623 research outputs found
Effect of seeding date, environment, and storage on canola seed vigour
Non-Peer ReviewedSeed vigour has been identified as one of the leading factors limiting stand establishment and yield in western Canada. Field studies at Scott, SK demonstrated that seed derived from Fall and April-sown canola produced higher plant densities, higher biomass at bolting, and higher seed yield than seed derived from May-sown canola. This study established the impact of seeding date on seed quality and vigour, which in turn affected emergence, seedling vigour and yield. Also, seed vigour slowly declines within one year, primarily from seed derived from the May-sown canola. Currently we are in the process of uncovering which genes and proteins are in common with vigour irrespective of seed source. We will combine our analysis with synchrotron technologies for a much more in-depth understanding of what constitutes “seed
vigour” to develop a rapid, simple, and inexpensive method that will identify intrinsic characteristics of superior seed lots, as well as seed lots that lose vigour when stored under adverse conditions. In addition, we have initiated a study to compare hormones and metabolites during cold acclimation and freeze-induced injury/recovery to correlate these changes with winter survival. This research will identify traits that can be used in marker-assisted/molecular breeding programs for winter hardiness and possible genetic engineering studies on abiotic stress tolerance of seeds and plants. To further understand the processes involved in stress tolerance, we utilized gene transfer techniques to produce a PNT canola that over-expresses a novel gene which results in higher yields under stressful conditions. These PNT lines were tested in the field over 3 years across Western Canada in non-stressed, moderately stressed, or severely
stressed areas. At each location, several lines flowered and matured 1 to 3 weeks earlier. The faster maturating PNT lines (up to 55% more mature at harvest) had increased yields (up to 32% increase) and enhanced seed quality (up to 87% increase in larger and more mature seed) versus the control. These results, both in controlled laboratory tests and in field trials, have been optimistic for genetic engineering of plants for enhanced stress tolerance without losing agronomical important characteristics
Shake-up Processes in a Low-Density Two-Dimensional Electron Gas: Spin-Dependent Transitions to Higher Hole Landau Levels
A theory of shake-up processes in photoabsorption of an interacting
low-density two-dimensional electron gas (2DEG) in strong magnetic fields is
presented. In these processes, an incident photon creates an electron-hole pair
and, because of Coulomb interactions, simultaneously excites one particle to
higher Landau levels (LL's). In this work, the spectra of correlated charged
spin-singlet and spin-triplet electron-hole states in the first hole LL and
optical transitions to these states (i.e., shake-ups to the first hole LL) are
studied. Our results indicate, in particular, the presence of optically-active
three-particle quasi-discrete states in the exciton continuum that may give
rise to surprisingly sharp Fano resonances in strong magnetic fields. The
relation between shake-ups in photoabsorption of the 2DEG and in the 2D hole
gas (2DHG), and shake-ups of isolated negative X^- and positive X^+ trions are
discussed.Comment: 8 pages, 8 figures. References updated, one figure added (Fig. 6).
Accepted in Phys. Rev.
Nuclear effects in the Drell-Yan process at very high energies
We study Drell-Yan (DY) dilepton production in proton(deuterium)-nucleus and
in nucleus-nucleus collisions within the light-cone color dipole formalism.
This approach is especially suitable for predicting nuclear effects in the DY
cross section for heavy ion collisions, as it provides the impact parameter
dependence of nuclear shadowing and transverse momentum broadening, quantities
that are not available from the standard parton model. For p(D)+A collisions we
calculate nuclear shadowing and investigate nuclear modification of the DY
transverse momentum distribution at RHIC and LHC for kinematics corresponding
to coherence length much longer than the nuclear size. Calculations are
performed separately for transversely and longitudinally polarized DY photons,
and predictions are presented for the dilepton angular distribution.
Furthermore, we calculate nuclear broadening of the mean transverse momentum
squared of DY dileptons as function of the nuclear mass number and energy. We
also predict nuclear effects for the cross section of the DY process in heavy
ion collisions. We found a substantial nuclear shadowing for valence quarks,
stronger than for the sea.Comment: 46 pages, 18 figures, title changed and some discussion added,
accepted for publication in PR
From nonassociativity to solutions of the KP hierarchy
A recently observed relation between 'weakly nonassociative' algebras A (for
which the associator (A,A^2,A) vanishes) and the KP hierarchy (with dependent
variable in the middle nucleus A' of A) is recalled. For any such algebra there
is a nonassociative hierarchy of ODEs, the solutions of which determine
solutions of the KP hierarchy. In a special case, and with A' a matrix algebra,
this becomes a matrix Riccati hierarchy which is easily solved. The matrix
solution then leads to solutions of the scalar KP hierarchy. We discuss some
classes of solutions obtained in this way.Comment: 7 pages, 4 figures, International Colloquium 'Integrable Systems and
Quantum Symmetries', Prague, 15-17 June 200
Screened Coulomb interactions in metallic alloys: II Screening beyond the single-site and atomic sphere approximations
A quantitative description of the configurational part of the total energy of
metallic alloys with substantial atomic size difference cannot be achieved in
the atomic sphere approximation: It needs to be corrected at least for the
multipole moment interactions in the Madelung part of the one-electron
potential and energy. In the case of a random alloy such interactions can be
accounted for only by lifting the atomic sphere and single-site approximations,
in order to include the polarization due to local environment effects.
