149 research outputs found
Common Representation of Information Flows for Dynamic Coalitions
We propose a formal foundation for reasoning about access control policies
within a Dynamic Coalition, defining an abstraction over existing access
control models and providing mechanisms for translation of those models into
information-flow domain. The abstracted information-flow domain model, called a
Common Representation, can then be used for defining a way to control the
evolution of Dynamic Coalitions with respect to information flow
Collisional Ionization Equilibrium for Optically Thin Plasmas. I. Updated Recombination Rate Coefficients for Bare though Sodium-like Ions
Reliably interpreting spectra from electron-ionized cosmic plasmas requires
accurate ionization balance calculations for the plasma in question. However,
much of the atomic data needed for these calculations have not been generated
using modern theoretical methods and are often highly suspect. This translates
directly into the reliability of the collisional ionization equilibrium (CIE)
calculations. We make use of state-of-the-art calculations of dielectronic
recombination (DR) rate coefficients for the hydrogenic through Na-like ions of
all elements from He up to and including Zn. We also make use of
state-of-the-art radiative recombination (RR) rate coefficient calculations for
the bare through Na-like ions of all elements from H through to Zn. Here we
present improved CIE calculations for temperatures from to K
using our data and the recommended electron impact ionization data of
\citet{Mazz98a} for elements up to and including Ni and Mazzotta (private
communication) for Cu and Zn. DR and RR data for ionization stages that have
not been updated are also taken from these two additional sources. We compare
our calculated fractional ionic abundances using these data with those
presented by Mazzotta et al. for all elements from H to Ni. The differences in
peak fractional abundance are up to 60%. We also compare with the fractional
ionic abundances for Mg, Si, S, Ar, Ca, Fe, and Ni derived from the modern DR
calculations of \citet{Gu03a,Gu04a} for the H-like through Na-like ions, and
the RR calculations of \citet{Gu03b} for the bare through F-like ions. These
results are in better agreement with our work, with differences in peak
fractional abundance of less than 10%.Comment: 83 pages, 38 figures, 41 tables Accepted to ApJ
Carbon Ionization Stages as a Diagnostic of the Solar Wind
Oxygen charge states measured by in situ instrumentation have long been used as a powerful diagnostic of the solar corona and to discriminate between different solar wind regimes, both because they freeze in very close to the Sun, and because the oxygen element abundance is comparatively high, allowing for statistically relevant measures. Like oxygen, carbon is also rather abundant and freezes in very close to the Sun. Here, we show an analysis of carbon and oxygen ionic charge states. First, through auditory and Fourier analysis of in situ measurements of solar wind ion composition by ACE /SWICS we show that some carbon ion ratios are very sensitive to solar wind type, even more sensitive than the commonly used oxygen ion ratios. Then we study the evolution of the ionization states of carbon and oxygen by means of a freeze-in code, and find that carbon ions, commonly found in the solar wind, freeze in at comparable coronal distances, while oxygen ions evolve over a much larger range of coronal distances. Finally, we show that carbon and oxygen ion abundance ratios have similar sensitivity to the electron plasma temperature, but the carbon ratios are more robust against atomic physics uncertainties and a better indicator of the temperature of the solar wind source regions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98573/1/0004-637X_744_2_100.pd
Ionization state, excited populations and emission of impurities in dynamic finite density plasmas: I. The generalized collisional-radiative model for light elements
The paper presents an integrated view of the population structure and its role in establishing the ionization state of light elements in dynamic, finite density, laboratory and astrophysical plasmas. There are four main issues, the generalized collisional-radiative picture for metastables in dynamic plasmas with Maxwellian free electrons and its particularizing to light elements, the methods of bundling and projection for manipulating the population equations, the systematic production/use of state selective fundamental collision data in the metastable resolved picture to all levels for collisonal-radiative modelling and the delivery of appropriate derived coefficients for experiment analysis. The ions of carbon, oxygen and neon are used in illustration. The practical implementation of the methods described here is part of the ADAS Project
Seropositivity to Leptospira interrogans serovar Bratislava associated to reproductive problems without significant biochemical or hematological alterations in horses
Parental cultural models and resources for understanding mathematical achievement in culturally diverse school settings
This paper proposes that the theoretical concept of cultural models can offer useful insights into parental involvement in their child’s mathematical achievement and the resources they use to go about gaining information in culturally diverse learning settings. This examination takes place within a cultural-developmental framework and draws on the notion of cultural models to explicate parental understandings of their child’s mathematics achievement and what resources are used to make sense of this. Three parental resources are scrutinized: (a) the teacher, (b) examination test results, and (c) constructions of child development. The interviews with 22 parents revealed some ambiguity around the interpretation of these resources by the parent, which was often the result of incongruent cultural models held between the home and the school. The resources mentioned are often perceived as being unambiguous but show themselves instead to be highly interpretive because of the diversity of cultural models in existence in culturally diverse settings. Parents who are in minority or marginalized positions tend to have difficulties in interpreting cultural models held by school, thereby disempowering them to be parentally involved in the way the school would like
