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NASA NTRS1985

An experimental and computational study of turbulent boundary layers in oscillating flows

An experimental-computational study of the behavior of turbulent boundary layers for oscillating air flows over a plane surface with a small favorable mean pressure gradient is described. Experimental data were obtained for boundary layers generated on the test section wall of a new type of facility that produces a mean flow velocity with a superposed sinusoidal component over a wide frequency range. Experimental results for unsteady velocity profiles and turbulence intensity obtained from hot wire measurements at a fixed stream-wise position on the surface are presented for frequencies ranging from 5 to 21 Hz. Numerical predictions were obtained using an unsteady boundary layer computational code and the Cebeci-Smith and Glushko turbulence models. Predicted quantities related to unsteady velocity profiles exhibit fair agreement with experiment when the Cebeci-Smith model is used.

Cook, W. J.↗

NASA NTRS2020

Representation of Tropical Storms by the Modern-Era Retrospective Analysis for Research and Applications Version 2

This study examines the veracity of the tropical cyclone (TC) statistics estimated from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) global atmospheric reanalysis, focusing on the climatological-mean genesis regions, tracks and their lifetime maximum intensity, as well as the interannual and intraseasonal variations in TC activity. The results are validated against the International Best Track Archive for Climate Stewardship (IBTrACS) data for 1980-2016. MERRA-2 represents the spatial distribution of the TC genesis location and the tracks realistically well over all main development regions (MDRs), but with notable discrepancies including too weak TC activity over the Arabian Sea and the South China Sea and too strong activity over the North Indian Ocean. Over the western North Pacific and the North Atlantic, MERRA-2 underestimates recurving TCs steered by background westerlies in the mid-latitudes and thereby exaggerates northwestward moving TCs, resulting in an overestimate of the landfall probability in East Asia and North America. Excessive development of TCs over the Bay of Bengal also tends to exaggerate the landfall probability in India. In spite of the discrepancies in the annual TC number, the seasonal variation of TC genesis is realistic in MERRA-2. MERRA-2 also captures the TC intensity relationship between the minimum pressure and the maximum surface wind speed at the mature stage, although the maximum intensity is weaker than in the observations. While MERRA-2 tends to reproduce the interannual variations of the observed TC number and the power dissipation index (PDI), the level of accuracy depends on the region. MERRA-2 describes the changes in the TC genesis region and tracks realistically according to the different phases of El Nino and the Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO), although it is less realistic over the North Indian Ocean.

International Best Track Archive for Climate Stewa↗

DOE OSTI2024

Truncated nonlinear interferometer-based sensor system

A truncated non-linear interferometer-based sensor system includes an input port that receives an optical beam and a non-linear amplifier that amplifies the optical beam with a pump beam and renders a probe beam and a conjugate beam. The system's local oscillators have a relationship with the respective beams. The system includes a sensor that transduces an input with the probe beam and the conjugate beam or their respective local oscillators. It includes one or more phase-sensitive detectors that detect a phase modulation between the respective local oscillators and the probe beam and the conjugate beam. Output from the phase-sensitive-detectors is based on the detected phase modulation. The phase-sensor-detectors include measurement circuitry that measure the phase signals. The measurement is the sum or difference of the phase signals in which the measured combination exhibit a quantum noise reduction in an intensity difference or a phase sum or an amplitude difference quadrature.

Pooser, Raphael C.↗

DOE OSTI2023

Principles and applications of x-ray light sources driven by laser wakefield acceleration

One of the most prominent applications of modern particle accelerators is the generation of radiation. In a synchrotron or an x-ray free electron laser (XFEL), high energy electrons oscillating in periodic magnetic structures emit bright x rays. In spite of their scientific appeal that will remain evident for many decades, one limitation of synchrotrons and XFELs is their typical mile-long size and their cost, which often limits access to the broader scientific community. Here, this tutorial reviews the principles and prospects of using plasmas produced by intense lasers as particle accelerators and x-ray light sources, as well as some of the applications they enable. A plasma is an ionized medium that can sustain electrical fields many orders of magnitude higher than that in conventional radio frequency accelerator structures and can be used to accelerate electrons. When short, intense laser pulses are focused into a gas, it produces electron plasma waves in which electrons can be trapped and accelerated to GeV energies. This process, laser-wakefield acceleration (LWFA), is analogous to a surfer being propelled by an ocean wave. Many radiation sources, from THz to gamma-rays, can be produced by these relativistic electrons. This tutorial reviews several LWFA-driven sources in the keV-MeV photon energy range: betatron radiation, inverse Compton scattering, bremsstrahlung radiation, and undulator/XFEL radiation. X rays from laser plasma accelerators have many emerging applications. They can be used in innovative and flexible x-ray imaging and x-ray absorption spectroscopy configurations, for use in biology, industry, and high-energy density science.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Förster Resonance Energy Transfer and Enhanced Emission in Cs 4 PbBr 6 Nanocrystals Encapsulated in Silicon Nano-Sheets for Perovskite Light Emitting Diode Applications

