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At least 1,369 records · Page 76

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NASA NTRS2014

Nondestructive Evaluation Techniques for Development and Characterization of Carbon Nanotube Based Superstructures

Recently, multiple commercial vendors have developed capability for the production of large-scale quantities of high-quality carbon nanotube sheets and yarns. While the materials have found use in electrical shielding applications, development of structural systems composed of a high volume fraction of carbon nanotubes is still lacking. A recent NASA program seeks to address this by prototyping a structural nanotube composite with strength-toweight ratio exceeding current state-of-the-art carbon fiber composites. Commercially available carbon nanotube sheets, tapes, and yarns are being processed into high volume fraction carbon nanotube-polymer nanocomposites. Nondestructive evaluation techniques have been applied throughout this development effort for material characterization and process control. This paper will report on the progress of these efforts, including magnetic characterization of residual catalyst content, Raman scattering characterization of nanotube diameter, defect ratio, and nanotube strain, and polarized Raman scattering for characterization of nanotube alignment.

Wincheski, Buzz↗

NASA NTRS1987

Auroral zone field-aligned currents observed in the magnetotail and at intermediate altitudes - An ISEE perspective

The relationship between low-altitude auroral-zone field-aligned currents and the geomagnetic tail is investigated on the basis of a statistical analysis of ISEE and DE observations. The data are compiled in diagrams and graphs and characterized in detail. It is shown that the large-scale current systems of low-altitude regions 1 and 2 are only reduplicated in 27 percent of the observations at 2-7 earth radii (those associated with the onset of a substorm expansion), while the flow at the plasma-sheet boundary opposes the region 1 polarity (the highest-latitude near-midnight currents being directed earthward).

Elphic, R. C.↗

NASA NTRS1976

Examples of plasma flows within the earth's magnetosphere

Examples of observed plasma flows in the dayside magnetosphere near the magnetopause, within the ring current in the local evening sector, and at two positions simultaneously in the plasma sheet are presented. These measurements were gained with plasma instruments on the IMP 6 and 7 satellites. Flow velocities inside the magnetopause in the dayside magnetosphere are typically 25 to 75 km/s and are directed generally parallel to the tangent to the nearby magnetopause with a small component directed into this boundary. Bulk flow speeds within the ring current ranged from the instrument threshold of about 20 km/s to speeds of 50 km/s. Strong tailward 'jetting' of plasma, in the range of 200 to 300 km/s, at geocentric radial distances of about 35 earth radii in the plasma sheet is found to be often associated with the occurrence of magnetic substorms.

Frank, L. A.↗

NASA NTRS1992

Excitation of Pc 5 pulsations in the morning sector by a local injection of particles in the magnetosphere

A characteristic of Pc 5 pulsation in the morning sector is determined by use of ground magnetometer and riometer data, in conjunction with data acquired with satellites which include the magnetic fields above the ionosphere and electron fluxes at geosynchronous orbit. It is found that the onset of a flux increase in energetic electrons of 30 keV to 200 keV at geosynchronous orbit almost coincides with the onset of Pc 5 pulsation activity and riometer absorption on the ground. It is confirmed when the Pc 5 pulsation occurs on the ground, the large-scale Birkeland current system observed at ionospheric altitude splits into a number of small-scale Birkeland current pairs. It is inferred that the electron flux enhancement, presumably supplied from the tail plasma sheet associated with the substorm onset, provides stress to cause the background large-scale plasma vortex to split into the small-scale vortices. It is suggested that the field-aligned currents in the small-scale vortices propagate along the field lines and sustain the standing Alfvenic oscillations at several different, but neighboring shells of the field lines.

