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Results for “Dynamic phases”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Phase mediated dynamics of self-propagating Co/Al nanolaminate reactions

The ignition of sputter deposited nanolaminate foils comprised of alternating Co and Al layers results in rapid, self-propagating formation reactions. The propagating waves present after ignition of 150 nm-thick foils are characterized in movie mode dynamic transmission electron microscopy where these are found to have reaction speeds and wave morphology that vary with bilayer thickness. High speed videography reveals different bilayer thickness-wave character relationships in 750 nm- and 7500 nm-thick Co/Al foils. The reaction speed dependencies on bilayer thickness are calculated for each total thickness by treating the effect of radiation loss as a perturbation from an analytical model described by the difference in the heat of reaction measured in calorimetry and the adiabatic heat of product formation. From this model, an effective activation energy, diffusion constant, and flame temperatures are obtained, which allows for an interpretation of the reaction phase variations with laminate design and their effects on propagating wave morphology.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Longitudinal Phase Space Dynamics in ERLs

Both the dynamics and the architecture of an energy recovery linac are primarily determined by the longitudinal match. This match can be manipulated by both the magnetic lattice and the RF systems. Here we will present a few examples of systems and the longitudinal solutions found for each. The first application is a free-electron laser application where a short bunch and high peak current are required. The laser increases the energy spread and lowers the energy and this must be compensated in the ERL design. The second application is for an internal target experiment where the need was for small energy spread rather than a short bunch. The third example is for an electron cooler where the bunch must be very long with extremely small energy spread. The beam disruption due to cooling is small but CSR and microbunching effects are a real challenge. In the FEL, the longitudinal matching is mainly accomplished via lattice matching while in the cooler application the RF system is the dominant method to control the phase space. The internal target can be addressed either way.

Benson, Stephen↗
DOE OSTI2014

What is the fate of runaway positrons in tokamaks?

In this study, massive runaway positrons are generated by runaway electrons in tokamaks. The fate of these positrons encodes valuable information about the runaway dynamics. The phase space dynamics of a runaway position is investigated using a Lagrangian that incorporates the tokamak geometry, loop voltage, radiation and collisional effects. It is found numerically that runaway positrons will drift out of the plasma to annihilate on the first wall, with an in-plasma annihilation possibility less than 0.1%. The dynamics of runaway positrons provides signatures that can be observed as diagnostic tools.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Recent progresses on physics and applications of vanadium dioxide

As a strongly correlated electron material, vanadium dioxide (VO 2 ) has been a focus of research since its discovery in 1959, owing to its well-known metal–insulator transition coupled with a structural phase transition. Recent years have witnessed both exciting discoveries in our understanding of the physics of VO 2 and developments in new applications of VO 2 -related materials. In this article, we review some of these recent progresses on the phase transition mechanism and dynamics, phase diagrams, and imperfection effects, as well as growth and applications of VO 2 . Our review not only offers a summary of the properties and applications of VO 2 , but also provides insights into future research of this material by highlighting some of the challenges and opportunities.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Vibrational Dynamics and Phase Transitions of Hydrazine to 50 GPa

The high pressure behavior of hydrazine, N 2 H 4 , has been investigated to 50 GPa at room temperature using infrared and Raman spectroscopy to explore pressure induced phase transitions and changes in hydrogen bonding. Three solid–solid phase transitions were detected at 11, 21, and 32 GPa on room temperature compression through dramatic changes in the lattice vibration and N–H stretching regions with increasing pressure in both measurement techniques. The transition to phase IV, which appears at 32 GPa, exhibits increased hydrogen bonding with significant hysteresis, persisting to 9 GPa on decompression. This work presents a detailed analysis of the pressure dependence of mode shifts and calculations of mode Grüneisen parameters as well as a determination of an approximate thermodynamic Grüneisen parameter. We compare these results to the behavior of other small molecular materials such as ammonia and water and explore the evolution of hydrogen bonding in hydrazine toward the symmetrically hydrogen bonded state, which has previously been suggested by theoretical computations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Quantum dynamics in phase space: Moyal trajectories 2

