231,524 research outputs found
Optimal controllers for finite wordlength implementation
When a controller is implemented in a digital computer, with A/D and D/A conversion, the numerical errors of the computation can drastically affect the performance of the control system. There exists realizations of a given controller transfer function yielding arbitrarily large effects from computational errors. Since, in general, there is no upper bound, it is important to have a systematic way of reducing these effects. Optimum controller designs are developed which take account of the digital round-off errors in the controller implementation and in the A/D and D/A converters. These results provide a natural extension to the Linear Quadratic Gaussian (LQG) theory since they reduce to the standard LQG controller when infinite precision computation is used. But for finite precision the separation principle does not hold
Thermal loading in the laser holography nondestructive testing of a composite structure
A laser holographic interferometry method that has variable sensitivity to surface deformation was applied to the investigation of composite test samples under thermal loading. A successful attempt was made to detect debonds in a fiberglass-epoxy-ceramic plate. Experimental results are presented along with the mathematical analysis of the physical model of the thermal loading and current conduction in the composite material
Extraordinary variability and sharp transitions in a maximally frustrated dynamic network
Using Monte Carlo and analytic techniques, we study a minimal dynamic network
involving two populations of nodes, characterized by different preferred
degrees. Reminiscent of introverts and extroverts in a population, one set of
nodes, labeled \textit{introverts} (), prefers fewer contacts (a lower
degree) than the other, labeled \textit{extroverts} (). As a starting point,
we consider an \textit{extreme} case, in which an simply cuts one of its
links at random when chosen for updating, while an adds a link to a random
unconnected individual (node). The model has only two control parameters,
namely, the number of nodes in each group, and ). In the steady
state, only the number of crosslinks between the two groups fluctuates, with
remarkable properties: Its average () remains very close to 0 for all
or near its maximum () if
. At the transition (), the fraction
wanders across a substantial part of , much like a pure random walk.
Mapping this system to an Ising model with spin-flip dynamics and unusual
long-range interactions, we note that such fluctuations are far greater than
those displayed in either first or second order transitions of the latter.
Thus, we refer to the case here as an `extraordinary transition.' Thanks to the
restoration of detailed balance and the existence of a `Hamiltonian,' several
qualitative aspects of these remarkable phenomena can be understood
analytically.Comment: 6 pages, 3 figures, accepted for publication in EP
Extreme Thouless effect in a minimal model of dynamic social networks
In common descriptions of phase transitions, first order transitions are
characterized by discontinuous jumps in the order parameter and normal
fluctuations, while second order transitions are associated with no jumps and
anomalous fluctuations. Outside this paradigm are systems exhibiting `mixed
order transitions' displaying a mixture of these characteristics. When the jump
is maximal and the fluctuations range over the entire range of allowed values,
the behavior has been coined an `extreme Thouless effect'. Here, we report
findings of such a phenomenon, in the context of dynamic, social networks.
Defined by minimal rules of evolution, it describes a population of extreme
introverts and extroverts, who prefer to have contacts with, respectively, no
one or everyone. From the dynamics, we derive an exact distribution of
microstates in the stationary state. With only two control parameters,
(the number of each subgroup), we study collective variables of
interest, e.g., , the total number of - links and the degree
distributions. Using simulations and mean-field theory, we provide evidence
that this system displays an extreme Thouless effect. Specifically, the
fraction jumps from to (in the
thermodynamic limit) when crosses , while all values appear with
equal probability at .Comment: arXiv admin note: substantial text overlap with arXiv:1408.542
Holographic nondestructive tests performed on composite samples of ceramic-epoxy-fiberglass sandwich structure
When a hologram storing more than one wave is illuminated with coherent light, the reconstructed wave fronts interfere with each other or with any other phase-related wave front derived from the illuminating source. This multiple wave front comparison is called holographic interferometry, and its application is called holographic nondestructive testing (HNDT). The theoretical aspects of HNDT techniques and the sensitivity of the holographic system to the geometrical placement of the optical components are briefly discussed. A unique HNDT system which is mobile and possesses variable sensitivity to stress amplitude is discribed, the experimental evidence of the application of this system to the testing of the hidden debonds in a ceramic-epoxy-fiberglass structure used for sample testing of the radome of the Pershing missile system is presented
Two-stage Turing model for generating pigment patterns on the leopard and the jaguar
Based on the results of phylogenetic analysis, which showed that flecks are the primitive pattern of the felid family and all other patterns including rosettes and blotches develop from it, we construct a Turing reaction-diffusion model which generates spot patterns initially. Starting from this spotted pattern, we successfully generate patterns of adult leopards and jaguars by tuning parameters of the model in the subsequent phase of patterning
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