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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Structural, electronic, and polarization properties of YN and LaN

ScN has attracted great attention for its electronic properties and its ability to enhance polarization of AlN; however, its sister compounds, YN and LaN, remain much less studied. Here, we use first-principles calculations to evaluate YN and LaN in their cubic and hexagonal phases. Rocksalt YN and LaN are semiconductors, although we show that LaN differs from ScN and YN in having a direct band gap, which we attribute to its weaker p-p coupling. Both have low electron effective masses. In addition to their rocksalt structures, we evaluate the layered hexagonal and wurtzite phases of YN and LaN. For YN, the wurtzite phase cannot be stabilized, and hexagonal YN is higher in energy than rocksalt YN. In contrast, for LaN, the wurtzite phase is favored, and it is comparable in energy to rocksalt LaN. Wurtzite LaN has a polarization of 0.608 C/m 2 (referenced to the centrosymmetric layered hexagonal phase), and a high piezoelectric coefficient e 33 = 1.78 C/m 2 . Interestingly, we find that the polarization of wurtzite LaN may be reversible; we find a relatively small switching barrier of 0.06 eV per formula unit, offering the potential for its use as a ferroelectric. Since wurtzite LaN is closely lattice matched to InP, we investigate a heterostructure between (0001) wurtzite LaN and (111) zinc-blende InP, and find the polarization discontinuity would yield a bound charge of 1.3 × 10 14 e/cm 2 , offering the potential for novel electronic applications such as tunnel junctions. Furthermore, our results compare and contrast ScN, YN, and LaN, and highlight the potential of these materials for adoption in electronic and ferroelectric devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Heterostructure engineering for wurtzite LaN

Wurtzite LaN (wz-LaN) is a semiconducting nitride with favorable piezoelectric and ferroelectric properties, making it promising for applications in electronics. Here, we use first-principles density functional theory with a hybrid functional to investigate several features that are key for its use in heterostructures. First, for the purposes of growing wz-LaN on a substrate or designing a heterostructure, we show that it can be lattice-matched with a number of cubic materials along their [111] axes. We also evaluate the bound charge at such interfaces, taking into account both the polarization discontinuity and the piezoelectric polarization due to pseudomorphic strain. Second, we investigate band alignments and assess the results for interfaces with zincblende-, rocksalt-, and perovskite-structure compounds, along with chemically similar wurtzite and rocksalt nitrides. Our results provide guidance for the development of electronic devices based on wz-LaN.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Point defects and doping in wurtzite LaN

Wurtzite LaN (wz-LaN) is a semiconducting nitride that has piezoelectric and ferroelectric properties, making it promising for applications in electronics, either as a binary compound or in alloys such as LaAlN. The prospects for wz-LaN in devices are influenced by the properties of point defects and impurities; here, we use first-principles density functional theory with a hybrid functional to calculate their formation energies, as well as their atomic and electronic structures. Among native point defects, we find that nitrogen-related defects, both vacancies ($V^+_N$) and interstitials ($N^-_i$), are energetically most favorable under most relevant chemical potentials and positions of the Fermi level; $V^0_N$ may additionally be observed under N-poor conditions, and $N^0_i$ may be prominent under N-rich conditions. We also investigate the incorporation of oxygen and hydrogen, which will likely be present as unintentional impurities. We find that the $O^+_N$ substitutional species readily forms, but oxygen will not lead to n-type conductivity due to formation of DX centers and compensation by interstitial defects. Similarly, substitutional HN and interstitial H i can compensate both p- and n-type dopants. Our results provide detailed, microscopic guidance for the development of electronic devices based on wz-LaN.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1981

Lanning 10 and 33 - The X-ray, UV, and optical fluxes

UV spectra from IUE, optical spectroscopy, broad band photometry, and upper limits on the X-ray flux from Einstein are used to specify the characteristics of Lanning 10 and 33. Data on Lanning 33 are consistent with a 22,000 K Be star at a distance of 5 to 7 kpc, and Lanning 10 appears to include a F5-G0 star plus a hot component greater than 35,000 K at a distance of 0.9 to 1.3 kpc. The optical eclipsed fluxes are subtracted from the uneclipsed, and the observed fluxed distribution of the eclipsed light does not follow a simple power law, but is closer to a 12,000 K + or - 1000 K blackbody. Lanning 10 is placed in the category of VY Scl variables.

