2,098 research outputs found
Volunteer canola (B. napus) in western Canada
Non-Peer ReviewedIn western Canada, survey and small plot research has shown that volunteer canola persists for at least four years in rotation (Derksen at al. 1999; Thomas et al. 1999). It is not clear whether this is due to persistence of the seedbank additions during harvest or the result of replenishment of the seedbank by subsequent volunteers. We are examining the life cycle of volunteer canola beginning with the seedbank additions incurred during harvest and as well as a focus on the seedbank ecology of this species in western Canada. Research in Europe has shown that B. napus can be readily induced into secondary dormancy by
a combination of darkness and moisture stress (Pekrun, 1994). Nonetheless, field studies have revealed that only a small proportion of seeds persist via secondary dormancy in Europe (Pekrun et al. 1998).
Canadian B. napus genotypes differ in their potential for induction into secondary dormancy using a laboratory assay. While some genotypes consistently exhibit low potential for the induction into secondary dormancy, others consistently exhibit high potential for the induction into secondary dormancy. High temperatures are perhaps the most important contributing factor to the induction of secondary dormancy, while low temperatures rapidly remove secondary dormancy. These observations suggest the seed ecology of a typical summer-annual weed. Furthermore, observations in a field experiment in 2000 revealed that volunteer canola germination was limited to the early portion of the growing season. Spring seedbank evaluations indicated far greater seed viability than was reflected by field emergence. It is was not clear if
the seeds that did not emerge lost viability or were induced into secondary dormancy as our lab results would suggest. A more detailed field experiment examining the persistence of B. napus and induction into secondary dormancy was initiated
Slow dynamics for the dilute Ising model in the phase coexistence region
In this paper we consider the Glauber dynamics for a disordered ferromagnetic
Ising model, in the region of phase coexistence. It was conjectured several
decades ago that the spin autocorrelation decays as a negative power of time
[Huse and Fisher, Phys. Rev. B, 1987]. We confirm this behavior by establishing
a corresponding lower bound in any dimensions , together with an
upper bound when . Our approach is deeply connected to the Wulff
construction for the dilute Ising model. We consider initial phase profiles
with a reduced surface tension on their boundary and prove that, under mild
conditions, those profiles are separated from the (equilibrium) pure plus phase
by an energy barrier.Comment: 44 pages, 6 figure
The Bailey Point Region and Other Muskox Refugia in the Canadian Arctic: A Short Review
The muskox (Ovibos moschatus) is widely distributed over much of arctic Canada but only at a few locations do their densities remain high and populations relatively stable. These refugia constitute the most favourable muskox ranges in the Canadian Arctic Archipelago .... Refugia for muskoxen in the High Arctic include lowlands on eastern Axel Heiberg Island in the Mokka Fiord region, the lowlands of northeastern Devon Island, and the Bailey Point region of Melville Island .... All of those regions historically have supported high densities of muskoxen from time to time but the Bailey Point region must be considered the best habitat for muskoxen in the Canadian High Arctic. ..
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Efficiency Improvement Opportunities for Light-Duty Natural-Gas-Fueled Vehicles
The purpose of this report is to evaluate and make recommendations concerning technologies that promise to improve the efilciency of compressed natural gas (CNG) light-duty vehicles. Technical targets for CNG automotive technology given in the March 1998 OffIce of Advanced Automotive Technologies research and development plan were used as guidance for this effort. The technical target that necessitates this current study is to validate technologies that enable CNG light vehicles to have at least 10% greater - fuel economy (on a miles per gallon equivalent basis) than equivalent gasoline vehicles by 2006. Other tar- gets important to natural gas (NG) automotive technology and this study are to: (1) increase CNG vehicle range to 380 miles, (2) reduce the incremental vehicle cost (CNG vs gasoline) to $1500, and (3) meet the California ultra low-emission vehicle (ULEV) and Federal Tier 2 emission standards expected to be in effect in 2004
The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks
Numerical hydrodynamics simulations have established that disks which are
evolved under the condition of local isothermality will fragment into small
dense clumps due to gravitational instabilities when the Toomre stability
parameter is sufficiently low. Because fragmentation through disk
instability has been suggested as a gas giant planet formation mechanism, it is
important to understand the physics underlying this process as thoroughly as
possible. In this paper, we offer analytic arguments for why, at low ,
fragments are most likely to form first at the corotation radii of growing
spiral modes, and we support these arguments with results from 3D hydrodynamics
simulations.Comment: 21 pages, 1 figur
Monitoring evolved stars for binarity with the HERMES spectrograph
Binarity is often invoked to explain peculiarities that can not be explained
by the standard theory of stellar evolution. Detecting orbital motion via the
Doppler effect is the best method to test binarity when direct imaging is not
possible. However, when the orbital period exceeds the duration of a typical
observing run, monitoring often becomes problematic. Placing a high-throughput
spectrograph on a small semi- robotic telescope allowed us to carry out a
radial-velocity survey of various types of peculiar evolved stars. In this
review we highlight some findings after the first four years of observations.
Thus, we detect eccentric binaries among hot subdwarfs, barium, S stars, and
post- AGB stars with disks, which are not predicted by the standard binary
interaction theory. In disk objects, in addition, we find signs of the on-
going mass transfer to the companion, and an intriguing line splitting, which
we attribute to the scattered light of the primary.Comment: To appear in the proceedings of the conference "Setting a new
standard in the analysis of binary stars", A. Tkachenko (ed.), European
Astron. Soc. Publ. Se
Microscopic theory of atom-molecule oscillations in a Bose-Einstein condensate
In a recent experiment at JILA [E.A. Donley et al., Nature (London) 417, 529
(2002)] an initially pure condensate of Rb-85 atoms was exposed to a specially
designed time dependent magnetic field pulse in the vicinity of a Feshbach
resonance. The production of new components of the gas as well as their
oscillatory behavior have been reported. We apply a microscopic theory of the
gas to identify these components and determine their physical properties. Our
time dependent studies allow us to explain the observed dynamic evolution of
all fractions, and to identify the physical relevance of the pulse shape. Based
on ab initio predictions, our theory strongly supports the view that the
experiments have produced a molecular condensate.Comment: 18 pages, 20 figure
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