Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “peak finding”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

In situ synchrotron pair distribution function analysis to monitor synthetic pathways under electromagnetic excitation

Electromagnetic (EM) fields, specifically microwave radiation (MWR), can significantly influence the synthesis of ceramic oxide materials and promote rapid, low-temperature growth. However, the mechanisms by which EM fields affect the phase formation process are not well understood. A major limitation to increasing this understanding has been the lack of information regarding dynamic changes in local atomic structure during MWR exposure compared to conventional hydrothermal synthesis routes. Here, we utilize in situ synchrotron X-ray pair distribution function (PDF) analysis to monitor MWR-assisted SnO 2 nanoparticle synthesis. A clear impact of the EM field is demonstrated, with MWR inducing changes in nearest neighbor distances and peaks in oxygen atomic displacement that do not occur during synthesis without MWR exposure. The observed local structural disorder serves as a precursor to rapid rutile SnO 2 nanoparticle crystallization, suggesting that EM field-assisted growth is mediated by changes to the oxygen sublattice. These findings further our understanding of the mechanisms underlying MWR-assisted synthesis and represent a step towards utilizing EM fields to engineer tailored atomic structures for a broad range of applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Laboratory Constraints on the Neutron-Spin Coupling of feV-Scale Axions

Ultralight axionlike particles can contribute to the dark matter near the Sun, leading to a distinct, stochastic signature in terrestrial experiments. We search for such particles through their neutron-spin coupling by reanalyzing approximately 40 days of data from a K- 3 He comagnetometer with a new frequency-domain likelihood-based formalism that properly accounts for stochastic effects over all axion coherence times relative to the experimental time span. Assuming that axions make up all of the dark matter in the Sun’s vicinity, we find a median 95% upper limit on the neutron-spin coupling of 2.4 × 10 −10 GeV −1 for most axion masses from 0.4 to 4 feV, which is about 5 orders of magnitude more stringent than previous laboratory bounds in that mass range. Although several peaks in the experiment’s magnetic power spectrum suggest the rejection of a white-noise null hypothesis, further analysis of their line shapes yields no positive evidence for a dark-matter axion.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Decimetric gyrosynchrotron emission during a solar flare

The implications of high time-resolution observations of a decimetric, microwave, and hard X-ray burst during a solar flare in which the 900-998 MHz, 8.4 GHz, and 10.4 GHz peak fluxes fit the optically thick spectrum of a homogeneous, thermal gyrosynchrotron source are reported and discussed. The hard X-ray spectrum from 30 to 463 keV is well represented by a thermal bremsstrahlung function, and a temperature derived from this spectrum is used to find the source area of about 10 to the 18th sq cm. An electron density of less than about 7 x 10 to the 9th/cu cm and a magnetic field of roughly 120 gauss are deduced from elementary plasma physics considerations and the lack of Razin-Tsytovich absorption of the 900-998 MHz flux. These conditions place the gyrosynchrotron source at high altitude in a coronal loop, in agreement with VLA observations of other flares.

Batchelor, D. A.↗
NASA NTRS1993

Cluster evolution as a probe of primordial density fluctuations

Although COBE's detection of large angle microwave background anisotropies fixes the amplitude of density fluctuations on length scales k exp -1 approximately = (300-6000) h(exp -1)Mpc, what is crucial for the level of large scale clustering is the amplitude of density fluctuations on scales (5-50) h(exp -1)Mpc. The level of dynamical clustering is usually parameterized by the size of the mass fluctuations in 8 h exp -1 Mpc spheres, sigma sub 8. For the cold dark matter model, COBE gives sigma sub 8 approximately = 1, while models with extra large scale power give sigma sub 8 approximately = 1/2. The most massive clusters of galaxies (greater than or approximately = 10 exp 15 solar mass) form from rare 'peak patches' found in the initial mass density distribution. Their abundance as a function of redshift is a sensitive probe of the wave number band k(exp -1) approx. (3-8) h(exp -1)Mpc, hence of sigma sub 8, and so cluster evolution can discriminate among models allowed by the COBE results. We use our Hierarchical Peaks Method, which accurately reproduces the results of P3M N-body simulations, to calculate the evolution of cluster x-ray flux counts, luminosity, and temperature functions as a function of sigma sub 8 for CDM models and those with more large scale power. We find that the EMSS and Edge et al. cluster samples support sigma sub 8 in the range from approx. 0.6-0.9, and that models with more large scale power (and hence flatter fluctuation spectra in the cluster regime) fit the x-ray bright end better.