Nevertheless a simple parameterization of the screened Coulomb interactions for
the ordinary single-site methods, including the generalized perturbation
method, is still possible. We obtained such a parameterization for bulk and
surface NiPt alloys, which allows one to obtain quantitatively accurate
effective interactions in this system.Comment: 24 pages, 2 figure
Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation
The fully nonlinear response of a many-level tunneling system to a strong
alternating field of high frequency is studied in terms of the
Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent
tunneling current is calculated exactly and its resonance structure is
elucidated. In particular, it is shown that under certain reasonable conditions
on the physical parameters, the Fourier component is sharply peaked at
, where is the spacing between
two levels. This frequency multiplication results from the highly nonlinear
process of photon absorption (or emission) by the tunneling system. It is
also conjectured that this effect (which so far is studied mainly in the
context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from
[email protected], submitted to Phys.Rev.
Brownian motion of a charged particle in electromagnetic fluctuations at finite temperature
The fluctuation-dissipation theorem is a central theorem in nonequilibrium
statistical mechanics by which the evolution of velocity fluctuations of the
Brownian particle under a fluctuating environment is intimately related to its
dissipative behavior. This can be illuminated in particular by an example of
Brownian motion in an ohmic environment where the dissipative effect can be
accounted for by the first-order time derivative of the position. Here we
explore the dynamics of the Brownian particle coupled to a supraohmic
environment by considering the motion of a charged particle interacting with
the electromagnetic fluctuations at finite temperature. We also derive
particle's equation of motion, the Langevin equation, by minimizing the
corresponding stochastic effective action, which is obtained with the method of
Feynman-Vernon influence functional. The fluctuation-dissipation theorem is
established from first principles. The backreaction on the charge is known in
terms of electromagnetic self-force given by a third-order time derivative of
the position, leading to the supraohmic dynamics. This self-force can be argued
to be insignificant throughout the evolution when the charge barely moves. The
stochastic force arising from the supraohmic environment is found to have both
positive and negative correlations, and it drives the charge into a fluctuating
motion. Although positive force correlations give rise to the growth of the
velocity dispersion initially, its growth slows down when correlation turns
negative, and finally halts, thus leading to the saturation of the velocity
dispersion. The saturation mechanism in a suparohmic environment is found to be
distinctly different from that in an ohmic environment. The comparison is
discussed.Comment: accepter by Foundation of Physics, for IARD 6, 200
True and intentionally fabricated memories
The aim of the experiment reported here was to investigate the processes underlying the construction of truthful and deliberately fabricated memories. Properties of memories created to be intentionally false - fabricated memories - were compared to properties of memories believed to be true - true memories. Participants recalled and then wrote or spoke true memories and fabricated memories of everyday events. It was found that true memories were reliably more vivid than fabricated memories and were nearly always recalled from a first person perspective. In contrast, fabricated differed from true memories in that they were judged to be reliably older, were more frequently recalled from a third person perspective, and linguistic analysis revealed that they required more cognitive effort to generate. No notable differences were found across modality of reporting. Finally, it was found that, intentionally fabricated memories were created by recalling and then ‘editing’ true memories. Overall, these findings show that true and fabricated memories systematically differ, despite the fact that both are based on true memories
Influence of mild cognitive impairment and body mass index on white matter integrity assessed by diffusion tensor imaging
Mild cognitive impairment (MCI), a prodromal stage of Alzheimer's disease, is characterized by decreased memory and cognition, which are linked to degenerative changes in the brain. To assess whether white matter (WM) integrity is compromised in MCI, we collected diffusion-weighted images from 60 healthy older adults (OA) (69.16 ± 0.7) and 20 older adults with amnestic MCI (72.45 ± 1.9). WM integrity differences were examined using Tract-Based Spatial Statistics (TBSS). We hypothesized that those with MCI would have diminished WM integrity relative to OA. In a whole-brain comparison, those with MCI showed higher axial diffusivity in the splenium (SCC) and body of the corpus callosum (BCC), superior corona radiata (SCR), and the retrolenticular part of the internal capsule (RLIC) (p's < .05 TFCE-corrected). Additionally, significant between-group connectivity differences were observed using probabilistic tractography between the SCC, chosen from the TBSS results, and forceps major and minor (p-value's < .05). To further relate a physical health indicator to WM alterations, linear regression showed significant interactions between cognitive status and body mass index (BMI) on diffusivity outcome measures from probabilistic tractography (p-value-'s < .05). Additionally, we examined the association between relational memory, BMI, and WM integrity. WM integrity was positively associated with relational memory performance. These findings suggest that these regions may be more sensitive to early markers of neurodegenerative disease and health behaviors, suggesting that modifiable lifestyle factors may affect white matter integrity
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