3,987 research outputs found
Assortative mixing in close-packed spatial networks
Background
In recent years, there is aroused interest in expressing complex systems as networks of interacting nodes. Using descriptors from graph theory, it has been possible to classify many diverse systems derived from social and physical sciences alike. In particular, folded proteins as examples of self-assembled complex molecules have also been investigated intensely using these tools. However, we need to develop additional measures to classify different systems, in order to dissect the underlying hierarchy.
Methodology and Principal Findings
In this study, a general analytical relation for the dependence of nearest neighbor degree correlations on degree is derived. Dependence of local clustering on degree is shown to be the sole determining factor of assortative versus disassortative mixing in networks. The characteristics of networks constructed from spatial atomic/molecular systems exemplified by self-organized residue networks built from folded protein structures and block copolymers, atomic clusters and well-compressed polymeric melts are studied. Distributions of statistical properties of the networks are presented. For these densely-packed systems, assortative mixing in the network construction is found to apply, and conditions are derived for a simple linear dependence.
Conclusions
Our analyses (i) reveal patterns that are common to close-packed clusters of atoms/molecules, (ii) identify the type of surface effects prominent in different close-packed systems, and (iii) associate fingerprints that may be used to classify networks with varying types of correlations
Solar EUV, XUV and soft X-ray telescope facilities
Facility class, high resolution instrumentation can enable maximum spatial, spectral and temporal resolutions and provide understanding of the complex physical conditions in the outer solar atmosphere and the mechanisms responsible for these conditions. The scientific rationale for facility class instruments operating in the EUV, XUV, and soft X ray spectral ranges are discussed. Possible configurations for these facilities and priorities for their development are considered
On Spectrum of Neighbourhood Corona Product of Signed Graphs
Given two signed graphs with nodes and
, the neighbourhood corona, is the signed graph
obtained by taking one copy of and copies of , and
joining every neighbour of the node with each nodes of the
copy of by a new signed edge. In this paper we will determine the
condition for to be balanced. We also determine the
adjacency spectrum of for arbitrary and
, and Laplacian and signless Laplacian spectrum of
for regular and arbitrary , in terms
of the corresponding spectrum of and
The Pinhole/Occulter Facility
A large occulting system in space can be used for high resolution X-ray observations and for large aperture coronagraphic observations in visible and UV light. The X-ray observations can combine high angular resolution in hand (10 keV) X-radiation with the high sensitivity of a multiple pinhole camera, and can permit sensitive observations of bremsstrahlung from nonthermal particles in the corona. The large aperture coronagraphs have two major advantages: high angular resolution and good photon collection. This will permit observations of small scale structures in the corona for the first time and will give sufficient counting rates above the coronal background rates for sensitive diagnostic analysis of intensities and line profiles for coronal structures in the solar wind acceleration region. The technical basis for performing observations with a large occulting system in these three wavelength ranges is described as well as a pinhole/occulter facility presently being considered for Spacelab. Some indications about future developments are included
Observed Variability of the Solar Mg II h Spectral Line
The Mg II h&k doublet are two of the primary spectral lines observed by the
Sun-pointing Interface Region Imaging Spectrograph (IRIS). These lines are
tracers of the magnetic and thermal environment that spans from the photosphere
to the upper chromosphere. We use a double gaussian model to fit the Mg II h
profile for a full-Sun mosaic dataset taken 24-Aug-2014. We use the ensemble of
high-quality profile fits to conduct a statistical study on the variability of
the line profile as it relates the magnetic structure, dynamics, and
center-to-limb viewing angle.
The average internetwork profile contains a deeply reversed core and is
weakly asymmetric at h2. In the internetwork, we find a strong correlation
between h3 wavelength and profile asymmetry as well h1 width and h2 width. The
average reversal depth of the h3 core is inversely related to the magnetic
field. Plage and sunspots exhibit many profiles which do not contain a
reversal. These profiles also occur infrequently in the internetwork. We see
indications of magnetically aligned structures in plage and network in
statistics associated with the line core, but these structures are not clear or
extended in the internetwork. The center-to-limb variations are compared with
predictions of semi-empirical model atmospheres. We measure a pronounced limb
darkening in the line core which is not predicted by the model. The aim of this
work is to provide a comprehensive measurement baseline and preliminary
analysis on the observed structure and formation of the Mg II profiles observed
by IRIS.Comment: Accepted for publicatio
WFIRST Coronagraph Technology Requirements: Status Update and Systems Engineering Approach
The coronagraphic instrument (CGI) on the Wide-Field Infrared Survey
Telescope (WFIRST) will demonstrate technologies and methods for high-contrast
direct imaging and spectroscopy of exoplanet systems in reflected light,
including polarimetry of circumstellar disks. The WFIRST management and CGI
engineering and science investigation teams have developed requirements for the
instrument, motivated by the objectives and technology development needs of
potential future flagship exoplanet characterization missions such as the NASA
Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR
Surveyor (LUVOIR). The requirements have been refined to support
recommendations from the WFIRST Independent External Technical/Management/Cost
Review (WIETR) that the WFIRST CGI be classified as a technology demonstration
instrument instead of a science instrument. This paper provides a description
of how the CGI requirements flow from the top of the overall WFIRST mission
structure through the Level 2 requirements, where the focus here is on
capturing the detailed context and rationales for the CGI Level 2 requirements.
The WFIRST requirements flow starts with the top Program Level Requirements
Appendix (PLRA), which contains both high-level mission objectives as well as
the CGI-specific baseline technical and data requirements (BTR and BDR,
respectively)... We also present the process and collaborative tools used in
the L2 requirements development and management, including the collection and
organization of science inputs, an open-source approach to managing the
requirements database, and automating documentation. The tools created for the
CGI L2 requirements have the potential to improve the design and planning of
other projects, streamlining requirement management and maintenance. [Abstract
Abbreviated]Comment: 16 pages, 4 figure
- …