Bond, J. Richard↗
NASA NTRS1994

The effects of temporal variability of mixed layer depth on primary productivity around Bermuda

Temporal variations in primary production and surface chlorophyll concentrations, as measured by ship and satellite around Bermuda, were simulated with a numerical model. In the upper 450 m of the water column, population dynamics of a size-fractionated phytoplankton community were forced by daily changes of wind, light, grazing stress, and nutrient availability. The temporal variations of production and chlorophyll were driven by changes in nutrient introduction to the euphotic zone due to both high- and low-frequency changes of the mixed layer depth within 32 deg-34 deg N, 62 deg-64 deg W between 1979 and 1984. Results from the model derived from high-frequency (case 1) changes in the mixed layer depth showed variations in primary production and peak chlorophyll concentrations when compared with results from the model derived from low-frequency (case 2) mixed layer depth changes. Incorporation of size-fractionated plankton state variables in the model led to greater seasonal resolution of measured primary production and vertical chlorophyll profiles. The findings of this study highlight the possible inadequacy of estimating primary production in the sea from data of low-frequency temporal resolution and oversimplified biological simulations.

Bissett, W. Paul↗
NASA NTRS2001

Grain Properties of Comet C/1995 O1 (Hale-Bopp) Deduced Through Computational Techniques

We present the computational analysis of the 7.6 - 13.2 micrometer infrared (IR) spectrophotometry (R approximately equal to 120) of comet C/1995 O1 (Hale-Bopp) in conjunction with concurrent observations which extend the spectral energy distribution from the near-infrared to far-infrared wavelengths. The observations include temporal epochs pre-perihelion, (1996 October UT and 1997 February UT), near perihelion (1997 April UT), and postperihelion (1997 June UT). Through the computational modeling of small amorphous carbon, and crystalline and amorphous silicate grains in Hale-Bopp's coma, we find that as the comet approached perihelion, the grain size distribution (the Hanner modified power law) steepened (N = 3.4 pre-perihelion, to N = 3.7 near and post-perihelion) along with an increase in the fractal porosity of larger (greater than 1 micrometer) grains. The peak of the grain size distribution remained constant (ap = 0.2 micrometer) at each epoch. We attribute the emergence of the 9.3 micrometer peak near perihelion to crystalline orthopyroxeno grains released from inside the nucleus. Crystalline silicates (olivine and orthopyroxene) make up about 30% (by mass) of the submicron sized (less than 1 micrometer) dust grains in Hale-Bopp's coma during each epoch.

Harker, David E.↗
NASA NTRS2002

Small Particle Response to Fluid Motion using Tethered Particles to Simulate Microgravity