Szkody, P.↗
NASA NTRS2006

Wireless Command-and-Control of UAV-Based Imaging LANs

Dual airborne imaging system networks were operated using a wireless line-of-sight telemetry system developed as part of a 2002 unmanned aerial vehicle (UAV) imaging mission over the USA s largest coffee plantation on the Hawaiian island of Kauai. A primary mission objective was the evaluation of commercial-off-the-shelf (COTS) 802.11b wireless technology for reduction of payload telemetry costs associated with UAV remote sensing missions. Predeployment tests with a conventional aircraft demonstrated successful wireless broadband connectivity between a rapidly moving airborne imaging local area network (LAN) and a fixed ground station LAN. Subsequently, two separate LANs with imaging payloads, packaged in exterior-mounted pressure pods attached to the underwing of NASA's Pathfinder-Plus UAV, were operated wirelessly by ground-based LANs over independent Ethernet bridges. Digital images were downlinked from the solar-powered aircraft at data rates of 2-6 megabits per second (Mbps) over a range of 6.5 9.5 km. An integrated wide area network enabled payload monitoring and control through the Internet from a range of ca. 4000 km during parts of the mission. The recent advent of 802.11g technology is expected to boost the system data rate by about a factor of five.

Herwitz, Stanley↗
DOE OSTI2020

Monolayer 1T-LaN 2 : Dirac spin-gapless semiconductor of p -state and Chern insulator with a high Chern number

Two-dimensional transition-metal dinitrides have attracted considerable attention in recent years due to their rich magnetic properties. Here, we focus on rare-earth-metal elements and propose a monolayer of lanthanum dinitride with a 1T structural phase, 1T-LaN 2 . Using first-principles calculations, we systematically investigated the structure, stability, magnetism, and band structure of this material. It is a flexible and stable monolayer exhibiting a low lattice thermal conductivity, which is promising for future thermoelectric devices. Here, the monolayer shows the ferromagnetic ground state with a spin-polarized band structure. Two linear spin-polarized bands cross at the Fermi level forming a Dirac point, which is formed by the p atomic orbitals of the N atoms, indicating that monolayer 1T-LaN 2 is a Dirac spin-gapless semiconductor of p-state. When the spin–orbit coupling is taken into account, a large nontrivial indirect bandgap (86/354 meV) can be opened at the Dirac point, and three chiral edge states are obtained, corresponding to a high Chern number of C = 3, implying that monolayer 1T-LaN 2 is a Chern insulator. Importantly, this kind of band structure is expected to occur in more monolayers of rare-earth-metal dinitride with a 1T structural phase.

2D materials↗
DOE OSTI2020

Materials Data on LaN by Materials Project

LaN crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one LaN sheet oriented in the (0, 0, 1) direction. La3+ is bonded to four equivalent N3- atoms to form a mixture of distorted corner and edge-sharing LaN4 trigonal pyramids. All La–N bond lengths are 2.44 Å. N3- is bonded to four equivalent La3+ atoms to form a mixture of distorted corner and edge-sharing NLa4 trigonal pyramids.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Lanning 14, a new DO white dwarf - Spectrophotometry and atmospheric parameters

Optical spectrophotometric observations are presented and analyzed for Lanning 14, which was recently classified as a DO white dwarf and has one of the strongest He II 4868 absorption lines of any known star, with strong He Bracket lines and weak He I. An effective temperature of 55,000 plus or minus 2500 K, log g near 8, and He/H ratio equal to or greater than 100, have been derived by means of a new grid of hot, high-gravity, mixed-composition models. It is concluded that Lanning 14 is both hotter and more helium-rich than the prototype DO star HZ 21.

Liebert, J.↗
NASA NTRS1991

Quad-Port Transceivers For A Dual-CRR LAN

Quad-port fiber-optic transceivers demonstrated successfully as physical-layer interface units in WhisperNet - local-area network (LAN) of computers and other devices in communication with each other. Each node of Dual-CRR LAN contains quad-port transceiver serving four pairs of optical fibers. Quad-port transceiver consists of two dual-port transceivers and ancillary equipment in compact package. Transceiver serves as interface between optical fibers and external computing devices. Because of high reliability, availability and "fail-soft" nature, network well suited to military and critical commercial applications.

Wiencko, Joseph A., Jr.↗
NASA NTRS2014

Extending the Capabilities of Closed-loop Distributed Engine Control Simulations Using LAN Communication

Distributed Engine Control (DEC) is an enabling technology that has the potential to advance the state-of-the-art in gas turbine engine control. To analyze the capabilities that DEC offers, a Hardware-In-the-Loop (HIL) test bed is being developed at NASA Glenn Research Center. This test bed will support a systems-level analysis of control capabilities in closed-loop engine simulations. The structure of the HIL emulates a virtual test cell by implementing the operator functions, control system, and engine on three separate computers. This implementation increases the flexibility and extensibility of the HIL. Here, a method is discussed for implementing these interfaces by connecting the three platforms over a dedicated Local Area Network (LAN). This approach is verified using the Commercial Modular Aero-Propulsion System Simulation 40k (C-MAPSS40k), which is typically implemented on one computer. There are marginal differences between the results from simulation of the typical and the three-computer implementation. Additional analysis of the LAN network, including characterization of network load, packet drop, and latency, is presented. The three-computer setup supports the incorporation of complex control models and proprietary engine models into the HIL framework.

