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At least 919 records · Page 51

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NASA NTRS1982

Low noise buffer amplifiers and buffered phase comparators for precise time and frequency measurement and distribution

Extremely low noise, high performance, wideband buffer amplifiers and buffered phase comparators were developed. These buffer amplifiers are designed to distribute reference frequencies from 30 KHz to 45 MHz from a hydrogen maser without degrading the hydrogen maser's performance. The buffered phase comparators are designed to intercompare the phase of state of the art hydrogen masers without adding any significant measurement system noise. These devices have a 27 femtosecond phase stability floor and are stable to better than one picosecond for long periods of time. Their temperature coefficient is less than one picosecond per degree C, and they have shown virtually no voltage coefficients.

Eichinger, R. A.↗

DOE OSTI2014

Statistics of particle time-temperature histories

Particles in non-isothermal turbulent flow are subject to a stochastic environment that produces a distribution of particle time-temperature histories. This distribution is a function of the dispersion of the non-isothermal (continuous) gas phase and the distribution of particles relative to that gas phase. In this work we extend the one-dimensional turbulence (ODT) model to predict the joint dispersion of a dispersed particle phase and a continuous phase. The ODT model predicts the turbulent evolution of continuous scalar fields with a model for the cascade of fluctuations to smaller scales (the ‘triplet map’) at a rate that is a function of the fully resolved one-dimensional velocity field. Stochastic triplet maps also drive Lagrangian particle dispersion with finite Stokes numbers including inertial and eddy trajectory-crossing effects included. Two distinct approaches to this coupling between triplet maps and particle dispersion are developed and implemented along with a hybrid approach. An ‘instantaneous’ particle displacement model matches the tracer particle limit and provides an accurate description of particle dispersion. A ‘continuous’ particle displacement model translates triplet maps into a continuous velocity field to which particles respond. Particles can alter the turbulence, and modifications to the stochastic rate expression are developed for two-way coupling between particles and the continuous phase. Each aspect of model development is evaluated in canonical flows (homogeneous turbulence, free-shear flows and wall-bounded flows) for which quality measurements are available. ODT simulations of non-isothermal flows provide statistics for particle heating. These simulations show the significance of accurately predicting the joint statistics of particle and fluid dispersion. Inhomogeneous turbulence coupled with the influence of the mean flow fields on particles of varying properties alters particle dispersion. The joint particle-temperature dispersion leads to a distribution of temperature histories predicted by the ODT. Predictions are shown for the lower moments and the full distributions of the particle positions, particle-observed gas temperatures and particle temperatures. An analysis of the time scales affecting particle-temperature interactions covers Lagrangian integral time scales based on temperature autocorrelations, rates of temperature change associated with particle motion relative to the temperature field and rates of diffusional change of temperatures. These latter two time scales have not been investigated previously; they are shown to be strongly intermittent having peaked distributions with long tails. The logarithm of the absolute value of these time scales exhibits a distribution closer to normal.

Hewson, John C.↗

NASA NTRS2006

Mineralogy at Gusev Crater and Meridiani Planum from the Moessbauer Spectrometers on the Mars Exploration Rovers

The Moessbauer spectrometers on the twin MER rovers Spirit and Opportunity have provided significant new information on the distribution of iron among its oxidation states, the identification of the mineralogical composition of iron-bearing phases, and the distribution of iron among those phases for rock and soil at Gusev Crater and Meridiani Planum. The plains of Gusev Crater are dominated by olivine-bearing basalt (approximately Fo(60)) and Fe(3+)/Fe(total)=0.1 - 0.5. The oxide mineral generally present is magnetite. In contrast, initial results for the Columbia Hills are consistent with the presence of hematite and a ferrous iron phase, possibly pyroxene. Gusev spectra also have a ferric doublet (not jarosite) that is tentatively associated with nano-phase ferric oxide. A wider diversity of material is present at Meridiani Planum. Significantly, jarosite-bearing outcrop is present throughout the region, with good exposures in impact craters such as Eagle and Endurance (Fe(3+)/Fe (total) approx. 0.9). The Moessbauer identification of jarosite (a hydroxyl-bearing sulfate mineral) is evidence for aqueous, acid-sulfate processes on Mars. Hematite is observed within the outcrop matrix and in the spheroidal particles (Blueberries) found within the outcrop and as a surface lag. An isolated rock (Bounce Rock) was the only sample at either landing site whose iron-bearing phase was dominated by pyroxene. The basaltic sand in the central portion of Eagle crater, in the intercrater plains, and between slabs of outcrop at both Eagle and Endurance craters is olivine-bearing basalt. The widespread occurrence of olivine-bearing basalt at both MER landing sites implies that physical, rather than chemical, weathering processes dominate at the surface of contemporary Mars.

