University of California, Riverside

Department of Mechanical Engineering

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2008-2009 Defense Announcements

Surface Potential Imaging of Chemical Vapor Deposition Graphene by Electrical Force Microscopy

Dan Qing Zhu, M.S. Candidate
Advisor: Professor Cengiz Ozkan

Friday, June 11, 1:00 - 2:00 p.m. WCH 202

Abstract: Recently, graphene-derived nanomaterials are heated studied as future replacement of silicon. In this study, electrical force miscroscopy (EFM) and surface potential imaging (SPI) are utilized to characterize the electrical properties of chemical vapor deposition graphene and micromechanical exfoliated graphene. A comparison of graphene came from both of these methods is investigated in terms of phase shifts and distinct tip bias. The presented results show that the phase shifts of graphene by these two methods share the same trend, and defects of CVD graphene as well as the micromechanical exfoliate ones, follow certain directions, which will trace back to the formation of defects in graphene. It is shown in this study that the similarity of both of these plots and the cause of the difference is further discussed. These results will encourage future studies regarding graphene-based electronics and applications of material defects manipulations.

Photomechanical, Photothermal and Photothermomechanical Mechanisms of Interaction of Nanosecond-Long Laser Pulses With Artificial Tissue Models and PigmentedMelanoma Cells in Medical Applications

Francisco G. Pérez-Gutiérrez, Ph.D. Candidate
Advisor: Professor Guillermo Aguilar

Friday, June 11th, 4:00 - 6:00 p.m. Bourns Hall A171

Nanosecond-long laser pulses are used in both branches of biomedical optics: where photons affect tissue (therapy) and where tissue affects photons (diagnostics). A current problem in vascular laser surgery is that small blood vessels, with short thermal relaxation time, remain after the treatment with laser pulses longer than such relaxation time. This problem is approached irradiating artificial skin models with nanosecond laser pulses. The objective is to take advantage of its high intensity to induce plasma that produces cavitation bubbles, which may serve as blood vessel photodisruption mechanism. Permanent and transient bubbles were identified as a function of the laser dose, number of pulses and repetition rate. Additionally, scattering effects were added to the skin models, which increased the threshold fluence for plasma formation...

Speaker Classification based on Multiple Criteria

Miaogeng Zhang, M.S. Candidate
Advisor: Professor V. Sundararajan

Wednesday March 17th, 3:00 - 5:00 p.m. WCH 202

This thesis presents techniques to classify speech signals produced by unfamiliar speakers into categories based on criteria such as gender and age. Such classification is useful to augment the efficiency of conventional video surveillance systems. Existing systems classify speakers along only one dimension. This thesis develops methods to classify speakers based on multiple categories. Age group (children and adults) and gender group (male and female) are used as examples to clarify these issues. Experimental evaluation indicates that 1) Speaker groups are dependent 2) The use of single classifier to sort speakers into multi-criteria groups yields sub-optimal results. Thus, a sequential approach is necessary 3) The sequence of classification affects the performance of the system.

Thermo-Fluid Dynamics of Flash Atomizing Sprays and Single Droplet Impacts

Henry Vu, Ph.D. Candidate
Advisor: Professor Guillermo Aguilar

Friday March 12th, 1:00 - 3:00 p.m. WCH 443

Spray atomization and droplet dynamics are research topics that have existed for many decades. Their prevalence in manufacturing, energy generation and other practical applications is undeniable, though researchers have often overlooked the importance of understanding the physics of atomization or droplet impact characteristics in the ongoing effort to improve efficiency. In this talk, I will address the atomization of thermodynamically unstable “flashing” sprays and the splashing mechanisms of single droplets impinging on flat, smooth surfaces. The related heat transfer phenomena for cooling applications are also addressed. These topics are motivated by efforts to improve the thermal protection provided by cryogenic spray cooling in laser dermatological procedures, increasing the throughput of the spray production of nano and micro-scale particulates used as dyes and catalysts, and in modeling of the release and dispersion of flammable or hazardous chemicals through large-scale collisions with storage containers......More

