible to conventional local observables. At high frequencies, the entanglement Hamiltonian acquires an intrinsic timescale decoupled from the drive period, rendering the transitions genuine steady-state features. Finite-size scaling reveals universal critical behavior with correlation-length exponent 𝜈 = 1, matching equilibrium Ising universality despite its emergence from purely dynamical mechanisms decoupled from static criticality. Furthermore, our work establishes TET as novel features in Floquet quantum matter.

36 MATERIALS SCIENCE↗

NASA NTRS1973

Decoupling in linear time-varying multivariable systems

The necessary and sufficient conditions for the decoupling of an m-input, m-output, linear time varying dynamical system by state variable feedback is described. The class of feedback matrices which decouple the system are illustrated. Systems which do not satisfy these results are described and systems with disturbances are considered. Some examples are illustrated to clarify the results.

Sankaran, V.↗

NASA NTRS1989

Bandwidth-limited robust nonlinear sliding control of pointing and tracking maneuvers

It is shown how multiaxial spacecraft tracking and pointing maneuvers with known control bandwidth and given tracking error bounds can be implemented by variable-structure control in the presence of uncertain vehicle and target dynamics. It is shown how to select a nonlinear sliding surface relating attitude and rate variables, as well as a Lyapunov function in the surface variables that absorbs multiplicative model undertainties, thereby simplifying the computation of control corrections. It is then shown how a boundary layer envelope can be designed, within which the components of the surface error dynamics can be modeled as the outputs of designer-selected decoupled low-pass filters. Closed-loop stability conditions accounting for the coupling between the attitude error dynamics and the surface error dynamics are then obtained.

Dwyer, Thomas A. W., III↗

DOE OSTI2025

Conservative Spin-Magnitude Change in Orbital Evolution in General Relativity

We show that physical scattering observables for compact spinning objects in general relativity can depend on additional degrees of freedom in the spin tensor beyond those described by the spin vector alone. The impulse, spin kick, and leading-order waveforms exhibit such a nontrivial dependence. A signal of this additional structure is the change in the magnitude of the spin vector under conservative Hamiltonian evolution, similar to our previous studies in electrodynamics. These additional degrees of freedom describe dynamical mass multipoles of compact objects and decouple for black holes. We also show that the conservative impulse, spin kick, and change of the additional degrees of freedom are encoded in the eikonal phase.

Classical black holes↗

DOE OSTI2021

Enabling Scalable and Extensible Memory-mapped Datastores in Userspace

Exascale workloads are expected to incorporate data-intensive processing in close coordination with traditional physics simulations. These emerging scientific, data-analytics and machine learning applications need to access a wide variety of datastores in flat files and structured databases. Programmer productivity is greatly enhanced by mapping datastores into the application process's virtual memory space to provide a unified “in-memory” interface. Currently, memory mapping is provided by system software primarily designed for generality and reliability. However, scalability at high concurrency is a formidable challenge on exascale systems. Also, there is a need for extensibility to support new datastores potentially requiring HPC data transfer services. In this article, we present UMap , a scalable and extensible userspace service for memory-mapping datastores. Furthermore, through decoupled queue management, concurrency aware adaptation, and dynamic load balancing, UMap enables application performance to scale even at high concurrency. We evaluate UMap in data-intensive applications, including sorting, graph traversal, database operations, and metagenomic analytics. Our results show that UMap as a userspace service outperforms an optimized kernel-based service across a wide range of intra-node concurrency by 1.22-1.9 × . We performed two case studies to demonstrate UMap 's extensibility. First, a new datastore residing in remote memory is incorporated into UMap as an application-specific plugin. Second, we present a persistent memory allocator Metall built atop UMap for unified storage/memory.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS2013

Crystal Shape Evolution in Detached Bridgman Growth

Detached (or dewetted) Bridgman crystal growth defines that process in which a gap exists between a growing crystal and the crucible wall. Existence of the gap provides several advantages, including no sticking of the crystal to the crucible wall, reduced thermal and mechanical stresses, reduced dislocations, and no heterogeneous nucleation by the crucible. Numerical calculations are used to determine the conditions in which a gap can exist. According to crystal shape stability theory, only some of these gap widths will be dynamically stable. Beginning with a crystal diameter that differs from stable conditions, the transient crystal growth process is analyzed. In microgravity, dynamic stability depends only on capillary effects and is decoupled from heat transfer. Depending on the initial conditions and growth parameters, the crystal shape will evolve towards the crucible wall, towards a stable gap width, or towards the center of the crucible, collapsing the meniscus. The effect of a tapered crucible on dynamic stability is also described

Volz, M. P.↗

NASA NTRS2013

Crystal Shape Evolution in Detached Bridgman Growth

Volz, M. P.↗

DOE OSTI2020

Dynamic Current–Voltage Analysis of Oxygen Vacancy Mobility in Praseodymium-Doped Ceria over Wide Temperature Limits

Not provided.

