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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

ASTEROSEISMOLOGY OF THE SOLAR ANALOGS 16 Cyg A AND B FROM KEPLER OBSERVATIONS

The evolved solar-type stars 16 Cyg A and B have long been studied as solar analogs, yielding a glimpse into the future of our own Sun. The orbital period of the binary system is too long to provide meaningful dynamical constraints on the stellar properties, but asteroseismology can help because the stars are among the brightest in the Kepler field. We present an analysis of three months of nearly uninterrupted photometry of 16 Cyg A and B from the Kepler space telescope. We extract a total of 46 and 41 oscillation frequencies for the two components, respectively, including a clear detection of octupole (l = 3) modes in both stars. We derive the properties of each star independently using the Asteroseismic Modeling Portal, fitting the individual oscillation frequencies and other observational constraints simultaneously. We evaluate the systematic uncertainties from an ensemble of results generated by a variety of stellar evolution codes and fitting methods. The optimal models derived by fitting each component individually yield a common age (t = 6.8 {+-} 0.4 Gyr) and initial composition (Z{sub i} = 0.024 {+-} 0.002, Y{sub i} = 0.25 {+-} 0.01) within the uncertainties, as expected for the components of a binary system, bolstering our confidence in the reliability of asteroseismic techniques. The longer data sets that will ultimately become available will allow future studies of differential rotation, convection zone depths, and long-term changes due to stellar activity cycles.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1997

Numerical Modeling of Tidal Effects in Polytropic Accretion Disks

A two-dimensional time-dependent hybrid Fourier-Chebyshev method of collocation is developed and used for the study of tidal effects in accretion disks, under the assumptions of a polytropic equation of state and a standard alpha viscosity prescription. Under the influence of the m = 1 azimuthal component of the tidal potential, viscous oscillations in the outer disk excite an m = 1 eccentric instability in the disk. While the m = 2 azimuthal component of the tidal potential excites a Papaloizou-Pringle instability in the inner disk (a saturated m = 2 azimuthal mode), with an elliptic pattern rotating at about a fraction (approx. = 1/3) of the local Keplerian velocity in the inner disk. The period of the elliptic mode corresponds well to the periods of the short-period oscillations observed in cataclysmic variables. In cold disks (r(Omega)/c(sub s) = M approx. = 40) we also find a critical value of the viscosity parameter (alpha approx. = 0.01), below which shock dissipation dominates and is balanced by the wave amplification due to the wave action conservation. In this case the double spiral shock propagates all the way to the inner boundary with a Mach number M(sub s) approx. = 1.3.

Godon, Patrick↗
NASA NTRS1995

Improved Performance of a Temperature Compensated LN2 Cooled Sapphire Oscillator

We report on improved stability in a whispering gallery sapphire resonator for which the dominant WGHn11 microwave mode family shows frequency-stable, compensated operation for temperatures above 77K. Several modifications during the past year have led to significant improvements in performance. Current tests with improved thermal stability provide Allan Deviation of frequency of 2.6 - 4 ? 10-13 for measurement times of 1#t#100 seconds. We project a frequency stability of 1014 for this resonator with stabilized housing temperature and with a mode Q of 107.!.

Temperature Compensated LN2 Cooled Sapphire Oscill↗
NASA NTRS2017

Spectral and Radiometric Calibration Using Tunable Lasers

A tunable laser system includes a tunable laser, an adjustable laser cavity for producing one or more modes of laser light emitted from the tunable laser, a first optical parametric oscillator positioned in a light path of the adjustable laser cavity, and a controller operable to simultaneously control parameters of at least the tunable laser, the first optical parametric oscillator, and the adjustable laser cavity to produce a range of wavelengths emitted from the tunable laser system. A method of operating a tunable laser system includes using a controller to simultaneously control parameters of a tunable laser, an adjustable laser cavity for producing one or more modes of laser light emitted from the tunable laser, and a first optical parametric oscillator positioned in a light path of the adjustable laser cavity, to produce a range of wavelengths emitted from the tunable laser system.

