718 research outputs found
The emergence of a "doctrinal culture" within the Canadian Air Force: where it came from, where it's at and where to from here? Part 1: Doctrine and the Canadian Air Force prior to the end of the Cold War
The culture of the Canadian Air Force, like most other Western air forces, has not been traditionally characterised by a tendency towards theoretical or doctrinal development. Instead, an oral (rather than written) culture of passing lessons from senior to junior officers evolved early in the history of the Canadian Air Force and subsequently became entrenched. This was accompanied by a tendency to pragmatically focus on contemporary issues, to the detriment of broader theoretical and doctrinal development
The emergence of a "doctrinal culture" within the Canadian Air Force: where it came from, where it's at and where to from here? Part 2 : Towards a doctrinal culture within the Canadian Air Force
Drawing on the background provided in Part 1, this article examines the Canadian Air Force's attempts to develop doctrine since the formation of Air Command in 1975. This examination is undertaken in three sections. First, limited doctrine development between 1975 and 1989 is briefly discussed. Second, doctrine development during the 1990s is analysed in relation to the international rejuvenation of air power theory that occurred during that decade. Third, the apparent emergence of a tentative doctrinal culture within the Canadian Air Force during the past decade is considered. In conclusion, the future potential of this tentative culture is addressed, and some challenges that remain to be overcome are highlighted
Correlating the Energetics and Atomic Motions of the Metal-Insulator Transition of M1 Vanadium Dioxide
Materials that undergo reversible metal-insulator transitions are obvious
candidates for new generations of devices. For such potential to be realised,
the underlying microscopic mechanisms of such transitions must be fully
determined. In this work we probe the correlation between the energy landscape
and electronic structure of the metal-insulator transition of vanadium dioxide
and the atomic motions occurring using first principles calculations and high
resolution X-ray diffraction. Calculations find an energy barrier between the
high and low temperature phases corresponding to contraction followed by
expansion of the distances between vanadium atoms on neighbouring sub-lattices.
X-ray diffraction reveals anisotropic strain broadening in the low temperature
structure's crystal planes, however only for those with spacings affected by
this compression/expansion. GW calculations reveal that traversing this barrier
destabilises the bonding/anti-bonding splitting of the low temperature phase.
This precise atomic description of the origin of the energy barrier separating
the two structures will facilitate more precise control over the transition
characteristics for new applications and devices.Comment: 11 Pages, 8 Figure
Deep machine learning provides state-of-the art performance in image-based plant phenotyping
Deep learning is an emerging field that promises unparalleled results on many data analysis problems. We show the success offered by such techniques when applied to the challenging problem of image-based plant phenotyping, and demonstrate state-of-the-art results for root and shoot feature identification and localisation. We predict a paradigm shift in image-based phenotyping thanks to deep learning approaches
Evaluating Systematic Dependencies of Type Ia Supernovae: The Influence of Deflagration to Detonation Density
We explore the effects of the deflagration to detonation transition (DDT)
density on the production of Ni-56 in thermonuclear supernova explosions (type
Ia supernovae). Within the DDT paradigm, the transition density sets the amount
of expansion during the deflagration phase of the explosion and therefore the
amount of nuclear statistical equilibrium (NSE) material produced. We employ a
theoretical framework for a well-controlled statistical study of
two-dimensional simulations of thermonuclear supernovae with randomized initial
conditions that can, with a particular choice of transition density, produce a
similar average and range of Ni-56 masses to those inferred from observations.
Within this framework, we utilize a more realistic "simmered" white dwarf
progenitor model with a flame model and energetics scheme to calculate the
amount of Ni-56 and NSE material synthesized for a suite of simulated
explosions in which the transition density is varied in the range 1-3x10^7
g/cc. We find a quadratic dependence of the NSE yield on the log of the
transition density, which is determined by the competition between plume rise
and stellar expansion. By considering the effect of metallicity on the
transition density, we find the NSE yield decreases by 0.055 +/- 0.004 solar
masses for a 1 solar metallicity increase evaluated about solar metallicity.
For the same change in metallicity, this result translates to a 0.067 +/- 0.004
solar mass decrease in the Ni-56 yield, slightly stronger than that due to the
variation in electron fraction from the initial composition. Observations
testing the dependence of the yield on metallicity remain somewhat ambiguous,
but the dependence we find is comparable to that inferred from some studies.Comment: 15 pages, 13 figures, accepted to ApJ on July 6, 201
HST/ACS Photometry of Old Stars in NGC 1569: The Star Formation History of a Nearby Starburst
(abridged) We used HST/ACS to obtain deep V- and I-band images of NGC 1569,
one of the closest and strongest starburst galaxies in the Universe. These data
allowed us to study the underlying old stellar population, aimed at
understanding NGC 1569's evolution over a full Hubble time. We focus on the
less-crowded outer region of the galaxy, for which the color-magnitude diagram
(CMD) shows predominantly a red giant branch (RGB) that reaches down to the red
clump/horizontal branch feature (RC/HB). A simple stellar population analysis
gives clear evidence for a more complicated star formation history (SFH) in the
outer region. We derive the full SFH using a newly developed code, SFHMATRIX,
which fits the CMD Hess diagram by solving a non-negative least squares
problem. Our analysis shows that the relative brightnesses of the RGB tip and
RC/HB, along with the curvature and color of the RGB, provide enough
information to ameliorate the age-metallicity-extinction degeneracy. The
distance/reddening combination that best fits the data is E(B-V) = 0.58 +/-
0.03 and D = 3.06 +/- 0.18 Mpc. Star formation began ~ 13 Gyr ago, and this
accounts for the majority of the mass in the outer region. However, the initial
burst was followed by a relatively low, but constant, rate of star formation
until ~ 0.5-0.7 Gyr ago when there may have been a short, low intensity burst
of star formation.Comment: 50 pages, including 17 figures. Accepted for publication in A
Relativistic Corrections to the Triton Binding Energy
The influence of relativity on the triton binding energy is investigated. The
relativistic three-dimensional version of the Bethe-Salpeter equation proposed
by Blankenbecler and Sugar (BbS) is used. Relativistic (non-separable)
one-boson-exchange potentials (constructed in the BbS framework) are employed
for the two-nucleon interaction. In a 34-channel Faddeev calculation, it is
found that relativistic effects increase the triton binding energy by about 0.2
MeV. Including charge-dependence (besides relativity), the final triton binding
energy predictions are 8.33 and 8.16 MeV for the Bonn A and B potential,
respectively.Comment: 25 pages of text (latex), 1 figure (not included, available upon
request
Overproduction of cosmic superstrings
We show that the naive application of the Kibble mechanism seriously
underestimates the initial density of cosmic superstrings that can be formed
during the annihilation of D-branes in the early universe, as in models of
brane-antibrane inflation. We study the formation of defects in effective field
theories of the string theory tachyon both analytically, by solving the
equation of motion of the tachyon field near the core of the defect, and
numerically, by evolving the tachyon field on a lattice. We find that defects
generically form with correlation lengths of order M_s^{-1} rather than H^{-1}.
Hence, defects localized in extra dimensions may be formed at the end of
inflation. This implies that brane-antibrane inflation models where inflation
is driven by branes which wrap the compact manifold may have problems with
overclosure by cosmological relics, such as domain walls and monopoles.Comment: 31 pages, 16 figures, JHEP style; References added; Improved
discussion of initial condition
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