Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Pr”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Lightning and Precipitation: Observational Analysis of LIS and PR

Lightning flash rate can identify areas of convective rainfall when the storms are dominated by ice-phase precipitation. Modeling and observational studies indicate that cloud electrification and microphysics are very closely related and it is of great interest to understand the relationship between lightning and cloud microphysical quantities. Analyzing data from the Lightning Image Sensor (LIS) and the Precipitation Radar (PR), we show a quantitative relationship between microphysical characteristics of thunderclouds and lightning flash rate. We have performed a complete analysis of all data available over the Mediterranean during the TRMM mission and show a range of reflective profiles as a function of lightning activity for both convective and stratiform regimes as well as seasonal variations. Due to the increasing global coverage of lightning detection networks, this kind of study can used to extend the knowledge about thunderstorms and discriminate between different regimes in regions where radar measurements are readilly available.

Adamo, C.↗
NASA NTRS2003

Spectral Retrieval of Latent Heating Profiles from TRMM PR Data: Comparison of Look-Up Tables

The primary goal of the Tropical Rainfall Measuring Mission (TRMM) is to use the information about distributions of precipitation to determine the four dimensional (i.e., temporal and spatial) patterns of latent heating over the whole tropical region. The Spectral Latent Heating (SLH) algorithm has been developed to estimate latent heating profiles for the TRMM Precipitation Radar (PR) with a cloud- resolving model (CRM). The method uses CRM- generated heating profile look-up tables for the three rain types; convective, shallow stratiform, and anvil rain (deep stratiform with a melting level). For convective and shallow stratiform regions, the look-up table refers to the precipitation top height (PTH). For anvil region, on the other hand, the look- up table refers to the precipitation rate at the melting level instead of PTH. For global applications, it is necessary to examine the universality of the look-up table. In this paper, we compare the look-up tables produced from the numerical simulations of cloud ensembles forced with the Tropical Ocean Global Atmosphere (TOGA) Coupled Atmosphere-Ocean Response Experiment (COARE) data and the GARP Atlantic Tropical Experiment (GATE) data. There are some notable differences between the TOGA-COARE table and the GATE table, especially for the convective heating. First, there is larger number of deepest convective profiles in the TOGA-COARE table than in the GATE table, mainly due to the differences in SST. Second, shallow convective heating is stronger in the TOGA COARE table than in the GATE table. This might be attributable to the difference in the strength of the low-level inversions. Third, altitudes of convective heating maxima are larger in the TOGA COARE table than in the GATE table. Levels of convective heating maxima are located just below the melting level, because warm-rain processes are prevalent in tropical oceanic convective systems. Differences in levels of convective heating maxima probably reflect differences in melting layer heights. We are now extending our study to simulations of other field experiments (e.g. SCSMEX and ARM) in order to examine the universality of the look-up table. The impact of look-up tables on the retrieved latent heating profiles will also be assessed.

Shige, Shoichi↗
NASA NTRS2010

Shallow and Deep Latent Heating Modes Over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

The global hydrological cycle is central to the Earth's climate system, with rainfall and the physics of its formation acting as the key links in the cycle. Two-thirds of global rainfall occurs in the Tropics. Associated with this rainfall is a vast amount of heat, which is known as latent heat. It arises mainly due to the phase change of water vapor condensing into liquid droplets; three-fourths of the total heat energy available to the Earth's atmosphere comes from tropical rainfall. In addition, fresh water provided by tropical rainfall and its variability exerts a large impact upon the structure and motions of the upper ocean layer. Three-dimensional distributions of latent heating estimated from Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR)utilizing the Spectral Latent Heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated latent heating averaged over the tropical oceans is estimated as approx.72.6 J/s (approx.2.51 mm/day), and that over tropical land is approx.73.7 J/s (approx.2.55 mm/day), for 30degN-30degS. It is shown that non-drizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems, deep systems and congestus. A rough estimate of shallow mode contribution against the total heating is about 46.7 % for the average tropical oceans, which is substantially larger than 23.7 % over tropical land. While cumulus congestus heating linearly correlates with the SST, deep mode is dynamically bounded by large-scale subsidence. It is notable that substantial amount of rain, as large as 2.38 mm day-1 in average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that even in the region with SST warmer than 28 oC, large-scale subsidence effectively suppresses the deep convection, remaining the heating by congestus clouds. Our results support that the entrainment of mid-to-lower-tropospheric dry air, which accompanies the large-scale subsidence is the major factor suppressing the deep convection. Therefore, representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and resultant large-scale circulation.

