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At least 865 records · Page 48

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NASA NTRS2012

Anomaly Detection Techniques with Real Test Data from a Spinning Turbine Engine-Like Rotor

Online detection techniques to monitor the health of rotating engine components are becoming increasingly attractive to aircraft engine manufacturers in order to increase safety of operation and lower maintenance costs. Health monitoring remains a challenge to easily implement, especially in the presence of scattered loading conditions, crack size, component geometry, and materials properties. The current trend, however, is to utilize noninvasive types of health monitoring or nondestructive techniques to detect hidden flaws and mini-cracks before any catastrophic event occurs. These techniques go further to evaluate material discontinuities and other anomalies that have grown to the level of critical defects that can lead to failure. Generally, health monitoring is highly dependent on sensor systems capable of performing in various engine environmental conditions and able to transmit a signal upon a predetermined crack length, while acting in a neutral form upon the overall performance of the engine system.

Abdul-Aziz, Ali↗

NASA NTRS1999

Results of Liquid Motion Experiment Analyzed

About half of all scientific and commercial spacecraft spin during some part of their mission. Although spinning has many benefits (increasing stability, controlling the location of liquid propellants, and distributing solar heat loads), it also creates problems because a precession (or wobble) motion is unavoidable. For modern spacecraft, by far the largest source of wobble is energy dissipation in the liquid of partially filled tanks. The liquid s energy dissipation cannot, however, be quantified adequately by any ground test. Current analytical models are also inadequate because fundamental data on fluid motion in low gravity are needed to validate them. Consequently, spacecraft attitude-control systems are designed and operated very conservatively. Nonetheless, spacecraft often still perform poorly in orbit, and some have been lost because of a rapid increase of the wobble rate. The Liquid Motion Experiment (LME) was designed to provide spacecraft designers accurate data on the wobble dynamics of spacecraft that contain large quantities of mobile liquids. LME, which was flown on the space shuttle mission STS-84, was built under contract to the NASA Lewis Research Center by the Southwest Research Institute of San Antonio, Texas. Major accomplishments for 1998 include reduction of the flight data and publication of the experimental results. LME was essentially a spin table that created a realistic nutation motion of scale-model tanks containing liquid. Two spherical and two cylindrical transparent tanks were tested simultaneously, and three sets of such tanks were employed to vary liquid viscosity, fill level, and propellant management device (PMD) design. All the tanks were approximately 4.5 in. in diameter. The primary test measurements were the radial and tangential torques exerted on the tanks by the liquid. These torques could not be measured on the ground because of the masking effects of gravity.

Chato, David J.↗

NASA NTRS2011

Free Body Dynamics of a Spinning Cylinder with Planar Restraint-(a.k.a. Barrel of Fun)

The dynamic motion of a cylinder is analyzed based on rotation about its center of mass and is restrained by a plane normal to the axis passing through its center of mass at an angle. The first part of this work presented an analysis of the stability of the motion. In the current report, the governing equations are numerically integrated in time and the steady state is obtained as a limit of the transient numerical solution. The calculated data are compared with observed behaviors.

Moraru, Laurentiu↗

DOE OSTI2023

Optically Enhanced Solid-State 1 H NMR Spectroscopy

Low sensitivity is the primary limitation to extending nuclear magnetic resonance (NMR) techniques to more advanced chemical and structural studies. Photochemically induced dynamic nuclear polarization (photo-CIDNP) is an NMR hyperpolarization technique where light is used to excite a suitable donor–acceptor system, creating a spin-correlated radical pair whose evolution drives nuclear hyperpolarization. Systems that exhibit photo-CIDNP in solids are not common, and this effect has, up to now, only been observed for 13 C and 15 N nuclei. However, the low gyromagnetic ratio and natural abundance of these nuclei trap the local hyperpolarization in the vicinity of the chromophore and limit the utility for bulk hyperpolarization. Here, we report the first example of optically enhanced solid-state 1 H NMR spectroscopy in the high-field regime. This is achieved via photo-CIDNP of a donor–chromophore–acceptor molecule in a frozen solution at 0.3 T and 85 K, where spontaneous spin diffusion among the abundant strongly coupled 1 H nuclei relays polarization through the whole sample, yielding a 16-fold bulk 1 H signal enhancement under continuous laser irradiation at 450 nm. These findings enable a new strategy for hyperpolarized NMR beyond the current limits of conventional microwave-driven DNP.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Creating Majorana modes from segmented Fermi surface

