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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 NTRS1975

A dynamic model for the time evolution of the modulated cosmic ray spectrum

A recently developed model predicts an energy dependent phase lag in the modulated cosmic ray density U(t) given by U(t) approximately equal to US (t - tau) where US is the solution to the Fokker-Planck equation under time independent conditions and tau is the average time spent by particles inside the modulating region. The delay times tau are functions of modulating parameters R (the radius of the modulating cavity), V (the solar wind velocity), and K (the effective average diffusion-coefficient which is a function of energy). This model is applied to predict the time evolution of the modulated cosmic ray proton spectrum over a simulated solar cycle. A modulation produced mostly by varying R over the solar cycle is less consistent with the observations.

Ogallagher, J. J.↗
DOE OSTI2020

Practical quantum computation of chemical and nuclear energy levels using quantum imaginary time evolution and Lanczos algorithms

Various methods have been developed for the quantum computation of the ground and excited states of physical and chemical systems, but many of them require either large numbers of ancilla qubits or high-dimensional optimization in the presence of noise. The quantum imaginary-time evolution (QITE) and quantum Lanczos (QLanczos) methods proposed in Motta et al. (2020) eschew the aforementioned issues. In this study, we demonstrate the practical application of these algorithms to challenging quantum computations of relevance for chemistry and nuclear physics, using the deuteron-binding energy and molecular hydrogen binding and excited state energies as examples. With the correct choice of initial and final states, we show that the number of timesteps in QITE and QLanczos can be reduced significantly, which commensurately simplifies the required quantum circuit and improves compatibility with NISQ devices. We have performed these calculations on cloud-accessible IBM Q quantum computers. With the application of readout-error mitigation and Richardson error extrapolation, we have obtained ground and excited state energies that agree well with exact results obtained from diagonalization.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Prime factorization using quantum variational imaginary time evolution

The road to computing on quantum devices has been accelerated by the promises that come from using Shor’s algorithm to reduce the complexity of prime factorization. However, this promise hast not yet been realized due to noisy qubits and lack of robust error correction schemes. Here we explore a promising, alternative method for prime factorization that uses well-established techniques from variational imaginary time evolution. We create a Hamiltonian whose ground state encodes the solution to the problem and use variational techniques to evolve a state iteratively towards these prime factors. We show that the number of circuits evaluated in each iteration scales as \(O(n^{5}d)\) , where n is the bit-length of the number to be factorized and d is the depth of the circuit. We use a single layer of entangling gates to factorize 36 numbers represented using 7, 8, and 9-qubit Hamiltonians. We also verify the method’s performance by implementing it on the IBMQ Lima hardware to factorize 55, 65, 77 and 91 which are greater than the largest number (21) to have been factorized on IBMQ hardware.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1983

Study of the time evolution of the lithosphere

The behavior and mechanical properties of the lithosphere were studied. This is a prerequisite to an understanding of the mechanisms and processes that occur in the Earth's mantle, which are masked by the lithospere. Geoid heights derived from the GEOS-3 and SEASAT radar altimeters were used. The correlation between bathymetry and geoid heights gives information on the mechanical properties of the lithosphere, such as its thickness, which is related to the age of the lithospheric plate. By probing in several locations spanning various temporal situations, the time evolution of the lithospheric plates were retraced.

Roufosse, M. C.↗
DOE OSTI2021

Real-Time Evolution and Deployment of Neuromorphic Computing at The Edge

Extremely low power neuromorphic systems are well-suited for deployment to the edge for many applications. In many use cases of neuromorphic computing for control, a spiking neural network is trained off-line using a simulation and then deployed to a neuromorphic system at the edge, where it will operate without ongoing training or learning. However, it may be desirable to continue training or learning at the edge to refine or adapt to the real-world system. In this work, we propose an approach for performing real-time evolutionary optimization for spiking neural networks for neuromorphic deployment at the edge. In particular, we propose a combination of simulation and real-world evaluations, along with feedback from the real-world environment, to train spiking neural networks for continuous deployment to the edge. We show that the real-time evolution at the edge approach achieves comparable performance to an evolution approach that requires constant evaluation in the realworld environment.

