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Wong, C.

Publications and source records attributed to Wong, C..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Energetic Electron Precipitation Driven by Electromagnetic Ion Cyclotron Waves from ELFIN’s Low Altitude Perspective

We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data collected by the energetic electron detector on the Electron Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibits a distinct signature in energy-spectrograms of the precipitating-to-trapped flux ratio: peaks at >0.5 MeV which are abrupt (bursty) (lasting ~17 s, or ΔL ~ 0.56) with significant substructure (occasionally down to sub-second timescale). We attribute the bursty nature of the precipitation to the spatial extent and structuredness of the wave field at the equator. Multiple ELFIN passes over the same MLT sector allow us to study the spatial and temporal evolution of the EMIC wave - electron interaction region. Case studies employing conjugate ground-based or equatorial observations of the EMIC waves reveal that the energy of moderate and strong precipitation at ELFIN approximately agrees with theoretical expectations for cyclotron resonant interactions in a cold plasma. Using multiple years of ELFIN data uniformly distributed in local time, we assemble a statistical database of ~50 events of strong EMIC wave-driven precipitation. Most reside at L ~ 5 – 7 at dusk, while a smaller subset exists at L ~ 8 – 12 at post-midnight. The energies of the peak-precipitation ratio and of the half-peak precipitation ratio (our proxy for the minimum resonance energy) exhibit an L-shell dependence in good agreement with theoretical estimates based on prior statistical observations of EMIC wave power spectra. The precipitation ratio’s spectral shape for the most intense events has an exponential falloff away from the peak (i.e., on either side of ~ 1.45 MeV). It too agrees well with quasi-linear diffusion theory based on prior statistics of wave spectra. It should be noted though that this diffusive treatment likely includes effects from nonlinear resonant interactions (especially at high energies) and nonresonant effects from sharp wave packet edges (at low energies). Sub-MeV electron precipitation observed concurrently with strong EMIC wave-driven >1 MeV precipitation has a spectral shape that is consistent with efficient pitch-angle scattering down to ~ 200-300 keV by much less intense higher frequency EMIC waves at dusk (where such waves are most frequent). At ~100 keV, whistler-mode chorus may be implicated in concurrent precipitation. These results confirm the critical role of EMIC waves in driving relativistic electron losses. Nonlinear effects may abound and require further investigation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The DISTINCTIVE University Consortium: Structural Integrity - 18272

The Engineering and Physical Sciences Research Council (EPSRC) sponsored DISTINCTIVE consortium (Decommissioning, Immobilisation and Storage Solutions for Nuclear Waste Inventories) is developing technologies for civil infrastructure repair, in-situ subsurface waste immobilisation, and groundwater protection during construction and decommissioning. The consortium has contributed to the development of skilled cross-disciplinary civil engineers and scientists, that have the knowledge and experience required to develop engineering solutions tailored for application within radiologically contaminated sites. The Structural Integrity Theme focuses on challenges ranging from site-scale infrastructure preservation and restoration, through injectable ground barriers for risk mitigation, to the remote characterisation and handling of individual waste packages. The main aim of the theme is to develop novel engineering solutions, tailored for use on radiologically contaminated sites, for: ground protection; infrastructure characterisation; concrete restoration and waste characterisation. Technologies should minimise current, and future, radiation exposure of the workforce whilst providing economically viable engineering solutions. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Dosimetry characterization of the Godiva Reactor under burst conditions

A series of sixteen (16) burst irradiations were performed in May 2014, fifteen of which were part of an international collaboration to characterize the Godiva IV fast burst reactor at the National Criticality Experiments Research Center (NCERC). Godiva IV is a bare cylindrical assembly of approximately 65 kg of highly enriched uranium fuel (93.2% 235 U metal alloyed with 1.5% molybdenum for strength) and is designed to perform controlled prompt critical excursions (Myers 2010, Goda 2013). Twelve of the irradiations were dedicated to neutron spectral measurements using a Bonner multiple sphere spectrometer. Three irradiations, with core temperature increases of 71.1°C, 136.9°C, and 229.9°C, were performed for generating comparative fluence data, establishing corrections for varying heights, testing linearity with burst temperature, and establishing gamma dose characteristics.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Awe Bonner sphere measurements of the neutron leakage spectrum from the GODIVIA-IV critical assembly at NCERC - 14413

The US National Criticality Experiments Research Centre (NCERC) is home to several critical assembly machines that were relocated from Los Alamos National Laboratory in the last decade. The centre is sponsored by the Department of Energy's Nuclear Criticality Safety Program (NCSP), which has the mission to ensure the safe handling of fissile materials from a criticality perspective. Under the auspices of the NCSP, Lawrence Livermore National Laboratory (LLNL) is planning to host an international inter-comparison of nuclear accident dosimetry (NAD) using the Godiva-IV assembly at NCERC. The inter-comparison is motivated by a decline in the frequency of performance testing of NADs (both in the US, the UK and France) and the desire to modernize and harmonize dosimetry systems. A pre-requisite for the inter-comparison is the characterisation of the neutron and gamma-ray leakage spectra associated with the Godiva-IV assembly at NCERC. AWE provided its Bonner-sphere spectrometry capability to LLNL for two experimental campaigns, in November 2013 and May 2014, to measure the neutron leakage spectrum of the assembly in both a sub-critical 'steady-state' and a super-prompt-critical 'burst'. Nine points, at distances from 2 to 4 meters from the machine were measured with the Bonner-sphere spectrometer using both an active He-3 detector and a passive technique employing gold foils. This paper presents the spectra unfolded from the data and integral dose values, and compares these to previously published data. The limitations of the work and future plans are also discussed. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

