26,439 research outputs found
Development of optimized, graded-permeability axial groove heat pipes
Heat pipe performance can usually be improved by uniformly varying or grading wick permeability from end to end. A unique and cost effective method for grading the permeability of an axial groove heat pipe is described - selective chemical etching of the pipe casing. This method was developed and demonstrated on a proof-of-concept test article. The process improved the test article's performance by 50 percent. Further improvement is possible through the use of optimally etched grooves
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
Alternative derivation of the Feigel effect and call for its experimental verification
A recent theory by Feigel [Phys. Rev. Lett. {\bf 92}, 020404 (2004)] predicts
the finite transfer of momentum from the quantum vacuum to a fluid placed in
strong perpendicular electric and magnetic fields. The momentum transfer arises
because of the optically anisotropic magnetoelectric response induced in the
fluid by the fields. After summarising Feigel's original assumptions and
derivation (corrected of trivial mistakes), we rederive the same result by a
simpler route, validating Feigel's semi-classical approach. We then derive the
stress exerted by the vacuum on the fluid which, if the Feigel hypothesis is
correct, should induce a Poiseuille flow in a tube with maximum speed m/s (2000 times larger than Feigel's original prediction). An experiment
is suggested to test this prediction for an organometallic fluid in a tube
passing through the bore of a high strength magnet. The predicted flow can be
measured directly by tracking microscopy or indirectly by measuring the flow
rate (ml/min) corresponding to the Poiseuille flow. A second
experiment is also proposed whereby a `vacuum radiometer' is used to test a
recent prediction that the net force on a magnetoelectric slab in the vacuum
should be zero.Comment: 20 pages, 1 figures. revised and improved versio
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
Quantifying Spatiotemporal Chaos in Rayleigh-B\'enard Convection
Using large-scale parallel numerical simulations we explore spatiotemporal
chaos in Rayleigh-B\'enard convection in a cylindrical domain with
experimentally relevant boundary conditions. We use the variation of the
spectrum of Lyapunov exponents and the leading order Lyapunov vector with
system parameters to quantify states of high-dimensional chaos in fluid
convection. We explore the relationship between the time dynamics of the
spectrum of Lyapunov exponents and the pattern dynamics. For chaotic dynamics
we find that all of the Lyapunov exponents are positively correlated with the
leading order Lyapunov exponent and we quantify the details of their response
to the dynamics of defects. The leading order Lyapunov vector is used to
identify topological features of the fluid patterns that contribute
significantly to the chaotic dynamics. Our results show a transition from
boundary dominated dynamics to bulk dominated dynamics as the system size is
increased. The spectrum of Lyapunov exponents is used to compute the variation
of the fractal dimension with system parameters to quantify how the underlying
high-dimensional strange attractor accommodates a range of different chaotic
dynamics
A transient heat transfer and thermodynamic analysis of the Apollo service module propulsion system. Vol. I, phase I - Transient thermal analysis Final report, 28 Jul. 1964 - 28 Jul. 1965
Transient heat transfer and thermodynamic behavior analysis for Apollo service module propulsion system - fuel cell effect on overheatin
Remote Sensing of Evaporation
Evaporation of water from the Earth's surface into the atmosphere is central to the terrestrial energy, water and carbon cycle. Remote sensing approaches to measure evaporation (ET) combine observable inputs to the energy and water balance within statistical or process-based methodologies. These ET products draw on satellite observations from across the electro-magnetic spectrum. The ET retrievals are grouped in two main categories. One category includes approaches that combine meteorological descriptions of potential evaporation with a range of strategies to estimate evaporative stress. A second category includes surface energy balance approaches that retrieve latent heat from the thermal signatures. For each category a practical implementation example is described, including an outlook on progress towards multi-model assessment of global evaporation
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