Morris, Richard V.↗

DOE OSTI2016

Measurement of Void Fraction Distribution in Steam-Water Two-Phase Flow in a 44 Bundle at 2 MPa

To contribute to the clarification of the Fukushima Daiichi Accident, JAEA is working on getting instantaneous void fraction distribution data in steam-water two-phase flow in rod bundle geometry under high pressure, high temperature condition, with using Wire Mesh Sensor (WMS) developed at JAEA for high pressure, high temperature condition (Up to 2.8 MPa, 230 deg. C), focusing on the low flow rate condition after the reactor scram. The data is expected to be used in the validation of the detailed two-phase flow codes TPFIT and ACE3D developed at JAEA. The time and space averaged void fraction data is also expected being used in the validation of the drift-flux models implemented in the two fluids codes, such as TRACE code. We are still in the middle of the data analyses and here we only report a part of the results. For the present bundle rod geometry, the void fraction shows easily gathered at the center area surrounded by 4 rods and the void fraction in the sub - channels between two adjacent rods are low. Under the same steam vapor flow rate condition, void faction increase with the decrease of the water flow rate. Under the same water flow rate, the void fraction increases with the increase of the steam vapor flow rate. In recent future, we will perform more experiments under further low water flow rate condition, including stagnation condition, to confirm this changing tendency. In the present experimental range, no effect of pressure on void fraction was observed. A 3-layer WMS, with a vertical distance between the adjacent layers of 1.3 mm, was used to measure the local instantaneous void fraction in this research. By using the correlation coefficient method, we can determine the time delay between the bubble detections from the upper and the lower layer sensors. Then the speed of the bubble, and its length, can be calculated. We are working on the establishment of the databank for the slug-churn bubbles information. (authors)

42 ENGINEERING↗

DOE OSTI2018

On Per-Phase Topology Control and Switching in Emerging Distribution Systems

This paper presents a new concept and approach for topology control and switching in distribution systems by extending the traditional circuit switching to laterals and single-phase loads. Voltage unbalance and other key performance indicators including voltage magnitudes, line loading, and energy losses are used to characterize and demonstrate the technical value of optimizing system topology on a per-phase basis in response to feeder conditions. The near-optimal per-phase topology control is defined as a series of hierarchical optimization problems. The proposed approach is respectively applied to IEEE 13-bus and 123-bus test systems for demonstration, which included the impact of integrating electric vehicles (EVs) in the test circuit. It is concluded that the proposed approach can be effectively leveraged to improve voltage profiles with electric vehicles, the extent of which depends upon the performance of the base case without EVs.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2016

Probing the Small- x Gluon Tomography in Correlated Hard Diffractive Dijet Production in Deep Inelastic Scattering

The close connection between the quantum phase space Wigner distribution of small-x gluons and the color dipole scattering amplitude is investigated, and studying it experimentally is proposed in the hard diffractive dijet production at the planned electron-ion collider. The angular correlation between the nucleon recoiled momentum and the dijet transverse momentum probes the nontrivial correlation in the phase space Wigner distribution. This experimental study not only provides three-dimensional tomographic pictures of gluons inside high energy protons - it gives a unique and interesting signal for the small-x dynamics with QCD evolution effects.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2014

Distribution System Voltage Regulation by Distributed Energy Resources

This paper proposes a control method to regulate voltages in 3 phase unbalanced electrical distribution systems. A constrained optimization problem to minimize voltage deviations and maximize distributed energy resource (DER) active power output is solved by harmony search algorithm. IEEE 13 Bus Distribution Test System was modified to test three different cases: a) only voltage regulator controlled system b) only DER controlled system and c) both voltage regulator and DER controlled system. The simulation results show that systems with both voltage regulators and DER control provide better voltage profile.

