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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The polar wind

The classical polar wind is considered to be an ambipolar outflow of thermal plasma from the terrestrial ionosphere at high latitudes. The paper reviews the characteristic features of this flow, with emphasis placed on recent theoretical predictions. Consideration is given to H(+) and He(+) outflow characteristics both with and without convection electric field effects, the collisionless polar wind characteristics (including the formation of temperature anisotropies), and the time-dependent polar wind behavior in response to localized density perturbations and localized heat sources.

Schunk, R. W.↗
NASA NTRS1991

The effect of the changing polarity and neutral sheet of the IMF on the cosmic ray diurnal anisotropy at neutron monitor energies

A drift with a simulated wavy neutral sheet have been used to study the effects of the reversal of the solar magnetic field every 11 years and the changes in the waviness of the heliospheric neutral sheet, corresponding to changes in solar activity, on the diurnal anisotropy at an energy of 20 GeV. The results indicate that the long-term behavior of the diurnal anisotropy, especially the phase shift from one solar minimum period to another, which seems to depend on the polarity of the IMF, has a theoretical explanation in the drift picture of the modulation of cosmic rays in the heliosphere.

Van Staden, M. L.↗
NASA NTRS1984

Correlation between proton anisotropy and magnetic field direction in the distant geotail

A statistical analysis has been conducted of the anisotropy of suprathermal protons and the polarity of the magnetic field during April 10-16, 1983. At this time, ISEE-3 was at lunar distances in the geomagnetic tail of the earth, and well within the nominal magnetopause. The first-order anisotropy is presently correlated with the latitude angle and the z-component of the magnetic field. The anisotropy direction's frequency distribution is strongly peaked in the earthward and tailward direction, indicating fast earthward and tailward flows. For large anisotropies, and within 5 earth radii of the nominal neutral sheet position, a strong correlation is found between the earthward-streaming suprathermal protons and the northward polarity of the magnetic field; large tailward anisotropies are generally correlated with southward magnetic field polarity. This correlation is most simply interpreted in terms of a neutral line or reconnection model.

Klecker, B.↗
NASA NTRS1979

Energetic solar particle behaviour in the magnetosphere

The behavior of energetic solar flare particles in the magnetosphere is discussed. In the absence of magnetospheric motion, the problem of particle transport can be treated as simple propagation of charged particles in a stationary magnetic field configuration using, for instance, trajectory calculations in model fields. This single particle approach is the basis for the determination of intensity and anisotropy structures over the polar caps and in the geomagnetic tail from different interplanetary conditions. Particle transport on closed field lines is in addition strongly affected by resonant interaction processes as pitch angle scattering and radial diffusion.

Scholer, M.↗
NASA NTRS2022

Anisotropy Measurements from the Near-Threshold Photodissociation of the N2−NO Complex

We have used velocity map ion imaging to measure the angular anisotropy of the NO (A) products from the photodissociation of the N 2 −NO complex. Our experiment ranged from 108 to 758 cm −1 above the threshold energy to form NO (A)+N 2 (X) products, and these measurements reveal, for the first time, a strong angular anisotropy from photodissociation. At 108 cm −1 above the photodissociation threshold, we observed NO (A) photoproducts recoil preferentially perpendicular to the laser polarization axis with an average anisotropy parameter, β = −0.25; however, as the available energy was increased, the anisotropy increased, and at 758 cm −1 above the threshold energy, we found an average β = +0.28. The observed changes in the angular anisotropy of the NO (A) photoproduct are qualitatively similar to those observed for the photodissociation of the Ar−NO complex and likely result from changes in the region of the excited state potential energy surface accessed during the electronic excitation. At the lowest available energy, we also noted a large contribution from hot band excitation; however, this contribution decreased as the available energy increased. The outsized contribution at the lowest available energy may result from hot bands having better Franck−Condon overlap with the excited electronic state near threshold. Finally, we contrast the experimental center of mass translational energy distribution with a statistical energy distribution determined from phase space theory. The experimental and statistical distributions show pronounced disagreement, particularly at low kinetic energies, with the experimental one showing less dissociation resulting in high rotational levels of the fragments.

Energy↗
NASA NTRS1974

Polarized electromagnetic response of the moon

The strong anisotropy in Apollo 15 Lunar Surface Magnetometer (LSM) signals resulting from electromagnetic induction in the moon, forced by fluctuations of the interplanetary magnetic field, is shown to result from intense polarization of the induced field. Arguments are given to show that the anisotropy cannot be explained wholly by asymmetric lunar induction in the presence of the diamagnetic cavity, but must be related to a regional influence. The weaker Apollo 12 anisotropy may also be associated with a regional influence. The site of Apollo 15 LSM at the edge of the Imbrium Basin suggests a preliminary model for calculations based on the possibility that Imbrium and perhaps Serenitatis are sources of the regional effect. Lastly, since the very low frequency induction seems free of the anisotropy, our earlier estimate of deep conductivity remains unchanged.