McCorkel, Joel↗
NASA NTRS1982

KC-135A Winglet Flight Flutter Program

The evaluation techniques, results and conclusions for the flight flutter testing conducted on a KC-135A airplane configured with and without winglets are discussed. Test results are presented for the critical symmetric and antisymmetric modes for a fuel distribution that consisted of 10,000 pounds in each wing main tank and empty reserve tanks. The results indicated that a lightly damped oscillation was experienced for a winglet configuration of a 0 deg cant and -4 deg incidence. The effects of cant and incidence angle variation on the critical modes are also discussed. Lightly damped oscillations were not encountered for any other winglet cant and incidence angles tested.

Kehoe, M. W.↗
DOE OSTI2013

Tuning cationic composition of La:EuTiO{sub 3−δ} films

Eu{sub 1−x}La{sub x}TiO{sub 3−δ} (x = 0, 0.3, 0.5) films were deposited in a p(Ar(96%)/H{sub 2}(4%)) = 4 × 10{sup −4} mbar atmosphere on (LaAlO{sub 3}){sub 0.3}-(Sr{sub 2}AlTaO{sub 6}){sub 0.7} vicinal substrates (0.1°). Reflection high-energy electron diffraction oscillation characteristics of a layer-by-layer growth mode were observed for stoichiometric and Ti-rich films and the laser fluence suited to deposit stoichiometric films was identified to be 1.25 J/cm{sup 2} independent of the La content. The variety of resulting film compositions follows the general trend of Eu-enrichment for low laser and Ti-enrichment for high laser fluence. X-ray diffraction confirms that all the films are compressively strained with a general trend of an increase of c-axis elongation for non-stoichiometric films. The surfaces of non-stoichiometric films have an increased roughness, the highest sheet resistances, exhibit the presence of islands, and are Eu{sup 3+} rich for films deposited at low laser fluence.

36 MATERIALS SCIENCE↗
NASA NTRS2005

Extratropical signature of the quasi-biennial oscillation

Using the assimilated data from the National Centers for Environmental Prediction (NCEP) reanalysis, we show that the extratropical signature of the tropical quasi-biennial oscillation (QBO) is seen mostly in the North Annular Mode (NAM) of atmospheric variability. To understand the extratropical manifestation of the QBO, we discuss two effects that have been suggested earlier: (1) The extratropical circulation is driven by the QBO modulation of the planetary wave flux, and (2) the extratropical circulation is driven by the QBO-induced meridional circulation. We found that the first effect is seen in wave 1 in the beginning of winter and in wave 2 in the end of winter. The QBO-induced circulation affects midlatitude regions over the entire winter. To investigate the QBONAM coupling, we use an equation that relates the stream function of the meridional circulation and the polar cap averaged temperature, which is a proxy for the NAM index. In addition to the annual (omega)a and the QBO frequency (omega)Q the spectrum of its solutions indicates the satellite frequencies at (omega)a +/- (o.

tropical quasi-biennial oscillation (QBO)↗
DOE OSTI2015

DIII-D research to address key challenges for ITER and fusion energy

DIII-D has made significant advances in the scientific basis for fusion energy. The physics mechanism of resonant magnetic perturbation (RMP) edge localized mode (ELM) suppression is revealed as field penetration at the pedestal top, and reduced coil set operation was demonstrated. Disruption runaway electrons were effectively quenched by shattered pellets; runaway dissipation is explained by pitch angle scattering. Modest thermal quench radiation asymmetries are well described NIMROD modeling. With good pedestal regulation and error field correction, low torque ITER baselines have been demonstrated and shown to be compatible with an ITER test blanket module simulator. However performance and long wavelength turbulence degrade as low rotation and electron heating are approached. The alternative QH mode scenario is shown to be compatible with high Greenwald density fraction, with an edge harmonic oscillation demonstrating good impurity flushing. Discharge optimization guided by the EPED model has discovered a new super H-mode with doubled pedestal height. Lithium injection also led to wider, higher pedestals. On the path to steady state, 1 MA has been sustained fully non inductively with β N = 4 and RMP ELM suppression, while a peaked current profile scenario provides attractive options for ITER and a β N = 5 future reactor. Energetic particle transport is found to exhibit a critical gradient behavior. Scenarios are shown to be compatible with radiative and snowflake diverter techniques. Physics studies reveal that the transition to H mode is locked in by a rise in ion diamagnetic flows. Intrinsic rotation in the plasma edge is demonstrated to arise from kinetic losses. New 3D magnetic sensors validate linear ideal MHD, but identify issues in nonlinear simulations. Detachment, characterized in 2D with sub-eV resolution, reveals a radiation shortfall in simulations. As a result, future facility development targets burning plasma physics with torque free electron heating, the path to steady state with increased off axis currents, and a new divertor solution for fusion reactors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Ferromagnetic Resonance in Square Lattices of Planar Magnetic Cross-Shaped Elements