Distributed energy resources↗

DOE OSTI2014

Quantum limits on optical phase estimation accuracy from classical rate-distortion theory

The classical information-theoretic lower bound on the distortion of a random variable upon transmission through a noisy channel is applied to quantum-optical phase estimation. An approach for obtaining Bayesian lower bounds on the phase estimation accuracy is described that employs estimates of the classical capacity of the relevant quantum-optical channels. The Heisenberg limit for lossless phase estimation is derived for arbitrary probe state and prior distributions of the phase, and shot-noise scaling of the phase accuracy is established in the presence of nonzero loss for a parallel entanglement-assisted strategy with a single probe mode.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1981

Phase space variations of near equatorially mirroring ring current ions

Observations of near equatorially mirroring ring current ions before and after a magnetic storm are presented in the form of phase space densities with respect to the first adiabatic invariant. Particle densities were obtained from the medium energy particles instrument covering the energy range 24-2081 keV on ISEE 1 at L values between 3 and 8 earth radii and ratios of the magnetic field at the satellite position to the magnetic field at the magnetic equator less than 1.2. Analysis of the phase space densities through the magnetosphere reveals a well-defined high magnetic moment peak in the prestorm near-equatorial ring current ion phase space density distribution, with the magnetic storm resulting from an enhancement of phase space densities at magnetic moment values below the peak and phase space densities remaining constant above the peak. Results are found to be in good agreement with those obtained by Explorer 45 six years previously, indicating that the observed phase space density variations are characteristic of energetic ion behavior during magnetic storms.

Williams, D. J.↗

NASA NTRS1990

Preliminary investigation of a NiAl composite prepared by cryomilling

An attempt has been made to improve the high temperature mechanical strength of the B2 cubic crystal structure intermetallic NiAl by dispersion strengthening. Prealloyed Ni-51 at. pct Al was cryomilled with a Y2O3 addition to form an yttria dispersoid within the intermetallic matrix. Following milling, the powder was hot extruded to full density and machined into test coupons. Compression testing between 1200 and 1400 K indicated that the cryogenic process yielded the strongest NiAl based material tested to date. Creep resistance was six times better than NiAl and twice that of a NiAl particulate composite containing 10 vol pct TiB2. Surprisingly, transmission electron microscopy revealed that the second phase was inhomogeneously distributed. Furthermore, X-ray analysis indicated that the second phase was not Y2O3 but rather AlN.

Whittenberger, J. Daniel↗

NASA NTRS1990

A distributed agent architecture for real-time knowledge-based systems: Real-time expert systems project, phase 1

We propose a distributed agent architecture (DAA) that can support a variety of paradigms based on both traditional real-time computing and artificial intelligence. DAA consists of distributed agents that are classified into two categories: reactive and cognitive. Reactive agents can be implemented directly in Ada to meet hard real-time requirements and be deployed on on-board embedded processors. A traditional real-time computing methodology under consideration is the rate monotonic theory that can guarantee schedulability based on analytical methods. AI techniques under consideration for reactive agents are approximate or anytime reasoning that can be implemented using Bayesian belief networks as in Guardian. Cognitive agents are traditional expert systems that can be implemented in ART-Ada to meet soft real-time requirements. During the initial design of cognitive agents, it is critical to consider the migration path that would allow initial deployment on ground-based workstations with eventual deployment on on-board processors. ART-Ada technology enables this migration while Lisp-based technologies make it difficult if not impossible. In addition to reactive and cognitive agents, a meta-level agent would be needed to coordinate multiple agents and to provide meta-level control.

Lee, S. Daniel↗

DOE OSTI2019

Simulations of post-recrystallization grain growth in monolithic U–10Mo fuel processing

In this study, the Potts Model was used to simulate the post-recrystallization grain growth behavior of U-10 wt.% Mo (U-10Mo). The fabrication process for monolithic U-10Mo fuels involves multiple stages of rolling, during which spatially heterogeneous distributions of second phase particles form in the alloy microstructure. These particles can strongly affect the post-recrystallization grain growth process. Absent particle dissolution effects, U-10Mo grain growth has been observed stagnating at increasing grain size with increasing annealing temperature. In this work, we simulate this effect in the Potts Model by making adjustments to the non-physical Monte Carlo temperature. This modification was used to account for the weakening pinning effect of the second phases with elevated annealing temperature. Simulated average grain sizes and grain size distributions were compared with experimentally obtained results for 700 °C, 800 °C, and 900 °C anneals of duration up to 240 hours. These simulations achieved reasonable agreement with experimentally observed grain growth behavior, but showed narrower grain size distributions. It is believed that this disagreement originates from the formation of bands of second-phase particles during rolling. Finally, these results demonstrate the capability to evaluate the post-recrystallization grain growth behavior for U-10Mo as a function of previous homogenization, rolling, and annealing treatments.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS1986