Schuman, Catherine↗
DOE OSTI2024

Null states and time evolution in a toy model of black hole dynamics

Abstract Spacetime wormholes can provide non-perturbative contributions to the gravitational path integral that make the actual number of statese S in a gravitational system much smaller than the number of states$$ {e}^{S_{\textrm{p}}} $$ e S p predicted by perturbative semiclassical effective field theory. The effects on the physics of the system are naturally profound in contexts in which the perturbative description actively involvesN=O(e S ) of the possible$$ {e}^{S_{\textrm{p}}} $$ e S p perturbative states; e.g., in late stages of black hole evaporation. Such contexts are typically associated with the existence of non-trivial quantum extremal surfaces. However, by forcing a simple topological gravity model to evolve in time, we find that such effects can also have large impact forN≪e S (in which case no quantum extremal surfaces can arise). In particular, even for smallN, the insertion of generic operators into the path integral can cause the non-perturbative time evolution to differ dramatically from perturbative expectations. On the other hand, this discrepancy is small for the special case where the inserted operators are non-trivial only in a subspace of dimensionD≪e S . We thus study this latter case in detail. We also discuss potential implications for more realistic gravitational systems.

Physics↗
DOE OSTI2026

Deterministic Quantum Trajectory via Imaginary Time Evolution

Stochastic quantum trajectories, such as pure state evolutions under unitary dynamics and random measurements, offer a crucial ensemble description of many-body open system dynamics. Recent studies have highlighted that individual quantum trajectories also encode essential physical information. Prominent examples include measurement-induced phase transitions, where a pure quantum state corresponding to fixed measurement outcomes (trajectories) exhibits distinct entanglement phases, depending on the measurement rate. However, direct observation of this effect is hindered by an exponential postselection barrier, whereby the probability of realizing a specific trajectory is exponentially small. We propose a deterministic method to efficiently prepare quantum trajectories in polynomial time using imaginary time evolution and, thus, overcome this fundamental challenge. Here, we demonstrate that our method applies to a certain class of quantum states, and argue that universal approaches do not exist for any quantum trajectories. Our result paves the way for experimentally exploring the physics of individual quantum trajectories at scale and enables direct observation of certain postselection-dependent phenomena.

Mittal, Shivan [Los Alamos National Laboratory (LA↗
NASA NTRS1996

Time Evolution of Radiation-Induced Luminescence in Terbium-Doped Silicate Glass

A study was made on two commercially available terbium-doped silicate glasses. There is an increased interest in silicate glasses doped with rare-earth ions for use in high-energy particle detection and radiographic applications. These glasses are of interest due to the fact that they can be formed into small fiber sensors; a property that can be used to increase the spatial resolution of a detection system. Following absorption of radiation, the terbium ions become excited and then emit photons via 4f-4f electronic transitions as they relax back to the ground state. The lifetime of these transitions is on the order of milliseconds. A longer decay component lasting on the order of minutes has also been observed. While radiative transitions in the 4f shell of rare-earth ions are generally well understood by the Judd-Olfelt theory, the pr'esence of a longer luminescence decay component is not. Experimental evidence that the long decay component is due, in part, to the thermal release of trapped charge carriers will be presented. In addition, a theoretical model describing the time evolution of the radiation-induced luminescence will be presented.

West, Michael S.↗
NASA NTRS2020

X-ray spectral and timing evolution of MAXI J1727-203 with NICER

We present a detailed X-ray spectral and variability study of the full 2018 outburst of MAXI J1727–203 using NICER observations. The outburst lasted approximately four months. Spectral modelling in the 0.3–10 keV band shows the presence of both a soft thermal and a hard Comptonised component. The analysis of these components shows that MAXI J1727–203 evolved through the soft, intermediate, and hard spectral states during the outburst. We find that the soft (disc) component was detected throughout almost the entire outburst, with temperatures ranging from ∼0.4 keV, at the moment of maximum luminosity, to ∼0.1 keV near the end of the outburst. The power spectrum in the hard and intermediate states shows broad-band noise up to 20 Hz, with no evidence of quasi-periodic oscillations. We also study the rms spectra of the broad-band noise at 0.3−10 keV of this source. We find that the fractional rms increases with energy in most of the outburst except during the hard state, where the fractional rms remains approximately constant with energy. We also find that, below 3 keV, the fractional rms follows the same trend generally observed at energies >3 keV, a behaviour known from previous studies of black holes and neutron stars. The spectral and timing evolution of MAXI J1727–203, as parametrised by the hardness–intensity, hardness–rms, and rms–intensity diagrams, suggest that the system hosts a black hole, although we could not rule out a neutron star.

