On the Elementwise Convergence of Continuous Functions of Hermitian Banded Toeplitz Matrices

Toeplitz matrices and functions of Toeplitz matrices (such as the inverse of a Toeplitz matrix, powers of a Toeplitz matrix or the exponential of a Toeplitz matrix) arise in many different theoretical and applied fields. They can be found in the mathematical modeling of problems where some kind of shift invariance occurs in terms of space or time. R. M. Gray's excellent tutorial monograph on Toeplitz and circulant matrices has been, and remains, the best elementary introduction to the Szegouml distribution theory on the asymptotic behavior of continuous functions of Toeplitz matrices. His asymptotic results, widely used in engineering due to the simplicity of its mathematical proofs, do not concern individual entries of these matrices but rather, they describe an "average" behavior. However, there are important applications where the asymptotic expressions of interest are directly related to the convergence of a single entry of a continuous function of a Toeplitz matrix. Using similar mathematical tools and to gain insight into the solutions of this sort of problems, the present correspondence derives new theoretical results regarding the convergence of these entries     

Spectral sensitivity, photopigments, and color vision in the guinea pig (Cavia porcellus).

Behavioral discrimination tests and electroretinogram (ERG) flicker photometry were used to measure spectral sensitivity and to define the spectral mechanisms of the guinea pig. Results from these 2 approaches converge to indicate that guinea pig retinas contain rods with peak sensitivity of about 494 nm and 2 classes of cone having peak sensitivities of about 429 nm and 529 nm. The presence of 2 classes of cones suggests a retinal basis for a color vision capacity. Behavioral tests of color vision were conducted that verified this prediction: Guinea pigs have dichromatic color vision with a spectral neutral point centered at about 480 nm. The cone pigment complement of the guinea pig is different from that known to characterize other rodents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transient Effects during Dynamic Operation of a Wall‐Cooled Fixed‐Bed Reactor for CO2 Methanation

The power‐to‐gas process is an option to transform fluctuating renewable electric energy into methane via water electrolysis and subsequent conversion of H₂ by methanation with CO₂. The dynamic behavior of the methanation reactor may then be a critical aspect. The kinetics of CO₂ methanation on a Ni‐catalyst were determined under isothermal and stationary conditions. Transient isothermal kinetic experiments showed a fast response of the rate on step changes of the concentrations of H₂, CO₂; in case of H₂O, the response was delayed. Non‐isothermal experiments were conducted in a wall‐cooled fixed‐bed reactor. Temperature profiles were measured and the effect of a changing volumetric flow was studied. The experimental data were compared with simulations by a transient reactor model.     

Liquid-Phase Isobutane/Butene-Alkylation Using Promoted Lewis-Acidic IL-Catalysts

Abstract  

The effect of different promoters on activity and selectivity of Lewis-acidic chloroaluminate ionic liquid catalysts was studied for isobutane/2-butene alkylation. When tert-butyl halides are used as promoters, the active species of the alkylation reaction, which is the tert-butyl cation, is directly generated whereas upon catalysis with Br?nsted-acid supported ionic liquids, this species is indirectly provided through a hydride shift between protonated 2-butene and isobutane. Experimental results both from batch and continuously operated liquid phase alkylation reactors indicate, that tert-butyl halides are able to speed up the reaction rate significantly and shift the C₈-selectivity towards the desired high-octane trimethylpentanes (TMPs). However, secondary reactions like oligomerization and cracking could not be suppressed by the use of this additives and high deactivation rates in continuous opperation were observed. Suggestions are made, how the product composition is effected by the additive and how the promoted IL-catalyst system is deactivated with time on stream.     

Polarization and phase control of remote surface-plasmon-mediated two-photon-induced emission and waveguiding

We report here on the control of remote surface-plasmon-mediated two-photon-induced luminescence of dendritic silver nanoparticle aggregates as observed by femtosecond laser microscopy. With a focal spot diameter approximately 1 microm, polarized remote emission has been observed 99 microm from the focal spot. We show control over the regions of emission by changing the polarization of the incident beam and by changing the spectral phase of the laser pulse.     

Erfahrungen mit einem Simulationsmodell in einer Aluminiumgießerei

Zusammenfassung Für die Hamburger Aluminium-Werk GmbH wurde vor einigen Jahren ein Simulationsmodell entwickelt, das den Produktionsablauf in der Gießerei detailliert abbildet. Wir beschreiben zunächst die Produktionsstruktur dieses Betriebes, die Aufgaben der Produktionsplanung und die Fragestellungen, die mit dem Simulationsmodell untersucht werden sollen. Dann werden die im Modell verwendete Simulationstechnik und die Vorgehensweise der Ablaufplanung dargestellt. Schließlich wird der bisherige Einsatz des Modells zur Unterstützung der strategischen Planung und zur Verbesserung der Ablaufplanung geschildert, der zu bemerkenswerten Kostensenkungen beigetragen hat.

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Summary For the Hamburger Aluminium-Werk GmbH a detailed simulation model of the production flow in the foundry has been developed. We first describe the production structure, the scheduling problem and the questions to be investigated by the simulation model. The simulation technique and the scheduling methods in the model are outlined. Finally, we explain the use of the model in the last three years for strategic planning problems and for improving the short-term scheduling from which remarkable savings resulted.

     

Aerosol size distribution from elutriator efficiency measurements

A method for obtaining approximate cumulative particle size distributions with high flow rate elutriators has been developed. Several multiple channel elutriators of different capacities are used to sample the aerosol simultaneously and in parallel. From their measured efficiencies, a mixture of monodisperse aerosols is found analytically which yields these efficiencies for each elutriator. The cumulative size distribution is inferred from the composition of the monodisperse aerosol mixture.