Results for “polar low” — Page 4

DOE OSTI2024

Simulations of Positron Capture at Ce+BAF

We present a capture concept for the continuous wave (CW) polarized positron injector for the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (Ce+BAF). This two-step concept is based on (1) the generation of bremsstrahlung radiation by a longitudinally polarized electron beam 1 mA, 120 MeV, 90% polarization), passing through a tungsten target, and (2) the production of e+e--pairs by these bremsstrahlung photons in the same target. To provide highly-polarized positron beams (>60% polarization) or high-current positron beams (>1 µA) with low polarization for nuclear physics experiments, the positron source requires a flexible capture system with an adjustable energy selection band. The results of beam dynamics simulations and calculations of the power deposited in the positron capture section are presented.

Ushakov, Andriy↗

NASA NTRS1992

Morning-evening differences in global and regional oceanic precipitation as observed by the SSM/I

For the present preliminary analysis of oceanic rainfall statistics, global oceanic SSM/I data were simply scanned for pixels which exhibited a 37 GHz polarization difference (vertically polarized brightness temperatures minus horizontally polarized brightness temperatures) of less than 15 K. Such a low polarization difference over the open ocean is a completely unambiguous indication of moderate to intense precipitation. Co-located brightness temperatures from all seven channels of the SSM/I were saved for each pixel so identified. Bad scans and geographically mislocated block of data were objectively identified and removed from the resulting data base. We collected global oceanic rainfall data for two time periods, each one month in length. The first period (20 July-19 August 1987) coincides with the peak of the Northern Hemisphere summer. The second period (13 January-12 February 1988) coincides with the Northern Hemisphere winter.

Petty, Grant W.↗

NASA NTRS1992

Morning-evening differences in global and regional oceanic precipitation as observed by the SSM/I

For the present preliminary analysis of oceanic rainfall statistics, global oceanic SSM/I data were simply scanned for pixels which exhibited a 37 GHz polarization difference (vertically polarized brightness temperatures minus horizontally polarized brightness temperatures) of less than 15 K. Such a low polarization difference over the open ocean is a completely unambiguous indication of moderate to intense precipitation. Co-located brightness temperatures from all seven channels of the SSM/I were saved for each pixel so identified. Bad scans and geographically mislocated block of data were objectively identified and removed from the resulting data base. We collected global oceanic rainfall data for two time periods, each one month in length. The first period (20 July-19 August 1987) coincides with the peak of the Northern Hemisphere summer. The second period (13 January-12 February 1988) coincides with the Northern Hemisphere winter.

Petty, Grant W.↗

NASA NTRS1980

The kinetics of the O2/CO2 reaction in molten carbonate - Reaction orders for O2 and CO2 on NiO

The kinetics of the O2/CO2 reaction in molten carbonate is investigated using paste electrolytes and nickel sinter electrodes. A two-step approach to the determination of reaction orders is employed. First, exchange currents at various P(CO2) and P(O2) were measured using the low polarization method. Second, alpha(+) and alpha(-) values were obtained from the slope of the Allen-Hickling plot for current densities low enough so that concentration polarization within the electrode can be neglected. The reaction orders are + 1/4 in CO2 and + 5/8 in O2 in the cathodic direction, and - 3/4 in CO2 and + 1/8 in O2 in the anodic direction.

Winnick, J.↗

NASA NTRS2011

Global Precipitation Measurement, Validation, and Applications Integrated Hydrologic Validation to Improve Physical Precipitation Retrievals for GPM