propulsion simulation↗
DOE OSTI2020

Materials Data on LaN by Materials Project

LaN is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. La3+ is bonded in a body-centered cubic geometry to eight equivalent N3- atoms. All La–N bond lengths are 2.75 Å. N3- is bonded in a body-centered cubic geometry to eight equivalent La3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaN by Materials Project

LaN is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. La3+ is bonded to four equivalent N3- atoms to form corner-sharing LaN4 tetrahedra. There are three shorter (2.44 Å) and one longer (2.46 Å) La–N bond lengths. N3- is bonded to four equivalent La3+ atoms to form corner-sharing NLa4 tetrahedra.

36 MATERIALS SCIENCE↗
NASA NTRS1982

A first look at the eclipsing cataclysmic variable Lanning 10

Photometry and spectroscopy of a new cataclysmic variable star, Lanning 10 are presented. The star is shown to be an eclipsing binary with a 7h 42m orbital period. Blue flickering is observed to occur on a time scale of 10 minutes. The light curve is analyzed with a numerical simulation of the eclipse of the accretion disk by the lobe-filling star. The disk nearly spans the Roche lobe of the white dwarf, and its surface brightness is a steep function of radius. Spectra show broad H alpha and He I 6678 A emission lines from the accretion disk and a weak absorption feature from the red dwarf. Radial velocity measurements of the H alpha emission line vary systematically with binary phase. The observed velocity amplitude 240 km/s, gives the mass function 0.46 solar masses. A phase shift of the velocity curve relative to the eclipse ephemeris indicates that a brightness asymmetry exists in the inner parts of the disk.

Horne, K.↗
NASA NTRS1991

Performance analysis of LAN bridges and routers

Bridges and routers are used to interconnect Local Area Networks (LANs). The performance of these devices is important since they can become bottlenecks in large multi-segment networks. Performance metrics and test methodology for bridges and routers were not standardized. Performance data reported by vendors is not applicable to the actual scenarios encountered in an operational network. However, vendor-provided data can be used to calibrate models of bridges and routers that, along with other models, yield performance data for a network. Several tools are available for modeling bridges and routers - Network II.5 was used. The results of the analysis of some bridges and routers are presented.

Hajare, Ankur R.↗
DOE OSTI2020

LAN: A Materials Notation for Two-Dimensional Layered Assemblies

Two-dimensional (2D) layered materials offer intriguing possibilities for novel physics and applications. Before any attempt at exploring the materials space in a systematic fashion, or combining insights from theory, computation, and experiment, a formal description of information about an assembly of arbitrary composition is required. Here, we introduce a domain-generic notation that is used to describe the space of 2D layered materials from monolayers to twisted assemblies of arbitrary composition, existent or not yet fabricated. The notation corresponds to a theoretical materials concept of stepwise assembly of layered structures using a sequence of rotation, vertical stacking, and other operations on individual 2D layers. Its scope is demonstrated with several example structures using common single-layer materials as building blocks. This work overall aims to contribute to the systematic codification, capture, and transfer of materials knowledge in the area of 2D layered materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Interfacing a high performance disk array file server to a Gigabit LAN

Our previous prototype, RAID-1, identified several bottlenecks in typical file server architectures. The most important bottleneck was the lack of a high-bandwidth path between disk, memory, and the network. Workstation servers, such as the Sun-4/280, have very slow access to peripherals on busses far from the CPU. For the RAID-2 system, we addressed this problem by designing a crossbar interconnect, Xbus board, that provides a 40MB/s path between disk, memory, and the network interfaces. However, this interconnect does not provide the system CPU with low latency access to control the various interfaces. To provide a high data rate to clients on the network, we were forced to carefully and efficiently design the network software. A block diagram of the system hardware architecture is given. In the following subsections, we describe pieces of the RAID-2 file server hardware that had a significant impact on the design of the network interface.

Seshan, Srinivasan↗
NASA NTRS1994

Performance evaluation of the NASA/KSC CAD/CAE and office automation LAN's

This study's objective is the performance evaluation of the existing CAD/CAE (Computer Aided Design/Computer Aided Engineering) network at NASA/KSC. This evaluation also includes a similar study of the Office Automation network, since it is being planned to integrate this network into the CAD/CAE network. The Microsoft mail facility which is presently on the CAD/CAE network was monitored to determine its present usage. This performance evaluation of the various networks will aid the NASA/KSC network managers in planning for the integration of future workload requirements into the CAD/CAE network and determining the effectiveness of the planned FDDI (Fiber Distributed Data Interface) migration.

Zobrist, George W.↗