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.

Removal of Stratospheric O3 by Radicals: In Situ Measurements of OH, HO2, NO, NO2, ClO, and BrO

Abstract: Simultaneous in situ measurements of the concentrations of OH, HO_2, ClO, BrO, NO, and NO_2 demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO_2 with ozone, accounted for nearly one-half of the total O_3 removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O_3; reactions involving BrO account for one-half of this loss. Catalytic destruction by NO_2, which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O_3 removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO_2 and ClO are inversely correlated with those of NO and NO_2. The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O_3 removal was inversely correlated with total NO_x, loading.

Cloud ice: A climate model challenge with signs and expectations of progress

Abstract: [1] Present-day shortcomings in the representation of upper tropospheric ice clouds in general circulation models (GCMs) lead to errors in weather and climate forecasts as well as account for a source of uncertainty in climate change projections. An ongoing challenge in rectifying these shortcomings has been the availability of adequate, high-quality, global observations targeting ice clouds and related precipitating hydrometeors. In addition, the inadequacy of the modeled physics and the often disjointed nature between model representation and the characteristics of the retrieved/observed values have hampered GCM development and validation efforts from making effective use of the measurements that have been available. Thus, even though parameterizations in GCMs accounting for cloud ice processes have, in some cases, become more sophisticated in recent years, this development has largely occurred independently of the global-scale measurements. With the relatively recent addition of satellite-derived products from Aura/Microwave Limb Sounder (MLS) and CloudSat, there are now considerably more resources with new and unique capabilities to evaluate GCMs. In this article, we illustrate the shortcomings evident in model representations of cloud ice through a comparison of the simulations assessed in the Intergovernmental Panel on Climate Change Fourth Assessment Report, briefly discuss the range of global observational resources that are available, and describe the essential components of the model parameterizations that characterize their "cloud" ice and related fields. Using this information as background, we (1) discuss some of the main considerations and cautions that must be taken into account in making model-data comparisons related to cloud ice, (2) illustrate present progress and uncertainties in applying satellite cloud ice (namely from MLS and CloudSat) to model diagnosis, (3) show some indications of model improvements, and finally (4) discuss a number of remaining questions and suggestions for pathways forward.

The Thermoelectric Properties of Bismuth Telluride

Abstract: DOI: 10.1002/aelm.201800904 made for efficient thermoelectric cooling or temperature management uses Bi2Te3 alloys. Such solid-state devices dominate the market for temperature control in optoelectronics. As the need to eliminate greenhouse-gas refrigerants increases, Peltier cooling is becoming more attractive particularly in small systems where efficiencies are comparable to traditional refrigerant based cooling. Such small devices may enable distributive heating/ cooling (only where and when it is needed) with higher system level energy efficiency, for example in electric vehicles where energy for heating/cooling competes with vehicle range. Even for thermoelectric power generation, e.g., recovery of waste heat, Bi2Te3 alloys are most used because of superior efficiency up to 200 °C and the technology to make devices with Bi2Te3 is most advanced.[1–3] While the material and production technology for making Bi2Te3-based devices has remained essentially unchanged since the 1960s, our understanding of these materials has advanced considerably. Most recently, the interest in topological insulators (TI) has led to new insights into the complex electronic structure[4,5] revealing that with the accuracy in assessing the band structures available today, improvements in the electronic structure by band engineering should not only be possible but predictable.[6–9] Indeed, the p-type alloys chosen for use in commercial Peltier coolers appear to have unintentionally arrived at a composition close to a band convergence. The understanding of defects and doping is also advancing rapidly that will lead to new strategies for additional improvements in the electronic properties. The thermal conductivity of Bi2Te3-based alloys can also be engineered, where in particular there is much recent interest in microstructure engineering or nanostructuring.[10–22] Reduced thermal conductivity has led to numerous reports of exceptionally high efficiency (zT) that would be sufficient to revolutionize the industry. However, between measurement and material uncertainties, a revolutionary new Bi2Te3-based material has not made it to the market. Because even small but reliable improvements could make significant impact, it is worthwhile to better understand all the complex, interdependent effects of band engineering and microstructure engineering. To demonstrate and quantify improvements in thermoelectric properties, it is necessary to have well characterized properties or reliable benchmarks for comparison. Bismuth telluride is the working material for most Peltier cooling devices and thermoelectric generators. This is because Bi2Te3 (or more precisely its alloys with Sb2Te3 for p-type and Bi2Se3 for n-type material) has the highest thermoelectric figure of merit, zT, of any material around room temperature. Since thermoelectric technology will be greatly enhanced by improving Bi2Te3 or finding a superior material, this review aims to identify and quantify the key material properties that make Bi2Te3 such a good thermoelectric. The large zT can be traced to the high band degeneracy, low effective mass, high carrier mobility, and relatively low lattice thermal conductivity, which all contribute to its remarkably high thermoelectric quality factor. Using literature data augmented with newer results, these material parameters are quantified, giving clear insight into the tailoring of the electronic band structure of Bi2Te3 by alloying, or reducing thermal conductivity by nanostructuring. For example, this analysis clearly shows that the minority carrier excitation across the small bandgap significantly limits the thermoelectric performance of Bi2Te3, even at room temperature, showing that larger bandgap alloys are needed for higher temperature operation. Such effective material parameters can also be used for benchmarking future improvements in Bi2Te3 or new replacement materials.

The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta

Abstract: The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko The very low reflectance of the nucleus (normal albedo of 0060 ± 0003 at 055 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 15 to 5% kA−1), and the broad absorption feature in the 29-to-36–micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun