1,304 research outputs found
The long-term effects of space weather on satellite operations
Integrated lifetime radiation damage may cause spacecraft to become
more susceptible to operational anomalies by changing material
characteristics of electronic components. This study demonstrates and
quantifies the impact of these effects by examining the National Oceanic and
Atmospheric Administration (NOAA) National Geophysical Data Center (NGDC)
satellite anomaly database. Energetic particle data from the Geostationary
Operational Environmental Satellites (GOES) is used to construct the total
lifetime particle exposure a satellite has received at the epoch of an
anomaly. These values are compared to the satellite's chronological age and
the average exposure per year (calculated over two solar cycles.) The results
show that many anomalies occur on satellites that have received a total
lifetime high-energy particle exposure that is disproportionate to their age.
In particular, 10.8% of all events occurred on satellites that received over
two times more 20 to 40 MeV proton lifetime particle exposure than predicted
using an average annual mean. This number inflates to 35.2% for 40 to 80 MeV
protons and 33.7% for ≥2 MeV electrons. Overall, 73.5% of all
anomalies occurred on a spacecraft that had experienced greater than two
times the expected particle exposure for one of the eight particle
populations used in this study. Simplistically, this means that the long term
radiation background exposure matters, and that if the background radiation
is elevated during the satellite's lifetime, the satellite is likely to
experience more anomalies than satellites that have not been exposed to the
elevated environment
An Evaluation of Formate as an Electron Donor to Facilitate Palladium (PD) - Catalyzed Destruction of Chlorinated Aliphatic Hydrocarbons
Chlorinated aliphatic hydrocarbons (CAHs) such as trichloroethylene (TCE), tetrachloroethylene (PCE), and trichloroethane (TCA) are probable human carcinogens that have been used widely within the DoD, primarily as solvents for cleaning and metal degreasing. These compounds are frequently found to be groundwater contaminants. In fact, TCE and PCE are the first and third most commonly detected groundwater contaminants nationwide. The focus of this study was to determine the effectiveness of using a palladium (Pd) catalyst with formate as a reductant to treat CAH-contaminated groundwater. TCE was used as a model CAH. Other investigators have focused on hydrogen gas (H2) as a reductant to treat CAH-contaminated groundwater. However, when using H2 as a reductant, catalyst deactivation is observed due to the production of hydrochloric acid. In this study, formic acid was used as the reductant, resulting in no observed catalyst deactivation even at high contaminant concentrations. Reaction rates achieved when using 100% H2 as a reductant could be matched by using 4 mM (184 mg/L) formic acid. At increased formic acid concentrations, system performance exceeded performance achievable when using H2. It is also noted that while hydrogen is an explosive, low solubility gas, formic acid can easily and safely be added to contaminated water. The aforementioned work has shown that this method for treating CAH-contaminated groundwater by using formic acid and a Pd-catalyst is more efficient, safe, and less costly than using hydrogen gas as a reductant
A maximum spreading speed for magnetopause reconnection
Past observations and numerical modeling find magnetic reconnection to initiate at a localized region and then spread along a current sheet. The rate of spreading has been proposed to be controlled by a number of mechanisms based on the properties within the boundary. At the Earth's magnetopause the spreading speed is also limited by the speed at which a shocked solar wind front can move along the magnetopause boundary. The speed at which a purely north to south rotational discontinuity propagates through the magnetosheath and contacts the magnetopause is measured here using the BlockâAdaptiveâTree Solar Wind RoeâType Upwind Scheme global magnetohydrodynamics model. The propagation speed along the magnetopause is fastest near the nose of the magnetopause and decreases with distance from the subsolar point. The average propagation speed along the dayside magnetopause is 847 km/s. This is significantly larger than observed rates of reconnection spreading at the magnetopause of 30â40 km/s indicating that, for the observed conditions, the speed of front propagation along the magnetopause does not limit or control the spreading rate of reconnection.Published versio
Outflow in global magnetohydrodynamics as a function of a passive inner boundary source
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106972/1/jgra50946.pd
The 2+1 Kepler Problem and Its Quantization
We study a system of two pointlike particles coupled to three dimensional
Einstein gravity. The reduced phase space can be considered as a deformed
version of the phase space of two special-relativistic point particles in the
centre of mass frame. When the system is quantized, we find some possibly
general effects of quantum gravity, such as a minimal distances and a foaminess
of the spacetime at the order of the Planck length. We also obtain a
quantization of geometry, which restricts the possible asymptotic geometries of
the universe.Comment: 59 pages, LaTeX2e, 9 eps figure
Panel Discussion - Management of Eurasian watermilfoil in the United States using native insects: State regulatory and management issues
While researchers have evaluated the potential of native
insect herbivores to manage nonindigenous aquatic plant
species such as Eurasian watermilfoil (
Myriophyllum spicatum
L.), the practical matters of regulatory compliance and implementation
have been neglected. A panel of aquatic nuisance
species program managers from three state natural
resource management agencies (Minnesota, Vermont and
Washington) discussed their regulatory and policy concerns.
