14,510 research outputs found
A flux calibration method for remote sensing satellites using stars
Star surveys and model analyses show that many stars have absolute stable
fluxes as good as 3% in 0.3-35{\mu}m wavebands and about 1% in the visible
wavebands. The relative flux calibrations between stars are better than 0.2%.
Some stars have extremely stable fluxes and can be used as long term flux
calibration sources. Stellar brightness is several orders of magnitude lower
than most ground objects while the stars do not usually appear in remote
sensing cameras, which makes the stars inappropriate for being calibration
sources. The calibration method using stars discussed in this paper is through
a mini-camera attached to remote sensing satellite. The mini-camera works at
similar wavebands as the remote sensing cameras and it can observe the stars
and the ground objects alternatively. High signal-to-noise ratio is achieved
for the relatively faint stars through longer exposure time. Simultaneous
precise cross-calibration is obtained as the mini-camera and remote sensing
cameras look at the ground objects at the same time. The fluxes from the stars
used as calibration standards are transferred to the remote sensing cameras
through this procedure. Analysis shows that a 2% accurate calibration is
possible.Comment: 12 page
An Energetic Variational Approach for ion transport
The transport and distribution of charged particles are crucial in the study
of many physical and biological problems. In this paper, we employ an Energy
Variational Approach to derive the coupled Poisson-Nernst-Planck-Navier-Stokes
system. All physics is included in the choices of corresponding energy law and
kinematic transport of particles. The variational derivations give the coupled
force balance equations in a unique and deterministic fashion. We also discuss
the situations with different types of boundary conditions. Finally, we show
that the Onsager's relation holds for the electrokinetics, near the initial
time of a step function applied field
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