Hamrin M.,Umea University |
Andersson L.,LASP |
Vaivads A.,Swedish Institute of Space Physics |
Pitkanen T.,Umea University |
Gunell H.,Belgian Institute for Space Aeronomy
Journal of Geophysical Research A: Space Physics | Year: 2015
In the vicinity of magnetic reconnection, magnetic energy is transferred into kinetic energy. A reconnection region hence corresponds to a load, and it should manifest itself as large and positive values of the power density, EJ 0, where E is the electric field and J the current density. In this article we analyze Cluster plasma sheet data from 2001-2004 to investigate the use of the power density for identifying possible magnetic reconnection events from large sets of observed data. From theoretical arguments we show that an event with EJ≳20 pW/m3 in the Earth's magnetotail observed by the Cluster instruments (X <- 10RE and |Y|10RE) is likely to be associated with reconnection. The power density can be used as a primary indicator of potential reconnection regions, but selected events must be reviewed separately to confirm any possible reconnection signatures by looking for other signatures such as Hall electric and magnetic fields and reconnection jets. The power density can be computed from multispacecraft data, and we argue that the power density can be used as a tool for identifying possible reconnection events from large sets of data, e.g., from the Cluster and the Magnetospheric Multiscale missions. Key Points Magnetic reconnection regions should manifest themselves as loads (power density EJ > 0) We show that an event with power density ≳20 pW/m3 is likely to be associated with tail reconnection EJ is useful for finding likely reconnection events in large data sets (e.g., Cluster and MMS) ©2015. American Geophysical Union. All Rights Reserved.
Pasachoff J.M.,Williams College |
Pasachoff J.M.,California Institute of Technology |
Person M.J.,Massachusetts Institute of Technology |
Bosh A.S.,Massachusetts Institute of Technology |
And 12 more authors.
Astronomical Journal | Year: 2016
We observed occultations by Pluto during a predicted series of events in 2014 July with the 1 m telescope of the Mt. John Observatory in New Zealand. The predictions were based on updated astrometry obtained in the previous months at the USNO, CTIO, and Lowell Observatories. We successfully detected occultations by Pluto of an R = 18 mag star on July 23 (14:23:32 ± 00:00:04 UTC to 14:25:30 ± 00:00:04 UTC), with a drop of 75% of the unocculted stellar signal, and of an R = 17 star on July 24 (11:41:30 ± 00:00:08 UTC to 11:43:28 ± 00:00:08 UTC), with a drop of 80% of the unocculted stellar signal, both with 20 s exposures with our frame-transfer Portable Occultation, Eclipse, and Transit System. Since Pluto had a geocentric velocity of 22.51 km s-1 on July 23 and 22.35 km s-1 on July 24, these intervals yield limits on the chord lengths (surface and lower atmosphere) of 2700 ±130 km and 2640 ±250 km, respectively, indicating that the events were near central, and therefore provide astrometric constraints on the prediction method. Our coordinated observations with the 4 m AAT in Australia on July 23 and the 6.5 m Magellan/Clay on Las Campanas, the 4.1 m Southern Astrophysical Research Telescope on Cerro Pachön, the 2.5 m DuPont on Las Campanas (LCO), the 0.6 m SARA-South on Cerro Tololo of the Southeastern Association for Research in Astronomy (SARA), the MPI/ESO 2.2 m on La Silla, and the 0.45 m Cerro Calán telescope and 0.36 telescope in Constitución in Chile on July 27 and 31, which would have provided higher-cadence observations for studies of Pluto's atmosphere, were largely foiled by clouds, but led to detection with the LCO Magellan/Clay and DuPont Telescopes on July 31 of the grazing occultation of a previously unknown 15th-magnitude star, completing the trio of occultations successfully observed and reported in this paper. © 2016. The American Astronomical Society. All rights reserved.
Fehlmann A.,PMOD WRC |
Kopp G.,LASP |
Schmutz W.,PMOD WRC |
Winkler R.,NPL |
And 2 more authors.
Metrologia | Year: 2012
We report the fourth World Radiometric Reference (WRR)-to-SI comparison. At the National Physical Laboratory we compared three transfer pyrheliometer instruments in power mode with the SI radiometric scale. Compared with the three previous comparisons, we improved the experiment by operating the transfer instruments in vacuum. At the Total solar irradiance Radiometer Facility (TRF) located at the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, we repeated the power comparison of one of the transfer instruments. The TRF also allowed the comparison and characterization of this instrument in irradiance mode. Using the WRR comparisons performed in Davos, we find that the WRR is 0.34% higher than the SI scale. Comparing irradiance mode calibrations with power mode calibrations reveals that previous estimates of stray light of PMO6-type radiometers were very low. The instrument calibrated at TRF was integrated in the space experiment PREMOS on the French satellite PICARD and carries the first vacuum irradiance calibration to space. © 2012 BIPM & IOP Publishing Ltd.
