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 Mass-size Relation from Clouds to Cores. II. Solar Neighborhood Clouds

Abstract: We measure the mass and size of cloud fragments in several molecular clouds continuously over a wide range of spatial scales (0.05 {approx}< r/pc {approx}< 3). Based on the recently developed 'dendrogram-technique', this characterizes dense cores as well as the enveloping clouds. 'Larson's Third Law' of constant column density, m(r) {proportional_to} r {sup 2}, is not well suited to describe the derived mass-size data. Solar neighborhood clouds not forming massive stars ({approx}<10 M {sub sun}; Pipe Nebula, Taurus, Perseus, and Ophiuchus) obey m(r) {<=} 870 M {sub sun}(r/pc){sup 1.33}. In contrast to this, clouds forming massive stars (Orion A, G10.15 - 0.34, G11.11 - 0.12) do exceed the aforementioned relation. Thus, this limiting mass-size relation may approximate a threshold for the formation of massive stars. Across all clouds, cluster-forming cloud fragments are found to be-at given radius-more massive than fragments devoid of clusters. The cluster-bearing fragments are found to roughly obey a mass-size law m {proportional_to} r {sup 1.27} (where the exponent is highly uncertain in any given cloud, but is certainly smaller than 1.5).

The far-infrared/radio correlation and radio spectral index of galaxies in the SFR–M∗ plane up to z~2

Abstract: We study the evolution of the radio spectral index and far-infrared/radio correlation (FRC) across the star-formation rate – stellar masse (i.e. SFR–M∗) plane up to z ~ 2. We start from a stellar-mass-selected sample of galaxies with reliable SFR and redshift estimates. We then grid the SFR–M∗ plane in several redshift ranges and measure the infrared luminosity, radio luminosity, radio spectral index, and ultimately the FRC index (i.e. qFIR) of each SFR–M∗–z bin. The infrared luminosities of our SFR–M∗–z bins are estimated using their stacked far-infrared flux densities inferred from observations obtained with the Herschel Space Observatory. Their radio luminosities and radio spectral indices (i.e. α, where Sν ∝ ν−α) are estimated using their stacked 1.4 GHz and 610 MHz flux densities from the Very Large Array and Giant Metre-wave Radio Telescope, respectively. Our far-infrared and radio observations include the most widely studied blank extragalactic fields – GOODS-N, GOODS-S, ECDFS, and COSMOS – covering a total sky area of ~2.0 deg2. Using this methodology, we constrain the radio spectral index and FRC index of star-forming galaxies with M∗ > 1010 M⊙ and 0

Visual odometry on the Mars exploration rovers - a tool to ensure accurate driving and science imaging

Abstract: In this paper, visual odometry is presented as an approach to position estimation to find features in a stereo image pair and track them from one frame to the next. Visual odometry has been a highly effective tool for maintaining vehicle safety while driving near obstacles on slopes, achieving difficult drive approaches in fewer sols, and ensuring accurate science imaging. Although it requires active pointing by human drivers in feature-poor terrain, the improved position knowledge enables more autonomous capability and better science return during planetary operations

The Observed State of the Energy Budget in the Early Twenty-First Century

Abstract: New objectively balanced observation-based reconstructions of global and continental energy budgets and their seasonal variability are presented that span the golden decade of Earth-observing satellites at the start of the twentyfirst century. In the absence of balance constraints, various combinations of modern flux datasets reveal that current estimates of net radiation into Earth’s surface exceed corresponding turbulent heat fluxes by 13–24 Wm 22 .T he largest imbalances occur over oceanic regions where the component algorithms operate independent of closure constraints.Recent uncertainty assessmentssuggestthat these imbalancesfall within anticipatederror bounds foreach dataset, but the systematic nature of required adjustments across different regions confirm the existence of biases in the component fluxes. To reintroduce energy and water cycle closure information lost in the development of independent flux datasets, a variational method is introduced that explicitly accounts for the relative accuracies in all component fluxes. Applying the technique to a 10-yr record of satellite observations yields new energy budget estimates that simultaneously satisfy all energy and water cycle balance constraints. Globally, 180 Wm 22 of atmospheric longwavecoolingisbalancedby74 Wm 22 ofshortwaveabsorptionand106 Wm 22 oflatentandsensibleheatrelease. Atthesurface,106Wm 22 ofdownwellingradiationisbalancedbyturbulentheattransfertowithinaresidualheatflux into the oceans of 0.45Wm 22 , consistent with recent observations of changes in ocean heat content. Annual mean energy budgets and their seasonal cycles for each of seven continents and nine ocean basins are also presented.

Interstitial Zn Atoms Do the Trick in Thermoelectric Zinc Antimonide, Zn4Sb3: A Combined Maximum Entropy Method X-ray Electron Density and Ab Initio Electronic Structure Study

Abstract: The experimental electron density of the high-performance thermoelectric material Zn4Sb3 has been determined by maximum entropy (MEM) analysis of short-wavelength synchrotron powder diffraction data. These data are found to be more accurate than conventional single-crystal data due to the reduction of common systematic errors, such as absorption, extinction and anomalous scattering. Analysis of the MEM electron density directly reveals interstitial Zn atoms and a partially occupied main Zn site. Two types of Sb atoms are observed: a free spherical ion (Sb3-) and Sb2(4-) dimers. Analysis of the MEM electron density also reveals possible Sb disorder along the c axis. The disorder, defects and vacancies are all features that contribute to the drastic reduction of the thermal conductivity of the material. Topological analysis of the thermally smeared MEM density has been carried out. Starting with the X-ray structure ab initio computational methods have been used to deconvolute structural information from the space-time data averaging inherent to the XRD experiment. The analysis reveals how interstitial Zn atoms and vacancies affect the electronic structure and transport properties of beta-Zn4Sb3. The structure consists of an ideal A12Sb10 framework in which point defects are distributed. We propose that the material is a 0.184:0.420:0.396 mixture of A12Sb10, A11BCSb10 and A10BCDSb10 cells, in which A, B, C and D are the four Zn sites in the X-ray structure. Given the similar density of states (DOS) of the A12Sb10, A11BCSb10 and A10BCDSb10 cells, one may electronically model the defective stoichiometry of the real system either by n-doping the 12-Zn atom cell or by p-doping the two 13-Zn atom cells. This leads to similar calculated Seebeck coefficients for the A12Sb10, A11BCSb10 and A10BCDSb10 cells (115.0, 123.0 and 110.3 microV K(-1) at T=670 K). The model system is therefore a p-doped semiconductor as found experimentally. The effect is dramatic if these cells are doped differently with respect to the experimental electron count. Thus, 0.33 extra electrons supplied to either kind of cell would increase the Seebeck coefficient to about 260 microV K(-1). Additional electrons would also lower sigma, so the resulting effect on the thermoelectric figure of merit of Zn4Sb3 challenges further experimental work.