SEARCH · Engineering Papers
Results for “NORMAL”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Target-normal single-spin asymmetry in elastic electron-nucleon scattering
Not Available
Echoes from anharmonic normal modes in model glasses
Glasses display a wide array of nonlinear acoustic phenomena at temperatures T ≲1 K. This behavior has traditionally been explained by an ensemble of weakly coupled, two-level tunneling states, a theory that is also used to describe the thermodynamic properties of glasses at low temperatures. One of the most striking acoustic signatures in this regime is the existence of phonon echoes, a feature that has been associated with two-level systems with the same formalism as spin echoes in NMR. Here we report the existence of a distinctly different type of acoustic echo in classical models of glassy materials. Our simulations consist of finite-ranged, repulsive spheres and also particles with attractive forces using Lennard-Jones interactions. We show that these echoes are due to anharmonic, weakly coupled vibrational modes and perhaps provide an alternative explanation for the phonon echoes observed in glasses at low temperatures.
High-angle deflection of the energetic electrons by a voluminous magnetic structure in near-normal intense laser-plasma interactions
The physics governing electron acceleration by a relativistically intense laser is not confined to the critical density surface; it also pervades the subcritical plasma in front of the target. Here particles can gain many times the ponderomotive energy from the overlying laser and strong fields can grow. Experiments using a high-contrast laser and a prescribed laser prepulse demonstrate that development of the preplasma has an unexpectedly strong effect on the most energetic, superponderomotive electrons. The presented two-dimensional particle-in-cell simulations reveal how strong, voluminous magnetic structures that evolve in the preplasma impact high-energy electrons more significantly than low-energy ones for longer pulse durations and how the common practice of tilting the target to a modest incidence angle can be enough to initiate strong deflection. In conclusion, the implications are that multiple angular spectral measurements are necessary to prevent misleading conclusions from past and future experiments.
Onset of a Two-Dimensional Superconducting Phase in a Topological-Insulator–Normal-Metal Bi 1 - x Sb x / Pt Junction Fabricated by Ion-Beam Techniques
Inducing superconductivity in a topological insulator can lead to novel quantum effects. However, experimental approaches to turn a topological insulator into a superconductor are limited. We report on superconductivity in topological insulator Bi 0.91 Sb 0.09 induced via focused ion-beam deposition of a Pt thin film. The superconducting phase exhibits a Berezinski-Kosterlitz-Thouless transition, demonstrative of its two-dimensional character. From the in-plane upper critical field measurements, we estimate the superconducting thickness to be ~ 17 nm for a 5.5-μm-thick sample. Our results provide evidence that the interface superconductivity could originate from the surface states of Bi 0.91 Sb 0.09 .
Cascades between Light and Heavy Fermions in the Normal State of Magic-Angle Twisted Bilayer Graphene
We present a framework for understanding the cascade transitions and the Landau level degeneracies of twisted bilayer graphene. The Coulomb interaction projected onto narrow bands causes the charged excitations at an integer filling to disperse, forming new bands. If the excitation moves the filling away from the charge neutrality point, then it has a band minimum at the moiré Brillouin zone center with a small mass that compares well with the experiment; if towards the charge neutrality point, then it has a much larger mass and a higher degeneracy. At a nonzero density away from an integer filling the excitations interact. The system on the small mass side has a large bandwidth and forms a Fermi liquid. On the large mass side the bandwidth is narrow, the compressibility is negative and the Fermi liquid is likely unstable. This explains the observed sawtooth features in compressibility, the Landau fans pointing away from charge neutrality and their degeneracies. The framework sets the stage for superconductivity at lower temperatures.
Measurements of Normalized Differential Cross Sections of Inclusive π 0 and K S 0 Production in e + e − Annihilation at Energies from 2.2324 to 3.6710 GeV
Not Available
Normal Fermi Surface in the Nodal Superconductor CeCoIn 5 Revealed via Thermal Conductivity
Not Available
High-dimensional maximum-entropy phase space tomography using normalizing flows
Particle accelerators generate charged-particle beams with tailored distributions in six-dimensional position-momentum space (phase space). Knowledge of the phase space distribution enables model-based beam optimization and control. In the absence of direct measurements, the distribution must be tomographically reconstructed from its projections. In this paper, we highlight that such problems can be severely underdetermined and that entropy maximization is the most conservative solution strategy. We leverage —invertible generative models—to extend maximum-entropy tomography to six-dimensional phase space and perform numerical experiments to validate the model's performance. Our numerical experiments demonstrate consistency with exact two-dimensional maximum-entropy solutions and the ability to fit complicated six-dimensional distributions to large measurement sets in reasonable time. Published by the American Physical Society 2024
Low-emittance tuning of storage rings using normal mode beam position monitor calibration
Not Available
Influence of fs-laser desorption on target normal sheath accelerated ions
Not Available
Refine your search to explore more results.