2014 CALIBAN and PROSPERO experiments for the criticality accident dosimetry intercomparison - 14529

Nuclear criticality accident dosimetry is very specific, due to the mixed fields and to energy and dose ranges which could be out of the range of classical individual dosimetry. The maximal neutron and gamma dose must be determined as well as other information such as the orientation of the victim in the radiation field. It is exceptionally challenging to establish doses in the event of partial body exposures. Therefore, frequent exercises are organized to maintain competencies and to train staff to perform such dosimetry. Experiments using the CALIBAN and PROSPERO reactors were performed in June and September 2014 in order to test various criticality accident dosimeters (CAD). These two metallic reactors are located at the CEA research center at Valduc (Cote-d'Or, France). They are composed of a metallic alloy of uranium with a high enrichment in the isotope {sup 235}U. These reactors are used for the production of mixed radiation fields primarily comprised of fission neutrons and gammas. CADs from three different laboratories (AWE, UK; IRSN, FR; LLNL, USA) were irradiated on water phantoms with three different orientations (0 deg. and 45 deg., front and rear faces) and free in air at both CALIBAN and PROSPERO reactors, in pulse and steady state modes. This paper will present the comparison of some results. These experiments will be useful preparation for other exercises planned in 2016 at the GODIVA-IV and FLATTOP reactors located at the Nevada National Security Site, USA. (authors)

42 ENGINEERING↗
DOE OSTI2015

Caffeine increases striatal dopamine D 2 /D 3 receptor availability in the human brain

Caffeine, the most widely consumed psychoactive substance in the world, is used to promote wakefulness and enhance alertness. Like other wake-promoting drugs (stimulants and modafinil), caffeine enhances dopamine (DA) signaling in the brain, which it does predominantly by antagonizing adenosine A 2A receptors (A 2A R). However, it is unclear if caffeine, at the doses consumed by humans, increases DA release or whether it modulates the functions of postsynaptic DA receptors through its interaction with adenosine receptors, which modulate them. We used positron emission tomography and [ 11 C]raclopride (DA D 2 /D 3 receptor radioligand sensitive to endogenous DA) to assess if caffeine increased DA release in striatum in 20 healthy controls. Caffeine (300mg p.o.) significantly increased the availability of D 2 /D 3 receptors in putamen and ventral striatum, but not in caudate, when compared with placebo. In addition, caffeine-induced increases in D 2 /D 3 receptor availability in the ventral striatum were associated with caffeine-induced increases in alertness. Our findings indicate that in the human brain, caffeine, at doses typically consumed, increases the availability of DA D 2 /D 3 receptors, which indicates that caffeine does not increase DA in the striatum for this would have decreased D 2 /D 3 receptor availability. Instead, we interpret our findings to reflect an increase in D 2 /D 3 receptor levels in striatum with caffeine (or changes in affinity). Furthermore, the association between increases in D 2 /D 3 receptor availability in ventral striatum and alertness suggests that caffeine might enhance arousal, in part, by upregulating D 2 /D 3 receptors.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1999

Evidence of SV40 infections in hospitalized children

Simian virus 40 (SV40) is known to have contaminated poliovirus vaccines used between 1955 and 1963. Accumulating reports have described the presence of SV40 DNA in human tumors and normal tissues, although the significance of human infections by SV40 is unknown. We investigated whether unselected hospitalized children had evidence of SV40 infections and whether any clinical correlations were apparent. Serum samples were examined for SV40 neutralizing antibody using a specific plaque reduction test; of 337 samples tested, 20 (5.9%) had antibody to SV40. Seropositivity increased with age and was significantly associated with kidney transplants (6 of 15 [40%] positive, P < .001). Many of the antibody-positive patients had impaired immune systems. Molecular assays (polymerase chain reaction and DNA sequence analysis) on archival tissue specimens confirmed the presence of SV40 DNA in 4 of the antibody-positive patients. This study, using 2 independent assays, shows the presence of SV40 infections in children born after 1980. We conclude that SV40 causes natural infections in humans.

NASA Discipline Regulatory Physiology↗
NASA NTRS1999

Molecular evidence of simian virus 40 infections in children

Recent studies have detected simian virus 40 (SV40) DNA in certain human tumors and normal tissues. The significance of human infections by SV40, which was first discovered as a contaminant of poliovirus vaccines used between 1955 and 1963, remains unknown. The occurrence of SV40 infections in unselected hospitalized children was evaluated. Polymerase chain reaction and DNA sequence analyses were done on archival tissue specimens from patients positive for SV40 neutralizing antibody. SV40 DNA was identified in samples from 4 of 20 children (1 Wilms' tumor, 3 transplanted kidney samples). Sequence variation among SV40 regulatory regions ruled out laboratory contamination of specimens. This study shows the presence of SV40 infections in pediatric patients born after 1982.

Non-NASA Center↗
NASA NTRS1998

Global Validation of Single-Station Schumann Resonance Lightning Location

Global measurements of large, optically bright lightning events from the Optical Transient Detector (OTD) satellite are used to validate estimates of lightning location from single-station Schumann resonance (SR) data. Bearing estimates are obtained through conventional magnetic direction-finding techniques, while source range is estimated from the range-dependent impedance spectrum of individual SR transients. An analysis of 40 such transients suggests that single-station techniques can locate lightning globally with an accuracy of 1-2mm. This is confirmed by further validation at close ranges from flashes detected by the National Lightning Detection-Network (NLDN). Observations with both OTD and SR systems may be useful for globally locating lightning with necessary, if not sufficient, characteristics to trigger mesospheric sprites.

Boccippio, Dennis↗