This paper reports on ground based work conducted to support the Spaceflight Definition project SHIVA (Spaceflight Holography Investigation in a Virtual Apparatus). SHIVA will advance our understanding of the movement of a particle in a fluid. Gravity usually dominates the equations of motion, but in microgravity as well as on earth other terms can become important. Before two members of our team found an analytical solution of the equations, numerical methods and/or neglecting terms were required. The general solution predicts that the usually neglected history term becomes important when the characteristic viscous time is in the same order as the vibration period and peaks when the two times are equal. In this case three force terms, the Stokes drag, the added mass, and the history drag must all be included in predicting particle movement. We also developed diagnostic recording methods using holography to save all of the particle field data, allowing the experiment to essentially be transferred from space back to earth in what we call the "virtual apparatus". Using state-of-the-art methods in holography we will quantify the three-dimensional motion of sets of particles, allowing us to test and apply the new analytical solutions. The motion of particles up to 4 mm in diameter in a fluid that oscillates at frequencies up to 100 Hz with amplitudes up to 200 microns is being examined. Ground studies to support the flight development program have employed various schemes to simulate microgravity. One of the most reliable and meaningful methods uses spheres tethered to a fine hair suspended in the fluid. We have also investigated particles with nearly neutral buoyancy. Recordings are made at the peak amplitudes of vibration of the cell providing a measure of the ratio of fluid to particle amplitude. The experiment requires precise location of the particle at the time of recording. The hologram of the particle provides microscopic images of the particle that are used for finding the position with an accuracy of a few microns. To make the experiment more versatile, the spaceflight system will record holograms both on film and electronically. The electronic holograms can be downlinked providing real time data. Results of the ground experiments, the flight experiment design, and data analysis procedures are reported.

Trolinger, J. D.↗
NASA NTRS2002

Small Particle Response to Fluid Motion using Tethered Particles to Simulate Microgravity

This paper reports on ground based work conducted to support the Spaceflight Definition project SHIVA (Spaceflight Holography Investigation in a Virtual Apparatus). SHIVA will advance our understanding of the movement of a particle in a fluid. Gravity usually dominates the equations of motion, but in microgravity as well as on earth other terms can become important. Before two members of our team found an analytical solution of the equations, numerical methods and/or neglecting terms were required. The general solution predicts that the usually neglected history term becomes important when the characteristic viscous time is in the same order as the vibration period and peaks when the two times are equal. In this case three force terms, the Stokes drag, the added mass, and the history drag must all be included in predicting particle movement. We also developed diagnostic recording methods using holography to save all of the particle field data, allowing the experiment to essentially be transferred from space back to earth in what we call the "virtual apparatus". Using state-of-the-art methods in holography we will quantify the three-dimensional motion of sets of particles, allowing us to test and apply the new analytical solutions. The motion of particles up to 4 mm in diameter in a fluid that oscillates at frequencies up to 100 Hz with amplitudes up to 200 microns is being examined. Ground studies to support the flight development program have employed various schemes to simulate microgravity. One of the most reliable and meaningful methods uses spheres tethered to a fine hair suspended in the fluid. We have also investigated particles with nearly neutral buoyancy. Recordings are made at the peak amplitudes of vibration of the cell providing a measure of the ratio of fluid to particle amplitude. The experiment requires precise location of the particle at the time of recording. The hologram of the particle provides microscopic images of the particle that are used for finding the position with an accuracy of a few microns. To make the experiment more versatile, the spaceflight system will record holograms both on film and electronically. The electronic holograms can be downlinked providing real time data. Results of the ground experiments, the flight experiment design, and data analysis procedures are reported.

Trolinger, J. D.↗
NASA NTRS2003

CME Prediction from Line-of-Sight Magnetogram

We have previously shown for bipolar active regions that measures of active-region nonpotentiality from vector magnetograms are correlated with active-region CME productivity. We have now obtained a measure from line-of-sight magnetograms that is well correlated both with our measures of active-region nonpotentiality from vector magnetograms and with active-region CME productivity. The measure is the length of strong-gradient main neutral line (L(sub G)). This is the length of the bipolar region's main neutral line on which the potential transverse field is greater than 150G, and the gradient in the line-of-sight field is greater than 50G/Mm. From the sample of 17 MSFC magnetograms of 12 basically bipolar active regions used in our previous paper, we find that L(sub G) is strongly correlated with one of our vector-magnetogram measures of nonpotentiality, the length of strong-gradient main neutral line L(sub SS) (99.7%). We also find that L(sub G) is as strongly correlated with CME productivity (99.7%) as is L(sub SS). Being obtainable from line-of-sight magnetograms, L(sub G) makes the much larger data set of line-of-sight magnetograms (i.e. from SOHO/MDI and Kitt Peak) available for CME prediction study. This is especially important for evolutionary studies, with SOHO/MDI having no daylight, cloudy weather, or atmospheric seeing problems. This work was supported by funding from NSF's division of Atmospheric Sciences (Space Weather and Shine Programs) and by NASA's office of Space Science (Living with a Star program Solar and Heliospheric Physics Supporting Research and Technology program).

