232,115 research outputs found
Motion-induced radiation from electrons moving in Maxwell's fish-eye
In \u{C}erenkov radiation and transition radiation, evanescent wave from
motion of charged particles transfers into radiation coherently. However, such
dissipative motion-induced radiations require particles to move faster than
light in medium or to encounter velocity transition to pump energy. Inspired by
a method to detect cloak by observing radiation of a fast-moving electron bunch
going through it by Zhang {\itshape et al.}, we study the generation of
electron-induced radiation from electrons' interaction with Maxwell's fish-eye
sphere. Our calculation shows that the radiation is due to a combination of
\u{C}erenkov radiation and transition radiation, which may pave the way to
investigate new schemes of transferring evanescent wave to radiation.Comment: 17 pages, 8 figures, including the Supplementary Information appended
in publication. Scientific Reports 201
Transition from ultrafast laser photo-electron emission to space charge limited current in a 1D gap
A one-dimensional (1D) model has been constructed to study the transition of
the time-dependent ultrafast laser photo-electron emission from a flat metallic
surface to the space charge limited (SCL) current, including the effect of
non-equilibrium laser heating on metals at the ultrafast time scale. At a high
laser field, it is found that the space charge effect cannot be ignored and the
SCL current emission is reached at a lower value predicted by a short pulse SCL
current model that assumed a time-independent emission process. The threshold
of the laser field to reach the SCL regime is determined over a wide range of
operating parameters. The calculated results agree well with particle-in-cell
(PIC) simulation. It is found that the space charge effect is more important
for materials with lower work function like tungsten (4.4 eV) as compared to
gold (5.4 eV). However for a flat surface, both materials will reach the space
charge limited regime at the sufficiently high laser field such as 5 GV/m
with a laser pulse length of tens to one hundred femtoseconds.Comment: 12 pages, 3 figures, printed in {\itshape J. Phys. D: Appl. Phys.
Thermal loading in the laser holography nondestructive testing of a composite structure
A laser holographic interferometry method that has variable sensitivity to surface deformation was applied to the investigation of composite test samples under thermal loading. A successful attempt was made to detect debonds in a fiberglass-epoxy-ceramic plate. Experimental results are presented along with the mathematical analysis of the physical model of the thermal loading and current conduction in the composite material
Holographic nondestructive tests performed on composite samples of ceramic-epoxy-fiberglass sandwich structure
When a hologram storing more than one wave is illuminated with coherent light, the reconstructed wave fronts interfere with each other or with any other phase-related wave front derived from the illuminating source. This multiple wave front comparison is called holographic interferometry, and its application is called holographic nondestructive testing (HNDT). The theoretical aspects of HNDT techniques and the sensitivity of the holographic system to the geometrical placement of the optical components are briefly discussed. A unique HNDT system which is mobile and possesses variable sensitivity to stress amplitude is discribed, the experimental evidence of the application of this system to the testing of the hidden debonds in a ceramic-epoxy-fiberglass structure used for sample testing of the radome of the Pershing missile system is presented
Heisenberg equation for a nonrelativistic particle on a hypersurface: from the centripetal force to a curvature induced force
In classical mechanics, a nonrelativistic particle constrained on an
curved hypersurface embedded in flat space experiences the centripetal
force only. In quantum mechanics, the situation is totally different for the
presence of the geometric potential. We demonstrate that the motion of the
quantum particle is "driven" by not only the the centripetal force, but also a
curvature induced force proportional to the Laplacian of the mean curvature,
which is fundamental in the interface physics, causing curvature driven
interface evolution.Comment: 4 page
The centripetal force law and the equation of motion for a particle on a curved hypersurface
It is pointed out that the current form of extrinsic equation of motion for a
particle constrained to remain on a hypersurface is in fact a half-finished
version for it is established without regard to the fact that the particle can
never depart from the geodesics on the surface. Once the fact be taken into
consideration, the equation takes that same form as that for centripetal force
law, provided that the symbols are re-interpreted so that the law is applicable
for higher dimensions. The controversial issue of constructing operator forms
of these equations is addressed, and our studies show the quantization of
constrained system based on the extrinsic equation of motion is favorable.Comment: 5 pages, major revisio
- …