Land surface modeling and data assimilation can provide dynamic land surface state variables necessary to support physical precipitation retrieval algorithms over land. It is well-known that surface emission, particularly over the range of frequencies to be included in the Global Precipitation Measurement Mission (GPM), is sensitive to land surface states, including soil properties, vegetation type and greenness, soil moisture, surface temperature, and snow cover, density, and grain size. In order to investigate the robustness of both the land surface model states and the microwave emissivity and forward radiative transfer models, we have undertaken a multi-site investigation as part of the NASA Precipitation Measurement Missions (PMM) Land Surface Characterization Working Group. Specifically, we will demonstrate the performance of the Land Information System (LIS; http://lis.gsfc.nasa.gov; Peters-Lidard et aI., 2007; Kumar et al., 2006) coupled to the Joint Center for Satellite Data Assimilation (JCSDA's) Community Radiative Transfer Model (CRTM; Weng, 2007; van Deist, 2009). The land surface is characterized by complex physical/chemical constituents and creates temporally and spatially heterogeneous surface properties in response to microwave radiation scattering. The uncertainties in surface microwave emission (both surface radiative temperature and emissivity) and very low polarization ratio are linked to difficulties in rainfall detection using low-frequency passive microwave sensors (e.g.,Kummerow et al. 2001). Therefore, addressing these issues is of utmost importance for the GPM mission. There are many approaches to parameterizing land surface emission and radiative transfer, some of which have been customized for snow (e.g., the Helsinki University of Technology or HUT radiative transfer model;) and soil moisture (e.g., the Land Surface Microwave Emission Model or LSMEM).

Peters-Lidar, Christa D.↗

NASA NTRSDate not supplied

Power Hibernation for Low-Cost Solar Powered Lunar Missions

Lunar Surface temperatures can span from equatorial highs near 400K and polar lows of 50K. The extreme cold combined with the 354-hour duration of the lunar night is particularly challenging for small robotic lander missions. NASA’s Commercial Lunar Payload Services (CLPS) missions involve robotic landers intended to provide low-cost access to the lunar surface. Current CLPS Missions are solar powered and are only intended to survive a single lunar day. The ability to survive the night and continue operations over many lunar cycles would provide a dramatic increase in science productivity. The Power Hibernation approach relies on battery cells that can tolerate the extreme cold night and recover once temperatures return to normal. System recovery from hibernation depends on power electronics that can “cold start” at lunar dawn and operate on solar array output alone. Once battery and avionics systems are restored the spacecraft resumes daytime operations. The challenge is to achieve this capability with minimum impact to the spacecraft design and payload capacity. This talk will describe recent and ongoing investigations in battery and electronics technologies that will enable power hibernation and recovery.

Space Power↗

NASA NTRSDate not supplied

Power Hibernation for Low-Cost Solar Powered Lunar Missions

Lunar Surface temperatures can span from equatorial highs near 400K and polar lows of 50K. The extreme cold combined with the 354-hour duration of the lunar night is particularly challenging for small robotic lander missions. NASA’s Commercial Lunar Payload Services (CLPS) missions involve robotic landers intended to provide low-cost access to the lunar surface. Current CLPS Missions are solar powered and are only intended to survive a single lunar day. The ability to survive the night and continue operations over many lunar cycles would provide a dramatic increase in science productivity. The Power Hibernation approach relies on battery cells that can tolerate the extreme cold night and recover once temperatures return to normal. System recovery from hibernation depends on power electronics that can “cold start” at lunar dawn and operate on solar array output alone. Once battery and avionics systems are restored the spacecraft resumes daytime operations. The challenge is to achieve this capability with minimum impact to the spacecraft design and payload capacity. This talk will describe recent and ongoing investigations in battery and electronics technologies that will enable power hibernation and recovery.

Space Power↗

NASA NTRS1997

The polarimetric capabilities of NICMOS

The polarimetric capabilities of Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) are demonstrated from data obtained during the Early Release Observations of IRC+10216 and CRL 2688 (the Egg Nebula). Preflight Thermal Vacuum tests revealed that each polarizer has a unique polarizing efficiency, and that the position angle offsets differ from the nominal positions of O deg, 120 deg and 240 deg. Therefore an algorithm different from that of an ideal polarizer is required for proper reduction of astronomical polarimetry data. We discuss this new algorithm and the results of its application to NICMOS data. We also present preliminary estimates of the Instrumental Polarization, the sensitivity of the grisms to polarized light, and the accuracy of NICMOS imaging polarimetry for faint and low polarization objects. Finally, we suggest strategies for maximizing the success of NICMOS polarimetry observations.