Chemistry↗

NASA NTRS2011

On Transients in Detached Bridgman Growth

In detached Bridgman growth, a gap exists between the growing crystal and the crucible wall. According to crystal shape stability theory, only specific gap widths will be dynamically stable. Beginning with a crystal diameter that differs from stable conditions, the transient crystal growth process is analyzed. The transient shapes are calculated assuming that the growth angle is constant. Anisotropy and dynamic contact angle effects are considered. In microgravity, dynamic stability depends only on capillary effects and is decoupled from heat transfer. However, heat transfer will influence the crystal-melt interface shape. The local angles and the crystal-melt-vapor triple junction are analyzed and the applicability of the Herring formula is discussed. A potential microgravity experiment is proposed which would enhance our understanding of the detached growth dynamic stability problem.

Mazuruk, K.↗

NASA NTRS1992

Structural dynamics for new launch vehicles

An overview is presented of current studies that will permit more robust designs and reduce the safety hazards of maximum dynamic pressure during launches. Key considerations in the assessment of future operable launch capabilities are the dynamics problems that arise during the initial minutes of transition from the static configuration on the launch pad to the attainment of orbital velocity. Attention is given to a typical attempt to achieve robustness that involves creating a design in which the first bending mode will have a high enough frequency to allow decoupling between the autopilot design and the flexible body dynamics.

Neighbors, Joyce↗

DOE OSTI2023

How do axisymmetric black holes grow monopole and dipole hair?

Here, we study the dynamical formation of scalar monopole and dipole hair in scalar Gauss-Bonnet theory and dynamical Chern-Simons theory. We prove that the spherically symmetric mode of the dipole hair is completely determined by the product of the mass of the spacetime and the value of the monopole hair. We then show that the dynamics of the ℓ = 1 mode of the dipole hair is intimately tied to the appearance of the event horizon during axisymmetric collapse, which results in the radiation of certain modes that could have been divergent in the future of the collapse. We confirm these analytical predictions by simulating the gravitational collapse of a rapidly rotating neutron star in the decoupling limit, both in scalar Gauss-Bonnet and dynamical Chern-Simons theory. Our results, combined with those provide a clear physical picture of the dynamics of scalar monopole and dipole radiation in axisymmetric and spherical gravitational collapse in these theories.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Flexible Reinforcement Learning Framework for Building Control using EnergyPlus-Modelica Energy Models

In recent years, reinforcement learning (RL) methods have been greatly enhanced by leveraging deep learning approaches. RL methods applied to building control have shown potential in many applications due to their ability to complement or replace conventional methods such as model-based or rule-based controls. However, RL-based building control software is likely tailored either to one target building system or to a specific RL method so that significant additional effort would be required to customize the RL-based controller for use in other building systems or with other RL approaches. Also, RL-based building controls usually depend on building energy simulations to train controllers, so emulating building dynamics (i.e., thermal dynamics and control dynamics) and capturing sub-hourly dynamic profiles are crucial to further the development of effective RL-based building control methods. To address these challenges, we present an open source RL-based control software employing a high-fidelity hybrid EnergyPlus-Modelica building energy model which emulates building dynamics at 1-minute resolution. This software consists of decoupled components (environment, building emulator, control agent, and RL algorithm), which allows for quick prototyping and benchmarking of standard RL algorithms in different systems; for example, a single component can be replaced without revising all of the software. To demonstrate this software framework, we conducted a benchmark study using an EnergyPlus-Modelica building energy model for a Chicago office building with an RL-based controller to dynamically control the chilled water temperature setpoint and the air handling unit supply air temperature setpoint on selected floors.