Abstract—Ferromagnetic resonance (FMR) in planar thin film structures comprised of magnetic cross-shaped elements arranged into square lattices has been studied by micromagnetic simulation. FMR spectra and spatial distributions of amplitudes of resonant oscillations were determined for vortex and antivortex states of magnetization in lattice crosses. Resonant modes have the shape of rotating magnetization distributions. Herewith, modes with the same configuration of magnetization but rotating in reverse directions are frequency split. The observed nonreciprocity of propagation of resonant spin oscillations is determined by the sign of magnetization distribution vorticity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Current measurements in the intermittent-contact mode of atomic force microscopy using the Fourier method: a feasibility analysis

Atomic force microscopy (AFM) is an important tool for measuring a variety of nanoscale surface properties, such as topography, viscoelasticity, electrical potential and conductivity. Some of these properties are measured using contact methods (static contact or intermittent contact), while others are measured using noncontact methods. Some properties can be measured using different approaches. Conductivity, in particular, is mapped using the contact-mode method. However, this modality can be destructive to delicate samples, since it involves continuously dragging the cantilever tip on the surface during the raster scan, while a constant tip–sample force is applied. In this paper we discuss a possible approach to develop an intermittent-contact conductive AFM mode based on Fourier analysis, whereby the measured current response consists of higher harmonics of the cantilever oscillation frequency. Such an approach may enable the characterization of soft samples with less damage than contact-mode imaging. To explore its feasibility, we derive the analytical form of the tip–sample current that would be obtained for attractive (noncontact) and repulsive (intermittent-contact) dynamic AFM characterization, and compare it with results obtained from numerical simulations. Although significant instrumentation challenges are anticipated, the modelling results are promising and suggest that Fourier-based higher-harmonics current measurement may enable the development of a reliable intermittent-contact conductive AFM method.

14 SOLAR ENERGY↗
NASA NTRS1987

Stability and resonance in grooved-channel flows

Numerical simulation using the spectral element method is used to study the stability and resonant response of incompressible moderate-Reynolds-number flows in periodically-grooved channels. For Reynolds numbers below a critical value, the flow is shown to approach a stable steady-state, and the least stable modes resemble Tollmien-Schlichting channel waves. For Reynolds numbers greater than the critical value, self-sustained oscillations result. Oscillatory perturbation of the grooved-channel flow at the frequency of the least stable mode of the linearized system is found to result in subcritical resonant excitation as the critical Reynolds number is approached. The importance of nonhomogeneous geometry in the forced response of the flow is discussed.

Ghaddar, Nasreen K.↗
DOE OSTI2016

Catalytic conversion in nanoporous materials: Concentration oscillations and spatial correlations due to inhibited transport and intermolecular interactions

We show that steady-state catalytic conversion in nanoporous materials can occur in a quasi-counter-diffusion mode with the reactant (product) concentration strongly decaying (growing) into the pore, but also with oscillations in the total concentration. These oscillations reflect the response of the fluid to the transition from an extended to a confined environment near the pore opening. We focus on the regime of strongly inhibited transport in narrow pores corresponding to single-file diffusion. Here, limited penetration of the reactant into the pores and the associated low reaction yield is impacted by strong spatial correlations induced by both reaction (non-equilibrium correlations) and also by intermolecular interactions (thermodynamic correlations). We develop a generalized hydrodynamic formulation to effectively describe inhibited transport accounting for the effect of these correlations, and incorporate this description of transport into appropriate reaction-diffusion equations. These equations accurately describe both shorter-range concentration oscillations near the pore opening and the longer-range mesoscale variation of concentration profiles in the pore (and thus also describe reaction yield). Success of the analytic theory is validated by comparison with a precise kinetic Monte Carlo simulation of an appropriate molecular-level stochastic reaction-diffusion model. As a result, this work elucidates unconventional chemical kinetics in interacting confined systems.