Encapsulating Cs 4 PbBr 6 quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated Cs 4 PbBr 6 ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from Cs 4 PbBr 6 pseudo-spherical quantum dots is quenched and is dominated with Pb 2+ ion/silicene emission, which is very stable during the whole measurement period. For a high concentration of Cs 4 PbBr 6 ellipsoidal nanocrystals in silicon nano-sheets, we have observed Förster resonance energy transfer with up to 87% efficiency through the oscillation of two PL peaks when UV excitation switches between on and off, using recorded video and PL lifetime measurements. In an area of a non-uniform sample containing both ellipsoidal nanocrystals and pseudo-spherical quantum dots, where Pb 2+ ion/silicene emissions, broadband emissions from quantum dots, and bandgap edge emissions (515 nm) appear, the 515 nm peak intensity increases five times over 30 min of UV excitation, probably due to a photon recycling effect. This irradiated sample has been stable for one year of ambient storage. Cs 4 PbBr 6 quantum dots encapsulated in silicon nano-sheets can lead to applications of halide perovskite light emitting diodes (PeLEDs) and integration with traditional semiconductor materials.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Photophysical Properties and Electronic Structure of Zinc(II) Porphyrins Bearing 0–4 meso -Phenyl Substituents: Zinc Porphine to Zinc Tetraphenylporphyrin (ZnTPP)

Six zinc(II) porphyrins bearing 0–4 meso-phenyl substituents have been examined spectroscopically and theoretically. Comparisons with previously examined free base analogues afford a deep understanding of the electronic and photophysical effects of systematic addition of phenyl groups in porphyrins containing a central zinc(II) ion versus two hydrogen atoms. Trends in the wavelengths and relative intensities of the absorption bands are generally consistent with predictions from time-dependent density functional theory calculations and simulations from Gouterman’s four-orbital model. These trends derive from a preferential effect of the meso-phenyl groups to raise the energy of the highest occupied molecular orbital. The calculations reveal additional insights, such as a progressive increase in oscillator strength in the violet-red (B-Q) absorption manifold with increasing number of phenyls. Progressive addition of 0–4 phenyl substituents to the zinc porphyrins in O 2 -free toluene engenders a reduction in the measured lifetime of the lowest singlet excited state (2.5–2.1 ns), an increase in the S 1 → S o fluorescence yield (0.022–0.030), a decrease in the yield of S 1 → T 1 intersystem crossing (0.93–0.88), and an increase in the yield of S 1 → S o internal conversion (0.048–0.090). The derived rate constants for S 1 decay reveal significant differences in the photophysical properties of the zinc chelates versus free base forms. Here, the unexpected finding of a larger rate constant for internal conversion for zinc chelates versus free bases is particularly exemplary. Collectively, the findings afford fundamental insights into the photophysical properties and electronic structure of meso-phenylporphyrins, which are widely used as benchmarks for tetrapyrrole-based architectures in solar energy and life sciences research.

14 SOLAR ENERGY↗

NASA NTRS1995

(abstract) Vibration Damping of the Cassini Spacecraft Structure

Cassini will be protected during launch ascent through the atmosphere by a lightweight aluminum payload fairing (PLF). As a result of the extreme noise levels generated by the powerful Titan IV at liftoff, and the acoustic transparency of the PLF, Cassini is predicted to experience severe acoustic levels. Furthermore, the high acoustic levels, coupled with the size and configuration of the spacecraft, will induce intense random vibration on the structure and critical spacecraft components. Efforts to mitigate the vibroacoustic environment by modifying the spacecraft structure were pursued. Preliminary studies indicated that a structural damping treatment using viscoelastic materials (VEMs) represented a viable technique of reducing vibration with minimum impact on weight, cost, and redesign. Tuned Vibration Absorbers (TVAs) - compact, single degree-of-freedom mechanical oscillators in which a VEM serves as the spring and damping element - will be used also. The operating principles, design, and installation of the TVAs are described, the test program is outlined, and test results are presented which show that significant vibration attenuation was achieved.