Hines, D. C.↗

NASA NTRS1994

The synchrotron continuum of the highly polarized quasar PKS 1546+027

The wavelength dependence of optical linear polarization of the highly polarized quasar (HPQ) PKS 1546+027 is investigated for the first time. Both spectropolarimetry and broad-band filter polarimetry are presented for a period when the object was undergoing a strong ourburst in flux and polarization. The rapid polarization variations observed argues that an optically thin synchrotron-emitting region, similar in polarization properties to BL Lacertae objects and optically violent variable (OVV) quasars, is the major source of polarized flux from this object. The continuum polarization increases dramatically with wavelength and is about twice as high at 8000 A than at 4000 A. Spectropolarimetry reveals that the emission-line flux from PKS 1546+027 dilutes the continuum polarization and is probably unpolarized. There is no evidence for any variation in polarization position angle with wavelength. The polarized flux spectrum is well-represented by a steep power law with a spectral index of -2.2, supporting the view that the polarized flux has a nonthermal origin. The observed polarization properties of PKS 1546+027 are consistent with a model that has been proposed to explain the optical to ultraviolet continua of several OVVs. In this model the optical to near-UV spectral flux distribution is a combination of light from a polarized synchrotron component plus an unpolarized component with spectral properties typical of low-polarization quasars.

Smith, Paul S.↗

NASA NTRS2006

Hubble Space Telescope NICMOS Polarization Measurements of OMC-1

We present 2 micrometer polarization measurements of positions in the BN region of the Orion Molecular Cloud (OMC-1) made with NICMOS Camera 2 (0.2" resolution) on Hubble Space Telescope. Our goals are to seek the sources of heating for IRc2, 3, 4, and 7, identify possible young stellar objects (YSOs), and characterize the grain alignment in the dust clouds along the lines-of-sight to the stars. Our results are as follows: BN is approximately 29% polarized by dichroic absorption and appears to be the illuminating source for most of the nebulosity to its north and up to approximately 5" to its south. Although the stars are probably all polarized by dichroic absorption, there are a number of compact, but non-point-source, objects that could be polarized by a combination of both dichroic absorption and local scattering of star light. We identify several candidate YSOs, including an approximately edge-on bipolar YSO 8.7" east of BN, and a deeply-embedded IRc7, all of which are obviously self-luminous at mid-infrared wavelengths and may be YSOs. None of these is a reflection nebula illuminated by a star located near radio source I, as was previously suggested. Other IRc sources are clearly reflection nebulae: IRc3 appears to be illuminated by IRc2-B or a combination of the IRc2 sources, and IRc4 and IRc5 appear to be illuminated by an unseen star in the vicinity of radio source I, or by Star n or IRc2-A. Trends in the magnetic field direction are inferred from the polarization of the 26 stars that are bright enough to be seen as NICMOS point sources. Their polarization ranges from N less than or equal to 1% (all stars with this low polarization are optically visible) to greater than 40%. The most polarized star has a polarization position angle different from its neighbors by approximately 40 degrees, but in agreement with the grain alignment inferred from millimeter polarization measurements of the cold dust cloud in the southern part of OMC-1. The polarization position angle of another highly-polarized, probable star also requires a grain alignment and magnetic field orientation substantially different from the general magnetic field orientation of OMC-1.

Simpson, Janet P.↗

NASA NTRS1992

Validation and applications of the POLAR code

The Potentials of Large Objects in the Auroral Region (POLAR) code was written to model the charging of large spacecraft by auroral electrons in low polar orbit. It has also proven to be a powerful tool for analysis of active and voltage-plasma interactions. POLAR combines 3-D object definition, direct solution to Poisson's equation, space charge transport, and surface charge computation. Physical effects treated by POLAR include the plasma wake and ram, the geomagnetic field, ionization, sheath and barrier formation, and photo and secondary electron generation and transport. Polar development is complete and it is now available to the aerospace community. The methodology of POLAR is reviewed but concentration is on the applications of POLAR to physical problems and observations with the intent of demonstrating both the code's capabilities, and its limitations. These applications include the Space Shuttle, the Defense Meteorological Satellite Program (DMSP) satellites, sounding rockets, plasma chamber experiments, and things not yet flown.