Majorana bound states provide a fertile ground for both investigation of fundamental phenomena as well as for applications in quantum computation. However, despite enormous experimental and theoretical efforts, the currently available Majorana platforms suffer from a multitude of issues that prevent full realization of their potential. Therefore, improved Majorana systems are still highly sought after. Here we present a platform for creating Majorana bound states from 2D gapless superconducting state in spin-helical systems under the in-plane magnetic or Zeeman field. Topological 1D channels are formed by quantum confinement of quasiparticles via Andreev reflection from the surrounding fully gapped superconducting region. Our proposal can be realized using narrow strips of magnetic insulators on top of proximitized 3D topological insulators. This setup has key advantages that include: small required fields, no necessity of fine-tuning of chemical potential, removal of the low-energy detrimental states, and large attainable topological gap.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Origin of core-to-core x-ray emission spectroscopy sensitivity to structural dynamics

Recently, coherent structural dynamics in the excited state of an iron photosensitizer was observed through oscillations in the intensity of Kα x-ray emission spectroscopy (XES). Understanding the origin of the unexpected sensitivity of core-to-core transitions to structural dynamics is important for further development of femtosecond time-resolved XES methods and, we believe, generally necessary for interpretation of XES signals from highly non-equilibrium structures that are ubiquitous in photophysics and photochemistry. Here, we use multiconfigurational wavefunction calculations combined with atomic theory to analyze the emission process in detail. The sensitivity of core-to-core transitions to structural dynamics is due to a shift of the minimum energy metal–ligand bond distance between 1s and 2p core-hole states. A key effect is the additional contraction of the non-bonding 3s and 3p orbitals in 1s core-hole states, which decreases electron– electron repulsion and increases overlap in the metal–ligand bonds. The effect is believed to be general and especially pronounced for systems with strong bonds. The important role of 3s and 3p orbitals is consistent with the analysis of radial charge and spin densities and can be connected to the negative chemical shift observed for many transition metal complexes. The XES sensitivity to structural dynamics can be optimized by tuning the emission energy spectrometer, with oscillations up to ±4% of the maximum intensity for the current system. The theoretical predictions can be used to design experiments that separate electronic and nuclear degrees of freedom in ultrafast excited state dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Non-Gaussian Generalized Two-Mode Squeezing: Applications to Two-Ensemble Spin Squeezing and Beyond

Bosonic two-mode squeezed states are paradigmatic entangled Gaussian states that have wide utility in quantum information and metrology. Here, in this study, we show that the basic structure of these states can be generalized to arbitrary bipartite quantum systems in a manner that allows simultaneous, Heisenberg-limited estimation of two independent parameters for finite-dimensional systems. Further, we show that these general states can always be stabilized by a relatively simple Markovian dissipative process. In the specific case where the two subsystems are ensembles of two-level atoms or spins, our generalized states define a notion of two-mode spin squeezing that is valid beyond the Gaussian limit and that enables true multiparameter estimation. We discuss how generalized Ramsey measurements allow one to reach the two-parameter quantum Cramér-Rao bound, and how the dissipative preparation scheme is compatible with current experiments.

