Phi-four solitary waves in a parabolic potentia: existence, stability, and collisional dynamics

We explore a φ4 model with an added external parabolic potential term. This term dramatically alters the spectral properties of the system. We identify single and multiple kink solutions and examine their stability features; importantly, all of the stationary structures turn out to be unstable. We complement these with a dynamical study of the evolution of a single kink in the trap, as well as of the scattering of kink and anti-kink solutions of the model. We observe that some of the key characteristics of kink-antikink collisions, such as the critical velocity and the multi-bounce windows, are sensitively dependent on the trap strength parameter, as well as the initial displacement of the kink and antikink.Accepted manuscrip

Two-soliton collisions in a near-integrable lattice system

We examine collisions between identical solitons in a weakly perturbed Ablowitz-Ladik (AL) model, augmented by either onsite cubic nonlinearity (which corresponds to the Salerno model, and may be realized as an array of strongly overlapping nonlinear optical waveguides), or a quintic perturbation, or both. Complex dependences of the outcomes of the collisions on the initial phase difference between the solitons and location of the collision point are observed. Large changes of amplitudes and velocities of the colliding solitons are generated by weak perturbations, showing that the elasticity of soliton collisions in the AL model is fragile (for instance, the Salerno's perturbation with the relative strength of 0.08 can give rise to a change of the solitons' amplitudes by a factor exceeding 2). Exact and approximate conservation laws in the perturbed system are examined, with a conclusion that the small perturbations very weakly affect the norm and energy conservation, but completely destroy the conservation of the lattice momentum, which is explained by the absence of the translational symmetry in generic nonintegrable lattice models. Data collected for a very large number of collisions correlate with this conclusion. Asymmetry of the collisions (which is explained by the dependence on the location of the central point of the collision relative to the lattice, and on the phase difference between the solitons) is investigated too, showing that the nonintegrability-induced effects grow almost linearly with the perturbation strength. Different perturbations (cubic and quintic ones) produce virtually identical collision-induced effects, which makes it possible to compensate them, thus finding a special perturbed system with almost elastic soliton collisions.Comment: Phys. Rev. E, in pres

Effect of cropping frequency, wheat classes, and flexible rotations on yield, production, and nitrogen economy in a Brown Chernozem

Non-Peer ReviewedProducers in the semiarid Canadian prairies frequently summerfallow (F) to conserve water, control weeds, and to maximize soil N reserves; however, this practice often results in soil degradation. A crop rotation experiment was initiated in 1987 on a medium textured, Orthic Brown Chernozem at Swift Current, to determine the most ideal cropping frequency for this region and whether a fixed rotation such as fallow-wheat-wheat (F-W-W) would be more effective than flexible rotations in which fallowing is decided each spring based on criteria such as available soil water (if water), or the need to control perennial weed infestations (if weeds). The study also compares the production of traditional Canada Western Red Spring (CWRS) wheat class with the newer higher yielding (Hy), Canada Prairie Spring (CPS) wheat class. The rotations included F-W-W, F-W-W-W, F-Hy-Hy, Continuous wheat (Cont W), Cont W (if weeds), and Cont W (if water). Over the study period (1987-1998), weather conditions were generally favourable and yields were above average for this region. Canada Prairie Spring wheat out-yielded CWRS by 35% when grown on fallow and by 15% when grown on stubble; however, straw yields of the two wheat classes were similar on fallow and CPS was 7% less than CWRS on stubble. Harvest index (HI) averaged 45% for CPS and 40% for CWRS wheat. Grain N concentration averaged 25.5 g kg-1 for CWRS and 22.5 g kg-1 for CPS; straw N concentration averaged 4.0 g kg-1 for CWRS and 4.6 g kg-1 for CPS. Nitrogen yield for grain from CPS was 13% greater than from CWRS when grown on fallow, but class had no effect when wheat was grown on stubble. Nitrogen yield of straw was generally not affected by wheat class. Nitrogen yield of the above-ground plant parts generally mimicked grain N yield responses. Nitrogen harvest index (NHI) averaged 80% for both wheat classes, whether grown on fallow or stubble. On a rotation basis, F-W-W-W and Cont W (if weeds) produced 9% more grain than F-W-W, while Cont W (if water) produced 24% more grain, and Cont W and F-Hy-Hy produced 29% more grain than FW-W. Nitrogen production in the grain, straw and above-ground plant material was lowest in F-W-W, highest in Cont W, and intermediate for other rotations

Managing an annual legume green manure crop for fallow replacement in southwestern Saskatchewan