Cooke, David L.↗

NASA NTRS2012

Mirror coatings with atomic layer deposition : initial results

The new technology of Atomic Layer Deposition (ALD) holds promise to enable a future strategic mission that can address both ultraviolet (UV) astrophysics and optical exoplanet science with a shared telescope. The technology path to a shared telescope requires the development of a mirror coating with high reflectance from 100 nm to 1000 nm, and low polarization effects (i.e., s-p phase shifts that can vary with angle of incidence across a primary and secondary mirror) in the optical range. Currently, UV coatings have low reflectance, and conventional optical coatings have poor polarization properties for high-contrast coronagraph applications. In this paper we attempt to take a first step toward solving both problems simultaneously by using ALD, taking advantage of the fact that ALD can potentially produce mirror coatings with denser layers than conventional coatings (hence better reflectance, durability, and water resistance). In addition, ALD can potentially produce coatings with new composite materials (hence better control of polarization). We report here the results of our initial experiments with mirror coatings using ALD.

Traub, Wesley↗

NASA NTRS1973

Access of solar protons to the earth's polar caps.

Energetic solar proton observations in the interplanetary medium by Explorer 33 and Explorer 35 and over the polar caps by Injun 5 during the period from September 1968 through March 1970 have been examined in detail. The solar proton intensities observed over the polar regions were compared with the interplanetary intensities on an absolute basis. The high polar latitude (HPL) proton intensities tracked the magnetic field aligned interplanetary intensities well (solar-antisolar intensities as determined from the sectored Explorer data). The tracking was in agreement with the open magnetosphere model about 90% of the time - i.e., the intensities observed on the HPL magnetic lines of force, which would be connected to magnetic lines of force from the sun in an interconnected geomagnetic and interplanetary magnetic field, were in agreement with the maximum intensity of the interplanetary proton pitch angle distribution. The intensities observed at the HPL region of the opposite polar cap were in agreement with the minimum intensity of the interplanetary pitch angle distribution. The low polar latitude intensities generally tracked the maximum interplanetary intensity very well.

Fennell, J. F.↗

NASA NTRS1981

NASA launches dual Dynamics Explorer spacecraft

A Delta launch vehicle was used to insert Dynamics Explorer A into a highly elliptical polar orbit, ranging from 675 to 24,945 km, and Dynamics Explorer B satellite into a low polar orbit, ranging from 306 to 1,300 km. The two spacecraft are designed to provide specific knowledge about the interaction of energy, electric currents, electric fields, and plasmas between the magnetosphere, the ionosphere, and the atmosphere.

Source record↗

NASA NTRS1982

Advanced 30/20 GHz multiple-beam antennas for communications satellites

Design concepts under development utilize two separate spacecraft antenna systems, one uplink at 30 GHz and the other a downlink at 20 GHz, where each antenna provides multiple fixed and scanning beams. Two contractors completed configuration trade-off studies and breadboarding of critical technology components, and are fabricating and testing proof-of-concept (POC) models to demonstrate the technology feasibility. Technology developments required for the proposed systems are presented, along with each contractor's progress to date. The technology development areas discussed include: (1) offset Cassegrain and shaped reflector systems for narrow beams with low sidelobes and wideangle off-axis scan; (2) diplexed beam-forming networks for dual polarization, low sidelobes, and fixed and scan-beam operation; (3) fast switching networks for scanning beams; and (4) fabrication of precision feed components and large offset reflectors.