Continuing a previous paper [G. Braunss, J. Phys. A: Math. Theor. 43, 025302 (2010)] where we had calculated Planck-Constant-Over-Two-Pi {sup 2}-approximations of quantum phase space viz. Moyal trajectories of examples with one and two degrees of freedom, we present in this paper the calculation of Planck-Constant-Over-Two-Pi {sup 2}-approximations for four examples: a two-dimensional Toda chain, the radially symmetric Schwarzschild field, and two examples with three degrees of freedom, the latter being the nonrelativistic spherically Coulomb potential and the relativistic cylinder symmetrical Coulomb potential with a magnetic field H. We show in particular that an Planck-Constant-Over-Two-Pi {sup 2}-approximation of the nonrelativistic Coulomb field has no singularity at the origin (r= 0) whereas the classical trajectories are singular at r= 0. In the third example, we show in particular that for an arbitrary function {gamma}(H, z) the expression {beta}{identical_to}p{sub z}+{gamma}(H, z) is classically ( Planck-Constant-Over-Two-Pi = 0) a constant of motion, whereas for Planck-Constant-Over-Two-Pi {ne} 0 this holds only if {gamma}(H, z) is an arbitrary polynomial of second order in z. This statement is shown to extend correspondingly to a cylinder symmetrical Schwarzschild field with a magnetic field. We exhibit in detail a number of properties of the radially symmetric Schwarzschild field. We exhibit finally the problems of the nonintegrable Henon-Heiles Hamiltonian and give a short review of the regular Hilbert space representation of Moyal operators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Topological resonance in graphene-like materials

Abstract In topological materials, interacting with short and strong optical pulses, electrons can accumulate a topological phase during the pulse. Such phase can compensate the dynamic phase resulting in topological resonance, which is visible as a large inter-band transfer of electron population. We study theoretically the topological resonance in materials of the gapped multilayer graphene type. We show that the resonance can be observed only in the systems with finite bandgap. For graphene monolayer the topological resonance can occur only in the field of an elliptically polarized pulse, while for graphene systems with many layers the topological resonance can be also realized in a linearly polarized pulse.

Physics↗
DOE OSTI2020

Loschmidt-amplitude wave function spectroscopy and the physics of dynamically driven phase transitions

In this work, we introduce the Loschmidt amplitude as a powerful tool to perform spectroscopy of generic many-body wave functions and use it to interrogate the wave function obtained after ramping the transverse field quantum Ising model through its quantum critical point. Previous results are confirmed and a more complete understanding of the population of defects and of the effects of magnon-magnon interaction or finite-size corrections is obtained. The influence of quantum coherence is clarified.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Space and time renormalization in phase transition dynamics

Here, when a system is driven across a quantum critical point at a constant rate, its evolution must become nonadiabatic as the relaxation time τ diverges at the critical point. According to the Kibble-Zurek mechanism (KZM), the emerging post-transition excited state is characterized by a finite correlation length ξˆ set at the time tˆ=τˆ when the critical slowing down makes it impossible for the system to relax to the equilibrium defined by changing parameters. This observation naturally suggests a dynamical scaling similar to renormalization familiar from the equilibrium critical phenomena. We provide evidence for such KZM-inspired spatiotemporal scaling by investigating an exact solution of the transverse field quantum Ising chain in the thermodynamic limit.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Lattice dynamics and phase transition in CrI 3 single crystals

Here, the vibrational properties of CrI 3 single crystals were investigated using Raman spectroscopy and were analyzed with respect to the changes of the crystal structure. All but one mode are observed for both the low-temperature R¯3 and the high-temperature C2/m phase. For all observed modes the energies and symmetries are in good agreement with DFT calculations. The symmetry of a single layer was identified as p¯31/m . In contrast to previous studies we observe the transition from the R¯3 to the C2/m phase at 180 K and find no evidence for coexistence of both phases over a wide temperature range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Dynamics and phases of nonunitary Floquet transverse-field Ising model

Inspired by current research on measurement-induced quantum phase transitions, we analyze the nonunitary Floquet transverse-field Ising model with complex nearest-neighbor couplings and complex transverse fields. Unlike its unitary counterpart, the model shows a number of steady phases, stable to integrability-breaking perturbations. Some phases have robust edge modes and/or spatiotemporal long-range orders in the bulk. The transitions between the phases have extensive entanglement entropy, whose scaling with the system size depends on the number of the real quasiparticle modes in the spectrum at the transition. In particular, the volume-law scaling appears on some critical lines, protected by pseudo-Hermiticity. Both the scaling of entanglement entropy in steady states and the evolution after a quench are compatible with the non-Hermitian generalization of the quasiparticle picture of Calabrese and Cardy at least qualitatively. Published by the American Physical Society 2024

Su, Lei (ORCID:0009000455290786)↗