Falconer, D. A.↗
NASA NTRS2001

Effect of long-duration spaceflight on postural control during self-generated perturbations

This report is the first systematic evaluation of the effects of prolonged weightlessness on the bipedal postural control processes during self-generated perturbations produced by voluntary upper limb movements. Spaceflight impacts humans in a variety of ways, one of which is compromised postflight postural control. We examined the neuromuscular activation characteristics and center of pressure (COP) motion associated with arm movement of eight subjects who experienced long-duration spaceflight (3--6 mo) aboard the Mir space station. Surface electromyography, arm acceleration, and COP motion were collected while astronauts performed rapid unilateral shoulder flexions before and after spaceflight. Subjects generally displayed compromised postural control after flight, as evidenced by modified COP peak-to-peak anterior-posterior and mediolateral excursion, and pathlength relative to preflight values. These changes were associated with disrupted neuromuscular activation characteristics, particularly after the completion of arm acceleration (i.e., when subjects were attempting to maintain upright posture in response to self-generated perturbations). These findings suggest that, although the subjects were able to assemble coordination modes that enabled them to generate rapid arm movements, the subtle control necessary to maintain bipedal equilibrium evident in their preflight performance is compromised after long-duration spaceflight.

NASA Discipline Neuroscience↗
NASA NTRS2007

High-frequency Electrocardiogram Analysis in the Ability to Predict Reversible Perfusion Defects during Adenosine Myocardial Perfusion Imaging

Background: A previous study has shown that analysis of high-frequency QRS components (HF-QRS) is highly sensitive and reasonably specific for detecting reversible perfusion defects on myocardial perfusion imaging (MPI) scans during adenosine. The purpose of the present study was to try to reproduce those findings. Methods: 12-lead high-resolution electrocardiogram recordings were obtained from 100 patients before (baseline) and during adenosine Tc-99m-tetrofosmin MPI tests. HF-QRS were analyzed regarding morphology and changes in root mean square (RMS) voltages from before the adenosine infusion to peak infusion. Results: The best area under the curve (AUC) was found in supine patients (AUC=0.736) in a combination of morphology and RMS changes. None of the measurements, however, were statistically better than tossing a coin (AUC=0.5). Conclusion: Analysis of HF-QRS was not significantly better than tossing a coin for determining reversible perfusion defects on MPI scans.

Tragardh, Elin↗
NASA NTRS2012

Staring at 4U 1909+07 with Suzaku (Research Note)

We present an analysis of the neutron star High Mass X-ray Binary (HMXB) 4U 1909+07 mainly based on Suzaku data. We extend the pulse period evolution, which behaves in a random-walk like manner, indicative of direct wind accretion. Studying the spectral properties of 4U 1909+07 between 0.5 to 90keV we find that a power-law with an exponential cutoff can describe the data well, when additionally allowing for a blackbody or a partially covering absorber at low energies. We find no evidence for a cyclotron resonant scattering feature (CRSF), a feature seen in many other neutron star HMXBs sources. By performing pulse phase resolved spectroscopy we investigate the origin of the strong energy dependence of the pulse profile, which evolves from a broad two-peak profile at low energies to a profile with a single, narrow peak at energies above 20keV. Our data show that it is very likely that a higher folding energy in the high energy peak is responsible for this behavior. This in turn leads to the assumption that we observe the two magnetic poles and their respective accretion columns at different phases, and that these accretions column have slightly different physical conditions.