Myhre, R. W.↗

NASA NTRS1983

Advanced 30/20 GHz multiple-beam antennas for communications satellites

Design concepts under development utilize two separate spacecraft antenna systems, one uplink at 30 GHz and the other a downlink at 20 GHz, where each antenna provides multiple fixed and scanning beams. Two contractors completed configuration trade-off studies and breadboarding of critical technology components, and are fabricating and testing proof-of-concept (POC) models to demonstrate the technology feasibility. Technology developments required for the proposed systems are presented, along with each contractor's progress to date. The technology development areas discussed include: (1) offset Cassegrain and shaped reflector systems for narrow beams with low sidelobes and wideangle off-axis scan; (2) diplexed beam-forming networks for dual polarization, low sidelobes, and fixed and scan-beam operation; (3) fast switching networks for scanning beams; and (4) fabrication of precision feed components and large offset reflectors.

Myhre, R. W.↗

DOE OSTI2025

Solvent Polarity Independent Symmetry-Breaking Charge Separation in a Slip-Stacked Covalent Terrylene Monoimide Dimer

The design of organic materials capable of efficient photoinduced charge separation in low-polarity environments is a critical challenge for advancing organic photovoltaics. Symmetry-breaking charge separation (SB-CS) offers a promising route to efficient charge separation with minimal energy loss; however, in conventional organic materials this process typically relies on polar solvents to stabilize the charge-separated state. Here, we investigate a slip-stacked terrylene monoimide dimer (TMI 2 ) engineered with intrinsic electronic asymmetry to circumvent this limitation. We demonstrate through a comprehensive suite of ultrafast spectroscopic techniques that TMI 2 undergoes remarkably efficient SB-CS regardless of solvent polarity enabled by the permanent dipole moment of TMI and the accessible intramolecular charge-transfer (ICT) character of its monomer units. Furthermore, analysis of vibronic coherences reveals that the initial state mixing is actively driven by a 193 cm –1 intermolecular mode, while the final SB-CS state is marked by a distinct vibrational fingerprint of the radical ion pair product. Our findings reveal how the intrinsic electronic asymmetry of the TMI monomers that constitute TMI 2 creates an efficient charge separation pathway that precludes the need for external stabilization from a polar solvent. Here, this work establishes a powerful molecular design principle for leveraging intrinsic monomeric asymmetry to achieve efficient charge separation in low-dielectric environments, with significant implications for the development of next-generation organic optoelectronic materials.

Aromatic compounds↗

NASA NTRS2006

The Distant Magnetotail Under Long Duration, Very Northward IMF Conditions: October 22-24, 2003

A unique 32 hour interval of very northward Interplanetary Magnetic Field (IMF) on October 22-24, 2003 created a exceptionally thick cold dense magnetotail plasma sheet, a small polar cap and accompanying small tail lobe. These features were detected by the Cluster DMSP and FAST spacecraft and modeled by a global simulation as described in papers by Oieroset et al. (2005) and Li et al. (2005). During the same interval the Wind spacecraft was passing through the center of the magnetotail about 130 Re downstream of Earth. Wind results will be described that reveal a very unusual magnetotail characterized by (1) continual tailward flow of 200-400 km/s with densities in the range 0.2-3/cc, both of whch are clearly less than those expected in the magnetosheath, (2) a mostly northward Bz but with a predominant Bx field component with sign reversals indicating crossings between the two hemispheres of the tail, and (3) velocity waves superposed on the downstream flow with peak-to-peak amplitudes of 100 to 200 km/s, periods of 10 to 20 minutes and clockwise polarization. Low altitude DMSP and Fast measurements reveal an auroral oval with enhanced latitudinal thickness and a small polar cap filled with structured precipitzting electrons and few ions. A new global MHD simulation of the event exhibits a highly elliptical tail of diminished cross-section at 130 Re with major axis aligned with the northward IMF. The tail current sheet also tends to be aligned in a north-south direction with the two tail hemispheres to the east and west with their polarities depending on prior history of the IMF. The simulation appears to be consistent with many, but not all, of the observations. High latitude cusp reconnection and subsequent downtail flow of closed field lines may explain the tail structure, but the waves are more likely due to the Kelvin-Helmholtz instability often thought to occur during northward IMF conditions.

Fairfield, Donald H.↗