Compact Electron Gun Based on Secondary Emission Through Ionic Bombardment
We present a new compact electron gun based on the secondary emission through ionic bombardment principle. The driving parameters to develop such a gun are to obtain a quite small electron gun for an in-flight instrument performing Electron Beam Fluorescence measurements (EBF) on board of a reentry vehicle in the upper atmosphere. These measurements are useful to characterize the gas flow around the vehicle in terms of gas chemical composition, temperatures and velocity of the flow which usually presents thermo-chemical non-equilibrium. Such an instrument can also be employed to characterize the upper atmosphere if placed on another carrier like a balloon. In ground facilities, it appears as a more practical tool to characterize flows in wind tunnel studies or as an alternative to complex electron guns in industrial processes requiring an electron beam. We describe in this paper the gun which has been developed as well as its different features which have been characterized in the laboratory.
Linearization instability of gravity waves
Gravity waves in irrotational dust spacetimes are characterized by a nonzero magnetic Weyl tensor ${H}_{\mathrm{ab}}.$ In the linearized theory, the divergence of ${H}_{\mathrm{ab}}$ is set to zero. Recently Lesame, Ellis, and Dunsby [Phys. Rev. D 53, 738 (1996)] presented an argument to show that, in the exact nonlinear theory, $\mathrm{}\mathrm{div}H=0$ forces ${H}_{\mathrm{ab}}=0$, thus implying a linearization instability for gravity waves interacting with matter. However a sign error in the equations invalidates their conclusion. Bianchi type V spacetimes are shown to include examples with $\mathrm{}\mathrm{div}H=0\ensuremath{\ne}{H}_{\mathrm{ab}}.$ An improved covariant formalism is used to show that in a generic irrotational dust spacetime the covariant constraint equations are preserved under evolution. It is shown elsewhere that $\mathrm{}\mathrm{div}H=0$ does not generate further conditions.
Fragment Rotational State Distributions From The Dissociation Of NeIBr: Experimental And Theoretical Results
The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump–probe laser‐induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I–Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (D0) is calculated to be 65.5±1.2 cm−1 for the A electronic state, v=16. For the X electronic state, v=0, D0=71.8±1.2 cm−1. Quantum mechanical bound state calculations carried out on a model A electronic state potential energy surface are in quantitative agreement with this result. The rotational distributions are broader than that predicted by either a Franck–Condon or classical impulsive model for the dissociation. The distributions are qualitatively in accord with classical trajectory calc...