K Jativa↗
NASA NTRS1989

Time evolution of cloud fields from ISCCP observations

The time series of 280 km regional cloud amounts to characterize the evolution of the cloud fields is presented. New observations from the International Satellite Cloud Climatology Project (ISCCP) allow use of this data to attack the problem of simulating clouds and cloud changes from purely an empirical approach. It is shown that both persistence of cloud and cloud lifetimes indicate very long time scales to 40 hours for lifetime and weeks for persistent cloud systems. The simulation of these effects in GCM's requires more than attempting to simulate the variations of individual cloud elements. The tropical regions over the oceans show shorter lifetimes because there are basically local controls to the presence of clouds.

Campbell, G. G.↗
NASA NTRS1999

The Timing Evolution of 4U 1630-47 During its Outbursts

We report on the timing analysis of Rossi X-ray Timing Explorer (RXTE) observations of 4U 1630-47 made during its 1998 outburst. In addition we use two BeepoSAX observation on the late decline. 4U1630-47 showed seven distinct types of timing behaviour, most of which show differences with the canonical black hole spectral/timing states. In marked contrast to previous outbursts we find quasi periodic oscillation (QPO) signals during nearly all stages of the outburst. In addition to 2 to 13 Hz QPO slow 0.01Hz QPO are observed. These slow QPO can dominate the light curve as quasi-regular 5 sec, 9--16% deep dips. During these dips we track the behaviour of two QPO's; one remaining constant near 13.5 Hz and the other varying between 7 and 4 Hz. The evolution of the timing and the concurrent spectral changes are mapped using a combination harness-intensity and colour-colour diagrams.

Dieters, S. W.↗
NASA NTRS2015

Late-Time Evolution of Composite Supernova Remnants: Deep Chandra Observations and Hydrodynamical Modeling of a Crushed Pulsar Wind Nebula in SNR G327.1-1.1

In an effort to better understand the evolution of composite supernova remnants (SNRs) and the eventual fate of relativistic particles injected by their pulsars, we present a multifaceted investigation of the interaction between a pulsar wind nebula (PWN) and its host SNR G327.1-1.1. Our 350 ks Chandra X-ray observations of SNR G327.1-1.1 reveal a highly complex morphology; a cometary structure resembling a bow shock, prong-like features extending into large arcs in the SNR interior, and thermal emission from the SNR shell. Spectral analysis of the non-thermal emission offers clues about the origin of the PWN structures, while enhanced abundances in the PWN region provide evidence for mixing of supernova ejecta with PWN material. The overall morphology and spectral properties of the SNR suggest that the PWN has undergone an asymmetric interaction with the SNR reverse shock(RS) that can occur as a result of a density gradient in the ambient medium and or a moving pulsar that displaces the PWN from the center of the remnant. We present hydrodynamical simulations of G327.1-1.1 that show that its morphology and evolution can be described by a approx. 17,000 yr old composite SNR that expanded into a density gradient with an orientation perpendicular to the pulsar's motion. We also show that the RSPWN interaction scenario can reproduce the broadband spectrum of the PWN from radio to gamma-ray wavelengths. The analysis and modeling presented in this work have important implications for our general understanding of the structure and evolution of composite SNRs.

Evolution↗
DOE OSTI2024

Real-time evolution of texture and temperature during friction stir processing of a magnesium alloy: An operando neutron diffraction study

The real-time development of texture and the evolution of temperature during friction stir processing (FSP) of a Mg alloy were investigated using an operando neutron diffraction measurement. A novel approach was applied in this study where the real-time, quasi-steady state measurements performed as a function of position during FSP are converted to a Lagrangian dataset that reveals the transient behavior as a function of time. The in-situ FSP was carried out under two different thermo-mechanical processing conditions represented by the Zener-Hollomon parameter, Z. Further, the results show that: (i) a shear texture develops from the initial strong basal texture with the peak temperature reaching about 774 K during a low-Z processing and (ii) a strong off-normal texture develops with a peak temperature of 616 K during a high-Z processing. Moreover, time-temperature-texture diagrams were established to reveal the real-time development of the texture during the processing for both the low Z and high Z processing conditions. The changes in texture will be discussed in terms of plastic deformation mechanisms active during various stages of the FSP under the two different processing conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Plio-Pleistocene time evolution of the 100-kyr cycle in marine paleoclimate records