vibroacoustic environment↗

NASA NTRS2018

Southeast Greenland Winter Precipitation Strongly Linked to the Icelandic Low Position

Greenland's largest precipitation flux occurs in its southeast (SE) region during the winter, controlled primarily by easterly winds and frequent cyclogenesis in the North Atlantic. Several studies have attempted to link SE Greenland precipitation to the North Atlantic Oscillation (NAO) but results are inconsistent. This work uses reanalysis, automatic weather station data, and regional climate model output to show that the east-west position of the Icelandic low is a better predictor of SE Greenland precipitation (average correlation of r equals -0.48 in DJF (December January February)) than climate indices such as the NAO (r equals -0.06 in DJF). In years when the Icelandic low is positioned extremely west, moisture transport increases up to approximately 40 percent (or up to 40 kilograms per meter per second) off the SE Greenland coast compared to when the low is in an extreme east position. Furthermore, in years when the Icelandic low is positioned extremely west, storm track density and intensity increase just off the SE coast of Greenland. Thus, the Icelandic low's longitudinal position dominates SE Greenland ice sheet's wintertime precipitation, a positive term in the ice sheet mass balance. Given SE Greenland's importance in the overall ice sheet mass balance, the position of the Icelandic low is therefore important for making projections of future sea level.

Arctic↗

DOE OSTI2025

Neutrino Physics at a Muon Collider, and the Neutrino Kaleidoscope

Muon accelerators, a potential technology for enabling O(10 TeV) parton center of mass energy collisions, would also source an intense, collimated beam of neutrinos at TeV energies. There is currently a renewed effort to understand the possible scientific reach of such a neutrino beam in the context of neutrino physics. One possibility is the “Neutrino Kaleidoscope”: the pairing of a muon accelerator neutrino flux with a neutrino telescope detector. In particular, such a pairing would enable searches for non-standard oscillations of the beam neutrinos as they traverse the earth between source and detector. These non-standard neutrino oscillations could be sourced by Lorentz invariance violation, which a neutrino kaleidoscope could probe up to the quantum gravity-motivated Planck scale. Such a search would also have a reach on sterile neutrinos orders of magnitude beyond existing terrestrial limits. In this talk, I will introduce some of the exciting measurements being proposed with the neutrinos from a muon accelerator and then go into detail on the Neutrino Kaleidoscope concept (arxiv:2508.09249).

Putnam, Gray [Fermilab]↗

NASA NTRS2014

Variable Acceleration Force Calibration System (VACS)

Conventionally, force balances have been calibrated manually, using a complex system of free hanging precision weights, bell cranks, and/or other mechanical components. Conventional methods may provide sufficient accuracy in some instances, but are often quite complex and labor-intensive, requiring three to four man-weeks to complete each full calibration. To ensure accuracy, gravity-based loading is typically utilized. However, this often causes difficulty when applying loads in three simultaneous, orthogonal axes. A complex system of levers, cranks, and cables must be used, introducing increased sources of systematic error, and significantly increasing the time and labor intensity required to complete the calibration. One aspect of the VACS is a method wherein the mass utilized for calibration is held constant, and the acceleration is changed to thereby generate relatively large forces with relatively small test masses. Multiple forces can be applied to a force balance without changing the test mass, and dynamic forces can be applied by rotation or oscillating acceleration. If rotational motion is utilized, a mass is rigidly attached to a force balance, and the mass is exposed to a rotational field. A large force can be applied by utilizing a large rotational velocity. A centrifuge or rotating table can be used to create the rotational field, and fixtures can be utilized to position the force balance. The acceleration may also be linear. For example, a table that moves linearly and accelerates in a sinusoidal manner may also be utilized. The test mass does not have to move in a path that is parallel to the ground, and no re-leveling is therefore required. Balance deflection corrections may be applied passively by monitoring the orientation of the force balance with a three-axis accelerometer package. Deflections are measured during each test run, and adjustments with respect to the true applied load can be made during the post-processing stage. This paper will present the development and testing of the VASC concept.

