7,746 research outputs found
Entanglement reduction induced by geometrical confinement in polymer thin films
We report simulation results on melts of entangled linear polymers confined
in a free-standing thin film. We study how the geometric constraints imposed by
the confinement alter the entanglement state of the system compared to the
equivalent bulk system using various observables. We find that the confinement
compresses the chain conformation uniaxially, decreasing the volume pervaded by
the chain, which in turn reduces the number of the accessible inter-chain
contact that could lead to entanglements. This local and non-uniform effect
depends on the position of the chain within the film. We also test a recently
presented theory that predicts how the number of entanglements decreases with
geometrical confinement.Comment: 28 pages, 10 figure
The PX-EM algorithm for fast stable fitting of Henderson's mixed model
This paper presents procedures for implementing the PX-EM algorithm of Liu, Rubin and Wu to compute REML estimates of variance covariance components in Henderson's linear mixed models. The class of models considered encompasses several correlated random factors having the same vector length e.g., as in random regression models for longitudinal data analysis and in sire-maternal grandsire models for genetic evaluation. Numerical examples are presented to illustrate the procedures. Much better results in terms of convergence characteristics (number of iterations and time required for convergence) are obtained for PX-EM relative to the basic EM algorithm in the random regression
Modelling of influential parameters on a continuous evaporation process by Doehlert shells
The modelling of the parameters that influence the continuous evaporation of an alcoholic extract was considered using Doehlert matrices. The work was performed with a wiped falling film evaporator that allowed us to study the influence of the pressure, temperature, feed flow and dry matter of the feed solution on the dry matter contents of the resulting concentrate, and the productivity of the process. The Doehlert shells were used to model the influential parameters. The pattern obtained from the experimental results was checked allowing for some dysfunction in the unit. The evaporator was modified and a new model applied; the experimental results were then in agreement with the equations. The model was finally determined and successfully checked in order to obtain an 8% dry matter concentrate with the best productivity; the results fit in with the industrial constraints of subsequent processes
Computerized “Psychophysical Testing Platform” to Control and Evaluate Multichannel Electrical Stimulation-Based Sensory Feedback
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