SUNMONTUEWEDTHUFRISAT
Events for April 25, 2008
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Model, Identification & Analysis of Complex Stochastic Systems:
Fri, Apr 25, 2008 @ 11:00 AM - 01:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Sonjoy Das- PhD DefenseThe work presented in this dissertation focuses on characterization, identi¯-cation and analysis of stochastic systems. Stochastic systems refer to a physical
phenomena with inherent uncertainty in it, and are generally characterized by
two forms of representation: (1) a governing conservation law or partial dif-ferential equation (PDE) with some of its parameters interpreted as random
processes, and (2) a model-free random matrix operator. In this work, three
data-driven approaches are ¯rst introduced to characterize and construct consis-tent probability models of non-stationary and non-Gaussian random processes
or ¯elds within the polynomial chaos (PC) formalism. The resulting PC rep-resentations would be useful to probabilistically characterize the system input-output relationship for a variety of applications. Second, a novel hybrid physics-and data-based approach is proposed to characterize a complex stochastic sys-tems by using random matrix theory. Application of this approach to multiscale
mechanics problems is also presented. Also discussed in this work is a simple,
computationally e±cient and experiment-friendly coupling scheme based on fre-quency response function. This coupling scheme would be useful for analysis of
a complex stochastic system consisting of several subsystems characterized by,
e.g., stochastic PDEs or/and model-free random matrix operators.Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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Role of ammonia and water vapor on the formation of secondary organic aerosols in alkene/ozone react
Fri, Apr 25, 2008 @ 01:00 PM - 02:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Dr. Kwangsam NaBourns College of Engineering¡XCenter for Environmental Research and Technology (CE-CERT), University of California, RiversideAbstractThis study deals with the influence of ammonia (NH3) on secondary organic aerosol (SOA) formation from the ƒÑ-pinene/ozone systems in the dry and humid conditions. The effect of different OH scavengers on SOA formation is briefly described. The aerosol yield differed depending on which OH scavenger was used. Yield was the highest using CO, followed by cyclohexane and 2-butanol. It was found that the number and volume concentrations were quickly increased by 15% and 8%, respectively when NH3 was added after the reaction ceased. An increase in number concentration indicates the formation of new particles resulting from gas-to-particle conversion. Moreover, average size of particles increased from 242 nm to 248 nm. The resulting particles may be ammonium salts formed by the reaction between organic acids and NH3. When NH3 was added to an aerosolized cis-pinonic acid in the chamber reactor, a dramatic increase in both number and volume concentrations of cis-pinonic acid was observed. This is evidence that NH3 drives gas-phase organic acids into condensable salts, leading to elevated SOA formation. Initially present NH3 significantly enhanced aerosol yield in ƒÑ-pinene-ozone reactions, regardless of the presence of water vapor. However, the enhancing effect of NH3 on SOA formation was found to diminish in humid conditions. The degree of the increase in SOA yield in the presence of NH3 was higher in the humid condition than in the dry condition. The role of NH3 on SOA formation in the dry and humid conditions was further explained and discussed in terms of a theoretical modeling study.
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