Saka, O.↗

NASA NTRS2002

Self-Consistent Magnetosphere-Ionosphere Coupling and Associated Plasma Energization Processes

Magnetosphere-Ionosphere (MI) coupling and associated with this process electron and ion energization processes have interested scientists for decades and, in spite of experimental and theoretical research efforts, are still ones of the least well known dynamic processes in space plasma physics. The reason for this is that the numerous physical processes associated with MI coupling occur over multiple spatial lengths and temporal scales. One typical example of MI coupling is large scale ring current (RC) electrodynamic coupling that includes calculation of the magnetospheric electric field that is consistent with the ring current (RC) distribution. A general scheme for numerical simulation of such large-scale magnetosphere-ionosphere coupling processes has been presented earlier in many works. The mathematical formulation of these models are based on "modified frozen-in flux theorem" for an ensemble of adiabatically drifting particles in the magnetosphere. By tracking the flow of particles through the inner magnetosphere, the bounce-averaged phase space density of the hot ions and electrons can be reconstructed and the magnetospheric electric field can be calculated such that it is consistent with the particle distribution in the magnetosphere. The new a self-consistent ring current model has been developed that couples electron and ion magnetospheric dynamics with calculation of electric field. Two new features were taken into account in addition to the RC ions, we solve an electron kinetic equation in our model, self-consistently including these results in the solution. Second, using different analytical relationships, we calculate the height integrated ionospheric conductances as the function of precipitated high energy magnetospheric electrons and ions as produced by our model. This results in fundamental changes to the electric potential pattern in the inner magnetosphere, with a smaller Alfven boundary than previous potential formulations would predict but one consistent with recent satellite observations. This leads to deeper penetration of the plasma sheet ions and electrons into the inner magnetosphere and more effective ring current ions and electron energization.

Khazanov, G. V.↗

DOE OSTI2022

The contribution of Humboldt Glacier, northern Greenland, to sea-level rise through 2100 constrained by recent observations of speedup and retreat

Abstract. Humboldt Glacier, northern Greenland, has retreated and accelerated through the 21st century, raising concerns that it could be a significant contributor to future sea-level rise. We use a data-constrained ensemble of three-dimensional higher-order ice sheet model simulations to estimate the likely range of sea-level rise from the continued retreat of Humboldt Glacier. We first solve for basal traction using observed ice thickness, bed topography, and ice surface velocity from the year 2007 in a PDE-constrained (partial differential equation) optimization. Next, we impose calving rates to match mean observed retreat rates from winter 2007–2008 to winter 2017–2018 in a transient calibration of the exponent in the power-law basal friction relationship. We find that power-law exponents in the range of 1/7–1/5 – rather than the commonly used 1/3–1 – are necessary to reproduce the observed speedup over this period. We then tune an iceberg calving parameterization based on the von Mises stress yield criterion in another transient-calibration step to approximate both observed ice velocities and terminus position in 2017–2018. Finally, we use the range of basal friction relationship exponents and calving parameter values to generate the ensemble of model simulations from 2007–2100 under three climate forcing scenarios from CMIP5 (two RCP8.5 forcings, Representative Concentration Pathway) and CMIP6 (one SSP5-8.5 forcing, Shared Socioeconomic Pathway). Our simulations predict 5.2–8.7 mm of sea-level rise from Humboldt Glacier, significantly higher than a previous estimate (∼ 3.5 mm) and equivalent to a substantial fraction of the 40–140 mm predicted by ISMIP6 from the whole Greenland Ice Sheet. Our larger future sea-level rise prediction results from the transient calibration of our basal friction law to match the observed speedup, which requires a semi-plastic bed rheology. In many simulations, our model predicts the growth of a sizable ice shelf in the middle of the 21st century. Thus, atmospheric warming could lead to more retreat than predicted here if increased surface melt promotes hydrofracture of the ice shelf. Our data-constrained simulations of Humboldt Glacier underscore the sensitivity of model predictions of Greenland outlet glacier response to warming to choices of basal shear stress and iceberg calving parameterizations. Further, transient calibration of these parameterizations, which has not typically been performed, is necessary to reproduce observed behavior. Current estimates of future sea-level rise from the Greenland Ice Sheet could, therefore, contain significant biases.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2024