Mamaev, Mikhail [Univ. of Chicago, IL (United Stat↗

NASA NTRS1978

Estimate of procession and polar motion errors from planetary encounter station location solutions

Jet Propulsion Laboratory Deep Space Station (DSS) location solutions based on two JPL planetary ephemerides, DE 84 and DE 96, at eight planetary encounters were used to obtain weighted least squares estimates of precession and polar motion errors. The solution for precession error in right ascension yields a value of 0.3 X 10 to the minus 5 power plus or minus 0.8 X 10 to the minus 6 power deg/year. This maps to a right ascension error of 1.3 X 10 to the minus 5 power plus or minus 0.4 X 10 to the minus 5 power deg at the first Voyager 1979 Jupiter encounter if the current JPL DSS location set is used. Solutions for precession and polar motion using station locations based on DE 84 agree well with the solution using station locations referenced to DE 96. The precession solution removes the apparent drift in station longitude and spin axis distance estimates, while the encounter polar motion solutions consistently decrease the scatter in station spin axis distance estimates.

Pease, G. E.↗

NASA NTRS1986

Upwelling O(+) ion source characteristics

The characteristics of an upwelling ion source are discussed. A typical upwelling event is analyzed using Dynamic Explorer 1 satellite retarding ion mass spectrometer (RIMS) observations of the low-energy plasma, and energetic ion and local electromagnetic field observations. The RIMS spectrograms of the O(+) ion species, radial and axial head data for O(+), and spin plan O(+) distribution functions are examined. The features of the upwelling observed include: (1) transverse ion heating to temperature of 100,000 K, (2) large outward flows of O(+), (3) enhanced flow of H(+) and He (+), (4) moderately strong field-aligned current sheets, (5) an associated intense eastward convection channel, and (6) strong wave emissions in the range near and below the proton gyrofrequency. The association between the upwelling O(+) signature and auroral current is investigated. Plasma wave and electric field environments are studied and plasma flows and densities are derived. It is noted that the mechanism for ion heating which defines the source region for these polar ion outflows is related to field-aligned currents and an associated auroral convection channel or jet.

Moore, T. E.↗

NASA NTRS1986

Identification of the Ga interstitial in Al(x)Ga(1-x)As by optically detected magnetic resonance

A new optically detected magnetic resonance spectrum in Al(x)Ga(1-x)As is reported and assigned to native Ga interstitials. Luminescence-quenching signals were observed over the energy region from 0.75 to 1.1 eV. The optically detected magnetic resonance is nearly isotropic, with spin-Hamiltonian parameters g = 2.025 + or - 0.006, central hyperfine splitting A(Ga-69) = 0.050 + or - 0.001/cm, and A(Ga-71) = 0.064 + or - 0.001/cm for H near the 001 line. The strong hyperfine coupling denotes an electronic state of A1 symmetry, which current theories predict for the Ga interstitial but not the Ga antisite. The slight anisotropy probably indicates that the Ga(i) is paired with a second, unknown defect.

Kennedy, T. A.↗

NASA NTRS2004

Numerical Study of Flow Past a Circular Cylinder Using RANS, Hybrid RANS/LES and PANS Formulations

Two multiscale type turbulence models are implemented in the PAB3D solver. The models are based on modifying the Reynolds Averaged Navier-Stokes (RANS) equations. The first scheme is a hybrid RANS/LES model utilizing the two-equation (k(sub epsilon)) model with a RANS/LES transition function dependent on grid spacing and the computed turbulence length scale. The second scheme is a modified version of the partially averaged Navier-Stokes (PANS) model, where the unresolved kinetic energy parameter (f(sub k)) is allowed to vary as a function of grid spacing and the turbulence length scale. Solutions from these models are compared to RANS results and experimental data for a stationary and rotating cylinder. The parameter f(sub k) varies between zero and one and has the characteristic to be equal to one in the viscous sub layer, and when the RANS turbulent viscosity becomes smaller than the LES viscosity. The formulation, usage methodology, and validation example are presented to demonstrate the enhancement of PAB3D's time-accurate and turbulence modeling capabilities. The models are compared to RANS results and experimental data for turbulent separated flows (TS) and laminar separated flows (LS) around stationary and rotating cylinders. For a stationary cylinder, the TS case is accurately simulated using the general two-equation k(sub epsilon) turbulence model (eddy-viscosity model). PAB3D accurately predicts the drag coefficient (CD), lift coefficient (CL) and the Strouhal number (St). The LS case was a challenge for the RANS computation with an eddy-viscosity turbulence model. The RANS/LES and PANS performed well and showed marked improvements over the RANS solution. The modified PANS model was the most accurate. For the rotating cylinder, the spin ratio varied from zero to one, and the PANS results were in good agreement with published experimental data. RANS/LES and PANS capture both temporal and spatial fluctuations and produce large-scale structures that do not occur in the RANS simulation. The current results show promise for the capability of PANS in simulating unsteady and complex flow phenomena.

