946 research outputs found
Integrability and Conformal Symmetry in the BCS model
The exactly solvable BCS Hamiltonian of superconductivity is considered from
several viewpoints: Richardson's ansatz, conformal field theory, integrable
inhomogenous vertex models and Chern-Simons theory.Comment: Latex with macros included, 12 pages, Proceedings of the NATO
Advanced Research Workshop on Statistical Field Theories, Como 18-23 June
2001. Editors: Andrea Cappelli and Giuseppe Mussardo. to be published by
Kluwer, Academic Publishers. Corrected some typos and further acknowledgment
The long-term agronomic and economic effects of crop rotations in western Canada
Non-Peer ReviewedAgriculture Canada Research Stations in western Canada have conducted more than 68 long-term crop rotation experiments since the early 1900's; twenty of these are still ongoing. A committee of scientists, representing all Research Stations on the Prairies has just completed an in-depth review and summary of the major findings from these studies. Based on their findings, they also developed recommendations that can be used by managers in decision making and rationalization of resource use for current and future
studies of this kind. The resulting two publications which will be released in early 1990 include: i) a bulletin entitled 'Benefits of Crop Rotation for Sustainable Agriculture in Dryland Farming', 'Which presents producer recommendations on how to run an efficient, economical, and environmentally responsible cropping operation, and ii) a detailed technical book entitled 'Crop Rotation Studies on the Canadian Prairies', which is directed at the scientific community but is also useful for extension personnel and producers. This paper highlights some of the main aspects reported in these publications and attempts to give a coherent and broader interpretation of the underlying principles and processes of crop production. The discussion focuses on the effects of rotation length, crop sequence, substitutes for summerfallow, and N and P fertilizer, on crop production, grain and forage quality, soil moisture conservation and moisture use efficiency, N and P uptake by the plants, nutrient losses, soil quality, profitability, nonrenewable energy efficiency, and crop pests
Yang-Mills Solutions on Euclidean Schwarzschild Space
We show that the apparently periodic Charap-Duff Yang-Mills `instantons' in
time-compactified Euclidean Schwarzschild space are actually time independent.
For these solutions, the Yang-Mills potential is constant along the time
direction (no barrier) and therefore, there is no tunneling. We also
demonstrate that the solutions found to date are three dimensional monopoles
and dyons. We conjecture that there are no time-dependent solutions in the
Euclidean Schwarzschild background.Comment: 12 pages, references added, version to appear in PR
Dynamical Renormalization Group Approach to Quantum Kinetics in Scalar and Gauge Theories
We derive quantum kinetic equations from a quantum field theory implementing
a diagrammatic perturbative expansion improved by a resummation via the
dynamical renormalization group. The method begins by obtaining the equation of
motion of the distribution function in perturbation theory. The solution of
this equation of motion reveals secular terms that grow in time, the dynamical
renormalization group resums these secular terms in real time and leads
directly to the quantum kinetic equation. We used this method to study the
relaxation in a cool gas of pions and sigma mesons in the O(4) chiral linear
sigma model. We obtain in relaxation time approximation the pion and sigma
meson relaxation rates. We also find that in large momentum limit emission and
absorption of massless pions result in threshold infrared divergence in sigma
meson relaxation rate and lead to a crossover behavior in relaxation. We then
study the relaxation of charged quasiparticles in scalar electrodynamics
(SQED). While longitudinal, Debye screened photons lead to purely exponential
relaxation, transverse photons, only dynamically screened by Landau damping
lead to anomalous relaxation, thus leading to a crossover between two different
relaxational regimes. We emphasize that infrared divergent damping rates are
indicative of non-exponential relaxation and the dynamical renormalization
group reveals the correct relaxation directly in real time. Finally we also
show that this method provides a natural framework to interpret and resolve the
issue of pinch singularities out of equilibrium and establish a direct
correspondence between pinch singularities and secular terms. We argue that
this method is particularly well suited to study quantum kinetics and transport
in gauge theories.Comment: RevTeX, 40 pages, 4 eps figures, published versio
A Real-Space Full Multigrid study of the fragmentation of Li11+ clusters
We have studied the fragmentation of Li11+ clusters into the two
experimentally observed products (Li9+,Li2) and (Li10+,Li) The ground state
structures for the two fragmentation channels are found by Molecular Dynamics
Simulated Annealing in the framework of Local Density Functional theory.
Energetics considerations suggest that the fragmentation process is dominated
by non-equilibrium processes. We use a real-space approach to solve the
Kohn-Sham problem, where the Laplacian operator is discretized according to the
Mehrstellen scheme, and take advantage of a Full MultiGrid (FMG) strategy to
accelerate convergence. When applied to isolated clusters we find our FMG
method to be more efficient than state-of-the-art plane wave calculations.Comment: 9 pages + 6 Figures (in gzipped tar file
A remark on non-Abelian classical kinetic theory
It is known that non-Abelian classical kinetic theory reproduces the Hard
Thermal/Dense Loop (HTL/HDL) effective action of QCD, obtained after
integrating out the hardest momentum scales from the system, as well as the
first higher dimensional operator beyond the HTL/HDL level. We discuss here its
applicability at still higher orders, by comparing the exact classical
effective action obtained in the static limit, with the 1-loop quantum
effective potential. We remark that while correct types of operators arise, the
classical colour algebra reproduces correctly the prefactor of the 4-point
function only for matter in asymptotically high dimensional colour
representations.Comment: 6 page
On tolerable and desirable behaviors in supervisory control of discrete event systems
We formulate and solve a new supervisory control problem for discrete event systems. The objective is to design a logical controller—or supervisor—such that the discrete event system satisfies a given set of requirements that involve event ordering. The controller must deal with a limited amount of controllability in the form of uncontrollable events. Our problem formulation considers that the requirements for the behavior (i.e., set of traces) of the controlled system are specified in terms of a “desired” behavior and a larger “tolerated” behavior. Due to the uncontrollable events, one may wish to tolerate behavior that sometimes exceeds the ideal desired behavior if overall this results in achieving more of the desired behavior. The general solution of our problem is completely characterized. The nonblocking solution is also analyzed in detail. This solution requires the study of a new class of controllable languages. Several results are proved about this class of languages. Algorithms to compute certain languages of interest within this class are also presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45034/1/10626_2005_Article_BF01797143.pd
in NonCommutative Standard Model
We study the top quark decay to b quark and W boson in the NonCommutative
Standard Model (NCSM). The lowest contribution to the decay comes from the
terms quadratic in the matrix describing the noncommutative (NC) effects while
the linear term is seen to identically vanish because of symmetry. The NC
effects are found to be significant only for low values of the NC
characteristic scale.Comment: 11 page Latex file containing 2 eps figures (redrawn). More
discussion included. To appear in PR
Measuring Parton Densities in the Pomeron
We present a program to measure the parton densities in the pomeron using
diffractive deep inelastic scattering and diffractive photoproduction, and to
test the resulting parton densities by applying them to other processes such as
the diffractive production of jets in hadron-hadron collisions. Since QCD
factorization has been predicted NOT to apply to hard diffractive scattering,
this program of fitting and using parton densities might be expected to fail.
Its success or failure will provide useful information on the space-time
structure of the pomeron.Comment: Contains revisions based on Phys. Rev. D referee comments. RevTeX
version 3, epsf, 31 pages. Uuencoded compressed postscript figures appended.
Uncompressed postscript files available at
ftp://ftp.phys.psu.edu/pub/preprint/psuth136
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