Rhew, Ray D.↗

NASA NTRS2020

Revisiting the Relationship between Atlantic Dust and Tropical Cyclone Activity using Aerosol Optical Depth Reanalyses: 2003-2018

Previous studies have noted a relationship between African dust and Atlantic tropical cyclone (TC) activity. However, due to the limitations of past dust analyses, the strength of this relationship remains uncertain. The emergence of aerosol reanalyses, including the Navy Aerosol Analysis and Prediction System (NAAPS) aerosol optical depth (AOD) reanalysis, NASA Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), and ECMWF Copernicus Atmosphere Monitoring Service reanalysis (CAMSRA), enables an investigation of the relationship between African dust and TC activity over the tropical Atlantic and Caribbean in a consistent temporal and spatial manner for 2003–2018. Although June–July–August (JJA) 550 nm dust AOD (DAOD) from all three reanalysis products correlates significantly over the tropical Atlantic and Caribbean, the difference in DAOD magnitude between products can be as large as 60 % over the Caribbean and 20 % over the tropical North Atlantic. Based on the three individual reanalyses, we have created an aerosol multi-reanalysis consensus (MRC). The MRC presents overall better root mean square error over the tropical Atlantic and Caribbean compared to individual reanalyses when verified with ground-based AErosol RObotic NETwork (AERONET) AOD measurements. Each of the three individual reanalyses and the MRC have significant negative correlations between JJA Caribbean DAOD and seasonal Atlantic accumulated cyclone energy (ACE), while the correlation between JJA tropical North Atlantic DAOD and seasonal ACE is weaker. Possible reasons for this regional difference are provided. A composite analysis of 3 high-JJA-Caribbean-DAOD years versus 3 low-JJA-Caribbean-DAOD years reveals large differences in overall Atlantic TC activity. We also show that JJA Caribbean DAOD is significantly correlated with large-scale fields associated with variability in interannual Atlantic TC activity including zonal wind shear, mid-level moisture, and sea surface temperature (SST), as well as the El Niño–Southern Oscillation (ENSO) and the Atlantic Meridional Mode (AMM), implying confounding effects of these factors on the dust–TC relationship. We find that seasonal Atlantic DAOD and the AMM, the leading mode of coupled Atlantic variability, are inversely related and intertwined in the dust–TC relationship. Overall, DAOD in both the tropical Atlantic and Caribbean is negatively correlated with Atlantic hurricane frequency and intensity, with stronger correlations in the Caribbean than farther east in the tropical North Atlantic.

Dust particles↗

NASA NTRS1988

Solar magnetic field studies using the 12 micron emission lines. I - Quiet sun time series and sunspot slices

The use of the extremely Zeeman-sensitive IR emission line Mg I, at 12.32 microns, to study solar magnetic fields. Time series observations of the line in the quiet sun were obtained in order to determine the response time of the line to the five-minute oscillations. Based upon the velocity amplitude and average period measured in the line, it is concluded that it is formed in the temperature minimum region. The magnetic structure of sunspots is investigated by stepping a small field of view in linear 'slices' through the spots. The region of penumbral line formation does not show the Evershed outflow common in photospheric lines. The line intensity is a factor of two greater in sunspot penumbrae than in the photosphere, and at the limb the penumbral emission begins to depart from optical thinness, the line source function increasing with height. For a spot near disk center, the radial decrease in absolute magnetic field strength is steeper than the generally accepted dependence.

Deming, Drake↗

NASA NTRS1994

The Global Oscillation Network Group site survey, 2: Results

The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile. Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable networks assembled from the individual site records is compared using a statistical principal components analysis. An accompanying paper descibes the analysis methods in detail; here we present the results of both the network and individual site analyses. The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 x 10(exp -4) with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum.

Hill, Frank↗

DOE OSTI2020

High sensitivity pump–probe measurements of magnetic, thermal, and acoustic phenomena with a spectrally tunable oscillator

We describe an optical pump/probe system for sensitive measurements of time-resolved optical measurements of material dynamics. The instrument design is optimized for time-resolved magneto-optic Kerr effect (TR-MOKE) measurements of dynamics in magnetic materials. The system also allows for time-domain thermoreflectance (TDTR) measurements of thermal transport properties and picosecond acoustic measurements of film thickness and/or elastic constants. The system has several advantages over the conventional designs for TRMOKE and/or TDTR systems. Measurements of pump-induced changes to the probe beam intensity are shot-noise limited. The system’s design allows for MOKE and/or thermoreflectance measurements of both sides of a sample. Pumping and probing the sample on opposite sides allows nanoscale flash diffusivity measurements of transport properties. The wavelengths of the pump and probe beams are straightforward to tune between 350–525 nm and 690–1050 nm. A tunable wavelength allows for optical resonances in a wide array of materials to be excited and/or probed. Finally, the setup is calibrated to allow for the real and imaginary components of Kerr signals to be separately quantified.