Fuerst, F.↗
DOE OSTI2024

Dispersal of high-burnup fuel fragment surrogate particles during and after loss-of-coolant accident tests

The issue of fuel fragmentation, relocation, and dispersal is critical in the licensing and use of high-burnup (>62 GWd/MTU) nuclear fuel in light water reactors (LWRs). In this work, two test series are reported that examine the fragment dispersal during a burst event and an additional dispersal following the burst due to vibrations in the rod, such as those induced by accident recovery systems. To examine dispersal during the balloon and burst portion of a Loss-of-Coolant Accident event, HfO 2 fragments and yttria-stabilized zirconia pellets were filled into an as-fabricated cladding tube, which was then pressurized and subjected to loss-of-coolant accident testing in steam. Results from this test were found to be highly non-prototypic, and dispersal was both significantly more violent and significantly greater in magnitude than identified for actual fuel tests. These findings were attributed to the conservative (more dispersive) nature of the particles chosen for dispersal and to the details of the test conditions used that led to particularly wide bursts. Further, the second set of tests examined dispersal following the burst when vibrations were induced in the rod, primarily via recovery activities such as Emergency Core Cooling System actuation leading to rapid water addition. Post-burst dispersal testing was performed by inducing sinusoidal oscillations with 2–25 nm peak-to-peak amplitude and 2–5 Hz frequencies in pre-burst rods that had been refilled with HfO 2 fragments or high-burnup fragment surrogate mixture of HfO 2 fragments and yttria-stabilized zirconia sands. Testing revealed that rods with large burst openings (7 mm wide in this work) led to unmitigated dispersal from above the burst zone but that smaller bursts (5 mm wide), although still much larger than the mean fragment size of 3 mm, led to effectively no dispersal because of interparticle locking. Additionally, mixture and moisture were found to impact the amount of dispersal: mixtures increased dispersal, and moisture drastically reduced it. The implications of these findings on likely dispersal from actual fuel are discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1994

Modeling of the hydrogen maser disk in MWC 349

Maser amplification in a Keplerian circumstellar disk seen edge on-the idea put forward by Gordon (1992), Martin-Pintado, & Serabyn (1992), and Thum, Martin-Pintado, & Bachiller (1992) to explain the millimeter hydrogen recombination lines in MWC 349-is further justified and developed here. The double-peaked (vs. possible triple-peaked) form of the observed spectra is explained by the reduced emission from the inner portion of the disk, the portion responsible for the central ('zero velocity') component of a triple-peaked spectrum. Radial gradient of electron density and/or free-free absorption within the disk are identified as the probable causes of this central 'hole' in the disk and of its opacity. We calculate a set of synthetic maser spectra radiated by a homogeneous Keplerian ring seen edge-on and compare them to the H30-alpha observations of Thum et al., averaged over about 1000 days. We used a simple graphical procedure to solve an inverse problem and deduced the probable values of some basic disk and maser parameters. We find that the maser is essentially unsaturated, and that the most probable values of electron temperature. Doppler width of the microturbulence, and electron density, all averaged along the amplification path are, correspondingly, T(sub e) less than or equal to 11,000 K, V(sub micro) less than or equal to 14 km/s, n(sub e) approx. = (3 +/- 2) x 10(exp 7)/cu cm. The model shows that radiation at every frequency within the spectrum arises in a monochromatic 'hot spot.' The maximum optical depth within the 'hot spot' producing radiation at the spectral peak maximum is tau(sub max) approx. = 6 +/- 1; the effective width of the masing ring is approx. = 0.4-0.7 times its outer diameter; the size of the 'hot spot' responsible for the radiation at the spectral peak frequency is approx. = 0.2-0.3 times the distance between the two 'hot spots' corresponding to two peaks. An important derivation of our model is the dynamical mass of the central star, M(sub *) approx. = 26 solar masses (D/1.2 kpc), D being the distance to the star. Prospects for improving the model are discussed.