Elmiligui, Alaa A.↗

NASA NTRS1977

Low-temperature thermionic emitter

An improved photodelineatable cathode material is disclosed comprising a combination of triple carbonate (TC) and a hydrocarbon polymeric photoresist PR. A mixture of TC powder and PR is applied to a cathode by spraying, spinning or dipping and is then subjected to activation at a temperature from about 800.degree. C up to the melting temperature. The cathodes can be activated at a temperature as low as 800.degree. C and still deliver a 0-field, temperature-limited current density of 750 milliamperes per sq. centimeter at 600.degree. C. If a pattern is desired, the coating is exposed through a suitable mask to actinic light to harden the photoresist in the desired areas. Following exposure, the exposed image areas are developed and the unexposed portions of the coating are removed with solvent. When dry, the cathode is ready for activation.

Remington, Richard W.↗

NASA NTRS2009

The Status of the Mock LISA Data Challenges

For the last four years, many gravitational-wave researchers around the world have participated in the Mock LISA Data Challenges (MLDCs), a program to demonstrate and encourage the development of LISA data-analysis capabilities, tools and techniques. In this poster, we present a summary of the results of MLDC 3, which was completed in 2009. During MLDC 3, 27 participants from 15 institutions successfully analyzed data sets that included Galactic binaries, coalescing spinning massive black holes, extreme-mass-ratio inspirals, cosmic-string cusp bursts and a stochastic gravitational-wave background. We also describe the technical and scientific challenges that will be addressed by future MLI)Cs, starting with MLDC 4, which is currently in progress.

Baker, John↗

DOE OSTI2024

Quantum octets in high mobility pentagonal two-dimensional PdSe 2

Two-dimensional (2D) materials have drawn immense interests in scientific and technological communities, owing to their extraordinary properties and their tunability by gating, proximity, strain and external fields. For electronic applications, an ideal 2D material would have high mobility, air stability, sizable band gap, and be compatible with large scale synthesis. Here we demonstrate air stable field effect transistors using atomically thin few-layer PdSe 2 sheets that are sandwiched between hexagonal BN (hBN), with large saturation current > 350 μA/μm, and high field effect mobilities of ~ 700 and 10,000 cm 2 /Vs at 300 K and 2 K, respectively. At low temperatures, magnetotransport studies reveal unique octets in quantum oscillations that persist at all densities, arising from 2-fold spin and 4-fold valley degeneracies, which can be broken by in-plane and out-of-plane magnetic fields toward quantum Hall spin and orbital ferromagnetism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Advanced spectroscopic studies of (PPh 4 ) 2 [Co(N 3 ) 4 ], a field-induced single-ion magnet

