228 research outputs found
Recommended from our members
Practical beam transport for PFI
The Planet Formation Imager (PFI) is a future kilometric-baseline infrared interferometer to image the complex physical processes of planet formation. Technologies that could be used to transport starlight to a central beam-combining laboratory in PFI include free-space propagation in air or vacuum, and optical fibres. This paper addresses the design and cost issues associated with free-space propagation in vacuum pipes. The signal losses due to diffraction over long differential paths are evaluated, and conceptual beam transport designs employing pupil management to ameliorate these losses are presented and discussed.This is the author accepted manuscript. The final version is available from SPIE via http://dx.doi.org/10.1117/12.223238
The Mount Wilson optical interferometer: The first automated instrument and the prospects for lunar interferometry
Before contemplating an optical interferometer on the Moon one must first review the accomplishments achieved by this technology in scientific applications for astronomy. This will be done by presenting the technical status of optical interferometry as achieved by the Mount Wilson Optical Interferometer. The further developments needed for a future lunar-based interferometer are discussed
Radical loss in a chain reaction of CO and NO in the presence of water: Implications for the radical amplifier and atmospheric chemistry
Comparison of Stellar Angular Diameters from the NPOI, the Mark III Optical Interferometer, and the Infrared Flux Method
IRAS observations of giant molecular clouds in the Milky Way
The IRAS data base has been used to study infrared radiation from molecular clouds in our galaxy. The sample of clouds was restricted to those with reliably determined molecular masses from large area, multi-isotope CO maps. They were normalized to X(CO-13)= 2x10 to the -6. Flux densities at 60 microns and 100 microns were determined by integrating the flux density within rectangles drawn on the sky flux plates after subtracting a suitable background. The rectangles were chosen to be coextensive with the areas mapped in CO. Color corrections were made and luminosites calculated by assuming the optical depths were proportional to frequency. The flux densities were converted to dust masses with a value for 4a rho/3Q = .04 g/cm at 100 microns
The effect of organic compounds on the growth rate of cloud droplets in marine and forest settings
International audienceOrganic matter represents an important fraction of the fine particle aerosol, yet our knowledge of the roles of organics in the activation of aerosol particles into cloud droplets is poor. A cloud condensation nucleus (CCN) counter is used to examine the relative growth rates of cloud droplets for case studies from field measurements on the North Pacific Ocean and in a coniferous forest. A model of the condensational growth of water droplets, on particles dissolving according to their solubility in water, is used to simulate the initial scattering of the droplets as they grow in the CCN counter. Simulations of the growth rates of fine particles sampled in the marine boundary layer of the North Pacific Ocean indicate that the main influence of the marine organic material on the water uptake rate is from its effect on the size distribution of the sulphate. Simulations of the observations of water uptake on biogenic organic aerosol particles sampled in a coniferous forest indicate an impact of the organic on the water uptake rates, but one that is still smaller than that of pure sulphate. The solubility of the organic becomes an important factor in determining the water uptake as the organic mass increases relative to sulphate. The values of the organic component of the hygroscopicity parameter ? that describes the CCN activity were found to be negligible for the marine particles and 0.02?0.05 for the forest particles
Measurements of binary stars with coherent integration of NPOI data
In this paper we use coherently integrated visibilities (see separate paper
in these proceedings, Jorgensen et al. 2008) to measure the properties of
binary stars. We use only the phase of the complex visibility and not the
amplitude. The reason for this is that amplitudes suffer from the calibration
effect (the same for coherent and incoherent averages) and thus effectively
provide lower accuracy measurements. We demonstrate that the baseline phase
alone can be used to measure the separation, orientation and brightness ratio
of a binary star, as a function of wavelength.Comment: 2008 SPIE Astronomical Telescopes and Instrumentatio
Sound propagation in density wave conductors and the effect of long-range Coulomb interaction
We study theoretically the sound propagation in charge- and spin-density
waves in the hydrodynamic regime. First, making use of the method of comoving
frame, we construct the stress tensor appropriate for quasi-one dimensional
systems within tight-binding approximation. Taking into account the screening
effect of the long-range Coulomb interaction, we find that the increase of the
sound velocity below the critical temperature is about two orders of magnitude
less for longitudinal sound than for transverse one. It is shown that only the
transverse sound wave with displacement vector parallel to the chain direction
couples to the phason of the density wave, therefore we expect significant
electromechanical effect only in this case.Comment: revtex, 14 pages (in preprint form), submitted to PR
- …