8,096 research outputs found
Optimal Cosmic-Ray Detection for Nondestructive Read Ramps
Cosmic rays are a known problem in astronomy, causing both loss of data and
data inaccuracy. The problem becomes even more extreme when considering data
from a high-radiation environment, such as in orbit around Earth or outside the
Earth's magnetic field altogether, unprotected, as will be the case for the
James Webb Space Telescope (JWST). For JWST, all the instruments employ
nondestructive readout schemes. The most common of these will be "up the ramp"
sampling, where the detector is read out regularly during the ramp. We study
three methods to correct for cosmic rays in these ramps: a two-point difference
method, a deviation from the fit method, and a y-intercept method. We apply
these methods to simulated nondestructive read ramps with single-sample groups
and varying combinations of flux, number of samples, number of cosmic rays,
cosmic-ray location in the exposure, and cosmic-ray strength. We show that the
y-intercept method is the optimal detection method in the read-noise-dominated
regime, while both the y-intercept method and the two-point difference method
are best in the photon-noise-dominated regime, with the latter requiring fewer
computations.Comment: To be published in PASP. This paper is 12 pages long and includes 15
figure
Gas-Surface Dynamics and Profile Evolution during Etching of Silicon
Scattering of energetic F atoms on a fluorinated Si surface is studied by molecular beam methods. The energy transfer closely follows hard-sphere collision kinematics. Energy and angular distributions of unreacted F atoms suggest significant multiple-bounce scattering in addition to single-bounce scattering and trapping desorption. An empirical model of the atom-surface interaction dynamics is used in a Monte Carlo simulation of topography evolution during neutral beam etching of Si. Model predictions of profile phenomena are validated by experiments
Mean-field results on the Anderson impurity model out of equilibrium
We investigate the mean-field phase diagram of the Anderson impurity model
out of equilibrium. Generalising the unrestricted Hartree-Fock approach to the
non-equilibrium situation we derive and analyse the system of equations
defining the critical surface separating the magnetic regime from the
non-magnetic one. An exact analytic solution for the phase boundary as a
function of the applied voltage is found in the symmetric case. Surprisingly,
we find that as soon as there is an asymmetry, even small, between the
contacts, no finite voltage is able to destroy the magnetic regime which
persists at arbitrary high voltages.Comment: 4 pages, 2 figures (eps files); to appear in PRB Brief Report
- …