The high-spin Co II complex (PPh 4 ) 2 [Co(N 3 ) 4 ] (Co-N 3 )has been investigated using advanced spectroscopic techniques [far-IR magneto-spectroscopy (FIRMS), high-frequency and high-field EPR (HFEPR), and inelastic neutron scattering (INS)] to study its zero-field-splitting (ZFS), giving spin-Hamiltonian (SH) parameters. The analysis of multi-frequency HFEPR reveals the easy-axis anisotropy with a D value of −10.39(5) cm −1 and a rhombic ratio (E/D) of 0.21(1). The magnetic properties have also been probed by direct-current (DC) magnetometry, suggesting minor differences in anisotropy from the previously reported polymorph (Co-N 3 ′). Ligand-field theory (LFT) analysis indicates that the structures of Co-N 3 and Co-N 3 ′ are closer to D 2d symmetry than other symmetries considered. Alternate-current (AC) susceptibility reveals slow magnetic relaxation under an applied field, indicating that Co-N 3 is a field-induced single-ion magnet (SIM). Here, while both Co-N 3 and Co-N 3 ′ were studied by DC magnetometry, one unusual aspect of the current work on Co-N 3 is that advanced spectroscopies HFEPR, FIRMS, and INS were used to directly observe transitions between ZFS split states, giving accurate SH parameters.

Hand, Adam T. [Univ. of Tennessee, Knoxville, TN (↗

DOE OSTI2021

Skyrmion-Based Programmable Logic Device with Complete Boolean Logic Functions

A skyrmionic programmable logic device (SkrPLD) with complete Boolean logic functions is proposed and analyzed by micromagnetic simulations. The SkrPLD is based on an antiferromagnet/ferromagnet bilayer structure, in which the antiferromagnetic layer supports the interfacial Dzyaloshinskii–Moriya interaction and the out-of-plane exchange bias field for stabilizing a zero-field skyrmion. By varying the local exchange bias field, artificial pinning sites are introduced for trapping the skyrmions. Depending on the input currents and the initial position of skyrmions at different pinning sites, different logic functions can be realized. Micromagnetic simulations show that the proposed SkrPLD has robust performance even under thermal fluctuations and inhomogeneity effects. Our work can provide insights for the design of programmable spin logic devices.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Helical magnetic order and Fermi surface nesting in noncentrosymmetric ScFeGe

Here, an investigation of the structural, magnetic, thermodynamic, and charge transport properties of noncentrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below T N =36 K. Neutron diffraction measurements discovered a temperature and field independent helical wave vector k = (0 0 0.193) with magnetic moments of 0.53 μ B per Fe confined to the ab-plane. Density functional theory calculations are consistent with these measurements and find several bands that cross the Fermi level along the c-axis with a nearly degenerate set of flat bands just above the Fermi energy. The anisotropy found in the electrical transport is reflected in the calculated Fermi surface, which consists of several warped flat sheets along the c-axis with two regions of significant nesting, one of which has a wave vector that closely matches that found in the neutron diffraction. The electronic structure calculations, along with a strong anomaly in the c-axis conductivity at TN, signal a Fermi surface driven magnetic transition, similar to that found in spin density wave materials. Magnetic fields applied in the ab-plane result in a metamagnetic transition with a threshold field of ≈ 6.7 T along with a sharp, strongly temperature dependent discontinuity and a change in sign of the magnetoresistance for in-plane currents. Thus, ScFeGe is an ideal system to investigate the effect of in-plane magnetic fields on a helimagnet with a c-axis propagation vector, where the relative strength of the magnetic interactions and anisotropies determine the topology and magnetic structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Momentum distribution of the uniform electron gas at finite temperature: Effects of spin polarization

We carry out extensive direct path integral Monte Carlo (PIMC) simulations of the uniform electron gas (UEG) at finite temperature for different values of the spin-polarization ξ. This allows us to unambiguously quantify the impact of spin effects on the momentum distribution function n(k) and related properties. We find that interesting physical effects like the interaction-induced increase in the occupation of the zero-momentum state n(0) substantially depend on ξ. Our results further advance the current understanding of the UEG as a fundamental model system, and are of practical relevance for the description of transport properties of warm dense matter in an external magnetic field. All PIMC results are freely available online and can be used as a benchmark for the development of methods and applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