21,029 research outputs found
Interaction of gases with lunar materials
The surface properties of lunar fines were investigated. Results indicate that, for the most part, these properties are independent of the chemical composition and location of the samples on the lunar surface. The leaching of channels and pores by adsorbed water vapor is a distinguishing feature of their surface chemistry. The elements of air, if adsorbed in conjunction with water vapor or liquid water, severely impedes the leaching process. In the absence of air, liquid water is more effective than water vapor in attacking the grains. The characteristics of Apollo 17 orange fines were evaluated and compared with those of other samples. The interconnecting channels produced by water vapor adsorption were found to be wider than usual for other types of fines. Damage tracks caused by heavy cosmic ray nuclei and an unusually high halogen content might provide for stronger etching conditions upon exposure to water vapor
Interaction of gases with lunar materials
The surface chemistry of Apollo 17 lunar fines samples 74220 (the orange soil) and 74241 (the gray control soil) has been studied by measuring the adsorption of nitrogen, argon, and oxygen (all at 77 K) and also water vapor (at 20 or 22 C). In agreement with results for samples from other missions, both samples had low initial specific surface areas, consisted of nonporous particles, and were attacked by water vapor at high relative pressure to give an increased specific surface area and create a pore system which gave rise to a capillary condensation hysteresis loop in the adsorption isotherms. In contrast to previous samples, both of the Apollo 17 soils were partially hydrophobic in their initial interaction with water vapor (both samples were completely hydrophilic after the reaction with water). The results are consistent with formation at high temperatures without subsequent exposure to significant amounts of water
Interaction of gases with lunar materials
Quantitative efforts to assess the surface properties of lunar fines, particularly water induced porosity are discussed. Data show that: (1) changes induced in lunar fines are not visible in high energy electron micrographs, (2) scanning micrographs show no change in particle size distribution as a result of reaction with water, (3) water induced changes are internal to the particles themselves, (4) normal laboratory atmosphere blocks alteration reaction with water, and (5) surface properties of mature lunar soils appear to be almost independent of chemical composition and mineralogy, but there are some variations in their reactivity toward water
Atlantic Ocean Heat Transport Enabled by Indo-Pacific Heat Uptake and Mixing
The ocean transports vast amounts of heat around the planet, helping to regulate regional climate. One important component of this heat transport is the movement of warm water from equatorial regions toward the poles, with colder water flowing in return. Here, we introduce a framework relating meridional heat transport to the diabatic processes of surface forcing and turbulent mixing that move heat across temperature classes. Applied to a (1/4)° global ocean model the framework highlights the role of the tropical Indo‐Pacific in the global ocean heat transport. A large fraction of the northward heat transport in the Atlantic is ultimately sourced from heat uptake in the eastern tropical Pacific. Turbulent mixing moves heat from the warm, shallow Indo‐Pacific circulation to the cold deeper‐reaching Atlantic circulation. Our results underscore a renewed focus on the tropical oceans and their role in global circulation pathways
The self-consistent gravitational self-force
I review the problem of motion for small bodies in General Relativity, with
an emphasis on developing a self-consistent treatment of the gravitational
self-force. An analysis of the various derivations extant in the literature
leads me to formulate an asymptotic expansion in which the metric is expanded
while a representative worldline is held fixed; I discuss the utility of this
expansion for both exact point particles and asymptotically small bodies,
contrasting it with a regular expansion in which both the metric and the
worldline are expanded. Based on these preliminary analyses, I present a
general method of deriving self-consistent equations of motion for arbitrarily
structured (sufficiently compact) small bodies. My method utilizes two
expansions: an inner expansion that keeps the size of the body fixed, and an
outer expansion that lets the body shrink while holding its worldline fixed. By
imposing the Lorenz gauge, I express the global solution to the Einstein
equation in the outer expansion in terms of an integral over a worldtube of
small radius surrounding the body. Appropriate boundary data on the tube are
determined from a local-in-space expansion in a buffer region where both the
inner and outer expansions are valid. This buffer-region expansion also results
in an expression for the self-force in terms of irreducible pieces of the
metric perturbation on the worldline. Based on the global solution, these
pieces of the perturbation can be written in terms of a tail integral over the
body's past history. This approach can be applied at any order to obtain a
self-consistent approximation that is valid on long timescales, both near and
far from the small body. I conclude by discussing possible extensions of my
method and comparing it to alternative approaches.Comment: 44 pages, 4 figure
Properties of planetary fluids at high pressure and temperature
In order to derive models of the interiors of Uranus, Neptune, Jupiter and Saturn, researchers studied equations of state and electrical conductivities of molecules at high dynamic pressures and temperatures. Results are given for shock temperature measurements of N2 and CH4. Temperature data allowed demonstration of shock induced cooling in the the transition region and the existence of crossing isotherms in P-V space
Quantum and classical chaos for a single trapped ion
In this paper we investigate the quantum and classical dynamics of a single
trapped ion subject to nonlinear kicks derived from a periodic sequence of
Guassian laser pulses. We show that the classical system exhibits diffusive
growth in the energy, or 'heating', while quantum mechanics suppresses this
heating. This system may be realized in current single trapped-ion experiments
with the addition of near-field optics to introduce tightly focussed laser
pulses into the trap.Comment: 8 pages, REVTEX, 8 figure
Strain enhancement of superconductivity in CePd2Si2 under pressure
We report resistivity and calorimetric measurements on two single crystals of
CePd2Si2 pressurized up to 7.4 GPa. A weak uniaxial stress induced in the
pressure cell demonstrates the sensitivity of the physics to anisotropy. Stress
applied along the c-axis extends the whole phase diagram to higher pressures
and enhances the superconducting phase emerging around the magnetic
instability, with a 40% increase of the maximum superconducting temperature,
Tc, and a doubled pressure range. Calorimetric measurements demonstrate the
bulk nature of the superconductivity.Comment: 4 pages, 4 figure
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