Quantum octets in high mobility pentagonal two-dimensional PdSe 2

Two-dimensional (2D) materials have drawn immense interests in scientific and technological communities, owing to their extraordinary properties and their tunability by gating, proximity, strain and external fields. For electronic applications, an ideal 2D material would have high mobility, air stability, sizable band gap, and be compatible with large scale synthesis. Here we demonstrate air stable field effect transistors using atomically thin few-layer PdSe 2 sheets that are sandwiched between hexagonal BN (hBN), with large saturation current > 350 μA/μm, and high field effect mobilities of ~ 700 and 10,000 cm 2 /Vs at 300 K and 2 K, respectively. At low temperatures, magnetotransport studies reveal unique octets in quantum oscillations that persist at all densities, arising from 2-fold spin and 4-fold valley degeneracies, which can be broken by in-plane and out-of-plane magnetic fields toward quantum Hall spin and orbital ferromagnetism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Preliminary Screening of Features, Events, and Processes for an Arctic-Focused Climate Intervention Performance Assessment

Geoengineering, the deliberate large-scale intervention in Earth's climate system, holds significant potential in the rapidly warming Arctic, where temperatures currently rise at more than twice the global average, accelerating ice sheet and permafrost melt. This contributes to global sea-level rise and releases methane, a potent greenhouse gas. Strategies like solar radiation management (SRM) and carbon dioxide removal (CDR) could mitigate these effects; for instance, SRM techniques aim to reflect a portion of the sun's energy back into space, potentially slowing ice melt and stabilizing permafrost. However, geoengineering in the Arctic faces challenges, including potential unintended consequences on the fragile ecosystem, disruption of local weather patterns, and impacts on indigenous communities. Effective governance requires robust international cooperation, environmental impact assessments, and regulatory frameworks. Despite these challenges, geoengineering's potential benefits make it a critical research area. This report explores application of the Performance Assessment (PA) methodology to Arctic Climate Intervention, providing an initial screening of relevant features, events, and processes (FEPs). At the core of the PA approach is the identification and evaluation of FEPs that could impact the performance of the intervention scheme. Here we provide an initial screening of FEPs to consider in the application of PA to Arctic Climate Intervention.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1973

The magnetotail and substorms

The tail plays a very active and important role in substorms. Magmetic flux eroded from the dayside magnetosphere is stored here. As more and more flux is transported to the magnetotail and stored, the boundary flares more, the field strength in the tail increases, and the currents strengthen and move closer to the earth. Further, the plasma sheet thins and the magnetic flux crossing the neutral sheet lessens. The experimental evidence for these processes is discussed and a phenomenological or qualitative model of the substorm sequence is presented. In this model, the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields. During the growth phase of substorms the merging rate on the dayside magnetosphere exceeds the reconnection rate in the neutral sheet.

Russell, C. T.↗

NASA NTRS1979

A study of trends and techniques for space base electronics

The use of dry processing and alternate dielectrics for processing wafers is reported. A two dimensional modeling program was written for the simulation of short channel MOSFETs with nonuniform substrate doping. A key simplifying assumption used is that the majority carriers can be represented by a sheet charge at the silicon dioxide-silicon interface. In solving current continuity equation, the program does not converge. However, solving the two dimensional Poisson equation for the potential distribution was achieved. The status of other 2D MOSFET simulation programs are summarized.

Trotter, J. D.↗

NASA NTRS1987

Electron/ion whistler instabilities and magnetic noise bursts

Two whistler instabilities are investigated by means of the linear Vlasov dispersion equation. They are called the electron/ion parallel and oblique whistler instabilities, and are driven by electron/ion relative drifts along the magnetic field. It is demonstrated that the enhanced fluctuations from these instabilities can explain several properties of magnetic noise bursts in and near the plasma sheet in the presence of ion beams and/or field-aligned currents. At sufficiently high plasma beta, these instabilities may affect the current system in the magnetotail.

