乙烯超声速燃烧的数值模拟研究

利用Fluent软件、ISAT算法与由CARM(Computer Assisted Reduction Method)简化而来的11组分、7步反应的乙烯简化机理对碳氢燃料/空气的超声速燃烧问题进行数值模拟.研究结果表明这种方法是可利用的.计算得到的压力数据与试验压力值可以比较.

采用简化机理模拟乙烯在超声速气流中自点火燃烧过程

本文采用由CARM生成的11组分/7步反应简化机理对二维超声速气流中热乙烯横向喷射、自点火燃烧过程进行了非定常模拟。同时，计算采用了SST 湍流模型、涡耗散概念(EDC)燃烧模型以及ISAT积分算法等技术。数值研究了马赫数2.5、总温1800K来流中，不同当量比条件下乙烯的自点火燃烧过程。研究发现：乙烯首先在凹腔内着火；在当量比较低时，燃烧主要发生在凹腔下游，并且燃烧区域为超声速；随着当量比的提高，由于释热量的增加，使得燃烧室内气流发生热雍塞，乙烯在亚声速气流中燃烧，燃烧效率显著提高，燃烧主要发生在凹腔区。另外，采用总包反应模型计算的结果表明由于模型过于简单，使得燃烧效率偏高、总温偏大，与简化机理给出的结果差别显著。

Switching-off in a minimal time a fitzhugh-nagumo system

This paper deals with a system that describes an electrical circuitcomposed by a linear system coupled to a nonlinear one involving a tunneldiode in a flush-and-fill circuit. One of the most comprehensive models for thiskind of circuits was introduced by R. Fitzhugh in 1961, when taking on carebiological tasks. The equation has in its phase plane only two periodic solutions,namely, the unstable singular point S0 and the stable cycle Γ. If the system isat rest on S0, the natural flow of orbits seeks to switch-on the process by going- as time goes by - toward its steady-state, Γ. By using suitable controls it ispossible to reverse such natural tendency going in a minimal time from Γ toS0, switching-off in this way the system. To achieve this goal it is mandatorya minimal enough strength on controls. These facts will be shown by means ofconsiderations on the null control sets in the process.

Angiographic Results in Intracranial Aneurysms Treated with Inert Platinum Coils

This study was designed in an attempt to identify the risk factors that could be significantly associated with angio graphic recurrences after selective endovascular treatment of aneurysms with inert platinum coils. A retrospective analysis of all patients with selective endovascular coil occlusion of intracranial aneurysms was prospectively collected from 1999 to 2003. There were 455 aneurysms treated with inert platinum coils and followed by digital subtraction angiography. Angio graphic results were classified according Roy and Raymond's classification. Recurrences were subjectively divided into minor and major. The most significant predictors for angio graphic recurrences were determined by ANOVAs logistic regression, Cochran-Mantel-Haenszel test, Fisher exact probability. Short-term (4.3 +/- 1.4 months) follow-up angiograms were available in 377 aneurysms, middle-term (14.1 +/- 4.0 months) in 327 and long-term (37.4 +/- 11.5 months) in 180. Recurrences were found in 26.8% of treated aneurysms with a mean of 21 +/- 15.7 months of follow-up. Major recurrences needing retreatment were present in 8.8% during a mean period follow-up of 17.9 +/- 12.29 months after the initial endovascular treatment. One patient (0.2%) experienced a bleed during the follow-up period. Recurrences after endovascular treatment of aneurysms with inert platinum coils are frequent, but hemorrhages are unusual. Single aneurysm, ruptured aneurysm, neck greater than 4 mm and time of follow-up were risk factors for recurrence after endovascular treatment. The retreatment of recurrent aneurysm decreases the risk of major recurrences 9.8 times. Long-term angiogram monitoring is necessary for the population with significant recurrence predictors.

Comprehensive secondary pyrolysis in fluidized-bed fast pyrolysis of biomass, a fluid dynamics based modelling effort

Homogenous secondary pyrolysis is category of reactions following the primary pyrolysis and presumed important for fast pyrolysis. For the comprehensive chemistry and fluid dynamics, a probability density functional (PDF) approach is used; with a kinetic scheme comprising 134 species and 4169 reactions being implemented. With aid of acceleration techniques, most importantly Dimension Reduction, Chemistry Agglomeration and In-situ Tabulation (ISAT), a solution within reasonable time was obtained. More work is required; however, a solution for levoglucosan (C6H10O5) being fed through the inlet with fluidizing gas at 500 °C, has been obtained. 88.6% of the levoglucosan remained non-decomposed, and 19 different decomposition product species were found above 0.01% by weight. A homogenous secondary pyrolysis scheme proposed can thus be implemented in a CFD environment and acceleration techniques can speed-up the calculation for application in engineering settings.