Chiropractic care and the risk of vertebrobasilar stroke: results of a case–control study in U.S. commercial and Medicare Advantage populations
Electron-ion Recombination of Fe X forming Fe IX and of Fe XI forming Fe X: Laboratory Measurements and Theoretical Calculations
We have measured electron-ion recombination for Fe forming Fe
and for Fe forming Fe using merged beams at the TSR heavy-ion
storage-ring in Heidelberg. The measured merged beams recombination rate
coefficients (MBRRC) for relative energies from 0 to 75 eV are presented,
covering all dielectronic recombination (DR) resonances associated with 3s->3p
and 3p->3d core transitions in the spectroscopic species Fe X and Fe XI,
respectively. We compare our experimental results to multi-configuration
Breit-Pauli (MCBP) calculations and find significant differences. From the
measured MBRRC we have extracted the DR contributions and transform them into
plasma recombination rate coefficients (PRRC) for astrophysical plasmas with
temperatures from 10^2 to 10^7 K. This spans across the regimes where each ion
forms in photoionized or in collisionally ionized plasmas. For both temperature
regimes the experimental uncertainties are 25% at a 90% confidence level. The
formerly recommended DR data severely underestimated the rate coefficient at
temperatures relevant for photoionized gas. At the temperatures relevant for
photoionized gas, we find agreement between our experimental results and MCBP
theory. At the higher temperatures relevant for collisionally ionized gas, the
MCBP calculations yield a Fe XI DR rate coefficent which is significantly
larger than the experimentally derived one. We present parameterized fits to
our experimentally derived DR PRRC.Comment: 44 Pages, 5 Figures. Accepted for publication in Astrophys.
LEMUR: Large European Module for solar Ultraviolet Research. European contribution to JAXA's Solar-C mission
Understanding the solar outer atmosphere requires concerted, simultaneous
solar observations from the visible to the vacuum ultraviolet (VUV) and soft
X-rays, at high spatial resolution (between 0.1" and 0.3"), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK, from the
chromosphere to the flaring corona), and the capability of measuring magnetic
fields through spectropolarimetry at visible and near-infrared wavelengths.
Simultaneous spectroscopic measurements sampling the entire temperature range
are particularly important.
These requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload providing a
significant improvement of imaging and spectropolarimetric capabilities in the
UV, visible, and near-infrared with respect to what is available today and
foreseen in the near future.
The Large European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload of
high-resolution imaging spectrographs and cameras. LEMUR consists of two major
components: a VUV solar telescope with a 30 cm diameter mirror and a focal
length of 3.6 m, and a focal-plane package composed of VUV spectrometers
covering six carefully chosen wavelength ranges between 17 and 127 nm. The
LEMUR slit covers 280" on the Sun with 0.14" per pixel sampling. In addition,
LEMUR is capable of measuring mass flows velocities (line shifts) down to 2
km/s or better.
LEMUR has been proposed to ESA as the European contribution to the Solar C
mission.Comment: 35 pages, 14 figures. To appear on Experimental Astronom
A Global Two-temperature Corona and Inner Heliosphere Model: A Comprehensive Validation Study
The recent solar minimum with very low activity provides us a unique opportunity for validating solar wind models. During CR2077 (2008 November 20 through December 17), the number of sunspots was near the absolute minimum of solar cycle 23. For this solar rotation, we perform a multi-spacecraft validation study for the recently developed three-dimensional, two-temperature, Alfvén-wave-driven global solar wind model (a component within the Space Weather Modeling Framework). By using in situ observations from the Solar Terrestrial Relations Observatory (STEREO) A and B , Advanced Composition Explorer ( ACE ), and Venus Express , we compare the observed proton state (density, temperature, and velocity) and magnetic field of the heliosphere with that predicted by the model. Near the Sun, we validate the numerical model with the electron density obtained from the solar rotational tomography of Solar and Heliospheric Observatory /Large Angle and Spectrometric Coronagraph C2 data in the range of 2.4 to 6 solar radii. Electron temperature and density are determined from differential emission measure tomography (DEMT) of STEREO A and B Extreme Ultraviolet Imager data in the range of 1.035 to 1.225 solar radii. The electron density and temperature derived from the Hinode /Extreme Ultraviolet Imaging Spectrometer data are also used to compare with the DEMT as well as the model output. Moreover, for the first time, we compare ionic charge states of carbon, oxygen, silicon, and iron observed in situ with the ACE /Solar Wind Ion Composition Spectrometer with those predicted by our model. The validation results suggest that most of the model outputs for CR2077 can fit the observations very well. Based on this encouraging result, we therefore expect great improvement for the future modeling of coronal mass ejections (CMEs) and CME-driven shocks.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98628/1/0004-637X_745_1_6.pd
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