Analysis of OGO-6 observations of the 0 I 5577A tropical nightglow

Atomic oxygen green line data from the horizon scanning photometer on OGO-6 was examined. Unfolding the satellite data from the tropical F-region yields altitude and latitude variations of the O(1S) emissions. The spatial variations of the tropical F-region electron density are then calculated by assuming dissociative recombination and using a model atmosphere. Where comparisons to ground-based data are possible the results are good. Thus, the satellite observations constitute a form of topside sounding of the ionosphere below the F-peak and provide synoptic data about this portion of the ionsphere otherwise impractical to obtain

Water on Mars and Venus

This paper reviews evidence relating to the abundance of water on early Mars and Venus from measurements of the present abundance of hydrogen compounds, deuterium to hydrogen (D/H) ratios and escape fluxes. For Mars, recent measurements of D/H ratios in SNC hydrous minerals provide data on the ratios at earlier times to augment present atmospheric values. Interpretation of these data shows that they are consistent with the presence of scores to hundreds of meters of liquid water on early Mars, as well as less, but still abundant, water in today’s crust. They also require concentrations of hydrogen compounds in the early atmosphere orders of magnitude higher than is present today to support large scale hydrogen escape. For Venus, a very large D/H enhancement (160 fold) implies at least 3 to 4 meters liquid equivalent of early water (depending on how much hydrogen is in the atmosphere today). It is consistent with much more, even the equivalent of a full terrestrial ocean. The low escape flux and high fractionation factor place severe constraints on volcanic or cometary sources. Some of the present water can have been injected by volcanism but comets as important sources appear to be excluded. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87493/2/154_1.pd

Solar cycle variations in H + and d + densities in the Venus ionosphere: Implications for escape

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95098/1/grl6482.pd

Venus methane and water

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94590/1/grl6638.pd

Why explore Venus?

This paper develops the rationale for a program of Venus exploration by man.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43769/1/11214_2005_Article_BF02186465.pd

Fractionation of noble gases by thermal escape from accreting planetesimals

A model for the selective loss of noble gases by thermal escape of the gases from planetesimals as they grow to form the terrestrial planets has been developed. The initial elemental and isotopic abundance ratios are assumed to be solar. Competition between gravitational binding and escape determines the degree of fractionation that occurs. Two classes of planetesimals can be formed on a time scale consistent with modern models of accretion. One class is depleted in neon and, in some cases, partly in 36Ar. The other class is neon rich. Subject to the validity of some assumptions regarding loss of planetary atmospheres following collisions between very large embryo planets and a strong radial dependence in the rate of accumulation of neon-rich planetesimals, the mechanism can account for all known properties of the noble gas volatiles on the terrestrial planets except one. This is the 36Ar/38Ar ratios for Earth and Mars which are predicted to be much lower than observed. This failure is probably fatal for the hypothesis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26175/1/0000254.pd

Cold gas in the Intra Cluster Medium: implications for flow dynamics and powering optical nebulae

We show that the mechanical energy injection rate generated as the intra-cluster medium (ICM) flows around cold clouds may be sufficient to power the optical and near infra-red emission of nebulae observed in the central regions of a sample of seven galaxy clusters. The energy injection rate is extremely sensitive to the velocity difference between the ICM and cold clouds, which may help to explain why optical and infra-red luminosity is often larger than expected in systems containing AGNs. We also find that mass recycling is likely to be important for the dynamics of the ICM. This effect will be strongest in the central regions of clusters where there is more than enough cold gas for its evaporation to contribute significantly to the density of the hot phase.Comment: 8 pages, 2 figures, accepted for publication in MNRA

The regulation of hydrogen and oxygen escape from Mars

It is shown that under present conditions the Jeans escape flux of hydrogen from Mars in the form of H and H2 is constrained to be the same as twice the non-thermal ([McElroy, 1972]) escape of O atoms. The mediation of the chemical chain that recombines CO2 plays an essential role in regulating the escape of hydrogen to match that of oxygen, confirming a mechanism postulated by [McElroy and Donahue, 1972]. It is also shown that if the oxygen flux changes, a change in the O2 mixing ratio results and the consequence is to induce a large change in the odd hydrogen concentration, and consequently in H2 production and hydrogen escape. The effect is to stabilize the hydrogen escape flux at twice the O flux. It is shown that surface chemistry should not change the operation of this mechanism but has consequences for the eddy coefficient variation at low altitudes. There is a strong correlation between low humidity, large solar zenith angles and large O3 abundances. The effect of argon in a mixing ratio as large as 0.3 on these results is also investigated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21758/1/0000152.pd

Experimental realization of a nonlinear acoustic lens with a tunable focus

We realize a nonlinear acoustic lens composed of a two-dimensional array of sphere chains interfaced with water. The chains are able to support solitary waves which, when interfaced with a linear medium, transmit compact pulses with minimal oscillations. When focused, the lens is able to produce compact pressure pulses of high amplitude, the “sound bullets.” We demonstrate that the focal point can be controlled via pre-compression of the individual chains, as this changes the wave speed within them. The experimental results agree well both spatially and temporally with analytical predictions over a range of focus locations

Direct observation of domain wall structures in curved permalloy wires containing an antinotch

The formation and field response of head-to-head domain walls in curved permalloy wires, fabricated to contain a single antinotch, have been investigated using Lorentz microscopy. High spatial resolution maps of the vector induction distribution in domain walls close to the antinotch have been derived and compared with micromagnetic simulations. In wires of 10 nm thickness the walls are typically of a modified asymmetric transverse wall type. Their response to applied fields tangential to the wire at the antinotch location was studied. The way the wall structure changes depends on whether the field moves the wall away from or further into the notch. Higher fields are needed and much more distorted wall structures are observed in the latter case, indicating that the antinotch acts as an energy barrier for the domain wal