LES of flame acceleration and DDT in hydrogen-air mixture using artificially thickened flame approach and detailed chemical kinetics

A large eddy simulation is performed to study the deflagration to detonation transition phenomenon in an obstructed channel containing premixed stoichiometric hydrogen–air mixture. Two-dimensional filtered reactive Navier–Stokes equations are solved utilizing the artificially thickened flame approach (ATF) for modeling sub-grid scale combustion. To include the effect of induction time, a 27-step detailed mechanism is utilized along with an in situ adaptive tabulation (ISAT) method to reduce the computational cost due to the detailed chemistry. The results show that in the slow flame propagation regime, the flame–vortex interaction and the resulting flame folding and wrinkling are the main mechanisms for the increase of the flame surface and consequently acceleration of the flame. Furthermore, at high speed, the major mechanisms responsible for flame propagation are repeated reflected shock–flame interactions and the resulting baroclinic vorticity. These interactions intensify the rate of heat release and maintain the turbulence and flame speed at high level. During the flame acceleration, it is seen that the turbulent flame enters the ‘thickened reaction zones’ regime. Therefore, it is necessary to utilize the chemistry based combustion model with detailed chemical kinetics to properly capture the salient features of the fast deflagration propagation.

Chemical Reaction Dynamics of the Liquid/Vapor Interface Studied by Mass Spectrometry

This thesis presents investigations of chemical reactions occurring at the liquid/vapor interface studied using novel sampling methodologies coupled with detection by mass spectrometry. Chapters 2 and 3 utilize the recently developed technique of field-induced droplet ionization mass spectrometry (FIDI-MS), in which the application of a strong electric field to a pendant microliter droplet results in the ejection of highly charged progeny droplets from the liquid surface. In Chapter 2, this method is employed to study the base-catalyzed dissociation of a surfactant molecule at the liquid/vapor interface upon uptake of ammonia from the gas phase. This process is observed to occur without significant modulation of the bulk solution pH, suggesting a transient increase in surface pH following the uptake of gaseous ammonia. Chapter 3 presents real-time studies of the oxidation of the model tropospheric organic compound glycolaldehyde by photodissociation of iron (III) oxalate complexes. The oxidation products of glycolaldehyde formed in this process are identified, and experiments in a deoxygenated environment identify the role of oxygen in the oxidation pathway and in the regeneration of iron (III) following photo-initiated reduction. Chapter 4 explores alternative methods for the study of heterogeneous reaction processes by mass spectrometric sampling from liquid surfaces. Bursting bubble ionization (BBI) and interfacial sampling with an acoustic transducer (ISAT) generate nanoliter droplets from a liquid surface that can be sampled via the atmospheric pressure interface of a mass spectrometer. Experiments on the oxidation of oleic acid by ozone using ISAT are also presented. Chapters 5 and 6 detail mechanistic studies and applications of free-radical-initiated peptide sequencing (FRIPS), a technique employing gas-phase free radical chemistry to the sequencing of peptides and proteins by mass spectrometry. Chapter 5 presents experimental and theoretical studies on the anomalous mechanism of dissociation observed in the presence of serine and threonine residues in peptides. Chapter 6 demonstrates the combination of FRIPS with ion mobility-mass spectrometry (IM-MS) for the separation of isomeric peptides.

Síntomas y factores ergonómicos asociados con trastornos musculoesqueléticos (TME) en una población de trabajadores administrativos de una empresa de servicios, 2015

Introducción. Los Trastornos Musculoesqueléticos (TME) son lesiones de músculos, tendones, nervios y articulaciones que tienen como principal síntoma el dolor y se presentan con gran frecuencia en trabajos que requieren una actividad física importante o como consecuencia de malas posturas sostenidas durante largos periodos de tiempo. Objetivo: Determinar la prevalencia de síntomas osteomusculares y su asociación con factores ergonómicos en una población de trabajadores administrativos de una empresa de servicios en Bogotá, Colombia, en el año 2015. Método: Se realizó un estudio de corte transversal. Se analizaron datos secundarios correspondientes a una base de datos de una población de 450 trabajadores pertenecientes al área administrativa de una empresa de servicios, de los cuales se incluyeron 150 registros que tenían la información completa de las variables del estudio. Se tuvieron en cuenta variables sociodemográficas, ocupacionales y la presencia de síntomas osteomusculares. Incluyó también el registro de condiciones de la estación de trabajo recolectada mediante inspecciones de puestos de trabajo (registro fotográfico y formato estandarizado para condiciones observadas). Se realizó un análisis descriptivo considerando las medidas de tendencia central para las variables cuantitativas y distribución de frecuencias para las variables cualitativas. Resultados: Predominó el género femenino (56%) dentro de la población estudiada, con una edad media para ambos géneros de 35 años (75%), (DS ± 7.0). El síntoma más frecuentemente reportado fue el dolor en cuello (17%) seguido por dolor en muñeca (11%) y dolor lumbar (8.7%). Del total de los trabajadores evaluados, el 80% correspondió al cargo ejecutivo, que reúne funciones administrativas especializadas complejas y/o de supervisión directa. De la población femenina objeto de estudio el 76% se desempeñaban en el cargo ejecutivo. Las condiciones ergonómicas por mejorar de mayor frecuencia fueron altura y distancia de la pantalla (42%) y cables sueltos (30%). La frecuencia de síntomas fue más alta en el rango de edad de 31 a 45 años. Conclusiones: En este estudio se encontró que los síntomas osteomusculares más frecuentes se ubicaron en el segmento axial (cuello y región lumbar) y en mano y que las condiciones de altura y distancia de la pantalla y cables sueltos presentaron las frecuencias más altas de condiciones por mejorar. Se hace necesaria la implementación de programas de prevención de TME, la vigilancia de casos y la intervención de las condiciones de los puestos de trabajo. Se debe promover la identificación y promoción de conductas saludables dentro del ámbito laboral y la prevención de condiciones que favorezcan la aparición del riesgo biomecánico.