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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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Enhancing Analytical Performance of (Mg,Fe)3O4/Glassy Carbon Electrodes by Tailoring Chemical Composition of (Mg,Fe)3O4 Nanoparticles

A series of MgxFe3-xO{sup 4} (x = 0-1) nanoparticles was synthesized in order to prepare novel MgxFe3-xO{sup 4}/glassy carbon modified electrodes. Effects of magnesium content (x) on the analytical performance of the modified electrodes in the detection of gallic acid were evaluated. It was found that magnesium concentration and crystallite/particle size of the prepared nanoparticles play significant roles in the sensing properties of modified electrodes. The increase of magnesium concentration up to the value of x = 0.4 in MgxFe3-xO{sup 4}/glassy carbon paste was accompanied by an increase of the corresponding oxidation current of gallic acid. However, further growth of x value caused decline of the obtained oxidation current. An electroanalytical procedure was established, and the analytical performance of the proposed Mg0.4Fe2.6O{sup }4#/glassy carbon paste electrode was monitored using previously optimized experimental conditions. A working linear range from 1-39 µM gallic acid was obtained with detection limit of 0.29 µM. According to these results, the developed procedure can be applied for detection of low concentrations of gallic acid with satisfactory selectivity in the presence of some common naturally occurring compounds. Experimental results indicate that the developed procedure could be a novel approach in the detection of antioxidant, overcoming some known disadvantages such as passivation, and could be a promising replacement for sophisticated chromatographic methods.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1987

Propulsion estimation techniques

A brief overview of statistical tools needed to perform post flight/test reconstruction of state variables is given. Linear regression, recursive linear regression, and the exact connection between the Kalman filter and linear regression are discussed. The regression connection is expected to serve as an aid in the application of a recently developed analytical method of flight reconstruction to single engine test firing data.

Temple, Enoch C.↗
NASA NTRS1988

Minimum weight design of rotorcraft blades with multiple frequency and stress constraints

Minimum weight designs of helicopter rotor blades with constraints on multiple coupled flap-lag natural frequencies are studied. Constraints are imposed on the minimum value of the blade autorotational inertia to ensure sufficient rotary inertia to autorotate in case of engine failure and on stresses to guard against structural failure due to blade centrifugal forces. Design variables include blade taper ratio, dimensions of the box beam located inside the airfoil and magnitudes of nonstructural weights. The program CAMRAD is used for the blade modal analysis; the program CONMIN is used for the optimization. A linear approximation involving Taylor series expansion is used to reduce the analysis effort. The procedure contains a sensitivity analysis consisting of analytical derivatives for objective function and constraints on autorotational inertia and stresses. Central finite difference derivatives are used for frequency constraints. Optimal designs are obtained for both rectangular and tapered blades. Using this method, it is possible to design a rotor blade with reduced weight, when compared to a baseline blade, while satisfying all the imposed design requirements.

Chattopadhyay, Aditi↗
NASA NTRS1990

Radiation from accelerated Alfven solitons in inhomogeneous plasmas

In a weakly inhomogeneous plasma, the large-amplitude Alfven waves propagating parallel to the ambient magnetic field are shown to evolve into accelerated Alfven solitons. Nonlinear interaction of the accelerated Alfven solitons with the Langmuir waves results in the emission of coherent radiations. Analytical expression for the power radiated per unit solid angle from a soliton is derived for two inhomogeneity profiles, namely the linear profile and the parabolic profile. For the case of uniform plasmas, the emission occurs via a decay-type process or resonant modes. In the presence of inhomogeneity, nonresonant modes provide a new channel for the emission of radiation. The power radiated per unit solid angle is computed for the parameters relevant to Comet Halley's plasma environment. For the nonresonant modes it is found to be several orders of magnitude higher than that for the case of resonant modes.

Lakhina, G. S.↗
NASA NTRS1993

Probabilistic finite elements for fatigue and fracture analysis

An overview of the probabilistic finite element method (PFEM) developed by the authors and their colleagues in recent years is presented. The primary focus is placed on the development of PFEM for both structural mechanics problems and fracture mechanics problems. The perturbation techniques are used as major tools for the analytical derivation. The following topics are covered: (1) representation and discretization of random fields; (2) development of PFEM for the general linear transient problem and nonlinear elasticity using Hu-Washizu variational principle; (3) computational aspects; (4) discussions of the application of PFEM to the reliability analysis of both brittle fracture and fatigue; and (5) a stochastic computational tool based on stochastic boundary element (SBEM). Results are obtained for the reliability index and corresponding probability of failure for: (1) fatigue crack growth; (2) defect geometry; (3) fatigue parameters; and (4) applied loads. These results show that initial defect is a critical parameter.

