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.

The Frequency of Barred Spiral Galaxies in the Near-IR

Abstract: We have determined the fraction of barred galaxies in the H-band for a statistically well-defined sample of 186 spirals drawn from the Ohio State University Bright Spiral Galaxy survey. We find 56% of our sample to be strongly barred at H, while another 16% is weakly barred. Only 27% of our sample is unbarred in the near-infrared. The RC3 and the Carnegie Atlas of Galaxies both classify only about 30% of our sample as strongly barred. Thus strong bars are nearly twice as prevalent in the near-infrared as in the optical. The frequency of genuine optically hidden bars is significant, but lower than many claims in the literature: 40% of the galaxies in our sample that are classified as unbarred in the RC3 show evidence for a bar in the H-band, while for the Carnegie Atlas this fraction is 66%. Our data reveal no significant trend in bar fraction as a function of morphology in either the optical or H-band. Optical surveys of high redshift galaxies may be strongly biased against finding bars, as bars are increasingly difficult to detect at bluer rest wavelengths.

Interannual variability in upper ocean heat content, temperature, and thermosteric expansion on global scales

Abstract: [1] Satellite altimetric height was combined with approximately 1,000,000 in situ temperature profiles to produce global estimates of upper ocean heat content, temperature, and thermosteric sea level variability on interannual timescales. Maps of these quantities from mid-1993 through mid-2003 were calculated using the technique developed by Willis et al. [2003]. The time series of globally averaged heat content contains a small amount of interannual variability and implies an oceanic warming rate of 0.86 ± 0.12 watts per square meter of ocean (0.29 ± 0.04 pW) from 1993 to 2003 for the upper 750 m of the water column. As a result of the warming, thermosteric sea level rose at a rate of 1.6 ± 0.3 mm/yr over the same time period. Maps of yearly heat content anomaly show patterns of warming commensurate with ENSO variability in the tropics, but also show that a large part of the trend in global, oceanic heat content is caused by regional warming at midlatitudes in the Southern Hemisphere. In addition to quantifying interannual variability on a global scale, this work illustrates the importance of maintaining continuously updated monitoring systems that provide global coverage of the world's oceans. Ongoing projects, such as the Jason/TOPEX series of satellite altimeters and the Argo float program, provide a critical foundation for characterizing variability on regional, basin, and global scales and quantifying the oceans' role as part of the climate system.

Fabrication and deformation of three-dimensional hollow ceramic nanostructures

Abstract: Creating lightweight, mechanically robust materials has long been an engineering pursuit. Many siliceous skeleton species— such as diatoms, sea sponges and radiolarians—have remarkably high strengths when compared with man-made materials of the same composition, yet are able to remain lightweight and porous1–7. It has been suggested that these properties arise from the hierarchical arrangement of different structural elements at their relevant length scales8,9. Here, we report the fabrication of hollow ceramic scaffolds that mimic the length scales and hierarchy of biological materials. The constituent solids attain tensile strengths of 1.75 GPa without failure even after multiple deformation cycles, as revealed by in situ nanomechanical experiments and finite-element analysis. We discuss the high strength and lack of failure in terms of stress concentrators at surface imperfections and of local stresses within the microstructural landscape. Our findings suggest that the hierarchical design principles offered by hard biological organisms can be applied to create damage-tolerant lightweight engineering materials.

Mascons: Lunar Mass Concentrations

Abstract: Lunar Orbiter tracking data have been processed to supply a qualitatively consistent gravimetric map of the lunar nearside. While a simplified model was employed, the results indicate that there are large mass concentrations under the lunar ringed maria. These mass concentrations may have important implications for the various theories regarding lunar history.

Planning in Time: Windows and Durations for Activities and Goals

Abstract: A general purpose automated planner/scheduler is described which generates parallel plans to achieve goals with imposed time con-straints Both durations and start time windows may be specified for sets of goal conditions The parallel plans consist of not just actions but also of events (triggered by circumstances), inferences, and scheduled events (completely beyond the actor's control) Deterministic dura-tions of all such activities are explicitly modeled, and may be any com-putable function of the activity variables A start time window for each activity in the plan is updated dynamically during plan generation, in order to maintain consistency with the windows and durations of adja-cent activities and goals The plans are tailored around scheduled events The final plan network resembles a PERT chart From this a schedule of nominal start times for each activity is generated Ex-amples are drawn from the traditional blocksworld and also from a real-istic ``Spaceworld,'' in which an autonomous spacecraft photographs objects in deep space and transmits the information to Earth The author is with the Information Systems Research Section, Jet Propulsion Laboratory, Pasadena, CA 91109