36 MATERIALS SCIENCE↗
NASA NTRS1996

RSRM Chamber Pressure Oscillations: Transit Time Models and Unsteady CFD

Space Shuttle solid rocket motor low frequency internal pressure oscillations have been observed since early testing. The same type of oscillations also are present in the redesigned solid rocket motor (RSRM). The oscillations, which occur during RSRM burn, are predominantly at the first three motor cavity longitudinal acoustic mode frequencies. Broadband flow and combustion noise provide the energy to excite these modes at low levels throughout motor burn, however, at certain times during burn the fluctuating pressure amplitude increases significantly. The increased fluctuations at these times suggests an additional excitation mechanism. The RSRM has inhibitors on the propellant forward facing surface of each motor segment. The inhibitors are in a slot at the segment field joints to prevent burning at that surface. The aft facing segment surface at a field joint slot burns and forms a cavity of time varying size. Initially the inhibitor is recessed in the field joint cavity. As propellant burns away the inhibitor begins to protrude into the bore flow. Two mechanisms (transit time models) that are considered potential pressure oscillation excitations are cavity-edge tones, and inhibitor hole-tones. Estimates of frequency variation with time of longitudinal acoustic modes, cavity edge-tones, and hole-tones compare favorably with frequencies measured during motor hot firing. It is believed that the highest oscillation amplitudes occur when vortex shedding frequencies coincide with motor longitudinal acoustic modes. A time accurate computational fluid dynamic (CFD) analysis was made to replicate the observations from motor firings and to observe the transit time mechanisms in detail. FDNS is the flow solver used to detail the time varying aspects of the flow. The fluid is approximated as a single-phase ideal gas. The CFD model was an axisymmetric representation of the RSRM at 80 seconds into burn.Deformation of the inhibitors by the internal flow was determined through an iterative structural and CFD analysis. The analysis domain ended just upstream of the nozzle throat. This is an acoustic boundary condition that caused the motor to behave as a closed-open organ pipe. This differs from the RSRM which behaves like a closed-closed organ pipe. The unsteady CFD solution shows RSRM chamber pressure oscillations predominately at the longitudinal acoustic mode frequencies of a closed-open organ pipe. Vortex shedding in the joint cavities and at the inhibitors contribute disturbances to the flow at the second longitudinal acoustic mode frequency. Further studies are planned using an analysis domain that extends downstream of the nozzle throat.

Nesman, Tom↗
NASA NTRS2015

Drought Variability in the Eastern Australia and New Zealand Summer Drought Atlas (ANZDA, CE 1500-2012) Modulated by the Interdecadal Pacific Oscillation

Agricultural production across eastern Australia and New Zealand is highly vulnerable to drought, but there is a dearth of observational drought information prior to CE (Christian Era) 1850. Using a comprehensive network of 176 drought-sensitive tree-ring chronologies and one coral series, we report the first Southern Hemisphere gridded drought atlas extending back to CE 1500. The austral summer (December-February) Palmer drought sensitivity index reconstruction accurately reproduces historically documented drought events associated with the first European settlement of Australia in CE 1788, and the leading principal component explains over 50 percent of the underlying variance. This leading mode of variability is strongly related to the Interdecadal Pacific Oscillation tripole index (IPO), with a strong and robust antiphase correlation between (1) eastern Australia and the New Zealand North Island and (2) the South Island. Reported positive, negative, and neutral phases of the IPO are consistently reconstructed by the drought atlas although the relationship since CE 1976 appears to have weakened.

Palmer, Jonathan G.↗
DOE OSTI2012

Non-Markovian reduced dynamics based upon a hierarchical effective-mode representation

A reduced dynamics representation is introduced which is tailored to a hierarchical, Mori-chain type representation of a bath of harmonic oscillators which are linearly coupled to a subsystem. We consider a spin-boson system where a single effective mode is constructed so as to absorb all system-environment interactions, while the residual bath modes are coupled bilinearly to the primary mode and among each other. Using a cumulant expansion of the memory kernel, correlation functions for the primary mode are obtained, which can be suitably approximated by truncated chains representing the primary-residual mode interactions. A series of reduced-dimensional bath correlation functions is thus obtained, which can be expressed as Fourier-Laplace transforms of spectral densities that are given in truncated continued-fraction form. For a master equation which is second order in the system-bath coupling, the memory kernel is re-expressed in terms of local-in-time equations involving auxiliary densities and auxiliary operators.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2013

