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Cheng, C.

Publications and source records attributed to Cheng, C..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Isotope-selective strong-field ionization of semiheavy water

Semiheavy water (HOD) is one of the simplest molecules in which the bonds are labeled by isotope. We demonstrate that a pair of intense few-femtosecond infrared laser pulses can be used to selectively tunnel ionize along one of the two bonds. The first pulse doubly ionizes HOD, inducing rapid bond stretching and unbending. Femtoseconds later, the second pulse arrives and further ionization is selectively enhanced along the OH bond. These conclusions arise from 3D time-resolved measurements of H + , D + , and O + momenta following triple ionization. Published by the American Physical Society 2025

Howard, A. J. (ORCID:0000000303033222)↗
NASA NTRS1996

Visual Utility for the Localization of Corona-Accelerated Nuclei

There is considerable controversy as to whether flares are the sole producers of energetic protons or whether coronal mass ejections play a central role. We note that the system described in this paper is presently capable of computing flux predictions only for protons associated with solar-flare activity.

flares↗
NASA NTRS1984

Perfluoroalkylene-Ether Triazine Elastomers

New process yields product that resists heat and action of oxygen and water. Ring closing step, which gives elastomer its stability, imidoylamidine dinitrile reacts with perfluoroether acide, yielding prepolymer. Prepolymer then treated with ammonia and cured by heating to form polymer. Elastomers are highly resistant to heat, oxidation, and hydrolysis.

Rosser, R. W.↗
NASA NTRS1973

Dynamic response and stability of a gas-lubricated Rayleigh-step pad

The quasi-static, pressure characteristics of a gas-lubricated thrust bearing with shrouded, Rayleigh-step pads are determined for a time-varying film thickness. The axial response of the thrust bearing to an axial forcing function or an axial rotor disturbance is investigated by treating the gas film as a spring having nonlinear restoring and damping forces. These forces are related to the film thickness by a power relation. The nonlinear equation of motion in the axial mode is solved by the Ritz-Galerkin method as well as the direct, numerical integration. Results of the nonlinear response by both methods are compared with the response based on the linearized equation. Further, the gas-film instability of an infinitely wide Rayleigh step thrust pad is determined by solving the transient Reynolds equation coupled with the equation of the motion of the pad. Results show that the Rayleigh-step geometry is very stable for bearing number A up to 50. The stability threshold is shown to exist only for ultrahigh values of Lambda equal to or greater than 100, where the stability can be achieved by making the mass heavier than the critical mass.

Cheng, C.↗
NASA NTRS1971

Acceleration of electrons in solar flares

Acceleration of electrons by Langmuir plasma turbulence and by the Fermi mechanism are suggested to explain the two-stage acceleration processes observed in hard X-rays from solar flares. A model for particle acceleration in flares is presented.

Cheng, C.↗