Sonett, C. P.↗
NASA NTRS1987

The electromagnetic ion cyclotron beam anisotropy instability

Electromagnetic instabilities driven by an anisotropic, relatively cool ion beam are studied for the case in which both the beam and the instabilities propagate parallel or antiparallel to a uniform magnetic field. At modest beam-core relative drift speeds, sufficiently large perpendicular-to-parallel beam temperature ratios and sufficiently large plasma beta, the mode of fastest growth rate is the ion cyclotron beam anisotropy instability. Because the right-hand polarized waves observed upstream of slow shocks in the earth's magnetotail can lead to the appropriate beam anisotropy, the ion cyclotron instability may be present and account for the left-hand polarized magnetic waves observed there. Also, because of its relatively low phase speed, the ion cyclotron beam anisotropy instability may provide the scattering necessary for ion Fermi acceleration at slow shocks of sufficiently high plasma beta.

Peter Gary, S.↗
NASA NTRS2016

Advanced ACTPol Cryogenic Detector Arrays and Readout

Advanced ACTPol is a polarization-sensitive upgrade for the 6 m aperture Atacama Cosmology Telescope, adding new frequencies and increasing sensitivity over the previous ACTPol receiver. In 2016, Advanced ACTPol will begin to map approximately half the sky in five frequency bands (28-230 GHz). Its maps of primary and secondary cosmic microwave background anisotropies-imaged in intensity and polarization at few arcminute-scale resolution-will enable precision cosmological constraints and also awide array of cross-correlation science that probes the expansion history of the universe and the growth of structure via gravitational collapse. To accomplish these scientific goals, the AdvancedACTPol receiver will be a significant upgrade to the ACTPol receiver, including four new multichroic arrays of cryogenic, feedhorn-coupled AlMn transition edge sensor polarimeters (fabricated on 150 mm diameter wafers); a system of continuously rotating meta-material silicon half-wave plates; and a new multiplexing readout architecture which uses superconducting quantum interference devices and time division to achieve a 64-row multiplexing factor. Here we present the status and scientific goals of the Advanced ACTPol instrument, emphasizing the design and implementation of the AdvancedACTPol cryogenic detector arrays.

secondary cosmic microwave background anisotropies↗
NASA NTRS1995

Anisotropic Structure of Rotating Homogeneous Turbulence at High Reynolds Numbers

Large eddy simulation is used to investigate the development of anisotropies and the evolution towards a quasi two-dimensional state in rotating homogeneous turbulence at high Reynolds number. The present study demonstrates the existence of two transitions in the development of anisotropy. The first transition marks the onset of anisotropy and occurs when a macro-Rossby number (based on a longitudinal integral lengthscale) has decreased to near unity while the second transition occurs when a micro-Rossby number (defined in this work as the ratio of the rms fluctuating vorticity to background vorticity) has decreased to unity. The anisotropy marked by the first transition corresponds to a reduction in dimensionality while the second transition corresponds to a polarization of the flow, i.e., relative dominance of the velocity components in the plane normal to the rotation axis. Polarization is reflected by emergence of anisotropy measures based on the two-dimensional component of the turbulence. Investigation of the vorticity structure shows that the second transition is also characterized by an increasing tendency for alignment between the fluctuating vorticity vector and the background angular velocity vector with a preference for corrotative vorticity.

Cambon, Claude↗
NASA NTRS2016

Polarized Light Microscopy

Polarized light microscopy (PLM) is a technique which employs the use of polarizing filters to obtain substantial optical property information about the material which is being observed. This information can be combined with other microscopy techniques to confirm or elucidate the identity of an unknown material, determine whether a particular contaminant is present (as with asbestos analysis), or to provide important information that can be used to refine a manufacturing or chemical process. PLM was the major microscopy technique in use for identification of materials for nearly a century since its introduction in 1834 by William Fox Talbot, as other techniques such as SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infrared spectroscopy), XPD (X-ray Powder Diffraction), and TEM (Transmission Electron Microscopy) had not yet been developed. Today, it is still the only technique approved by the Environmental Protection Agency (EPA) for asbestos analysis, and is often the technique first applied for identification of unknown materials. PLM uses different configurations in order to determine different material properties. With each configuration additional clues can be gathered, leading to a conclusion of material identity. With no polarizing filter, the microscope can be used just as a stereo optical microscope, and view qualities such as morphology, size, and number of phases. With a single polarizing filter (single polars), additional properties can be established, such as pleochroism, individual refractive indices, and dispersion staining. With two polarizing filters (crossed polars), even more can be deduced: isotropy vs. anisotropy, extinction angle, birefringence/degree of birefringence, sign of elongation, and anomalous polarization colors, among others. With the use of PLM many of these properties can be determined in a matter of seconds, even for those who are not highly trained. McCrone, a leader in the field of polarized light microscopy, often advised, If you cant determine a specific optical property of a particle after two minutes, move onto another configuration. Since optical properties can be seen so very quickly and easily under polarized light, it is only necessary to spend a maximum of two minutes on a technique to determine a particular property, though often only a few seconds are required.

