341 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
Mapping the Space of Genomic Signatures
We propose a computational method to measure and visualize interrelationships
among any number of DNA sequences allowing, for example, the examination of
hundreds or thousands of complete mitochondrial genomes. An "image distance" is
computed for each pair of graphical representations of DNA sequences, and the
distances are visualized as a Molecular Distance Map: Each point on the map
represents a DNA sequence, and the spatial proximity between any two points
reflects the degree of structural similarity between the corresponding
sequences. The graphical representation of DNA sequences utilized, Chaos Game
Representation (CGR), is genome- and species-specific and can thus act as a
genomic signature. Consequently, Molecular Distance Maps could inform species
identification, taxonomic classifications and, to a certain extent,
evolutionary history. The image distance employed, Structural Dissimilarity
Index (DSSIM), implicitly compares the occurrences of oligomers of length up to
(herein ) in DNA sequences. We computed DSSIM distances for more than
5 million pairs of complete mitochondrial genomes, and used Multi-Dimensional
Scaling (MDS) to obtain Molecular Distance Maps that visually display the
sequence relatedness in various subsets, at different taxonomic levels. This
general-purpose method does not require DNA sequence homology and can thus be
used to compare similar or vastly different DNA sequences, genomic or
computer-generated, of the same or different lengths. We illustrate potential
uses of this approach by applying it to several taxonomic subsets: phylum
Vertebrata, (super)kingdom Protista, classes Amphibia-Insecta-Mammalia, class
Amphibia, and order Primates. This analysis of an extensive dataset confirms
that the oligomer composition of full mtDNA sequences can be a source of
taxonomic information.Comment: 14 pages, 7 figures. arXiv admin note: substantial text overlap with
arXiv:1307.375
Post-flare UV light curves explained with thermal instability of loop plasma
In the present work we study the C8 flare occurred on September 26, 2000 at
19:49 UT and observed by the SOHO/SUMER spectrometer from the beginning of the
impulsive phase to well beyond the disappearance in the X-rays. The emission
first decayed progressively through equilibrium states until the plasma reached
2-3 MK. Then, a series of cooler lines, i.e. Ca x, Ca vii, Ne vi, O iv and Si
iii (formed in the temperature range log T = 4.3 - 6.3 under equilibrium
conditions), are emitted at the same time and all evolve in a similar way. Here
we show that the simultaneous emission of lines with such a different formation
temperature is due to thermal instability occurring in the flaring plasma as
soon as it has cooled below ~ 2 MK. We can qualitatively reproduce the relative
start time of the light curves of each line in the correct order with a simple
(and standard) model of a single flaring loop. The agreement with the observed
light curves is greatly improved, and a slower evolution of the line emission
is predicted, if we assume that the model loop consists of an ensemble of
subloops or strands heated at slightly different times. Our analysis can be
useful for flare observations with SDO/EVE.Comment: 24 pages, 7 figures, accepted for publicatio
Updated Atomic Data and Calculations for X-ray Spectroscopy
We describe the latest release of AtomDB, version 2.0.2, a database of atomic
data and a plasma modeling code with a focus on X-ray astronomy. This release
includes several major updates to the fundamental atomic structure and process
data held within AtomDB, incorporating new ionization balance data,
state-selective recombination data, and updated collisional excitation data for
many ions, including the iron L-shell ions from Fe to Fe and
all of the hydrogen- and helium-like sequences. We also describe some of the
effects that these changes have on calculated emission and diagnostic line
ratios, such as changes in the temperature implied by the He-like G-ratios of
up to a factor of 2.Comment: Submitted to ApJ, 12 pages, 9 figure
Sphinx measurements of the 2009 solar minimum x-ray emission
The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured
soft X-ray emission in the 1-15 keV energy range during the deep solar minimum
of 2009 with a sensitivity much greater than GOES. Several intervals are
identified when the X-ray flux was exceptionally low, and the flux and solar
X-ray luminosity are estimated. Spectral fits to the emission at these times
give temperatures of 1.7-1.9 MK and emission measures between 4 x 10^47 cm^-3
and 1.1 x 10^48 cm^-3. Comparing SphinX emission with that from the Hinode
X-ray Telescope, we deduce that most of the emission is from general coronal
structures rather than confined features like bright points. For one of 27
intervals of exceptionally low activity identified in the SphinX data, the
Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT
(0.1-2.4 keV) was less than most nearby K and M dwarfs.Comment: Astrophysical Journal, in press. 14 pp, 3 figure
Gabapentinium picrate
The title compound {systematic name: [1-(carboxymethyl)cyclohexyl]methanaminium 2,4,6-trinitrophenolate}, C9H18NO2
+·C6H2N3O7
−, was synthesized from picric acid and gabapentin. The crystal packing is stabilized by intramolecular N—H⋯O=N and N—H⋯O—Ph hydrogen bonds. An O—H⋯O interaction is also present
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