475,428 research outputs found
Finite Temperature Dynamical Correlations in Massive Integrable Quantum Field Theories
We consider the finite-temperature frequency and momentum dependent two-point
functions of local operators in integrable quantum field theories. We focus on
the case where the zero temperature correlation function is dominated by a
delta-function line arising from the coherent propagation of single particle
modes. Our specific examples are the two-point function of spin fields in the
disordered phase of the quantum Ising and the O(3) nonlinear sigma models. We
employ a Lehmann representation in terms of the known exact zero-temperature
form factors to carry out a low-temperature expansion of two-point functions.
We present two different but equivalent methods of regularizing the divergences
present in the Lehmann expansion: one directly regulates the integral
expressions of the squares of matrix elements in the infinite volume whereas
the other operates through subtracting divergences in a large, finite volume.
Our central results are that the temperature broadening of the line shape
exhibits a pronounced asymmetry and a shift of the maximum upwards in energy
("temperature dependent gap"). The field theory results presented here describe
the scaling limits of the dynamical structure factor in the quantum Ising and
integer spin Heisenberg chains. We discuss the relevance of our results for the
analysis of inelastic neutron scattering experiments on gapped spin chain
systems such as CsNiCl3 and YBaNiO5.Comment: 54 pages, 10 figure
Statistical optimization for passive scalar transport: maximum entropy production vs maximum Kolmogorov-Sinay entropy
We derive rigorous results on the link between the principle of maximum
entropy production and the principle of maximum Kolmogorov-Sinai entropy using
a Markov model of the passive scalar diffusion called the Zero Range Process.
We show analytically that both the entropy production and the Kolmogorov-Sinai
entropy seen as functions of f admit a unique maximum denoted fmaxEP and
fmaxKS. The behavior of these two maxima is explored as a function of the
system disequilibrium and the system resolution N. The main result of this
article is that fmaxEP and fmaxKS have the same Taylor expansion at _rst order
in the deviation of equilibrium. We find that fmaxEP hardly depends on N
whereas fmaxKS depends strongly on N. In particular, for a fixed difference of
potential between the reservoirs, fmaxEP (N) tends towards a non-zero value,
while fmaxKS (N) tends to 0 when N goes to infinity. For values of N typical of
that adopted by Paltridge and climatologists we show that fmaxEP and fmaxKS
coincide even far from equilibrium. Finally, we show that one can find an
optimal resolution N_ such that fmaxEP and fmaxKS coincide, at least up to a
second order parameter proportional to the non-equilibrium uxes imposed to the
boundaries.Comment: Nonlinear Processes in Geophysics (2015
The dynamics and control of large flexible space structures - 12, supplement 11
The rapid 2-D slewing and vibrational control of the unsymmetrical flexible SCOLE (Spacecraft Control Laboratory Experiment) with multi-bounded controls is considered. Pontryagin's Maximum Principle is applied to the nonlinear equations of the system to derive the necessary conditions for the optimal control. The resulting two point boundary value problem is then solved by using the quasilinearization technique, and the near minimum time is obtained by sequentially shortening the slewing time until the controls are near the bang-bang type. The tradeoff between the minimum time and the minimum flexible amplitude requirements is discussed. The numerical results show that the responses of the nonlinear system are significantly different from those of the linearized system for rapid slewing. The SCOLE station-keeping closed loop dynamics are re-examined by employing a slightly different method for developing the equations of motion in which higher order terms in the expressions for the mast modal shape functions are now included. A preliminary study on the effect of actuator mass on the closed loop dynamics of large space systems is conducted. A numerical example based on a coupled two-mass two-spring system illustrates the effect of changes caused in the mass and stiffness matrices on the closed loop system eigenvalues. In certain cases the need for redesigning control laws previously synthesized, but not accounting for actuator masses, is indicated
Outer limit of subdifferentials and calmness moduli in linear and nonlinear programming
With a common background and motivation, the main contributions of this paper are developed in two different directions. Firstly, we are concerned with functions which are the maximum of a finite amount of continuously differentiable functions of n real variables, paying attention to the case of polyhedral functions. For these max-functions, we obtain some results about outer limits of subdifferentials, which are applied to derive an upper bound for the calmness modulus of nonlinear systems. When confined to the convex case, in addition, a lower bound on this modulus is also obtained. Secondly, by means of a KKT index set approach, we are also able to provide a point-based formula for the calmness modulus of the argmin mapping of linear programming problems without any uniqueness assumption on the optimal set. This formula still provides a lower bound in linear semi-infinite programming. Illustrative examples are given
Combustion analysis of a CI engine performance using waste cooking biodiesel fuel with an artificial neural network aid
[Abstract]: A comprehensive combustion analysis has been conducted to evaluate the performance of a
commercial DI engine, water cooled two cylinders, in-line, naturally aspirated, RD270 Ruggerini
diesel engine using waste vegetable cooking oil as an alternative fuel. In order to compare the brake
power and the torques values of the engine, it has been tested under same operating conditions with
diesel fuel and waste cooking biodiesel fuel blends. The results were found to be very comparable. The
properties of biodiesel produced from waste vegetable oil was measured based on ASTM standards.
The total sulfur content of the produced biodiesel fuel was 18 ppm which is 28 times lesser than the
existing diesel fuel sulfur content used in the diesel vehicles operating in Tehran city (500 ppm). The
maximum power and torque produced using diesel fuel was 18.2 kW and 64.2 Nm at 3200 and 2400
rpm respectively. By adding 20% of waste vegetable oil methyl ester, it was noticed that the maximum
power and torque increased by 2.7 and 2.9% respectively, also the concentration of the CO and HC
emissions have significantly decreased when biodiesel was used. An artificial neural network (ANN)
was developed based on the collected data of this work. Multi layer perceptron network (MLP) was
used for nonlinear mapping between the input and the output parameters. Different activation functions
and several rules were used to assess the percentage error between the desired and the predicted values. The results showed that the training algorithm of Back Propagation was sufficient enough in predicting the engine torque, specific fuel consumption and exhaust gas components for different engine speeds and different fuel blends ratios. It was found that the R2 (R: the coefficient of determination) values are 0.99994, 1, 1 and 0.99998 for the engine torque, specific fuel consumption,CO and HC emissions, respectively
Resonances and resonant frequencies for a class of nonlinear systems
Resonant phenomena for a class of nonlinear systems, which can be described by a SDOF model with a polynomial type nonlinear stiffness, are investigated using Nonlinear Output Frequency Response Functions (NOFRFs). The concepts of resonance and resonant frequencies are proposed for the first time for a class of nonlinear systems. The effects of damping on the resonances and resonant frequencies are also analyzed. These results produce a novel interpretation of energy transfer phenomena in this class of nonlinear systems and show how the damping effect influences the system resonant frequencies and amplitudes. The results are important for the design and fault diagnosis of mechanical systems and structures which can be described by the SDOF nonlinear model
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