Akimoto, K.↗

NASA NTRS1990

On the structure of the tail magnetic field

The configuration of the magnetic field in the Earth's geomagnetic tail is studied. The results in the lobe region and in the plasma sheet boundary layer region are compared. A systematic enhancement of the By component of the field is detected in the plasma sheet boundary layer with respect to the lobe; this enhancement leads to a lower rate of flaring of the magnetic field lines in the lobe with respect to the plasma sheet boundary layer. This observation is a signature of field aligned currents at the boundary. The direction of such field aligned currents agrees with the nightside region two current system.

Candidi, M.↗

NASA NTRS1991

Applications of the conjugate gradient FFT method in scattering and radiation including simulations with impedance boundary conditions

The theoretical and computational aspects related to the application of the Conjugate Gradient FFT (CGFFT) method in computational electromagnetics are examined. The advantages of applying the CGFFT method to a class of large scale scattering and radiation problems are outlined. The main advantages of the method stem from its iterative nature which eliminates a need to form the system matrix (thus reducing the computer memory allocation requirements) and guarantees convergence to the true solution in a finite number of steps. Results are presented for various radiators and scatterers including thin cylindrical dipole antennas, thin conductive and resistive strips and plates, as well as dielectric cylinders. Solutions of integral equations derived on the basis of generalized impedance boundary conditions (GIBC) are also examined. The boundary conditions can be used to replace the profile of a material coating by an impedance sheet or insert, thus, eliminating the need to introduce unknown polarization currents within the volume of the layer. A general full wave analysis of 2-D and 3-D rectangular grooves and cavities is presented which will also serve as a reference for future work.

Barkeshli, Kasra↗

NASA NTRS1991

Electric fields in the solar atmosphere - A review

A review is presented of remote sensing techniques which measure the electric field component transverse to the line of sight and achieve a sensitivity range of 5-10 V/cm. Three models are shown to predict quasistatic, macroscopic values of E(parallel), the electric field component parallel to the magnetic vector, beyond the sensitivity range considered. These processes are: the discharge model of flares; the models of return currents related to flare particle beams; and the models of neutral sheets related to two-ribbon flares and postflare loops. Time dependent electric fields related to MHD and plasma waves, and to plasma disturbance, may allow the detection of both E components (parallel and perpendicular). The uncertainty relating to the emission measures, time scales, volumes, and plasma conditions of these flares and electrified plasma volumes is emphasized. It is pointed out, however, that important information can be obtained by observing electric fields at existing sensitivity levels. By measuring these E-fields, the understanding of flares and related dynamic events can be improved.

Foukal, P.↗

NASA NTRS1994

Satellite measurements through the center of a substorm surge

Measurements have been made of electric and magnetic fields, plasma drifts, and electron precipatation within a surge at the westward, leading edge of the auroral 'bulge' at the peak of the substorm expansion phase. The trajectroy of the Dynamics Explorer 2 (DE 2) satellite over the auroral emissions is determined from nearly simultaneous observations with the imager on the DE 1 satellite at a higher altitude. The electric field and plasma drift measurements have enabled us to deduce the basic configuration of the ionospheric electric potential, or plasma convection, around the surge. The electric potential shows that the bulge is associated with a protrusion of the dawn convection cell into the dusk cell, poleward of the 'Harang discontinity.' This protrusion conains a westward electric field that strongly enhances the westard electrojet current by the creation of a "Cowling channel.' This westward electric field, and the associated Cowling current, appear to terminate within the surge, which contains an intense, upward field-aligned current. The magneitc field measurements show that the region containing this field-aligned current is shaped more like a cylinger rather than a long sheet. The total is found to exceed one-half million amperes.

