27,029 research outputs found
Systems Practice in Engineering: Reflections on Teaching Research Methods and Contribution to Methodological Development
Towards a Common Language of Infrastructure Interdependency
Infrastructure systems can exist interdependently with one another either by design, necessity or evolution. There is
evidence that interdependencies can be the source of emergent benefits and hazards, and therefore there is value in
their identification and management. Achieving this requires collaboration and communication between infrastructure
stakeholders across all relevant sectors.
Recognising, developing and sharing multiple understandings of infrastructure interdependency and dependency will
facilitate a wide range of multi-disciplinary and cross-sectorial work and support productive stakeholder dialogues.
This paper therefore aims to initiate discussion around the nature of infrastructure interdependency and dependency
in order to establish the basis of a useful, coherent and complete conceptual taxonomy. It sets out an approach for
locating this taxonomy and language within a framework of commonplace stakeholder viewpoints.
The paper looks at the potential structural arrangements of infrastructure interdependencies before exploring the
qualitative ways in which the relationships can be characterised. This builds on the existing body of knowledge as
well as experience through case studies in developing an Interdependency Planning and Management Framework for
Infrastructure
Norwegian Aerospace Activities: an Overview
Excerpts from a Governmental Investigation concerning Norwegian participation in the European Space Organization (ESA) is presented. The implications and advantages of such a move and a suggestion for the reorganization of Norwegian Aerospace activity is given
Topological Anderson Insulator in Three Dimensions
Disorder, ubiquitously present in solids, is normally detrimental to the
stability of ordered states of matter. In this letter we demonstrate that not
only is the physics of a strong topological insulator robust to disorder but,
remarkably, under certain conditions disorder can become fundamentally
responsible for its existence. We show that disorder, when sufficiently strong,
can transform an ordinary metal with strong spin-orbit coupling into a strong
topological `Anderson' insulator, a new topological phase of quantum matter in
three dimensions.Comment: 5 pages, 2 figures. For related work and info visit
http://www.physics.ubc.ca/~franz
Surface magnetic ordering in topological insulators with bulk magnetic dopants
We show that a three dimensional topological insulator doped with magnetic
impurities in the bulk can have a regime where the surface is magnetically
ordered but the bulk is not. This is in contrast to conventional materials
where bulk ordered phases are typically more robust than surface ordered
phases. The difference originates from the topologically protected gapless
surface states characteristic of topological insulators. We study the problem
using a mean field approach in two concrete models that give the same
qualitative result, with some interesting differences. Our findings could help
explain recent experimental results showing the emergence of a spectral gap in
the surface state of Bi2Se3 doped with Mn or Fe atoms, but with no measurable
bulk magnetism.Comment: 8 pages, 6 figure
Witten effect in a crystalline topological insulator
It has been noted a long time ago that a term of the form theta (e^2/2\pi h)
B dot E may be added to the standard Maxwell Lagrangian without modifying the
familiar laws of electricity and magnetism. theta is known to particle
physicists as the 'axion' field and whether or not it has a nonzero expectation
value in vacuum remains a fundamental open question of the Standard Model. A
key manifestation of the axion term is the Witten effect: a unit magnetic
monopole placed inside a medium with non-zero theta is predicted to bind a
(generally fractional) electric charge -e(theta/2 pi+n) with n integer. Here we
conduct a first test of the Witten effect, based on the recently established
fact that the axion term with theta=pi emerges naturally in the description of
the electromagnetic response of a new class of crystalline solids called
topological insulators - materials distinguished by strong spin-orbit coupling
and non-trivial band structure. Using a simple physical model for a topological
insulator, we demonstrate the existence of a fractional charge bound to a
monopole by an explicit numerical calculation. We also propose a scheme for
generating an 'artificial' magnetic monopole in a topological insulator film,
that may be used to facilitate the first experimental test of Witten's
prediction.Comment: 7 pages, 2 figures. Version to appear in PRB; minor changes,
discussion of several issues expande
The Arecibo Dual-Beam Survey: The HI Mass Function of Galaxies
We use the HI-selected galaxy sample from the Arecibo Dual-Beam Survey
(Rosenberg & Schneider 2000) to determine the shape of the HI mass function of
galaxies in the local universe using both the step-wise maximum likelihood and
the 1/V_tot methods. Our survey region spanned all 24 hours of right ascension
at selected declinations between 8 and 29 degrees covering ~430 deg^2 of sky in
the main beam. The survey is not as deep as some previous Arecibo surveys, but
it has a larger total search volume and samples a much larger area of the sky.
We conducted extensive tests on all aspects of the galaxy detection process,
allowing us to empirically correct for our sensitivity limits, unlike the
previous surveys. The mass function for the entire sample is quite steep, with
a power-law slope of \alpha ~ -1.5. We find indications that the slope of the
HI mass function is flatter near the Virgo cluster, suggesting that
evolutionary effects in high density environments may alter the shape of the HI
mass function. These evolutionary effects may help to explain differences in
the HI mass function derived by different groups. We are sensitive to the most
massive sources (log M > 5x10^10 M\solar) over most of the declination range,
\~1 sr, and do not detect any massive low surface brightness galaxies. These
statistics restrict the population of Malin 1-like galaxies to <5.5x10^-6
Mpc^-3.Comment: ApJ accepted, 12 page
Photometric catalog of nearby globular clusters (I)
We present the first part of the first large and homogeneous CCD
color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular
clusters (GGC) imaged in the V and I bands using only two telescopes (one for
each hemisphere). The observed clusters represent 75% of the known Galactic
globulars with (m-M)v<=16.15 mag, cover most of the globular cluster
metallicity range (-2.2 <= [Fe/H] <= -0.4), and span Galactocentric distances
from ~1.2 to ~18.5 kpc.
In this paper, the CMDs for the 39 GGCs observed in the southern hemisphere
are presented. The remaining 13 northern hemisphere clusters of the catalog are
presented in a companion paper. For four clusters (NGC 4833, NGC 5986, NGC
6543, and NGC 6638) we present for the first time a CMD from CCD data. The
typical CMD spans from the 22nd V magnitude to the tip of the red giant branch.
Based on a large number of standard stars, the absolute photometric calibration
is reliable to the ~0.02 mag level in both filters.
This catalog, because of its homogeneity, is expected to represent a useful
data base for the measurement of the main absolute and relative parameters
characterizing the CMD of GGCs.Comment: 34 pages, 108 figures, Astronomy & Astrophysics Supplement Series, in
press. Full resolution figures can be obtained from the authors upon reques
- …