Latitudinal plasma distribution in the dusk plasmaspheric bulge - Refilling phase and quasi-equilibrium state

Very low-energy trapped ions, mostly protons, have been observed in a region of moderate density characteristic of the plasmapause boundary and of the plasmaspheric bulge. The present paper is concerned with an examination of the latitudinal structure of the bulge under quasi-steady conditions and the conditions of the recovery phase. Details regarding the data base are considered along with observations of the morphology and dynamics of the bulge, the latitudinal density distribution in the expanded bulge, the convection scenario during the replenishment phase, and latitudinal effects on plasma characteristics during plasmasphere refilling. The data utilized have been mainly provided by the DE 1 and GEOS 2 spacecraft traveling in two perpendicular planes. It is found that the bulge is a dynamic region, where no reasonable interpretation of the observed density distribution can be achieved without taking into account the mechanism of magnetospheric convection.

Decreau, P. M. E.↗

DOE OSTI2017

Structure in the 3D Galaxy Distribution. III. Fourier Transforming the Universe: Phase and Power Spectra

We demonstrate the effectiveness of a relatively straightforward analysis of the complex 3D Fourier transform of galaxy coordinates derived from redshift surveys. Numerical demonstrations of this approach are carried out on a volume-limited sample of the Sloan Digital Sky Survey redshift survey. The direct unbinned transform yields a complex 3D data cube quite similar to that from the Fast Fourier Transform of finely binned galaxy positions. In both cases, deconvolution of the sampling window function yields estimates of the true transform. Simple power spectrum estimates from these transforms are roughly consistent with those using more elaborate methods. The complex Fourier transform characterizes spatial distributional properties beyond the power spectrum in a manner different from (and we argue is more easily interpreted than) the conventional multipoint hierarchy. We identify some threads of modern large-scale inference methodology that will presumably yield detections in new wider and deeper surveys.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2017

Structure in the 3D Galaxy Distribution. III. Fourier Transforming the Universe: Phase and Power Spectra

Galaxies↗

NASA NTRS2017

Structure in the 3D Galaxy Distribution: III. Fourier Transforming the Universe: Phase and Power Spectra

We demonstrate the effectiveness of a relatively straightforward analysis of the complex 3D Fourier transform of galaxy coordinates derived from redshift surveys. Numerical demonstrations of this approach are carried out on a volume-limited sample of the Sloan Digital Sky Survey redshift survey. The direct unbinned transform yields a complex 3D data cube quite similar to that from the Fast Fourier Transform (FFT) of finely binned galaxy positions. In both cases deconvolution of the sampling window function yields estimates of the true transform. Simple power spectrum estimates from these transforms are roughly consistent with those using more elaborate methods. The complex Fourier transform characterizes spatial distributional properties beyond the power spectrum in a manner different from (and we argue is more easily interpreted than) the conventional multi-point hierarchy. We identify some threads of modern large scale inference methodology that will presumably yield detections in new wider and deeper surveys.

Galactic clusters↗

DOE OSTI2011

High-order-harmonic generation using gas-phase H{sub 2}O molecules

We investigate high-order-harmonic generation of isotropically distributed gas-phase H{sub 2}O molecules exposed to an intense laser field. The induced dipole of each individual molecule by the laser field is first calculated using the recently developed quantitative rescattering theory. In a thin medium, harmonic spectra generated coherently from all the molecules are then calculated by solving Maxwell's equation of propagation. By using accurate transition dipoles of H{sub 2}O, we show that the harmonics in the lower plateau region are quite different from models that employ the simpler strong-field approximation. We also examine the magnitude and phase of the harmonics and their dependence on laser focusing conditions.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2014

Electron acoustic wave driven vortices with non-Maxwellian hot electrons in magnetoplasmas

Linear dispersion characteristics of the Electron Acoustic Wave (EAW) and the corresponding vortex structures are investigated in a magnetoplasma in the presence of non-Maxwellian hot electrons. In this regard, kappa and Cairns distributed hot electrons are considered. It is noticed that the nonthermal distributions affect the phase velocity of the EAW. Further, it is found that the phase velocity of EAW increases for Cairns and decreases for kappa distributed hot electrons. Nonlinear solutions in the form of dipolar vortices are also obtained for both stationary and non-stationary ions in the presence of kappa distributed hot electrons and dynamic cold electrons. It is found that the amplitude of the nonlinear vortex structures also reduces with kappa factor like the electron acoustic solitons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