Jet Propulsion Laboratory

About: Jet Propulsion Laboratory is a facility organization based out in La Cañada Flintridge, California, United States. It is known for research contribution in the topics: Mars Exploration Program & Telescope. The organization has 8801 authors who have published 14333 publications receiving 548163 citations. The organization is also known as: JPL & NASA JPL.

Investigations of dust heating in M81, M83 and NGC 2403 with the Herschel Space Observatory

Abstract: We use Spitzer Space Telescope and Herschel Space Observatory far-infrared data along with ground-based optical and near-infrared data to understand how dust heating in the nearby face-on spiral galaxies M81, M83 and NGC 2403 is affected by the starlight from all stars and by the radiation from star-forming regions. We find that 70/160 m surface brightness ratios tend to be more strongly influenced by star-forming regions. However, the 250/350 m and 350/500 m surface brightness ratios are more strongly affected by the light from the total stellar populations, suggesting that the dust emission at >250 m originates predominantly from a component that is colder than the dust seen at <160 m and that is relatively unaffected by star formation activity. We conclude by discussing the implications of this for modelling the spectral energy distributions of both nearby and more distant galaxies and for using far-infrared dust emission to trace star formation.

Evaluation of the TOPEX/POSEIDON dual-frequency ionosphere correction

Abstract: The NASA altimeter on board TOPEX/POSEIDON exploits the difference in the delays of the Ku and C band radar pulses to estimate an ionosphere correction to the range measurement. The dependence of the ionosphere correction on ocean and satellite parameters is less than 1 cm. The standard deviation of the 1-s averaged ionosphere correction depends on the height of the ocean waves and ranges from 5 to 14 mm. The accuracy of the ionosphere correction is better than 1 cm at the 1 sigma confidence level. The ionosphere correction should be averaged over 140 km (20 s) along track in order to minimize its noise without sacrificing its accuracy. Ionosphere models must achieve an independent sample spacing of 900 km or less in order to allow a single-frequency altimeter to have an ionosphere correction comparable in accuracy to that of the NASA dual-frequency altimeter.

Obscured AGN and the X-ray, Optical and Far-Infrared Number Counts of AGN in the GOODS Fields

Abstract: The deep X-ray, optical, and far-infrared fields that constitute GOODS are sensitive to obscured AGN (N_H>10^{22} cm^{-2}) at the quasar epoch (z~2-3), as well as to unobscured AGN as distant as z~7. Luminous X-ray emission is a sign of accretion onto a supermassive black hole and thus reveals all but the most heavily obscured AGN. We combine X-ray luminosity functions with appropriate spectral energy distributions for AGN to model the X-ray, optical and far-infrared flux distributions of the X-ray sources in the GOODS fields. A simple model based on the unified paradigm for AGN, with ~3 times as many obscured AGN as unobscured, successfully reproduces the z-band flux distributions measured in the deep HST ACS observations on the GOODS North and South fields. This model is also consistent with the observed spectroscopic and photometric redshift distributions once selection effects are considered. The previously reported discrepancy between observed spectroscopic redshift distributions and the predictions of population synthesis models for the X-ray background can be explained by bias against the most heavily obscured AGN generated both by X-ray observations and the identification of sources via optical spectroscopy. We predict the AGN number counts for Spitzer MIPS 24 um and IRAC 3.6-8 um observations in the GOODS fields, which will verify whether most AGN in the early Universe are obscured in the optical. Such AGN should be very bright far-infrared sources and include some obscured AGN missed even by X-ray observations.

A systematic method of hybrid position/force control of a manipulator

Abstract: The feasibility of applying robot manipulators to complex handling and assembly problems in indus try and space depends on the ability to control manipulators precisely, even when there are uncertainties and variations in the environment. This can be done by giving a manipulator hand sensors that provide information about the progress of interactions with the environment. A method is presented for controlling both the position of a manipulator and the contact forces generated at the hand. This hybrid controller has the feature of permitting trajectories to be specified in a convenient Cartesian coordinate system, while offering advantages over the existing approximate "free joint" methods. An experimental implementation of the controller was developed and used to control two joints of a modified Scheinman manipulator equipped with a wrist mounted force sensor. Data from this implementation are presented along with the results from a simple simulation.

Noise Properties of Superconducting Coplanar Waveguide Microwave Resonators

Abstract: We have measured noise in thin-film superconducting coplanar waveguide resonators. This noise appears entirely as phase noise, equivalent to a jitter of the resonance frequency. In contrast, amplitude fluctuations are not observed at the sensitivity of our measurement. The ratio between the noise power in the phase and amplitude directions is large, in excess of 30 dB. These results have important implications for resonant readouts of various devices such as detectors, amplifiers, and qubits. We suggest that the phase noise is due to two-level systems in dielectric materials.