Belytschko, Ted↗
NASA NTRS1988

Probabilistic system identification in the time domain

The objective of system identification is to determine reliable dynamical models of a structure by systematically using its measured excitation and response. It brings together in an integrated fashion, experimental, analytical, and computational techniques in structural dynamics. Areas of application for system identification include the following: (1) Model Evaluation--assessing assumptions (linearity and equivalent viscous damping) and techniques (finite-element modeling) used to construct theoretical models of a structure; (2) Model Improvement--updating of a theoretical model to enable more accurate response predictions for possible future loads on the structure, or for control of the structure; (3) Empirical Modelling--developing empirical relationships (nonlinear models) or empirical parameter values (modal damping) because the present state of the art does not provide theoretical results; and (4) Damage Detection and Assessment--continual or episodic updating of a structural model through vibration monitoring to detect and locate any structural damage. It can be argued that since the construction or modification of models using test data is subject to inherent uncertainties, the above problems should be properly treated within a Bayesian probabilistic framework. Such a methodology is presented which allows the precision of the estimates of the model parameters to be computed. It also leads to a guiding principle in applications. Namely, when selecting a single model from a given class of models, one should take the most probable model in the class based on the experimental data. Practical applications of this principle are given which are based on the utilization of measured seismic motions in large civil structures. Examples include the application of a computer program MODE-ID to identify modal properties directly from seismic excitation and response time histories from a nine-story steel-frame building at JPL and from a freeway overpass bridge.

Beck, James L.↗
NASA NTRS1998

Magnetic Field Effect on Convective Fluid Flow in a Vertical Bridgman System

We studied the magnetic field effects on convective fluid flow in a differentially heated HgCdTe Bridgman growth system with linearly stratified vertical HgTe concentration. We followed J. E. Hart's system set-up, boundary conditions, and formulation. We obtained analytical steady parallel flow solutions for fluid flow's velocity and solutal concentration. These solutions depend only on solutal Rayleigh number. Our analytical solutions had different expressions from that of Hart's, but had similar numerical simulation results for the mean fluid velocity and solutal concentration gradient as a function of solutal Rayleigh number. We studied the effects of a transverse magnetic field on the fluid flow of the Bridgman growth systems both on the ground and in the space. The simulation results and comparison with experimental results will be presented.

Wang, J. C.↗
NASA NTRS2006

Analytic evaluation of the weighting functions for remote sensing of blackbody planetary atmospheres : the case of limb viewing geometry

In a recent publication (Ustinov, 2002), we proposed an analytic approach to evaluation of radiative and geophysical weighting functions for remote sensing of a blackbody planetary atmosphere, based on general linearization approach applied to the case of nadir viewing geometry. In this presentation, the general linearization approach is applied to the limb viewing geometry. The expressions, similar to those obtained in (Ustinov, 2002), are obtained for weighting functions with respect to the distance along the line of sight. Further on, these expressions are converted to the expressions for weighting functions with respect to the vertical coordinate in the atmosphere. Finally, the numerical representation of weighting functions in the form of matrices of partial derivatives of grid limb radiances with respect to the grid values of atmospheric parameters is used for a convolution with the finite field of view of the instrument.

remote sensing↗
NASA NTRS2017

Mars Organic Molecule Analyzer (MOMA) Laser Desorption/Ionization Source Design and Performance Characterization

The Mars Organic Molecule Analyzer (MOMA), a dual-source, ion trap-based instrument capable of both pyrolysis-gas chromatography mass spectrometry (pyr/GC-MS) and laser desorption/ionization mass spectrometry (LDI-MS), is the core astrobiology investigation on the ExoMars rover. The MOMA instrument will be the first spaceflight mass analyzer to exploit the LDI technique to detect refractory organic compounds and characterize host mineralogy; this mode of analysis will be conducted at Mars ambient conditions. In order to achieve high performance in the Martian environment while keeping the instrument compact and low power, a number of innovative designs and components have been implemented for MOMA. These include a miniaturized linear ion trap (LIT), a fast actuating aperture valve with ion inlet tube, and a Microelectromechanical System (MEMS) Pirani sensor. Advanced analytical capabilities like Stored Waveform Inverse Fourier Transform (SWIFT) for selected ion ejection and tandem mass spectrometry (MS/MS) are realized in LDI-MS mode, and enable the isolation and enhancement of specific mass ranges and structural analysis, respectively. We report here the technical details of these instrument components as well as system-level analytical capabilities, and we review the applications of this technology to Mars and other high-priority targets of planetary exploration.

