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.

Spitzer/MIPS Observations of Stars in the Beta Pictoris Moving Group

Abstract: We present Multiband Imaging Photometer for Spitzer (MIPS) observations at 24 and 70 microns for 30 stars, and at 160 microns for a subset of 12 stars, in the nearby (~30 pc), young (~12 Myr) Beta Pictoris Moving Group (BPMG). In several cases, the new MIPS measurements resolve source confusion and background contamination issues in the IRAS data for this sample. We find that 7 members have 24 micron excesses, implying a debris disk fraction of 23%, and that at least 11 have 70 micron excesses (disk fraction of >=37%). Five disks are detected at 160 microns (out of a biased sample of 12 stars observed), with a range of 160/70 flux ratios. The disk fraction at 24 and 70 microns, and the size of the excesses measured at each wavelength, are both consistent with an "inside-out" infrared excess decrease with time, wherein the shorter-wavelength excesses disappear before longer-wavelength excesses, and consistent with the overall decrease of infrared excess frequency with stellar age, as seen in Spitzer studies of other young stellar groups. Assuming that the infrared excesses are entirely due to circumstellar disks, we characterize the disk properties using simple models and fractional infrared luminosities. Optically thick disks, seen in the younger TW Hya and eta Cha associations, are entirely absent in the BPMG. Additional flux density measurements at 24 and 70 microns are reported for nine Tucanae-Horologium Association member stars. Since this is <20% of the association membership, limited analysis on the complete disk fraction of this association is possible.

Differential Versus Limiter--Discriminator Detection of Narrow-Band FM

Abstract: The error probability performance of differential detection of narrow-band FM is determined and compared with the analogous results for limiter-discriminator detection of the same modulation. It is shown that over a large class of benign and hostile environments, e.g., Gaussian IF filter, 1 \leq BT \leq 3, h \leq 1 , AWGN, partial-band noise jamming, the differential detector offers no theoretical performance advantage over the limiter-discriminator receiver with integrate-and-dump postdetection filtering.

Optical properties and environmental stability of oxide coatings deposited by reactive sputtering

Abstract: Refractory metal-oxide coatings are deposited by reactive dc magnetron sputtering in an oxygen environment. The optical constants and the environmental stability of silicon oxide, aluminium oxide, hafnium oxide, zirconium oxide, tantalum oxide, titanium oxide, and a blend of hafnium oxide with silicon oxide are investigated. Properties of both single-layer and multilayer interference filters are examined.

The Galileo Solid-State Imaging Experiment

Abstract: The Solid State Imaging (SSI) experiment on the Galileo Orbiter spacecraft utilizes a high-resolution (1500 mm focal length) television camera with an 800 × 800 pixel virtual-phase, charge-coupled detector It is designed to return images of Jupiter and its satellites that are characterized by a combination of sensitivity levels, spatial resolution, geometric fiedelity, and spectral range unmatched by imaging data obtained previously The spectral range extends from approximately 375 to 1100 nm and only in the near ultra-violet region (~350nm) is the spectral coverage reduced from previous missions The camera is approximately 100 times more sensitive than those used in the Voyager mission, and, because of the nature of the satellite encounters, will produce images with approximately 100 times the ground resolution (ie, ~50mlp−1) on the Galilean satellites We describe aspects of the detector including its sensitivity to energetic particle radiation and how the requirements for a large full-well capacity and long-term stability in operating voltages led to the choice of the virtual phase chip The F/85 camera system can reach point sources of F(mag) ~ 11 with S/N ~ 10 and extended sources with surface brightness as low as 20 kR in its highest gain state and longest exposure mode We describe the performance of the system as determined by ground calibration and the improvements that have been made to the telescope (same basic catadioptric design that was used in Mariner 10 and the Voyager high-resolution cameras) to reduce the scattered light reaching the detector The images are linearly digitized 8-bits deep and, after flat-fielding, are cosmetically clean Information ‘preserving’ and ‘non-preserving’ on-board data compression capabilities are outlined A special “summation” mode, designed for use deep in the Jovian radiation belts, near Io, is also described The detector is ‘preflashed’ before each exposure to ensure the photometric linearity The dynamic range is spread over 3 gain states and an exposure range from 417 ms to 512 s A low-level of radial, third-order, geometric distortion has been measured in the raw images that is entirely due to the optical design The distortion is of the pincushion type and amounts to about 12 pixels in the corners of the images It is expected to be very stable

Parallel proton fire hose instability in the expanding solar wind: Hybrid simulations

Abstract: [1] Oblique fire hose instability is investigated using hybrid simulations for proton betas of the order of one and for proton parallel temperatures sufficiently greater than the perpendicular ones. The simulations confirm previous simulation results showing that this instability has self-destructing properties and efficiently reduces the proton temperature anisotropy. A parametric study using one-dimensional standard hybrid simulations shows that stronger changes in the temperature anisotropy and stronger wave emissions appear for larger initial temperature anisotropies. An ideal, slow plasma expansion, modeled by a two-dimensional hybrid expanding box simulation, leads to a generation of proton temperature anisotropy. The anisotropy leads first to destabilization of the dominant parallel fire hose, which interacts mainly with minor supra-Alfvenic protons, whereas the evolution of core protons is determined by expansion. Consequently, the effective anisotropy is only slightly reduced and the system eventually becomes unstable with respect to the oblique fire hose instability. The oblique fire hose strongly scatters the protons and removes the anisotropy disrupting the parallel fire hose. An important portion of the fluctuating wave energy is dissipated to protons, and only long wavelength waves remain in the system. The system with low wave activity then develops again larger temperature anisotropies, and the evolution repeats itself. It is concluded that both parallel and oblique proton fire hose instabilities constrain the proton temperature anisotropy in the expanding solar wind, with the latter one constituting a final frontier for the anisotropy. These results give a possible explanation of some apparent discrepancies between observations and linear predictions. In addition, a simple bounded anisotropy model is developed to include some of the kinetic effects of the fire hose instabilities in fluid models.