Ponomarev, Victor O.↗
DOE OSTI2026

Understanding Recombination Pathways of CdSeTe/CdTe Devices Using Temperature Dependence of Fill Factor

Understanding the temperature dependence of photovoltaic parameters is critical for identifying performance limiting mechanisms in CdTe-based solar cells. In this study, we investigate the temperature dependence of fill factor (FF(T)) in CdSeTe/CdTe solar cells using a combination of experimental current density-voltage (JV) measurements and numerical simulations. The measured FF(T) exhibits a nonlinear response with temperature, peaking at moderate temperature values (10–30°C). Through numerical modeling, we reveal that this peaking behavior in FF(T) arises when the dominant recombination mechanism transitions from bulk to interface with increasing temperature. This transition is primarily driven by low hole mobility (0.6–1.2 cm2/V·s), while electron mobility, interface recombination velocities, and carrier lifetime also contribute to the effect. Our findings demonstrate that FF(T) analysis is a promising diagnostic tool for distinguishing recombination pathways and guiding the optimization of thin-film CdTe solar cells under real-world conditions.

CdTe photovoltaics↗
DOE OSTI2021

Branching ratios for the three most intense gamma rays in the decay of 47 Ca

A sample of 47 Ca produced through isotope harvesting at the National Superconducting Cyclotron Laboratory was used to measure branching ratios of 7.17(5)%, 7.11(5)%, and 75.0(5)% for the 489.2, 807.9, and 1297.1 keV characteristic gamma rays, respectively. Based on these updated branching ratios, the ground state to ground state 47 Ca to 47 Sc beta decay branching ratio has been indirectly measured as 17.7(5)% and the ground state to 1297.1 keV excited state as 82.2(5)%. Here these values represent a greatly increased precision for all five branching ratios compared to the currently accepted values. The measurements presented here were made relative to the ingrown 47Sc daughter in a 47 Ca sample and the well-established 159.4 keV gamma-ray branching ratio and the half-life for the decay of 47 Sc. These measurements were supported by verifying that the half-lives measured from characteristic gamma-ray peaks over multiple spectra for both 47 Ca and 47 Sc were consistent with previously reported values. Additionally, the half-lives of both 47 Ca and 47 Sc were independently measured with Liquid Scintillation Counting to reverify the previously reported values used in this study to find updated gamma-ray branching ratio values.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Short-Range Mechanisms in the Creation of a ZnO/InGaAs Interface

Here we perform quantitative analysis of the X-ray absorption data taken in situ during the earliest cycles of the ZnO atomic layer deposition on atomically flat InGaAs (001) surfaces. As deposition progresses, we observe a transition from an amorphous structure to a nanocrystalline one. The former retains much of the characteristics of a ZnO crystal in the Zn coordination shell, while the latter shows atomic ordering up to at least the third neighbor shell of Zn atoms, despite the absence of Bragg X-ray diffraction peaks. We show that the different chemical preparation of the substrate surface affects the ZnO local structure and that, counterintuitively, a stronger short-range order is obtained in the nanostructures characterized by lower local order at the interface. We propose a model that accounts for these findings.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Electronic Polarization on the Spectral Density

Accurate spectral densities are necessary for computing realistic exciton dynamics and nonlinear optical spectra of chromophores in condensed-phase environments, including multichromophore pigment–protein systems. However, due to the significant computational cost of computing spectral densities from first principles, requiring many thousands of excited-state calculations, most simulations of realistic systems rely on treating the environment as fixed-point charges. In this work, using a number of representative systems ranging from solvated chromophores to the photoactive yellow protein (PYP), we demonstrate that the quantum mechanical (QM) electronic polarization of the environment is key to obtaining accurate spectral densities and line shapes within the cumulant framework. We show that the QM environment can enhance or depress the coupling of fast chromophore degrees of freedom to the energy gap, altering the electronic–vibrational coupling and the resulting vibronic progressions in the absorption spectrum. In analyzing the physical origin of peaks in the spectral density, we identify vibrational modes that couple the electron and the hole as being particularly sensitive to the QM screening of the environment. For PYP, we reveal the need for careful determination of the appropriate QM region to obtain reliable spectral densities. Our findings suggest that the QM polarization of the environment can be crucial not just for excitation energies but also for electronic–vibrational coupling in complex systems with implications for the correct modeling of linear and nonlinear optical spectroscopy in the condensed phase as well as energy transfer in pigment–protein complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