3,652 research outputs found
Stability of travelling-wave solutions for reaction-diffusion-convection systems
We are concerned with the asymptotic behaviour of classical solutions of
systems of the form u_t = Au_xx + f(u, u_x), x in R, t>0, u(x,t) a vector in
RN, with u(x,0)= U(x), where A is a positive-definite diagonal matrix and f is
a 'bistable' nonlinearity satisfying conditions which guarantee the existence
of a comparison principle. Suppose that there is a travelling-front solution w
with velocity c, that connects two stable equilibria of f. We show that if U is
bounded, uniformly continuously differentiable and such that w(x) - U(x) is
small when the modulus of x is large, then there exists y in R such that u(.,
t) converges to w(.+y-ct) in the C1 norm at an exponential rate as t tends to
infinity. Our approach extends an idea developed by Roquejoffre, Terman and
Volpert in the convectionless case, where f is independent of u_x.Comment: 23 pages. To appear in Topological Methods in Nonlinear Analysi
POLICY CHANGE AND THE DAIRY COOPERATIVES SECTOR, 1980-1988: AN EXAMINATION OF OPERATIONAL PERFORMANCE
This paper employs the dual approach to trace the impact of public policy instruments upon the operational and financial performance of U.S. dairy cooperatives. A restricted profit function is applied to the Operations and Finance Statements for years 1980-1988 of thirty major dairy cooperatives. The data set for this study is provided by the Agricultural Cooperatives Service, USDA. A specification search such as described in Mountain and Hsaio (1989) is conducted to ensure the most appropriate fit for the data provided. From the estimated parameters, output supply and factor demand elasticities will be obtained by way of well-known functional relationships. From these elasticities, the short-run effect of any change in Federal Marketing Order prices upon cooperative revenues may be calculated in a straightforward manner. By retracing the price effects of Federal Order policy changes in a stepwise manner, the impact on cooperative operations and revenues of these changes is approximated.Agribusiness, Agricultural and Food Policy,
The Horizon Problem and New Generation Cooperatives: Another Look at Minnesota Corn Processors
Agribusiness,
Key challenges in agent-based modelling for geo-spatial simulation
Agent-based modelling (ABM) is fast becoming the dominant paradigm in social simulation due primarily to a worldview that suggests that complex systems emerge from the bottom-up, are highly decentralised, and are composed of a multitude of heterogeneous objects called agents. These agents act with some purpose and their interaction, usually through time and space, generates emergent order, often at higher levels than those at which such agents operate. ABM however raises as many challenges as it seeks to resolve. It is the purpose of this paper to catalogue these challenges and to illustrate them using three somewhat different agent-based models applied to city systems. The seven challenges we pose involve: the purpose for which the model is built, the extent to which the model is rooted in independent theory, the extent to which the model can be replicated, the ways the model might be verified, calibrated and validated, the way model dynamics are represented in terms of agent interactions, the extent to which the model is operational, and the way the model can be communicated and shared with others. Once catalogued, we then illustrate these challenges with a pedestrian model for emergency evacuation in central London, a hypothetical model of residential segregation tuned to London data which elaborates the standard Schelling (1971) model, and an agent-based residential location built according to spatial interactions principles, calibrated to trip data for Greater London. The ambiguities posed by this new style of modelling are drawn out as conclusions
Detection of benzimidazole carbamates and amino metabolites in liver by surface plasmon resonance-biosensor
This research was funded by the Irish Department of Agriculture, Fisheries and Food under the Food Institutional Research Measure as part of the National Development Plan (Project 05/R&D/TN/355)peer-reviewedTwo surface plasmon resonance (SPR) biosensor screening assays were developed and validated to detect 11 benzimidazole carbamate (BZT) and four amino-benzimidazole veterinary drug residues in liver tissue. The assays used polyclonal antibodies, raised in sheep, to detect BZTs and amino-benzimidazoles. A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction method was developed to isolate benzimidazole carbamate residues. Liver samples were extracted using an acetonitrile extraction method. BZTs were purified by dispersive solid phase extraction (d-SPE) using C18 sorbent. Residues of amino-benzimidazoles were effectively cleaned-up using a simple cyclohexane defatting step. The assays were validated in accordance with the performance criteria described in 2002/657/EC. The BZT assay limit of detection was calculated to be 32 μg kg−1, the detection capability (CCβ) was determined to be 50 μg kg−1 and the mean recovery of analytes was in the range 77–132%. The amino-benzimidazole assay limit of detection was determined to be 41 μg kg−1, the CCβ was determined to be 75 μg kg−1 and analyte recovery was in the range 103–116%. Biosensor assay performance was tested by analysing liver tissue from animals treated with benzimidazole drugs and comparing the results with an ultra high performance liquid chromatography tandem mass spectrometry (UHPLC–MS/MS) confirmatory method. All non-compliant samples were identified using the biosensor assays.Department of Agriculture, Food and the Marin
Measuring thermodynamic length
Thermodynamic length is a metric distance between equilibrium thermodynamic
states. Among other interesting properties, this metric asymptotically bounds
the dissipation induced by a finite time transformation of a thermodynamic
system. It is also connected to the Jensen-Shannon divergence, Fisher
information and Rao's entropy differential metric. Therefore, thermodynamic
length is of central interest in understanding matter out-of-equilibrium. In
this paper, we will consider how to define thermodynamic length for a small
system described by equilibrium statistical mechanics and how to measure
thermodynamic length within a computer simulation. Surprisingly, Bennett's
classic acceptance ratio method for measuring free energy differences also
measures thermodynamic length.Comment: 4 pages; Typos correcte
Temperature-extended Jarzynski relation: Application to the numerical calculation of the surface tension
We consider a generalization of the Jarzynski relation to the case where the
system interacts with a bath for which the temperature is not kept constant but
can vary during the transformation. We suggest to use this relation as a
replacement to the thermodynamic perturbation method or the Bennett method for
the estimation of the order-order surface tension by Monte Carlo simulations.
To demonstrate the feasibility of the method, we present some numerical data
for the 3D Ising model
Non-equilibrium Relations for Spin Glasses with Gauge Symmetry
We study the applications of non-equilibrium relations such as the Jarzynski
equality and fluctuation theorem to spin glasses with gauge symmetry. It is
shown that the exponentiated free-energy difference appearing in the Jarzynski
equality reduces to a simple analytic function written explicitly in terms of
the initial and final temperatures if the temperature satisfies a certain
condition related to gauge symmetry. This result is used to derive a lower
bound on the work done during the non-equilibrium process of temperature
change. We also prove identities relating equilibrium and non-equilibrium
quantities. These identities suggest a method to evaluate equilibrium
quantities from non-equilibrium computations, which may be useful to avoid the
problem of slow relaxation in spin glasses.Comment: 8 pages, 2 figures, submitted to JPS
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