1,007 research outputs found
Zonal analysis of two high-speed inlets
Using a zonal technique, thin layer Navier-Stokes solutions for two high speed inlet geometries are presented and compared with experimental data. The first configuration consists of a 3-D inlet preceded by a sharp flat plate. Results with two different grids demonstrate the importance of adequate grid refinement in high speed internal flow computations. The fine grid solution has reasonably good agreement with experimental heat transfer and pressure values inside the inlet. The other configuration consists of a 3-D inlet mounted on a research hypersonic forebody. Numerical results for this configuration have good agreement with experimental pressure data along the forebody, but not inside the inlet. A more refined grid calculation is currently being done to better predict the flowfield in the inlet
Primordial helium recombination III: Thomson scattering, isotope shifts, and cumulative results
Upcoming precision measurements of the temperature anisotropy of the cosmic
microwave background (CMB) at high multipoles will need to be complemented by a
more complete understanding of recombination, which determines the damping of
anisotropies on these scales. This is the third in a series of papers
describing an accurate theory of HeI and HeII recombination. Here we describe
the effect of Thomson scattering, the He isotope shift, the contribution of
rare decays, collisional processes, and peculiar motion. These effects are
found to be negligible: Thomson and He scattering modify the free electron
fraction at the level of several . The uncertainty in the
rate is significant, and for conservative estimates gives
uncertainties in of order . We describe several convergence
tests for the atomic level code and its inputs, derive an overall
error budget, and relate shifts in to the changes in , which
are at the level of 0.5% at . Finally, we summarize the main
corrections developed thus far. The remaining uncertainty from known effects is
in .Comment: 19 pages, 15 figures, to be submitted to PR
Method of Preparing a Chiral Substrate Surface By Electrodeposition
A solid substrate comprising a surface comprising an achiral array of atoms having thereupon a chiral metal oxide surface. The chiral metal oxide surface is prepared by electrodeposition of a chiral metal oxide array from a solution of a chiral salt of the metal. In one embodiment, chiral CuO is grown on achiral Au(001) by epitaxial electrodeposition. The handedness of the film is determined by the specific enantiomer of tartrate ion in the deposition solution. (R,R)- tartrate produces an S—CuO(l 1 T) film, while (S,S)-tartrate produces an R—CuO(Tl 1) film. These chiral CuO films are enantiospecific for the electrochemical oxidation of(R,R) and (S,S)-tartrate
Book Reviews
Reviews of the following books: University of Maine 1971 Seminar in MARITIME AND REGIONAL STUDIES, Clark G. Reynolds, William J. McAndrew, editors; Ride the Sandy River by L.P. Cornwall and Jack W. Farrell; The Canadian Frontier, 1834-1760 by William J. Eccles; The Red Schoolhouse Neighborhood by Ben and Natalie Butler; Pokey and Timothy of Stonehouse Farm by Marion Jaques Smit
Primordial helium recombination II: two-photon processes
Interpretation of precision measurements of the cosmic microwave background
(CMB) will require a detailed understanding of the recombination era, which
determines such quantities as the acoustic oscillation scale and the Silk
damping scale. This paper is the second in a series devoted to the subject of
helium recombination, with a focus on two-photon processes in He I. The
standard treatment of these processes includes only the spontaneous two-photon
decay from the 2^1S level. We extend this treatment by including five
additional effects, some of which have been suggested in recent papers but
whose impact on He I recombination has not been fully quantified. These are:
(i) stimulated two-photon decays; (ii) two-photon absorption of redshifted HeI
line radiation; (iii) two-photon decays from highly excited levels in HeI (n^1S
and n^1D, with n>=3); (iv) Raman scattering; and (v) the finite width of the
2^1P^o resonance. We find that effect (iii) is highly suppressed when one takes
into account destructive interference between different intermediate states
contributing to the two-photon decay amplitude. Overall, these effects are
found to be insignificant: they modify the recombination history at the level
of several parts in 10^4.Comment: 19 pages, 11 figures, to be submitted to PR
A Method for Individual Source Brightness Estimation in Single- and Multi-band Data
We present a method of reliably extracting the flux of individual sources
from sky maps in the presence of noise and a source population in which number
counts are a steeply falling function of flux. The method is an extension of a
standard Bayesian procedure in the millimeter/submillimeter literature. As in
the standard method, the prior applied to source flux measurements is derived
from an estimate of the source counts as a function of flux, dN/dS. The key
feature of the new method is that it enables reliable extraction of properties
of individual sources, which previous methods in the literature do not. We
first present the method for extracting individual source fluxes from data in a
single observing band, then we extend the method to multiple bands, including
prior information about the spectral behavior of the source population(s). The
multi-band estimation technique is particularly relevant for classifying
individual sources into populations according to their spectral behavior. We
find that proper treatment of the correlated prior information between
observing bands is key to avoiding significant biases in estimations of
multi-band fluxes and spectral behavior, biases which lead to significant
numbers of misclassified sources. We test the single- and multi-band versions
of the method using simulated observations with observing parameters similar to
that of the South Pole Telescope data used in Vieira, et al. (2010).Comment: 11 emulateapj pages, 3 figures, revised to match published versio
Electrochemical Deposition and Characterization of Fe₃O₄ Films Produced by the Reduction of Fe(III)-triethanolamine
In this paper, we demonstrate that films of magnetite, Fe3O4, can be deposited by the electrochemical reduction of a Fe(III)-triethanolamine complex in aqueous alkaline solution. the films were deposited with a columnar microstructure and a [100] preferred orientation on stainless steel substrates. In-plane electrical transport and magnetoresistance measurements were performed on the films after they were stripped off onto glass substrates. the resistance of the films was dependent on the oxygen partial pressure. We attribute the increase in resistance in O2 and the decrease in resistance in Ar to the oxidation and reduction of grain boundaries. the decrease in resistance in an Ar atmosphere exhibited first-order kinetics, with an activation energy of 0.2 eV. the temperature dependence of the resistance showed a linear dependence of log(R) versus T-1/2, consistent with tunneling across resistive grain boundaries. a room-temperature magnetoresistance of -6.5% was observed at a magnetic field of 9 T
Fiber Optic Cables for Transmission of High-Power Laser Pulses in Spaceflight Applications
Lasers with high peak power pulses are commonly used in spaceflight missions for a wide range of applications, from LIDAR systems to optical communications. Due to the high optical power needed, the laser has to be located on the exterior of the satellite or coupled through a series of free space optics. This presents challenges for thermal management, radiation resistance, and mechanical design. Future applications will require multiple lasers located close together, which further complicates the design. Coupling the laser energy into a fiber optic cable allows the laser to be relocated to a more favorable position on the spacecraft. Typical fiber optic termination procedures are not sufficient for injection of these high-power laser pulses without catastrophic damage to the fiber endface. In the current study, we will review the causes of fiber damage during high-power injection and discuss our new manufacturing procedures that overcome these issues to permit fiber use with high reliability in these applications. We will also discuss the proper methods for launching the laser pulses into the fiber to avoid damage and how this is being implemented for current spaceflight missions
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