Front Structures in a Real Ginzburg-Landau Equation Coupled to a Mean Field

Localized traveling wave trains or pulses have been observed in various experiments in binary mixture convection. For strongly negative separation ratio, these pulse structures can be described as two interacting fronts of opposite orientation. An analytical study of the front solutions in a real Ginzburg-Landau equation coupled to a mean field is presented here as a first approach to the pulse solution. The additional mean field becomes important when the mass diffusion in the mixture is small as is the case in liquids. Within this framework it can lead to a hysteretic transition between slow and fast fronts when the Rayleigh number is changed.Comment: to appear in J. Bif. and Chaos, 7 pages (LaTeX) 1 figur

Circular 62

This is the eighth publication of grain performance trials in the Tanana River Valley. The first, published 7 years ago, included the results of spring cereal-variety tests conducted at Fairbanks and Delta Junction during the 1978 and 1979 growing seasons. Beginning in 1980, the variety-test results were annual publications. This report, like last year’s, is a shorter version than the first 6 publications of the series. It reflects continued budget constraints caused by Alaska’s sagging economy

Wavy stripes and squares in zero P number convection

A simple model to explain numerically observed behaviour of chaotically varying stripes and square patterns in zero Prandtl number convection in Boussinesq fluid is presented. The nonlinear interaction of mutually perpendicular sets of wavy rolls, via higher mode, may lead to a competition between the two sets of wavy rolls. The appearance of square patterns is due to the secondary forward Hopf bifurcation of a set of wavy rolls.Comment: 8 pages and 3 figures, late

Quasiperiodic waves at the onset of zero Prandtl number convection with rotation

We show the possibility of quasiperiodic waves at the onset of thermal convection in a thin horizontal layer of slowly rotating zero-Prandtl number Boussinesq fluid confined between stress-free conducting boundaries. Two independent frequencies emerge due to an interaction between a stationary instability and a self-tuned wavy instability in presence of coriolis force, if Taylor number is raised above a critical value. Constructing a dynamical system for the hydrodynamical problem, the competition between the interacting instabilities is analyzed. The forward bifurcation from the conductive state is self-tuned.Comment: 9 pages of text (LaTex), 5 figures (Jpeg format

Fluid boundary of a viscoplastic Bingham flow for finite solid deformations

The modelling of viscoplastic Bingham fluids often relies on a rheological constitutive law based on a "plastic rule function" often identical to the yield criterion of the solid state. It is also often assumed that this plastic rule function vanishes at the boundary between the solid and fluid states, based on the fact that it is true in the limit of small deformations of the solid state or for simple yield criteria. We show that this is not the case for finite deformations by considering the example of a two state flow on a tilted plane where the solid state is described by a Neo-Hookean model with a Von Mises yield criterion. This opens new approaches for the modelling and the computation of the fluid state boundaries

Patterns and bifurcations in low-Prandtl number Rayleigh-Benard convection

We present a detailed bifurcation structure and associated flow patterns for low-Prandtl number ($P=0.0002, 0.002, 0.005, 0.02$) Rayleigh-B\'{e}nard convection near its onset. We use both direct numerical simulations and a 30-mode low-dimensional model for this study. We observe that low-Prandtl number (low-P) convection exhibits similar patterns and chaos as zero-P convection \cite{pal:2009}, namely squares, asymmetric squares, oscillating asymmetric squares, relaxation oscillations, and chaos. At the onset of convection, low-P convective flows have stationary 2D rolls and associated stationary and oscillatory asymmetric squares in contrast to zero-P convection where chaos appears at the onset itself. The range of Rayleigh number for which stationary 2D rolls exist decreases rapidly with decreasing Prandtl number. Our results are in qualitative agreement with results reported earlier