47 OTHER INSTRUMENTATION↗

NASA NTRS1974

Nonlinear gas oscillations in pipes. II - Experiment

The problem of forced acoustic oscillations in a pipe was experimentally investigated, taking into account the response of both open and closed tubes to near-resonant excitation by large amplitude oscillations of a piston at one end of the tube. Attention was given to the effect of the orifice area on shock waves. By comparing the experimental results with nonlinear theory, wave reflection coefficients of the orifice plates were determined at both closed-tube and open-tube resonant frequencies. This approach can even be used when the terminating elements are subjected to intense periodic pressure pulses.

Sturtevant, B.↗

NASA NTRS1992

Plasma wave observations at Neptune

Phenomena detected by the plasma wave instrument during the Voyager 2 flyby of Neptune are reviewed. Particular attention given to radio emissions, electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic electron cyclotron waves and upper hybrid resonance (UHR) waves, whistler mode noise, and dust impacts. The radio emissions which occur in a broad range of about 5 to 50 kHz are considered to be generated by mode conversion from UHR waves at the magnetic equator. The inner magnetosphere has relatively low plasma wave intensities (less than 100 microV/m). Many small micron-sized dust particles which were detected striking the spacecraft had the maximum impact rate of about 280 impacts per sec at the bound ring plane crossing, and about 110 impacts per sec at the outbound ring plane crossing. Most of the particles were concentrated in a dense disk, about one thousand km thick, near the equatorial plane.

Gurnett, D. A.↗

NASA NTRS1998

A Broad-band Spectral and Timing Study of the X-Ray Binary System Centaurus X-3

This dissertation describes a multi-mission investigation of the high mass X-ray binary pulsar Centaurus X-3. Cen X-3 was observed with the Broad Band X-Ray Telescope (BBXRT) in December 1990. This was the first high-resolution solid state X-ray spectrometer to cover the iron K fluorescence region. The Fe K emission feature was resolved into two components for the first time. A broad 6.7 keV feature was found to be a blend of lines from Fe XXI-Fe XXVI with energies ranging from 6.6 to 6.9 keV due to photoionization of the companion's stellar wind. A narrow line at 6.4 keV due to fluorescence of iron in relatively low ionization states was also found. The quasi-periodic oscillations (QPO) at about 40 mHz were used to estimate the surface magnetic field of Cen X-3 as approx. 2.6 x 10(exp 12) G and to predict that there should be a cyclotron scattering resonance absorption feature (CSRF) near 30 keV. In order to further resolve the iron line complex and to investigate the pulse-phase dependence of the iron line intensities, Cen X-3 was observed with the Advanced Satellite for Cosmology and Astrophysics (ASCA). Using ASCA's state-of-the-art non-dispersive X-ray spectrometers the 6.4 keV fluorescent iron line was found to be pulsing while the intensities of the 6.7 and 6.9 keV recombination lines do not vary with pulse phase. This confirms that the 6.4 keV line is due to reflection by relatively neutral matter close to the neutron star while the recombination lines originate in the extended stellar wind. The continuum spectrum was found to be modified by reflection from matter close to the neutron star. Observations with the EXOSAT GSPC were used to search for a CSRF. The EXOSAT spectra were consistent with the presence of a CSRF but an unambiguous detection was not possible because of a lack of sensitivity at energies higher than the cyclotron energy. Cen X-3 was then observed with the Rossi X-Ray Timing Explorer (RXTE) and evidence for a CSRF at 25.1 +/- 0.3 keV was found. This corresponds to a magnetic field of (2.16 +/- 0.03) X 10(exp 12) G and is consistent with the value obtained from the QPO analysis.

Audley, Michael Damian↗

NASA NTRS1998

SRG 1621-47

We have analyzed 9200 s of RXTE pointed observations made on June 26 of SGR 1627-41 (IAUC 6944), which were centered on the possibly-associated supernova remnant G337.0-0.1 (cf. IAUC 6948, 6950). We detected one burst, confirming flux detection from the new source and strengthening the association of the two sources. Power spectral analysis of the observations reveals a quasi-periodic oscillation (QPO) peak centered at 0.15 Hz (about 6.7 s), with a r.m.s. of at least 3.2 percent, depending upon background and source contributions to the signal. Also within the RXTE field-of-view is the black-hole candidate 4U 1630-47, from which QPOs have been observed (IAUC 6823). However, no QPOs near the above frequency have been reported, and the intensity of 1630-47 was low during our observations. Further observations are required to determine which source is the origin of the QPO."

Dieters, Stefan↗