Sound transmission in strongly-curved slowly-varying cylindrical and annular lined ducts with flow

In this paper we consider the propagation of acoustic waves along a curved hollow or annular duct with lined walls. The curvature of the duct centreline and the wall radii vary slowly along the duct, allowing application of an asymptotic multiple scales analysis. This generalises Rienstra's analysis of a straight duct of varying cross-sectional radius. The result of the analysis is that the modal wavenumbers and mode shapes are determined locally as modes of a torus with the same local curvature, while the amplitude of the modes evolves as the mode propagates along the duct. The duct modes are found numerically at each axial location using a pseudo-spectral method. Unlike the case of a straight duct, there is a fundamental asymmetry between upstream and downstream propagating modes, with some mode shapes tending to be concentrated on either the inside or outside of the bend depending on the direction of propagation. The interaction between the presence of wall lining and curvature is investigated in particular; for instance, in a representative case it is found that the curvature causes the first few acoustic modes to be more heavily damped by the duct boundary than would be expected for a straight duct. Analytical progress can be made in the limit of very high mode order, in which case well-known 'whispering gallery' modes, localised close to the wall, can be identified.

The Pressure Transient Analysis Of Deformation Of Fractal Medium

The assumption of constant rock properties in pressure-transient analysis of stress-sensitive reservoirs can cause significant errors in the estimation of temporal and spatial variation of pressure. In this article, the pressure transient response of the fractal medium in stress-sensitive reservoirs was studied by using the self-similarity solution method and the regular perturbation method. The dependence of permeability on pore pressure makes the flow equation strongly nonlinear. The nonlinearities associated with the governing equation become weaker by using the logarithm transformation. The perturbation solutions for a constant pressure production and a constant rate production of a linear-source well were obtained by using the self-similarity solution method and the regular perturbation method in an infinitely large system, and inquire into the changing rule of pressure when the fractal and deformation parameters change. The plots of typical pressure curves were given in a few cases, and the results can be applied to well test analysis.

Optimal bounded control of first-passage failure of strongly non-linear oscillators under combined harmonic and white-noise excitations

A procedure for designing the optimal bounded control of strongly non-linear oscillators under combined harmonic and white-noise excitations for minimizing their first-passage failure is proposed. First, a stochastic averaging method for strongly non-linear oscillators under combined harmonic and white-noise excitations using generalized harmonic functions is introduced. Then, the dynamical programming equations and their boundary and final time conditions for the control problems of maximizing reliability and of maximizing mean first-passage time are formulated from the averaged Ito equations by using the dynamical programming principle. The optimal control law is derived from the dynamical programming equations and control constraint. Finally, the conditional reliability function, the conditional probability density and mean of the first-passage time of the optimally controlled system are obtained from solving the backward Kolmogorov equation and Pontryagin equation. An example is given to illustrate the proposed procedure and the results obtained are verified by using those from digital simulation. (C) 2003 Elsevier Ltd. All rights reserved.

Diagnóstico de las empresas familiares con estudiantes de Lic. En Agronegocios, modalidad regular, Facultad de Desarrollo Rural, Universidad Nacional Agraria, año 2014

La empresa familiar forma parte fundamental de las estructuras productivas, tanto de las economías industrializadas como en vías de desarrollo; a pesar de carecer de datos rigorosos que permitan corroborarlo, la empresa familiar tiene un papel preponderante en la generación de riqueza nacional; el objetivo fundamental del estudio fue conocer el grado de conocimiento y el rol que ejercen los estudiantes en una empresa familiar y el número de empresas familiares existentes en la carrera de Lic. Agronegocios, Facultad de Desarrollo Rural, Universidad Nacional Agraria- Managua, esto se realizó a través de la implementación de encuesta a los estudiantes que formaron parte de la muestra logrando realizar posteriormente un análisis de datos que facilitó la redacción del documento presentado a continuación; la ejecución de esta temática se dio debido la poca importancia que se le ha dado al tema de las empresas familiares dentro de la economía de Nicaragua a pesar de que estas aportan el 50% del PIB, la falta de información y estudios relacionados que nos ayuden a conocer la realidad de estas empresas tanto en el ámbito organizativo como en el económico; de las negocios encontrados entre la muestra el 33% forma parte de las MIPYMES divididos el 21% en la micro empresas, el 8% en la pequeña empresa y el 3% en la mediana empresa, el 67% restante de la muestra total son negocios de emprendimiento categorizados así por facturar menos de 37360.83 dólares; por otro parte el 18% de los estudiantes matriculados en la Lic. Agronegocios forman parte de una empresa familiar de este porcentaje el 10% tiene conocimiento amplio sobre la temática, un 14 % posee únicamente ciertos conocimientos derivados de algunos temas relacionados mientras que el 76% no tienen ningún tipo de conocimiento acerca de la temática.

O legislativo vai à escola : as instituições políticas e o poder legislativo no âmbito da educação regular

Discute a participação política de jovens e a sua relação com a educação formal. Argumentando a favor de mais conhecimento e envolvimento dos jovens na política institucionalizada, busca analisar as oportunidades abertas pelas normativas da educação e pelas inovações produzidas nos legislativos do país para a inclusão, no contexto da educação escolar, da temática das instituições políticas e do Poder Legislativo.