Impact of the Dominant Large-scale Teleconnections on Winter Temperature Variability over East Asia

Monthly mean geopotential height for the past 33 DJF seasons archived in Modern Era Retrospective analysis for Research and Applications reanalysis is decomposed into the large-scale teleconnection patterns to explain their impacts on winter temperature variability over East Asia. Following Arctic Oscillation (AO) that explains the largest variance, East Atlantic/West Russia (EA/WR), West Pacific (WP) and El Nino-Southern Oscillation (ENSO) are identified as the first four leading modes that significantly explain East Asian winter temperature variation. While the northern part of East Asia north of 50N is prevailed by AO and EA/WR impacts, temperature in the midlatitudes (30N-50N), which include Mongolia, northeastern China, Shandong area, Korea, and Japan, is influenced by combined effect of the four leading teleconnections. ENSO impact on average over 33 winters is relatively weaker than the impact of the other three teleconnections. WP impact, which has received less attention than ENSO in earlier studies, characterizes winter temperatures over Korea, Japan, and central to southern China region south of 30N mainly by advective process from the Pacific. Upper level wave activity fluxes reveal that, for the AO case, the height and circulation anomalies affecting midlatitude East Asian winter temperature is mainly located at higher latitudes north of East Asia. Distribution of the fluxes also explains that the stationary wave train associated with EA/WR propagates southeastward from the western Russia, affecting the East Asian winter temperature. Investigation on the impact of each teleconnection for the selected years reveals that the most dominant teleconnection over East Asia is not the same at all years, indicating a great deal of interannual variability. Comparison in temperature anomaly distributions between observation and temperature anomaly constructed using the combined effect of four leading teleconnections clearly show a reasonable consistency between them, demonstrating that the seasonal winter temperature distributions over East Asia are substantially explained by these four large-scale circulation impacts.

El Nino-Southern Oscillation↗
NASA NTRS1990

Measurement and analysis of a microwave oscillator stabilized by a sapphire dielectric ring resonator for ultra-low noise

Phase-noise measurements are presented for a microwave oscillator whose frequency is stabilized by a whispering-gallery sapphire ring resonator with Q of 200,000. This mode involves little metallic conduction and allows nearly full use of the very low dielectric loss in sapphire. Several mode families have been identified, in good agreement with frequency calculations. For a 5-cm wheel resonator in a 7.6-cm container, Q values above 100,000 were found at room temperature for all of the modes in this sequence. Coupling Q-values for these same modes ranged from 10,000 (n = 5) to 100,000 (n = 10) for a WR112 waveguide port at the center of the cylinder wall of the containing can. Phase noise measurements for a transistor oscillator locked to the n = 10 (7.84-GHz) mode showed a 1/f cubed dependence for low offset frequencies, and a value of L(f) = -55 dB/Hz at an offset of 10 Hz from the carrier.

Dick, G. John↗
NASA NTRS1948

A Theoretical Investigation of the Dynamic Lateral Stability Characteristics of the MX-838 (XB-51) Airplane

At the request of the Air Material Command, U. S. Air Force, a theoretical study has been made of the dynamic lateral stability characteristics of the MX-838 (XB-51) airplane. The calculations included the determination of the neutral-oscillatory-stability boundary (R = 0), the period and time to damp to one-half amplitude of the lateral oscillation, end the time to damp to one-half amplitude for the spiral mode. Factors varied in the investigation were lift coefficient, wing incidence, wing loading, and altitude. The results of the investigation showed that the lateral oscillation of the airplane is unstable below a lift coefficient of 1.2 with flaps . deflected 40deg but is stable over the entire speed range with flaps deflected 20deg or 0deg. The results showed that satisfactory oscillatory stability can probably be obtained for all lift coefficients with the proper variation of flap deflection and wing incidence with airspeed. Reducing the positive wing incidence improved the oscillatory stability characteristics. The airplane is spirally unstable for most conditions but the instability is mild and the Air Force requirements are easily met.

Paulson, Jon W.↗