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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.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

HAT-P-50b, HAT-P-51b, HAT-P-52b, AND HAT-P-53b: THREE TRANSITING HOT JUPITERS AND A TRANSITING HOT SATURN FROM THE HATNET SURVEY

We report the discovery and characterization of four transiting exoplanets by the HATNet survey. The planet HAT-P-50b has a mass of 1.35 M{sub J} and radius of 1.29 R{sub J}, and orbits a bright (V=11.8 mag) M=1.27 M{sub ⊙}, R=1.70 R{sub ⊙} star every P=3.1220 days. The planet HAT-P-51b has a mass of 0.31 M{sub J} and radius of 1.29 R{sub J}, and orbits a V=13.4 mag, M=0.98 M{sub ⊙}, R=1.04 R{sub ⊙} star with a period of P=4.2180 days. The planet HAT-P-52b has a mass of 0.82 M{sub J} and radius of 1.01 R{sub J}, and orbits a V=14.1 mag, M=0.89 M{sub ⊙}, R=0.89 R{sub ⊙} star with a period of P=2.7536 days. The planet HAT-P-53b has a mass of 1.48 M{sub J} and radius of 1.32 R{sub J}, and orbits a V=13.7 mag, M=1.09 M{sub ⊙}, R=1.21 R{sub ⊙} star with a period of P=1.9616 days. All four planets are consistent with having circular orbits and have masses and radii measured to better than 10% precision. The low stellar jitter and favorable R{sub p}/R{sub ⋆} ratio for HAT-P-51 make it a promising target for measuring the Rossiter–McLaughlin effect for a Saturn-mass planet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Dry and hot: the hydraulic consequences of a climate change-type drought for Amazonian trees

How plants respond physiologically to leaf warming and low water availability may determine how they will perform under future climate change. In 2015-2016 an unprecedented drought occurred across Amazonia with record-breaking high temperatures and low soil moisture, offering a unique opportunity to evaluate the performances of Amazonian trees to a severe climatic event. We quantified the responses of leaf water potential, sap velocity, whole-tree hydraulic conductance (Kwt), turgor loss and xylem embolism, during and after the 2015-2016 El Niño for five canopy-tree species. Leaf/xylem safety margins (SM), sap velocity and Kwt showed a sharp drop during warm periods. SMs were negatively correlated with vapor pressure deficit but had no significant relationship with soil water storage. Based on our calculations of canopy stomatal and xylem resistances, the decrease in sap velocity and Kwt was due to a combination of xylem cavitation, and stomatal closure. Our results suggest extremely warm droughts greatly amplify the degree of trees’ physiological stress and can lead to mortality. Given the extreme nature of the 2015-2016 El Niño and that temperatures are predicted to increase, this work can serve as a case study of the possible impact climate warming can have on tropical trees.

Fontes, Clarissa G.↗
DOE OSTI2023

Detection of hot electrons originating from an upper valley at ∼1.7eV above the Γ valley in wurtzite GaN using electron emission spectroscopy

Using electron emission spectroscopy, measurement and analysis were conducted on the energy distribution of vacuum emitted electrons from electrically driven InGaN/GaN green (peak wavelengths 𝜆 ≈ 515nm) light-emitting diodes (LEDs) with and without a prewell superlattice (SL). Here, we report on the detection of a high-energy upper valley at ∼ 1.7eV above the Γ valley from samples with no prewell SL. We propose that these upper valley electrons originate predominantly from trap-assisted Auger recombination (TAAR) in green LEDs, as the intensity of these peaks is found to have quadratic dependence on the carrier density 𝑛 [see Espenlaub et al., J. Appl. Phys. 126, 184502 (2019)]. The high-energy upper valley peak was not observed in the sample with a prewell SL which is attributed to gettering by the prewell SL of still unidentified impurities that act as TAAR centers.

carrier generation & recombination↗
DOE OSTI2021

Insulation or Irradiance: Exploring Why Bifacial Photovoltaics Run Hot

Bifacial photovoltaics are predicted to become the dominant device architecture over the next couple of years, but their thermal performance is not yet well understood. In this study, we model the thermal effects of different backside lamination materials on the performance of bifacial PERC cells. Glass-glass laminated cells were found to operate hotter than equivalent glass-polymer backsheet packed cells. This was solely due to the increased absorption of rear side incident light.

bifacial↗
NASA NTRS1983

Ignition of confined gaseous mixtures by hot surfaces and hot wires

Ignition times and spatial and temporal variations of temperature and concentration in gaseous mixtures confined between two infinite parallel walls or two infinite cylinders have been obtained by numerical integration of the appropriate conservation equations written in Lagrangian coordinates. Ignition times and ignition energies are presented for the case of an isothermal wall in terms of the initial mixture pressure and equivalence ratio for both one and two-step chemical reaction mechanisms. The numerical results indicate that there is a critical mixture pressure for which the ignition time is minimum. The values of this critical pressure are larger (smaller) than 1 atm for the one- (two-) step reaction mechanism. The critical pressure for the ignition time is not equal to the critical pressure for the ignition energy. The ignition time and energy decrease with the equivalence ratio within a certain range and then remain constant.

Ramos, J. I.↗
NASA NTRS2005

Hot Chips and Hot Interconnects for High End Computing Systems

I will discuss several processors: 1. The Cray proprietary processor used in the Cray X1; 2. The IBM Power 3 and Power 4 used in an IBM SP 3 and IBM SP 4 systems; 3. The Intel Itanium and Xeon, used in the SGI Altix systems and clusters respectively; 4. IBM System-on-a-Chip used in IBM BlueGene/L; 5. HP Alpha EV68 processor used in DOE ASCI Q cluster; 6. SPARC64 V processor, which is used in the Fujitsu PRIMEPOWER HPC2500; 7. An NEC proprietary processor, which is used in NEC SX-6/7; 8. Power 4+ processor, which is used in Hitachi SR11000; 9. NEC proprietary processor, which is used in Earth Simulator. The IBM POWER5 and Red Storm Computing Systems will also be discussed. The architectures of these processors will first be presented, followed by interconnection networks and a description of high-end computer systems based on these processors and networks. The performance of various hardware/programming model combinations will then be compared, based on latest NAS Parallel Benchmark results (MPI, OpenMP/HPF and hybrid (MPI + OpenMP). The tutorial will conclude with a discussion of general trends in the field of high performance computing, (quantum computing, DNA computing, cellular engineering, and neural networks).

Saini, Subhash↗