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.

Large, Switchable Electrochromism in the Visible Through Far‐Infrared in Conducting Polymer Devices

Abstract: Advanced materials with large and dynamic variation in thermal properties, sought for urgent defense and space applications, have heretofore been elusive. Conducting polymers (CPs) have shown some intrinsic variation of mid- to far-infrared (IR) signature in this respect, but the practical utilization of this has remained elusive. We report herein the first significant IR electrochromism in any material, to our knowledge, in the 0.4 through 45 μm region. This is seen in practical CP devices in the form of thin (<0.5 mm), flexible, entirely solid-state, variable area (1 cm2 to 1 m2) flat panels. Typical properties include: very high reflectance variation; switching times <2 s; cyclabilities of 105 cycles; emittance variation from 0.32 to 0.79; solar absorptance variation from 0.39 to 0.79; operating temperatures of –35 to +85 °C; durability against γ-radiation to 7.6 Mrad, vacuum to 10–6 torr, and simulated solar wind (e.g., 6.5 × 1016 e/cm2 @ 10 keV).

The Astrophysics Of Nanohertz Gravitational Waves

Abstract: Pulsar timing array (PTA) collaborations in North America, Australia, and Europe, have been exploiting the exquisite timing precision of millisecond pulsars over decades of observations to search for correlated timing deviations induced by gravitational waves (GWs). PTAs are sensitive to the frequency band ranging just below 1 nanohertz to a few tens of microhertz. The discovery space of this band is potentially rich with populations of inspiraling supermassive black hole binaries, decaying cosmic string networks, relic post-inflation GWs, and even non-GW imprints of axionic dark matter. This article aims to provide an understanding of the exciting open science questions in cosmology, galaxy evolution, and fundamental physics that will be addressed by the detection and study of GWs through PTAs. The focus of the article is on providing an understanding of the mechanisms by which PTAs can address specific questions in these fields, and to outline some of the subtleties and difficulties in each case. The material included is weighted most heavily toward the questions which we expect will be answered in the near-term with PTAs; however, we have made efforts to include most currently anticipated applications of nanohertz GWs.

Atmospheric pressure loading effects on Global Positioning System coordinate determinations

Abstract: Earth deformation signals caused by atmospheric pressure loading are detected in vertical position estimates at Global Positioning System (GPS) stations. Surface displacements due to changes in atmospheric pressure account for up to 24% of the total variance in the GPS height estimates. The detected loading signals are larger at higher latitudes where pressure variations are greatest; the largest effect is observed at Fairbanks, Alaska (latitude 65 deg), with a signal root mean square (RMS) of 5 mm. Out of 19 continuously operating GPS sites (with a mean of 281 daily solutions per site), 18 show a positive correlation between the GPS vertical estimates and the modeled loading displacements. Accounting for loading reduces the variance of the vertical station positions on 12 of the 19 sites investigated. Removing the modeled pressure loading from GPS determinations of baseline length for baselines longer than 6000 km reduces the variance on 73 of the 117 baselines investigated. The slight increase in variance for some of the sites and baselines is consistent with expected statistical fluctuations. The results from most stations are consistent with approximately 65% of the modeled pressure load being found in the GPS vertical position measurements. Removing an annual signal from both the measured heights and the modeled load time series leaves this value unchanged. The source of the remaining discrepancy between the modeled and observed loading signal may be the result of (1) anisotropic effects in the Earth's loading response, (2) errors in GPS estimates of tropospheric delay, (3) errors in the surface pressure data, or (4) annual signals in the time series of loading and station heights. In addition, we find that using site dependent coefficients, determined by fitting local pressure to the modeled radial displacements, reduces the variance of the measured station heights as well as or better than using the global convolution sum.

Tracing the cosmic growth of supermassive black holes to z ∼ 3 with Herschel

Abstract: We study a sample of Herschel selected galaxies within the Great Observatories Origins Deep Survey-South and the Cosmic Evolution Survey fields in the framework of the Photodetector Array Camera and Spectrometer (PACS) Evolutionary Probe project. Starting from the rich multiwavelength photometric data sets available in both fields, we perform a broad-band spectral energy distribution decomposition to disentangle the possible active galactic nucleus (AGN) contribution from that related to the host galaxy. We find that 37 per cent of the Herschel-selected sample shows signatures of nuclear activity at the 99 per cent confidence level. The probability of revealing AGN activity increases for bright (L_(1−1000) > 10^(11) L_⊙) star-forming galaxies at z > 0.3, becoming about 80 per cent for the brightest (L_(1−1000) > 10^(12) L_⊙) infrared (IR) galaxies at z ≥ 1. Finally, we reconstruct the AGN bolometric luminosity function and the supermassive black hole growth rate across cosmic time up to z ∼ 3 from a far-IR perspective. This work shows general agreement with most of the panchromatic estimates from the literature, with the global black hole growth peaking at z ∼ 2 and reproducing the observed local black hole mass density with consistent values of the radiative efficiency ϵ_(rad) (∼0.07).

Evidence for subglacial water transport in the West Antarctic Ice Sheet through three‐dimensional satellite radar interferometry

Abstract: [1] RADARSAT data from the 1997 Antarctic Mapping Mission are used interferometrically to solve for the 3-dimensional surface ice motion in the interior of the West Antarctic Ice Sheet (WAIS). An area of ∼125 km2 in a tributary of the Kamb Ice Stream slumped vertically downwards by up to ∼50 cm between September 26 and October 18, 1997. Areas in the Bindschadler Ice Stream also exhibited comparable upward and downward surface displacements. As the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well, we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements. These results, and related lidar observations, imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult-to-observe subglacial environment, and its important influence on ice dynamics.