Takayabu, Yukari N.↗
NASA NTRS2017

Precipitating Cloud Characteristics During Changma as Seen in TRMM PR Observations

The climatological characteristics of precipitating clouds during Changma, the summer rainy period in the Korean Peninsula, were investigated using the Precipitation Radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) satellite. This investigation was further augmented with reanalysis data. Specifically, Changma clouds are compared with post-Changma clouds. Similarities and differences in cloud properties between the two periods are discussed based on seasonal changes in thermodynamic environments. For convective clouds migrating along the Changma (stationary) front, rain intensity is much stronger and cloud height is relatively higher than during any other summer period, including post-Changma. Convective rain clouds have a large seasonal variability, even during summer. The seasonal variability in rain parameters related to convective rain type appears to be due to the thermodynamic and dynamic environments.

precipitation↗
NASA NTRS2018

Mid-infrared Spectroscopy of Pr-Doped Materials

Solid state lanthanide doped lasers primarily operate in the ultraviolet, visible, near infrared and short-wavelength infrared out to around 2.1 μm. At longer wavelengths, the transitions in conventional oxide crystal and glass materials become susceptible to multiphonon quenching due to their relatively large phonon energy. The use of low phonon materials can minimize the nonradiative quenching, opening up possibilities for solid state lanthanide lasers operating in the mid-infrared (MIR). This provides motivation to study the spectroscopy of lanthanide ions in bromide, chloride and fluoride materials, which have relatively low phonon energies. In this article, the MIR spectroscopy or praseodymium ions in five different host materials is studied, specifically KPb2Br5 (KPB), LaF3, KYF4 (KYF), BaY2F8 (BYF) and YLiF4 (YLF) host crystals. The MIR emission cross sections have been measured from 3 to 6 μm and reciprocity of absorption and emission is utilized to validate the results. The lifetime dynamics in the MIR are covered for various pump and emission wavelengths. Results are also presented on MIR emission from 6.5 to 8.5 μm in a Pr: KPB crystal, which, to the best of the authors knowledge, is the first such measurement of luminescence in this wavelength range that has been published.

Brian M Walsh↗
DOE OSTI2020

Materials Data on Pr(Sb3Os)4 by Materials Project

PrOs4Sb12 is Skutterudite-derived structured and crystallizes in the cubic Im-3 space group. The structure is three-dimensional and consists of two praseodymium molecules and one OsSb3 framework. In the OsSb3 framework, Os+0.75- is bonded to six equivalent Sb atoms to form corner-sharing OsSb6 octahedra. The corner-sharing octahedral tilt angles are 55°. All Os–Sb bond lengths are 2.65 Å. Sb is bonded in a 2-coordinate geometry to two equivalent Os+0.75- and two equivalent Sb atoms. There are one shorter (2.96 Å) and one longer (3.02 Å) Sb–Sb bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pr(MoO2)6 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pr(SiP3)2 by Materials Project

PrSi2P5P crystallizes in the orthorhombic Cmc2_1 space group. The structure is two-dimensional and consists of sixteen phosphine molecules; sixteen praseodymium molecules; and four Si2P5 sheets oriented in the (0, 1, 0) direction. In each Si2P5 sheet, there are four inequivalent Si4- sites. In the first Si4- site, Si4- is bonded to four P+0.83+ atoms to form corner-sharing SiP4 tetrahedra. There are a spread of Si–P bond distances ranging from 2.23–2.30 Å. In the second Si4- site, Si4- is bonded to four P+0.83+ atoms to form corner-sharing SiP4 tetrahedra. There are a spread of Si–P bond distances ranging from 2.24–2.28 Å. In the third Si4- site, Si4- is bonded to four P+0.83+ atoms to form corner-sharing SiP4 tetrahedra. There are a spread of Si–P bond distances ranging from 2.20–2.29 Å. In the fourth Si4- site, Si4- is bonded to four P+0.83+ atoms to form corner-sharing SiP4 tetrahedra. There are a spread of Si–P bond distances ranging from 2.24–2.28 Å. There are twelve inequivalent P+0.83+ sites. In the first P+0.83+ site, P+0.83+ is bonded in a water-like geometry to two Si4- atoms. In the second P+0.83+ site, P+0.83+ is bonded in an L-shaped geometry to two equivalent Si4- atoms. In the third P+0.83+ site, P+0.83+ is bonded in a water-like geometry to two equivalent Si4- atoms. In the fourth P+0.83+ site, P+0.83+ is bonded in a water-like geometry to two equivalent Si4- atoms. In the fifth P+0.83+ site, P+0.83+ is bonded in a water-like geometry to two Si4- atoms. In the sixth P+0.83+ site, P+0.83+ is bonded in a single-bond geometry to one Si4- atom. In the seventh P+0.83+ site, P+0.83+ is bonded in a single-bond geometry to one Si4- atom. In the eighth P+0.83+ site, P+0.83+ is bonded in a single-bond geometry to one Si4- atom. In the ninth P+0.83+ site, P+0.83+ is bonded in a water-like geometry to two Si4- atoms. In the tenth P+0.83+ site, P+0.83+ is bonded in a water-like geometry to two Si4- atoms. In the eleventh P+0.83+ site, P+0.83+ is bonded in a water-like geometry to two equivalent Si4- atoms. In the twelfth P+0.83+ site, P+0.83+ is bonded in a single-bond geometry to one Si4- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pr(P3Os)4 by Materials Project

PrOs4P12 crystallizes in the cubic Im-3 space group. The structure is three-dimensional and consists of two praseodymium molecules and one OsP3 framework. In the OsP3 framework, Os+1.75- is bonded to six equivalent P+0.33+ atoms to form distorted corner-sharing OsP6 octahedra. The corner-sharing octahedral tilt angles are 62°. All Os–P bond lengths are 2.38 Å. P+0.33+ is bonded in a bent 120 degrees geometry to two equivalent Os+1.75- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pr(WO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