In addition, one ecological consultant attempting to market
one of the native insects to manage Eurasian watermilfoil
added his perspective on the special challenges of distributing
a native biological control agent for management of Eurasian
watermilfoil
Broad Absorption Line Variability in Radio-Loud Quasars
We investigate C IV broad absorption line (BAL) variability within a sample
of 46 radio-loud quasars (RLQs), selected from SDSS/FIRST data to include both
core-dominated (39) and lobe-dominated (7) objects. The sample consists
primarily of high-ionization BAL quasars, and a substantial fraction have large
BAL velocities or equivalent widths; their radio luminosities and
radio-loudness values span ~2.5 orders of magnitude. We have obtained 34 new
Hobby-Eberly Telescope (HET) spectra of 28 BAL RLQs to compare to earlier SDSS
data, and we also incorporate archival coverage (primarily dual-epoch SDSS) for
a total set of 78 pairs of equivalent width measurements for 46 BAL RLQs,
probing rest-frame timescales of ~80-6000 d (median 500 d). In general, only
modest changes in the depths of segments of absorption troughs are observed,
akin to those seen in prior studies of BAL RQQs. Also similar to previous
findings for RQQs, the RLQs studied here are more likely to display BAL
variability on longer rest-frame timescales. However, typical values of
|Delta_EW| and |Delta_EW|/ are about 40+/-20% lower for BAL RLQs when
compared with those of a timescale-matched sample of BAL RQQs. Optical
continuum variability is of similar amplitude in BAL RLQs and BAL RQQs; for
both RLQs and RQQs, continuum variability tends to be stronger on longer
timescales. BAL variability in RLQs does not obviously depend upon their radio
luminosities or radio-loudness values, but we do find tentative evidence for
greater fractional BAL variability within lobe-dominated RLQs. Enhanced BAL
variability within more edge-on (lobe-dominated) RLQs supports some geometrical
dependence to the outflow structure.Comment: 27 pages, 16 figures, 6 tables, accepted to MNRAS, full Appendix A at
http://www.macalester.edu/~bmille13/balrlqs.htm
The ionospheric source of magnetospheric plasma is not a black box input for global models
Including ionospheric outflow in global magnetohydrodynamic models of nearâEarth outer space has become an important step toward understanding the role of this plasma source in the magnetosphere. Of the existing approaches, however, few tie the outflowing particle fluxes to magnetospheric conditions in a selfâconsistent manner. Doing so opens the magnetosphereâionosphere system to nonlinear massâenergy feedback loops, profoundly changing the behavior of the magnetosphereâionosphere system. Based on these new results, it is time for the community eschew treating ionospheric outflow as a simple black box source of magnetospheric plasma.Key PointsIonospheric outflow plays a critical role in the magnetosphereThe magnetosphere affects outflowModelers must account for this twoâway relationshipPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133592/1/jgra52677_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133592/2/jgra52677.pd
Validation of SWMF magnetic field and plasma
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94788/1/swe345.pd
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