Non-Peer ReviewedSome scientists have suggested that in the Brown soil zone an annual legume green manure crop (GM) could be used as a partial-fallow replacement to protect the soil against erosion and increase its N fertility, particularly when combined with a snow trapping technique to replenish soil water used by the legume. We assessed this possibility by comparing yields, N economy, water use efficiency, and economic returns of hard red spring wheat (W) grown in rotation with Indianhead black lentil (i.e., GM-W-W) vs. that obtained in a F-W-W system. Further, we assessed whether a change in management of the GM crop (i.e., moving to earlier seeding and earlier turn-down) was advantageous to the overall performance of this practice. The study was conducted over 12 years (1988-99) on a loam soil at Swift Current, SK. (wheat stubble was left tall to trap snow, tillage was kept to a minimum, and the wheat was fertilized based on soil tests). When examined after 6 years, the results suggested that by waiting for full bloom of the legume (usually late July or early August) to maximize N2 fixation, soil water was being depleted to the detriment of yields of the following wheat crop. However, the change in management of the GM crop since 1994 has resulted in wheat yields following GM equalling those after fallow. It also produced a significant increase (after one rotation cycle) in grain protein and N yields of aboveground parts of wheat in the GM-W-W compared to the F-W-W system, and lead to a gradual decrease in fertilizer N requirements of wheat in the GM system in the last 6 years. These savings in N fertilizer, together with savings in tillage and herbicide costs for weed control on partial-fallow vs conventional-fallow areas, and higher revenues from the enhanced grain protein, more than offset the added costs for seed and management of the GM crop. Thus, our results imply that, with proper management and given sufficient time, an annual legume GMcereal rotation is a viable option for area producers

Quantitative changes in soil C over 17 years under minimum tillage, well fertilized crop rotations in the Brown Soil Zone

Non-Peer Reviewe

Metallic ferromagnetism without exchange splitting

In the band theory of ferromagnetism there is a relative shift in the position of majority and minority spin bands due to the self-consistent field due to opposite spin electrons. In the simplest realization, the Stoner model, the majority and minority spin bands are rigidly shifted with respect to each other. Here we consider models at the opposite extreme, where there is no overall shift of the energy bands. Instead, upon spin polarization one of the bands broadens relative to the other. Ferromagnetism is driven by the resulting gain in kinetic energy. A signature of this class of mechanisms is that a transfer of spectral weight in optical absorption from high to low frequencies occurs upon spin polarization. We show that such models arise from generalized tight binding models that include off-diagonal matrix elements of the Coulomb interaction. For certain parameter ranges it is also found that reentrant ferromagnetism occurs. We examine properties of these models at zero and finite temperatures, and discuss their possible relevance to real materials

Anomalies of ac driven solitary waves with internal modes: Nonparametric resonances induced by parametric forces

We study the dynamics of kinks in the $\phi^4$ model subjected to a parametric ac force, both with and without damping, as a paradigm of solitary waves with internal modes. By using a collective coordinate approach, we find that the parametric force has a non-parametric effect on the kink motion. Specifically, we find that the internal mode leads to a resonance for frequencies of the parametric driving close to its own frequency, in which case the energy of the system grows as well as the width of the kink. These predictions of the collective coordinate theory are verified by numerical simulations of the full partial differential equation. We finally compare this kind of resonance with that obtained for non-parametric ac forces and conclude that the effect of ac drivings on solitary waves with internal modes is exactly the opposite of their character in the partial differential equation.Comment: To appear in Phys Rev

A posteriori inclusion of parton density functions in NLO QCD final-state calculations at hadron colliders: The APPLGRID Project

A method to facilitate the consistent inclusion of cross-section measurements based on complex final-states from HERA, TEVATRON and the LHC in proton parton density function (PDF) fits has been developed. This can be used to increase the sensitivity of LHC data to deviations from Standard Model predictions. The method stores perturbative coefficients of NLO QCD calculations of final-state observables measured in hadron colliders in look-up tables. This allows the posteriori inclusion of parton density functions (PDFs), and of the strong coupling, as well as the a posteriori variation of the renormalisation and factorisation scales in cross-section calculations. The main novelties in comparison to original work on the subject are the use of higher-order interpolation, which substantially improves the trade-off between accuracy and memory use, and a CPU and computer memory optimised way to construct and store the look-up table using modern software tools. It is demonstrated that a sufficient accuracy on the cross-section calculation can be achieved with reasonably small look-up table size by using the examples of jet production and electro-weak boson (Z, W) production in proton-proton collisions at a center-of-mass energy of 14 TeV at the LHC. The use of this technique in PDF fitting is demonstrated in a PDF-fit to HERA data and simulated LHC jet cross-sections as well as in a study of the jet cross-section uncertainties at various centre-of-mass energies

Long-term productivity and economic performance of spring wheat production systems in southwestern Saskatchewan

Non-Peer Reviewe

Fluctuations and Intrinsic Pinning in Layered Superconductors

A flux liquid can condense into a smectic crystal in a pure layered superconductors with the magnetic field oriented nearly parallel to the layers. If the smectic order is commensurate with the layering, this crystal is {\sl stable} to point disorder. By tilting and adjusting the magnitude of the applied field, both incommensurate and tilted smectic and crystalline phases are found. We discuss transport near the second order smectic freezing transition, and show that permeation modes lead to a small non--zero resistivity and large but finite tilt modulus in the smectic crystal.Comment: 4 pages + 1 style file + 1 figure (as uufile) appended, REVTEX 3.