Xiang Li↗
DOE OSTI2015

Phosphazenes 2014

Phosphazene chemistry continues to expand in its breadth and application. This article discusses new research published in 2013 covering mono- and dimeric structures, cyclotriphosphazenes, linear polymers, and the use of phosphazenic structures as ligands on metal centres. Papers report new reactions and structures as well as materials designed for specific applications, such as biomedical, energy storage, flame retardant, and optical, among others. The critical similarity is the phosphazene P-N structure that gives this area of study wide variation. Mirroring the diversity in chemistry are the tools used to probe structure and behaviour. These techniques include Nuclear Magnetic Resonance (NMR) spectrometry, various optical methods, electrochemistry, membrane transport experiments, etc. Furthermore, computational methods, such as Density Functional Theory (DFT), have been used to provide additional insight. This article is organized by structure, beginning with monomeric, dimeric, and non-cyclic phosphazenes first, followed by the cyclic and linear morphologies, with reported potential applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane

The endeavour to reach higher brightness of electron beams in designs of future FEL is often challenged by the coherent synchrotron radiation (CSR) effect in bunch compression chicanes. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the chicane, the behaviour of the CSR interaction force will be influenced by the evolution of the 2D bunch charge-density distribution in the bending plane. Here we explore this 2D effect for over-compression cases using the previously developed semi-analytical study of the effective longitudinal CSR force for a bunch with evolving 4D Gaussian phase space distribution and an initial linear energy chirp. We will display the dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread for path lengths around that of the minimum bunch length. We will also present and discuss the comparison of these results with their counterparts in the 1D rigid-line bunch model.

Li, R.↗
DOE OSTI2010

MODELING THE LARGE-SCALE BIAS OF NEUTRAL HYDROGEN

We present new analytical estimates of the large-scale bias of neutral hydrogen (H I). We use a simple, non-parametric model which monotonically relates the total mass of a halo M{sub tot} with its H I mass M{sub HI} at zero redshift; for earlier times we assume limiting models for the {Omega}{sub HI} evolution consistent with the data presently available, as well as two main scenarios for the evolution of our M{sub HI}-M{sub tot} relation. We find that both the linear and the first nonlinear bias terms exhibit a strong evolution with redshift, regardless of the specific limiting model assumed for the H I density over time. These analytical predictions are then shown to be consistent with measurements performed on the Millennium Simulation. Additionally, we show that this strong bias evolution does not sensibly affect the measurement of the H I power spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Emergence of a nocturnal low-level jet from a broad baroclinic zone

An analytical model is presented for the generation of a Blackadar-like nocturnal low-level jet in a broad baroclinic zone. The flow is forced from below (flat ground) by a surface buoyancy gradient and from above (free atmosphere) by a constant pressure gradient force. Diurnally-varying mixing coefficients are specified to increase abruptly at sunrise and decrease abruptly at sunset. With attention restricted to a surface buoyancy that varies linearly with a horizontal coordinate, the Boussinesq-approximated equations of motion, thermal energy, and mass conservation reduce to a system of one-dimensional equations that can be solved analytically. Sensitivity tests with southerly jets suggest that (i) stronger jets are associated with larger decreases of the eddy viscosity at sunset (as in Blackadar theory), (ii) the nighttime surface buoyancy gradient has little impact on jet strength, and (iii) for pure baroclinic forcing (no free-atmosphere geostrophic wind), the nighttime eddy diffusivity has little impact on jet strength, but the daytime eddy diffusivity is very important and has a larger impact than the daytime eddy viscosity. The model was applied to a jet that developed in fair weather conditions over the Great Plains from southern Texas to northern South Dakota on 1 May 2020. The ECMWF Reanalysis v5 (ERA5) for the afternoon prior to jet formation showed that a broad north-south-oriented baroclinic zone covered much of the region. The peak model-predicted winds were in good agreement with ERA5 winds and lidar data from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) central facility in north-central Oklahoma.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Kinetic simulations and reduced modeling of longitudinal sideband instabilities in non-linear electron plasma waves

Kinetic Vlasov simulations of one-dimensional finite amplitude Electron Plasma Waves are performed in a multi-wavelength long system. A systematic study of the most unstable linear sideband mode, in particular its growth rate γ and quasi- wavenumber δk, is carried out by scanning the amplitude and wavenumber of the initial wave. Simulation results are successfully compared against numerical and analytical solutions to the reduced model by Kruer et al. [Phys. Rev. Lett. 23, 838 (1969)] for the Trapped Particle Instability (TPI). A model recently suggested by Dodin et al. [Phys. Rev. Lett. 110, 215006 (2013)], which in addition to the TPI accounts for the so-called Negative Mass Instability because of a more detailed representation of the trapped particle dynamics, is also studied and compared with simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Interactions in Theories with Mixed Symmetry Tensor Fields: Yes-Go Results