Weimer, D. R.↗

NASA NTRS1982

Advanced Welding Tool

Accutron Tool & Instrument Co.'s welder was originally developed as a tool specifically for joining parts made of plastic or composite materials in any atmosphere to include the airless environment of space. Developers decided on induction or magnetic heating to avoid causing deformation and it also can be used with almost any type of thermoplastic material. Induction coil transfers magnetic flux through the plastic to a metal screen that is sandwiched between the sheets of plastic to be joined. When welder is energized, alternating current produces inductive heating on the screen causing the adjacent plastic surfaces to melt and flow into the mesh, creating a bond on the total surface area. Dave Brown, owner of Great Falls Canoe and Kayak Repair, Vienna, VA, uses a special repair technique based on operation of the Induction Toroid Welder to fix canoes. Whitewater canoeing poses the problem of frequent gashes that are difficult to repair. The main reason is that many canoes are made of plastics. The commercial Induction model is a self-contained, portable welding gun with a switch on the handle to regulate the temperature of the plastic melting screen. Welder has a broad range of applications in the automobile, appliance, aerospace and construction industries.

Source record↗

NASA NTRS2008

NASA Tech Briefs, August 2008

Customizable Digital Receivers for Radar Two-Camera Acquisition and Tracking of a Flying Target Visual Data Analysis for Satellites A Data Type for Efficient Representation of Other Data Types Hand-Held Ultrasonic Instrument for Reading Matrix Symbols Broadband Microstrip-to-Coplanar Strip Double-Y Balun A Topographical Lidar System for Terrain-Relative Navigation Programmable Low-Voltage Circuit Breaker and Tester Electronic Switch Arrays for Managing Microbattery Arrays Topics covered include: Lower-Dark-Current, Higher-Blue-Response CMOS Imagers; Fabricating Large-Area Sheets of Single-Layer Graphene by CVD; Support for Diagnosis of Custom Computer Hardware; Providing Goal-Based Autonomy for Commanding a Spacecraft; Dynamic Method for Identifying Collected Sample Mass; Optimal Planning and Problem-Solving; Attitude-Control Algorithm for Minimizing Maneuver Execution Errors; Grants Document-Generation System; Heat-Storage Modules Containing LiNO3 3H2O and Graphite Foam; Precipitation-Strengthened, High-Temperature, High-Force Shape Memory Alloys; Improved Relief Valve Would Be Less Susceptible to Failure; Safety Modification of Cam-and-Groove Hose Coupling; Using Composite Materials in a Cryogenic Pump; Using Electronic Noses to Detect Tumors During Neurosurgery; Producing Newborn Synchronous Mammalian Cells; Smaller, Lower-Power Fast-Neutron Scintillation Detectors; Rotationally Vibrating Electric-Field Mill; Estimating Hardness from the USDC Tool-Bit Temperature Rise; Particle-Charge Spectrometer; Automated Production of Movies on a Cluster of Computers; FIDO-Class Development Rover; and Tone-Based Command of Deep Space Probes Using Ground Antennas.

Source record↗

NASA NTRS1981

Broadband electrostatic noise and field-aligned currents in Jupiter's middle magnetosphere

Voyager 1 plasma wave observations have revealed the presence of an impulsive electrostatic emission localized to the Jovian middle magnetosphere that appears on the edges of the plasma sheet. This plasma mode has the same spectral and morphological characteristics of an emission that has been extensively studied in the earth's magnetosphere and has been associated with the presence of field-aligned currents. The results of a detailed study of the properties of this Jovian emission are presented by using comparisons with terrestrial observations as a basis for mode identification. The occurrence regions of the waves are compared with the measured magnetic field configuration to establish a correspondence with the plasma sheet. It is argued that this is a quasi-permanent global system of field-aligned currents linking the ionosphere of Jupiter to the middle magnetosphere, which powers energetic plasma heating processes occurring there. On the basis of knowledge of the consequences of field-aligned currents in the terrestrial magnetosphere, a scenario for acceleration/precipitation of inverted V electrons, concomitant aurorae, and energetic (approximately 10 keV) proton deposition into the middle magnetosphere resulting from field-aligned potential drops associated with this current system is suggested.

Barbosa, D. D.↗