A new time-series analysis technique (called envelope inversion), which is based on multiple taper spectral analysis, is used to address the question of an abrupt versus a gradual onset of the 100-kyr ice-age periodicity in the middle Pleistocene. Three long (greater than 2.6 m.y.) time series from Deep Sea Drilling Project site 607 (midlatitude Atlantic) and Ocean Drilling Program site 677 (equatorial Pacific) were analyzed using delta(O-18) records. Results do not yield compelling evidence for an abrupt change in the 100-kyr delta(O-18) signal. Rather, the results suggest that the 100-kyr delta(O-18) cycle is phase-locked with the 124-kyr eccentricity cycle some 300-400 kyr prior to its late Pleistocene growth in amplitude and phase lock with the 95-kyr eccentricity cycle.

Park, Jeffrey↗
DOE OSTI2021

Time evolution of ML-MCTDH wavefunctions. II. Application of the projector splitting integrator

The multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) approach can suffer from numerical instabilities whenever the wavefunction is weakly entangled. These instabilities arise from singularities in the equations of motion (EOMs) and necessitate the use of regularization of the EOMs. The Projector Splitting Integrator (PSI) has previously been presented as an approach for evolving ML-MCTDH wavefunctions that is free of singularities. Here, we will discuss the implementation of the multi-layer PSI with a particular focus on how the steps required relate to those required to implement standard ML-MCTDH. We demonstrate the efficiency and stability of the PSI for large ML-MCTDH wavefunctions containing up to hundreds of thousands of nodes by considering a series of spin-boson models with up to 106 bath modes and find that for these problems, the PSI requires roughly 3–4 orders of magnitude fewer Hamiltonian evaluations and 2–3 orders of magnitude fewer Hamiltonian applications than standard ML-MCTDH and 2–3/1–2 orders of magnitude fewer evaluations/applications than approaches that use improved regularization schemes. Finally, we consider a series of significantly more challenging multi-spin-boson models that require much larger numbers of single-particle functions with wavefunctions containing up to ~1.3×10 9 parameters to obtain accurate dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1988

Time evolution of surface chlorophyll patterns from cross-spectrum analysis of satellite color images

The rate of decorrelation of surface chlorophyll patterns as a function of the time separation between pairs of images was determined from two sequences of CZCS images of the Pacific Ocean area adjacent to Vancouver Island, Canada; cloud-free subareas were selected that were common to several images separated in time by 1-17 days. Image pairs were subjected to two-dimensional autospectrum and cross-spectrum analysis in an array processor, and squared coherence estimates found for several wave bands were plotted against time separation, in analogy with a time-lagged cross correlation function. It was found that, for wavelengths of 50-150 km, significant coherence was lost after 7-10 days, while for wavelengths of 25-50 km, significant coherence was lost after only 5-7 days. In both cases, offshore regions maintained coherence longer than coastal regions.

Denman, Kenneth L.↗
DOE OSTI2021

Latent-space time evolution of non-intrusive reduced-order models using Gaussian process emulation

Non-intrusive reduced-order models (ROMs) have recently generated considerable interest for constructing computationally efficient counterparts of nonlinear dynamical systems emerging from various domain sciences. They provide a low-dimensional emulation framework for systems that may be intrinsically high-dimensional. This is accomplished by utilizing a construction algorithm that is purely data-driven. It is no surprise, therefore, that the algorithmic advances of machine learning have led to non-intrusive ROMs with greater accuracy and computational gains. However, in bypassing the utilization of an equation-based evolution, it is often seen that the interpretability of the ROM framework suffers. This becomes more problematic when black-box deep learning methods are used which are notorious for lacking robustness outside the physical regime of the observed data. In this article, we propose the use of a novel latent-space interpolation algorithm based on Gaussian process regression. Notably, this reduced-order evolution of the system is parameterized by control parameters to allow for interpolation in space. The use of this procedure also allows for a continuous interpretation of time which allows for temporal interpolation. The latter aspect provides information, with quantified uncertainty, about full-state evolution at a finer resolution than that utilized for training the ROMs. This research assesses the viability of this algorithm for an advection-dominated system given by the inviscid shallow water equations.

97 MATHEMATICS AND COMPUTING↗