228 research outputs found
Comprehensive survey of energetic electron events in Mercury\u27s magnetosphere with data from the MESSENGER Gamma-Ray and Neutron Spectrometer
Data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Gamma-Ray and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury\u27s magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. From Neutron Spectrometer data taken between 18 March 2011 and 31 December 2013 we have identified 2711 EE events. EE event amplitudes versus energy are distributed as a power law and have a dynamic range of a factor of 400. The duration of the EE events ranges from tens of seconds to nearly 20âmin. EE events may be classified as bursty (large variation with time over an event) or smooth (small variation). Almost all EE events are detected inside Mercury\u27s magnetosphere on closed field lines. The precise occurrence times of EE events are stochastic, but the events are located in well-defined regions with clear boundaries that persist in time and form what we call âquasi-permanent structures.â Bursty events occur closer to dawn and at higher latitudes than smooth events, which are seen near noon-to-dusk local times at lower latitudes. A subset of EE events shows strong periodicities that range from hundreds of seconds to tens of milliseconds. The few-minute periodicities are consistent with the Dungey cycle timescale for the magnetosphere and the occurrence of substorm events in Mercury\u27s magnetotail region. Shorter periods may be related to phenomena such as north-south bounce processes for the energetic electrons
Pennsylvania Folklife Vol. 19, No. 3
⢠Cooking in Red and White ⢠Trade Cards, Catalogs, and Invoice Heads ⢠The Encyclopaedia Cinematographica and Folklife Studies ⢠The Cheese was Good ⢠Notes and Documents: Eighteenth-Century Letters from Germany ⢠The Ephrata Wall-Charts and Their Inscriptions ⢠Itinerants - Peddlers, Drovers, Wagoners, Gypsies, Tramps: Folk-Cultural Questionnaire No. 15 ⢠Engravings of Pennsylvania Millshttps://digitalcommons.ursinus.edu/pafolklifemag/1039/thumbnail.jp
Perception Is Reality: quality metrics in pancreas surgery â a Central Pancreas Consortium (CPC) analysis of 1399 patients
Several groups have defined pancreatic surgery quality metrics that identify centers delivering quality care. Although these metrics are perceived to be associated with good outcomes, their relationship with actual outcomes has not been established
Solar wind forcing at Mercury: WSAâENLIL model results
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97237/1/jgra50070.pd
Solar wind forcing at Mercury: WSA-ENLIL model results
Analysis and interpretation of observations from the MESSENGER spacecraft in orbit about Mercury require knowledge of solar wind âforcingâ parameters. We have utilized the Wang-Sheeley-Arge (WSA)-ENLIL solar wind modeling tool in order to calculate the values of interplanetary magnetic field (IMF) strength (B), solar wind velocity (V) and density (n), ram pressure (~nV2), cross-magnetosphere electric field (VâĂâB), AlfvĂŠn Mach number (MA), and other derived quantities of relevance for solar wind-magnetosphere interactions. We have compared upstream MESSENGER IMF and solar wind measurements to see how well the ENLIL model results compare. Such parameters as solar wind dynamic pressure are key for determining the Mercury magnetopause standoff distance, for example. We also use the relatively high-time-resolution B-field data from MESSENGER to estimate the strength of the product of the solar wind speed and southward IMF strength (Bs) at Mercury. This product VBs is the electric field that drives many magnetospheric dynamical processes and can be compared with the occurrence of energetic particle bursts within the Mercury magnetosphere. This quantity also serves as input to the global magnetohydrodynamic and kinetic magnetosphere models that are being used to explore magnetospheric and exospheric processes at Mercury. Moreover, this modeling can help assess near-real-time magnetospheric behavior for MESSENGER or other mission analysis and/or ground-based observational campaigns. We demonstrate that this solar wind forcing tool is a crucial step toward bringing heliospheric science expertise to bear on planetary exploration programs
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Mixing Interstellar Clouds Surrounding the Sun
On its journey through the Galaxy, the Sun passes through diverse regions of the interstellar medium. High-resolution spectroscopic measurements of interstellar absorption lines in spectra of nearby stars show absorption components from more than a dozen warm partially ionized clouds within 15 pc of the Sun. The two nearest clouds—the Local Interstellar Cloud (LIC) and Galactic (G) cloud—move toward each other. Their bulk heliocentric velocities can be compared with the interstellar neutral helium flow velocity obtained from space-based experiments. We combine recent results from Ulysses, IBEX, and STEREO observations to find a more accurate estimate of the velocity and temperature of the very local interstellar medium. We find that, contrary to the widespread viewpoint that the Sun resides inside the LIC, the locally observed velocity of the interstellar neutral helium is consistent with a linear combination of the velocities of the LIC and G cloud, but not with either of these two velocities. This finding shows that the Sun travels through a mixed-cloud interstellar medium composed of material from both these clouds. Interactions between these clouds explain the substantially higher density of the interstellar hydrogen near the Sun and toward stars located within the interaction region of these two clouds. The observed asymmetry of the interstellar helium distribution function also supports this interaction. The structure and equilibrium in this region require further studies using in situ and telescopic observations.
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Comprehensive survey of energetic electron events in Mercury's magnetosphere with data from the MESSENGER GammaâRay and Neutron Spectrometer
Data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) GammaâRay and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury's magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. From Neutron Spectrometer data taken between 18 March 2011 and 31 December 2013 we have identified 2711 EE events. EE event amplitudes versus energy are distributed as a power law and have a dynamic range of a factor of 400. The duration of the EE events ranges from tens of seconds to nearly 20âmin. EE events may be classified as bursty (large variation with time over an event) or smooth (small variation). Almost all EE events are detected inside Mercury's magnetosphere on closed field lines. The precise occurrence times of EE events are stochastic, but the events are located in wellâdefined regions with clear boundaries that persist in time and form what we call âquasiâpermanent structures.â Bursty events occur closer to dawn and at higher latitudes than smooth events, which are seen near noonâtoâdusk local times at lower latitudes. A subset of EE events shows strong periodicities that range from hundreds of seconds to tens of milliseconds. The fewâminute periodicities are consistent with the Dungey cycle timescale for the magnetosphere and the occurrence of substorm events in Mercury's magnetotail region. Shorter periods may be related to phenomena such as northâsouth bounce processes for the energetic electrons
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
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