Engineering↗
NASA NTRS2003

First Results From the Wilkinson Microwave Anisotropy Probe (WMAP)

The first findings from a year of WMAP satellite operations provide a detailed full sky map of the cosmic microwave background radiation. The observed temperature anisotropy, combined with the associated polarization information, encodes a wealth of cosmological information. The results have have implications for the history, content, and evolution of the universe, and its large scale properties. These and other aspects of the mission will be discussed.

Bennett, Charles↗
NASA NTRS2004

The Undiscovered World: Cosmology from WMAP

The first findings from a year of WMAP satellite operations provide a detailed full sky map of the cosmic microwave background radiation. The observed temperature anisotropy, combined with the associated polarization information, encodes a wealth of cosmological information. The results have implications for the history, content, and evolution of the universe, and its large scale properties. These and other aspects of the mission will be discussed.

Bennett, Charles↗
NASA NTRS2004

WMAP

The first findings from a year of WMAP satellite operations provide a detailed full sky map of the cosmic microwave background radiation. The observed temperature anisotropy, combined with the associated polarization information, encodes a wealth of cosmological information. The results have implications for the history, content, and evolution of the universe, and its large scale properties. These and other aspects of the mission will be discussed.

Bennett, Charles↗
NASA NTRS2004

The Undiscovered World Cosmology from WMAP

The first findings from a year of WMAP satellite operations provide a detailed full sky map of the cosmic microwave background radiation. The observed temperature anisotropy, combined with the associated polarization information, encodes a wealth of cosmological information. The results have implications for the history, content, and evolution of the universe, and its large scale properties. These and other aspects of the mission will be discussed.

Bennett, Charles↗
NASA NTRS2004

Baby Pictures of the Universe

The first findings from a year of WMAP satellite operations provide a detailed full sky map of the cosmic microwave background radiation. The observed temperature anisotropy, combined with the associated polarization information, encodes a wealth of cosmological information. The results have implications for the history, content, and evolution of the universe, and its large scale properties. These and other aspects of the mission will be discussed.

Bennett, Charles↗
NASA NTRS2016

The Imaging X-Ray Polarimetry Explorer (IXPE)

The Imaging X-ray Polarimetry Explorer (IXPE) is an exciting international collaboration for a scientific mission that dramatically brings together the unique talents of the partners to expand observation space by simultaneously adding polarization measurements to the array of source properties currently measured (energy, time, and location). IXPE uniquely brings to the table polarimetric imaging. IXPE will thus open new dimensions for understanding how X-ray emission is produced in astrophysical objects, especially systems under extreme physical conditions-such as neutron stars and black holes. Polarization singularly probes physical anisotropies-ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin-that are not otherwise measurable. Hence, IXPE complements all other investigations in high-energy astrophysics by adding important and relatively unexplored information to the parameter space for studying cosmic X-ray sources and processes, as well as for using extreme astrophysical environments as laboratories for fundamental physics.

X-ray astronomy x-ray polarimetry↗
NASA NTRS1972

Magnetospheric access of solar particles and the configuration of the distant geomagnetic field, volume 1

The access of 1.2 to 40 MeV protons and 0.4 to 1.0 MeV electrons from interplanetary space to the polar cap regions was investigated with an experiment on board a low altitude, polar-orbiting satellite (0G0 4). A total of 333 quiet time observations of the electron polar cap boundary give a mapping of the boundary between open and closed geomagnetic field lines. Observations of events associated with co-rotating regions of enhanced proton flux in interplanetary space were used to establish the characteristics of the 1.2 to 40 MeV proton access windows. The results were compared to particle access predictions of the distant geomagnetic tail configurations. The role played by interplanetary anisotropies in the observation of persistent polar cap features is discussed. Special emphasis is given to the problem of nonadiabatic particle entry through regions where the magnetic field is changing direction.

Evans, L. C.↗