Structure Factors and Their Distributions in Driven Two-Species Models

We study spatial correlations and structure factors in a three-state stochastic lattice gas, consisting of holes and two oppositely ``charged'' species of particles, subject to an ``electric'' field at zero total charge. The dynamics consists of two nearest-neighbor exchange processes, occuring on different times scales, namely, particle-hole and particle-particle exchanges. Using both, Langevin equations and Monte Carlo simulations, we study the steady-state structure factors and correlation functions in the disordered phase, where density profiles are homogeneous. In contrast to equilibrium systems, the average structure factors here show a discontinuity singularity at the origin. The associated spatial correlation functions exhibit intricate crossovers between exponential decays and power laws of different kinds. The full probability distributions of the structure factors are universal asymmetric exponential distributions.Comment: RevTex, 18 pages, 4 postscript figures included, mistaken half-empty page correcte

A Pre-Landing Assessment of Regolith Properties at the InSight Landing Site

This article discusses relevant physical properties of the regolith at the Mars InSight landing site as understood prior to landing of the spacecraft. InSight will land in the northern lowland plains of Mars, close to the equator, where the regolith is estimated to be ≥3--5 m thick. These investigations of physical properties have relied on data collected from Mars orbital measurements, previously collected lander and rover data, results of studies of data and samples from Apollo lunar missions, laboratory measurements on regolith simulants, and theoretical studies. The investigations include changes in properties with depth and temperature. Mechanical properties investigated include density, grain-size distribution, cohesion, and angle of internal friction. Thermophysical properties include thermal inertia, surface emissivity and albedo, thermal conductivity and diffusivity, and specific heat. Regolith elastic properties not only include parameters that control seismic wave velocities in the immediate vicinity of the Insight lander but also coupling of the lander and other potential noise sources to the InSight broadband seismometer. The related properties include Poisson’s ratio, P- and S-wave velocities, Young’s modulus, and seismic attenuation. Finally, mass diffusivity was investigated to estimate gas movements in the regolith driven by atmospheric pressure changes. Physical properties presented here are all to some degree speculative. However, they form a basis for interpretation of the early data to be returned from the InSight mission.Additional co-authors: Nick Teanby and Sharon Keda

Use of polarisation in double passage imaging through a random screen

It has recently been proposed that a deterministic object which is obscured by a random screen may be imaged by the double passage method. This essentially involves illuminating and viewing the object through a non-redundant aperture and time averaging over the statistics of the random screen, the time-averaged image thereby yielding the Fourier modulus of the object. We propose a simple method of obtaining this information without time averaging by manipulating the polarisation states of the illuminating and detected light

Estimation of anisoplanatism in adaptive optics by generalized SCIDAR profiling

We present the results of contemporaneous seeing measurements using a multi-object Shack-Hartmann wavefront sensor, SCIDAR optical turbulence profiling, and a DIMM seeing monitor at the William Herschel Telescope in La Palma. The data are used to determine the accuracy with which angular anisoplanatism can be predicted from generalized SCIDAR turbulence profile measurements. Theoretical predictions of the angular correlation of the Zernike aberration coefficients, based on the SCIDAR profiles, agree with direct measurements from the wavefront sensor to within 7 per cent rms. Estimates of the total seeing (integrated optical turbulence strength) from the methods agree to 10 per cent rms. We conclude that SCIDAR represents a reliable means for calibration of the spatially and temporally variable point-spread function for imaging with adaptive optics in astronomy

Measurement and analysis of analogue signals from a Linseis chart recorder using a BBC microcomputer

No abstract available