O'Connor G.M.,NCI Inc |
Seich Al Basatena N.-K.,Imperial College London |
Olavarria V.,Centro HTLV |
MacNamara A.,Imperial College London |
And 6 more authors.
Human Immunology | Year: 2012
While most carriers of human T-cell leukemia virus type 1 (HTLV-1) remain asymptomatic throughout their lifetime, infection is associated with the development of adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The exact parameters that determine these outcomes are unknown but are believed to include host genetic factors that control the immune response to infection. Host response to fellow retroviridae member HIV is influenced by the expression of members of the Killer Immunoglobulin Receptor (KIR) family including KIR3DS1. In this study we examined the association of KIR3DS1 with the outcome of HTLV-1 infection in three geographically distinct cohorts (Jamaican, Japanese and Brazilian). Despite increased prevalence of KIR3DS1 in the HAM/TSP patients of the Jamaican cohort, we found no evidence for a role of KIR3DS1 in influencing control of proviral load or disease outcome. This suggests that unlike HIV, KIR3DS1-mediated regulation of HTLV-1 infection does not occur, or is ineffective. © 2012.
Data downloaded and analyzed by the New Horizons team indicated the space environment around Pluto and its moons contained only about six dust particles per cubic mile, said CU-Boulder Professor Fran Bagenal, who leads the New Horizons Particles and Plasma Team. "The bottom line is that space is mostly empty," said Bagenal, a faculty member at the Laboratory for Atmospheric and Space Physics (LASP). "Any debris created when Pluto's moons were captured or created during impacts has long since been removed by planetary processes." Studying the microscopic dust grains can give researchers clues about how the solar system was formed billions of years ago and how it works today, providing information on planets, moons and comets, said Bagenal. A paper on Pluto's interaction with the space environment is being published in Science March 17. The study was led by Bagenal and involved more than other 20 researchers, including LASP physics Professor Mihaly Horanyi; CU-Boulder doctoral student Marcus Piquette of the Department of Astrophysical and Planetary Sciences; and Southwest Research Institute (SwRI) postdoctoral researcher Jamey Szalay, who received his doctorate in physics from CU-Boulder under Horanyi last year. Launched in 2006, the New Horizons mission was designed to help planetary scientists better understand the icy world at the edge of our solar system, including Pluto and the Kuiper Belt. A vast region thought to span more than a billion miles beyond Neptune's orbit, the Kuiper Belt is believed to harbor at least 70,000 objects more than 60 miles in diameter and contain samples of ancient material created during the solar system's violent formation some 4.5 billion years ago. Horanyi said the SDC logged thousands of dust grain hits over the spacecraft's nine year, 3 billion-mile journey to Pluto while most of other six instruments slept. "Now we are now starting to see seeing a slow but steady increase in the impact rate of larger particles, possibly indicating that we already have entered the inner edge of the Kuiper Belt," said Horanyi, the principal investigator for the SDC. The CU-Boulder dust counter is a thin film resting on a honeycombed aluminum structure the size of a cake pan mounted on the spacecraft's exterior. A small electronic box functions as the instrument's "brain" to assess each individual dust particle that strikes the detector, allowing the students to infer the mass of each particle. A revolving cast of more than 20 CU-Boulder students, primarily undergraduates, worked on designing and building the SDC for New Horizons between 2002 and 2005. Several students and researchers are now assessing data from the flyby. "Our instrument has been soaring through our solar system's dust disk and gathering data since launch," said Szalay, who works at SwRI headquarters in San Antonio. "It's going to be very exciting to get into the Kuiper Belt and see what we find there." New Horizons is traveling at a mind-blowing 750,000 miles a day. Images from closest approach were taken from roughly 7,700 miles above Pluto's surface. The spacecraft, about the size of a baby grand piano, carries six other instruments. The principal investigator of the New Horizons mission is Alan Stern of the SwRI Planetary Science Directorate in Boulder, who received his doctorate from CU-Boulder in 1989. "CU-Boulder is the only place in the world where students could have built an instrument that eventually flew off to another planet," said Bagenal. The next and final target of New Horizons is a 30-mile-in diameter Kuiper Belt object named 2014 MU69, which the spacecraft is expected to pass in January 2019. Bagenal also is a mission scientist for NASA's Juno Mission to Jupiter, launched in 2011 and which will begin orbiting the gas giant's poles in July. Explore further: Student dust counter breaks distance record on New Horizons mission to Pluto More information: "Pluto's interaction with its space environment: Solar wind, energetic Particles, and Dust," DOI: 10.1126/science.aad9045