Some recent yes-go results concerning consistent couplings involving mixed symmetry tensor fields are reported. Only particular classes of mixed symmetry tensor fields, which are dual to linearized gravity in various dimensions, are considered. The method used to generate consistent couplings is based on the deformation of the solution to the master equation combined with specific techniques of local Becchi-Rouet-Stora-Tyutin cohomology. In each case the deformations are constructed under the general hypotheses of analyticity in the coupling constant, space-time locality, Lorentz covariance, Poincare invariance, preservation of the differential order of the interacting field equations with respect to their free limit. The emerging results indicate that dual formulations of linearized gravity are far from being rigid under the introduction of consistent couplings, so there is still hope for providing an alternative, finite setting for General Relativity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Constitutive model fingerprints in medium-amplitude oscillatory shear

Rheologists have expectations for signatures of linear viscoelastic properties, such as shapes of G'(ω) and G"(ω). Medium amplitude (or asymptotically-nonlinear) oscillatory shear (MAOS) provides additional nonlinear rheological information with low dimensional, well-defined material functions. Here, we develop expectations of signatures (or fingerprints) for the four asymptotically-nonlinear material functions associated with MAOS, [e 1 ](ω), [e 3 ](ω), [v 1 ](ω), [v 3 ](ω). Although the linear fingerprints may be identical for different models, the asymptotically-nonlinear fingerprints may be different in magnitude, frequency-scaling, curve shapes, and sign changes. To perform the analysis, we collect/translate a library of available analytical strain-controlled MAOS fingerprints for seven different constitutive models. Using this library, we identify general trends and highlight key differences of asymptotic-nonlinear viscoelasticity. Asymptotic nonlinearities for all models considered here obey the terminal regime inter-relations and frequency scaling predicted by Bharadwaj and Ewoldt. Unlike the positive linear viscoelastic measures, at least one of the four asymptotic nonlinearities changes signs with Deborah number (De). Following sign interpretations of Ewoldt and Bharadwaj, we show that nonlinearities tend to be driven by strain-rates at small De, and by strains at large De, a trend observed for nearly all the constitutive models studied here, the exception being the model for dilute rigid dumbbell suspensions. Some constitutive models exhibit multiple sign changes at intermediate De and there may be no universal behavior of asymptotically-nonlinear fingerprints in this regime. Therefore, frequency-dependent signatures can be material-specific. Furthermore, this will allow inverse problems to infer structure, select models, and fit model parameters using asymptotically-nonlinear signatures. To illustrate this aspect, we demonstrate a fingerprint matching exercise with experimental measurements on a transiently cross-linked hydrogel system. We find that currently available model fingerprints can match the qualitative magnitudes and frequency dependence, but not the signs of the experimental transient network response.

42 ENGINEERING↗
NASA NTRS1993

On the stability of nongyrotropic ion populations - A first (analytic and simulation) assessment

The wave and dispersion equations for perturbations propagating parallel to an ambient magnetic field in magnetoplasmas with nongyrotropic ion populations show, in general, the occurrence of coupling between the parallel (left- and right-hand circularly polarized electromagnetic and longitudinal electrostatic) eigenmodes of the associated gyrotropic medium. These interactions provide a means to driving linearly one mode with free-energy sources of other modes in homogeneous media. Different types of nongyrotropy bring about distinct classes of coupling. The stability of a hydrogen magnetoplasma with anisotropic, nongyrotropic protons that only couple the electromagnetic modes to each other is investigated analytically (via solution of the derived dispersion equation) and numerically (via simulation with a hybrid code). Nongyrotropy enhances growth and enlarges the unstable spectral range relative to the corresponding gyrotropic situation. The relevance of the properties of nongyrotropic populations to space plasma environments is also discussed.

Brinca, A. L.↗
DOE OSTI2025

An explicit, energy-conserving particle-in-cell scheme

We present an explicit temporal discretization of particle-in-cell schemes for the non-relativistic Vlasov equation that results in exact energy conservation when combined with an appropriate spatial discretization. The scheme is inspired by a simple, second-order explicit scheme that conserves energy exactly in the Eulerian context. We show that direct translation to particle-in-cell does not result in strict conservation, but derive a simple correction based on an analytically solvable optimization problem that recovers conservation. While this optimization problem is not guaranteed to have a real solution for every particle, we provide a correction that makes imaginary values extremely rare and still admits $\mathcal{O}$(10 –12 ) fractional errors in energy for practical simulation parameters. We present the scheme in both electrostatic – where we use the Ampère formulation – and electromagnetic contexts. With an electromagnetic field solve, the field update is most naturally linearly implicit, but the more computationally intensive particle update remains fully explicit. Here, we also show how the scheme can be extended to use the fully explicit leapfrog and pseudospectral analytic time-domain (PSATD) field solvers. The scheme is tested on standard kinetic plasma problems, confirming its conservation properties.

Energy conservation↗