Lee, Joon-Yong↗

DOE OSTI2021

Nonlinear Architectures Can Alter the Dynamics of Polymer–Nanoparticle Composites

Polymer nanocomposites exhibit remarkable physical properties that are attractive for many applications. These systems have been so far investigated by using linear polymer chains; the role of polymer matrix architecture on local dynamics, bulk rheology and nanoparticle motion remains unexplored. Here, using quasielastic neutron scattering, bulk rheology and x-ray photon correlation spectroscopy, we investigated nanocomposites with spherical silica nanoparticles well dispersed in poly (ethylene oxide) matrices having different architectures (specifically linear, stars and hyperbranched). The results reveal that the mechanical reinforcement of the nanocomposites with the nonlinear polymers can be altered by orders of magnitude with respect to the conventional nanocomposite with the linear polymer. Additionally, the polymer compactness and inter-penetrability are found to play crucial roles in determining their bulk rheology. At microscopic level, average segmental dynamics is remarkably slowed down by the attractive NPs in the matrices of high degree of branching whereas no significant effect is observed in linear polymer matrix at the same NP loading. In addition, the nanoscale dynamics of particles in the compact nonlinear matrices exhibit strong decoupling from the bulk viscoelasticity, allowing their fast relaxation even at ≈ 30% by volume. These results provide an experimental evidence that macromolecular architecture is a powerful new tool for tuning the bulk rheological properties as well as the nanoscale dynamics of PNCs without the need for changing polymer molecular weight, nanoparticle size, shape, loading or dispersion state.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Understanding the lattice thermal conductivity of SrTiO 3 from an ab initio perspective

Here, we present a detailed analysis of the structure dependence of the lattice thermal conductivity of SrTiO 3 . We have used both ab initio molecular dynamic simulations and density functional theory calculations to decouple the effect of different structural distortions on the thermal conductivity. We have identified two main mechanisms for tuning the thermal conductivity when a distortion is applied. First, the modification of the acoustic-modes energy dispersion when a change in the lattice parameters is imposed and second, the low energy polar modes. In particular and counterintuitively, we have found that an increase in the angle of the oxygen octahedral rotations increases the thermal conductivity due to its coupling to these polar modes.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Investigation of the Impact of Flow on MHD Perturbations with the NIMROD Code (Final Report)

This work will enable improved understanding of tokamak edge flows and impurity-species dynamics and their impact on MHD stability as it relates to ELMs, RMPs and QH-mode by leveraging computational developments of the NIMROD code. Experimentally, it is established that the tokamak flows and impurities species can have a substantial effect on MHD stability. This is particularly true for the edge plasma where, for example, large flow shear is correlated with the occurrence of the Quiescent H-mode (QH- mode) state as opposed to operation with edge localized modes (ELMs). Understanding plasma flows is challenging because of the many physical effects that come into play: particle orbits loss, neutrals dynamics, and interaction between multiple ion species with decoupled motion. We will develop a model that incorporates multiple ion species into the MHD framework that includes self-consistent magnetic-field evolution. With this model we will understand how the presence of impurities impacts the tokamak edge-pedestal flows. Finally, we will quantify the impact of the new multiple species modeling on 3D QH-mode simulations. This work will have broader impacts on all MHD studies when multiple species are present (as is the case in modern tokamaks), as well as contributing to the edge and transport communities who also are interested in the studies of multiple-ion-species flows in the edge pedestal region.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1984

Inertially referenced instrument pointing platform with momentum compensated articulation

The characteristics of the Mariner Mark II Integrated Platform Pointing and Attitude Control System (IPPACS) microstep actuator with momentum compensation and the IPPACS optical reference tracker are examined, and the advantages of this new technology are identified. The momentum-compensated articulation acts to prevent platform articulation activity from disturbing the spacecaft. This guarantees dynamic stability, ensures a quiescent pointing environment, and decouples the design of the platform from the design of the spacecraft. A microstep actuator with harmonic drive provides platform angular step resolution to 0.5 arcsec for precision pointing of instruments. An optical reference tracker boresighted with scientific instruments guarantees accurate target-referenced closed-loop pointing. An IPPACS star and target tracker with 1 to 10 arcsec accuracy and wide 11 x 17 degrees field of view has been derived from Advanced Star and Target Reference Optical Sensor (ASTROS) CCD star tracker technology, greatly enhancing the optical referencing capabilities of future multimission interplanetary spacecraft.

Bell, C. E.↗