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11.
Violeta D'Accurso Francisco A. Manzano Verónica B. Slezak 《Applied physics. B, Lasers and optics》1996,63(4):375-380
A detailed model for the optogalvanic effect in a neon hollow cathode discharge irradiated by a chopped CW dye laser is presented. A rate equation formalism is used to calculate the evolution of the first and second electronic configuration populations coupled by the laser and of the electric charges number density. Processes as ambipolar-like electrons loss, electronic collisional coupling of level populations and electron emission by the cathode due to VUV radiation from the 1s
2 resonant level are taken into account and further discussed.The transients and steady-state magnitude of the optogalvanic signal are calculated, compared with experimental data and related to population changes. We predict sign changes of the optogalvanic signal when the laser is tuned over transitions originating from the resonant level with respect to transitions involving the metastables states. The optogalvanic signal is shown to be basically determined by the laser-induced variations of the excited-state populations while changes in the electron temperature, due to laser energy transfer by collisions between electrons and excited atoms, play a negligible role. 相似文献
12.
Generally, in homotopy theory a cylinder object (or, its dual, a path object) is used to define homotopy between morphisms,
and a cone object is used to build exact sequences of homotopy groups. Here, an axiomatic theory based on a cone functor is
given. Suspension objects are associated to based objects and cofibrations, obtaining homotopy groups referred to an object
and relative to a cofibration, respectively. Exact sequences of these groups are built. Algebraic and particular examples
are given. We point out that the main results of this paper were already stated in [3], and the purpose of this article is
to give full details of the foregoing. 相似文献
13.
Francisco‐Javier Sayas 《Numerical Methods for Partial Differential Equations》2003,19(5):555-570
This article presents and analyzes a simple method for the exterior Laplace equation through the coupling of finite and boundary element methods. The main novelty is the use of a smooth parametric artificial boundary where boundary elements fit without effort together with a straight approximate triangulation in the bounded area, with the coupling done only in nodes. A numerically integrated version of the algorithm is also analyzed. Finally, an isoparametric variant with higher order is proposed. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 555–570, 2003 相似文献
14.
We characterize the sequences of orthogonal polynomials on the unit circle whose derivatives are also orthogonal polynomials on the unit circle. Some relations for the sequences of derivatives of orthogonal polynomials are provided. Finally, we pose some problems about orthogonality-preserving maps and differential equations for orthogonal polynomials on the unit circle. 相似文献
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16.
Vanessa de Freitas Cunha Lins Geraldo Francisco de Andrade Reis Carlos Roberto de Araujo 《Applied Surface Science》2006,253(5):2875-2884
In this work, electrochemical impedance spectroscopy and linear polarization are used in determining porosity of zinc phosphates, and of nickel and manganese modified zinc phosphates on electrogalvanized steel. The porosity of the phosphate layers ranges from 0.1% for the manganese-modified hopeite to 8% for hopeite, using the linear polarization and the electrochemical impedance spectroscopy techniques. The porosity values measured using the two techniques were in agreement. All impedance spectra of coated samples showed two steps, with two capacitive arcs and an inductive looping. 相似文献
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18.
Jaime Pfretzschner Pedro Cobo Francisco Simón María Cuesta Alejandro Fernández 《Applied Acoustics》2006,67(1):62-73
Microperforated panels (MPPs) coupled to a rigid wall have been proposed recently as an alternative to porous absorbers in situations having concerns with bacterial contamination and small particles discharge, like food, pharmaceutical and microelectronic industries. There exists also an increasing interest for MPP absorbers in the transportation industry and civil engineering. In general, an optimally designed MPP with good broadband absorption requires many submillimetric holes distributed over a panel of also submillimetric thickness. Such thin plates or foils become so fragile that they need to be protected from mechanical damage. In this paper, an alternative strategy is investigated which allows the design of MPPs with panels of millimetric thickness while maintaining their acoustic performance. These absorbers, named microperforated insertion units (MIUs), avoid the structural problems of the classical MPPs. An assessment of the sound absorption properties of these structures is presented. Comparisons between calculations and measurements are also made under two experimental conditions: plane waves at normal incidence (impedance tube) and free field (anechoic room). 相似文献
19.
K. C. Nicolaou Dionisios Vourloumis Tianhu Li Joaquin Pastor Nicolas Winssinger Yun He Sacha Ninkovic Francisco Sarabia Hans Vallberg Frank Roschangar N. Paul King M. Ray V. Finlay Pareskevi Giannakakou Pascal Verdier-Pinard Ernest Hamel 《Angewandte Chemie (International ed. in English)》1997,36(19):2097-2103
20.