Circular 52

This is the sixth publication in this format on grain performance trials in the Tanana River Valley. The first, published 5 years ago, included the results o f spring cereal-variety tests conducted at Fairbanks and Delta Junction during the 1978 and 1979 growing seasons. The variety-test results from the 1980, 1981, 1982, and 1983 growing seasons were annual publications. Included in this report are a weather summary, the 1984 variety-test results, and a plant-disease section.Introduction -- Standard Bushel Weights and Conversion from English to Metric Units -- Part I: Climatic Data for and Germplasm Evaluation: Tanana Valley Weather Summary: Table 1: Climatic Data for Delta Junction during the 1984 Growing Season, Table 2: Climatic Data for Fairbanks during the 1984 Growing Season; Barley Performance Trials: Table 3: Long-Term Average and Range of Yields for Barley Standard Varieties Grown at Fairbanks and Delta Junction, 1971-1984, Table 4: Barley Variety Trials Conducted at Delta Junction and Fairbanks during the 1984 Growing Season, Variety Descriptions, Table 5: Barley Varieties Tested at Fairbanks and Delta Junction, 1971-1984 -- Oat Performance Trials: Table 6 : Long-Term Average and Range in Yields for Oat Standard Varieties Grow n at Fairbanks and Delta Junction, 1971-1984, Table 7: Oat Variety Trials Conducted at Delta Junction and Fairbanks during the 1984 Growing Season, Variety Descriptions, Table 8 : Oat Varieties Tested at Fairbanks and Delta Junction, 1971-1984 -- Spring Wheat Performance Trials: Table 9: Long-Term Average and Range in Yields for Wheat Standard Varieties Grown at Fairbanks and Delta Junction, 1971-1984, Table 10: W heat Variety Trials Conducted at Fairbanks and Delta Junction during the 1984 Growing Season -- Variety Descriptions: Table 11: W heat Varieties Tested at Fairbanks and Delta Junction, 1971-1984 -- Part II: Plant-Disease Evaluation: Barley Diseases: Table 12: Summary of Diseases Observed on Barley Varieties under Field Conditions in the Delta-Clearwater Area, Snow M old Disease Com plex on W inter W heat and Lawn G ra s s e s, Diseases on O ther C r o p, Diseases O bserved on Crops during the 1984 Growing Season and T heir S ym ptom

Variational assimilation for xenon dynamical forecasts in neutronic using advanced background error covariance matrix modelling

Data assimilation method consists in combining all available pieces of information about a system to obtain optimal estimates of initial states. The different sources of information are weighted according to their accuracy by the means of error covariance matrices. Our purpose here is to evaluate the efficiency of variational data assimilation for the xenon induced oscillations forecasts in nuclear cores. In this paper we focus on the comparison between 3DVAR schemes with optimised background error covariance matrix B and a 4DVAR scheme. Tests were made in twin experiments using a simulation code which implements a mono-dimensional coupled model of xenon dynamics, thermal, and thermal–hydraulic processes. We enlighten the very good efficiency of the 4DVAR scheme as well as good results with the 3DVAR one using a careful multivariate modelling of B

Role of uniform horizontal magnetic field on convective flow

The effect of uniform magnetic field applied along a fixed horizontal direction in Rayleigh-B\'enard convection in low-Prandtl-number fluids has been studied using a low dimensional model. The model shows the onset of convection (primary instability) in the form of two dimensional stationary rolls in the absence of magnetic field, when the Rayleigh number $R$ is raised above a critical value $R_c$. The flow becomes three dimensional at slightly higher values of Rayleigh number via wavy instability. These wavy rolls become chaotic for slightly higher values of $R$ in low-Prandtl-number ($P_r$) fluids. A uniform magnetic field along horizontal plane strongly affects all kinds of convective flows observed at higher values of $R$ in its absence. As the magnetic field is raised above certain value, it orients the convective rolls in its own direction. Although the horizontal magnetic field does not change the threshold for the primary instability, it affects the threshold for secondary (wavy) instability. It inhibits the onset of wavy instability. The critical Rayleigh number $R_o (Q,P_r)$ at the onset of wavy instability, which depends on Chandrasekhar's number $Q$ and $P_r$, increases monotonically with $Q$ for a fixed value of $P_r$. The dimensionless number $R_o (Q, P_r)/(R_c Q P_r)$ scales with $Q$ as $Q^{-1}$. A stronger magnetic field suppresses chaos and makes the flow two dimensional with roll pattern aligned along its direction.Comment: 6 pages, 8 figure