Mixed Convection in an Obstructed Two-Dimensional Open-Ended Cavity

Wenlu Shi, M.S. Candidate
Advisor: Professor Kambiz Vafai

Thurday, December 10th 11:00 a.m. Bourns Hall A277

Mixed convection in an obstructed cavity with heated horizontal walls is studied numerically. Brinkman-Forchheimer-extended Darcy model is utilized to describe the flow behavior within the porous medium for different angles of attack with respect to the forced convection.....More

Vibration Induced Mixed Convection in an Obstructed Vertical Cavity

Stephen Chung, M.S. Candidate
Advisor: Professor Kambiz Vafai

Thursday December 10, 12:00 p.m. Bourns Hall A277

Vibrational mixed convection inside an open-ended cavity filled with a porous medium is investigated in this work. Vertical vibration on the left wall and buoyancy induced flow are considered. The effect of variations in governing parameters, such as vibrational Reynolds number, modified Rayleigh number, and the Darcy number on streamlines, isotherms, and the average Nusselt number is discussed....More

Current Activated Pressure Assisted Densification (CAPAD) Processing of Ceramics Doped with Rare Earths for Functionality

Andrew Wieg, M.S. Candidate
Advisor: Professor Javier Garay

Tuesday, December 08, 2009, 10:00 a.m. Bourns Hall A171

The performance of Solid Oxide Fuel Cells (SOFCs) and Lasers are important to both society and science. With the aim of improving the performance of these devices through materials improvement, aluminum nitride (laser host material) and cerium oxide (SOFC electrolyte) with rare earth dopants Gd2O3 and (RE)2O3 (RE = Sm,Yb,Gd) respectively were densified using the current activated pressure assisted densification (CAPAD) process....More

Ph.D. Dissertation Defense-Characteristics of Graphitic Films for Carbon based Magnetism & Electronics

Jeongmin Hong, Ph.D. Candidate
Advisors: Sakhrat Khizroev & Qing Jiang

Tuesday, October 20th 11:00 a.m. WCH Room 215

This dissertation concentrates on the characteristics of the graphene: single layer of graphite which is defined as two-dimensional material for carbon based magnetism and electronics. Carbon materials, which are demonstrated by diamond and graphite, have always been of great interest for their unique properties. Moreover, in the last two decades, there have been three revolutionary milestones in the development of carbon materials, which were related to the discovery of fullerenes, carbon nanotubes, and graphene, respectively. Such research evolution led to the realization of the feasibility to tailor magnetic and electronic properties of graphiticsheets....More

Ph.D. Dissertation Defense Health Monitoring of Drive Connected Three-Phase Induction Motors from Wired Towards Wireless Sensor Networks

Xin Xue, Ph.D. Candidate
Advisor: Professor V. Sundararajan

Thursday, August 27, 2009, 11:00 a.m. Bourns Hall A171

Wireless sensor network (WSN), one of the featured technologies that the U.S. Department of Energy (DOE) has identified to help improve the overall energy efficiency of US industry, provides a potentially low-cost approach for the health monitoring and fault diagnosis of induction motors. The reduction of machine failures increases plant efficiency and productivity. Low-cost wireless sensor systems can help the health monitoring of manufacturing equipments by eliminating the cost of installation and increasing the flexibility of system diagnosis.

This research focuses on developing a nonintrusive, condition based health monitory system for drive connected induction motors using the wireless sensor network method. A hierarchical classification system is designed for motor fault diagnosis. To simulate and analyze a wide range of fault conditions that may arise in induction motors, an experimental test bed is also developed. Three major branches of induction motor faults are studied, either individually or in combination. Wired sensors are first used to find optimal features for motor fault classification. After performing feasibility studies of wireless sensors in electric machinery, two wireless sensor nodes are developed and implemented in the motor health monitoring and fault diagnosis system. The experimental results demonstrate the effectiveness and generalizability of the wireless sensor system for motor health monitoring and fault classification.

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University of California, Riverside
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Riverside, CA 92521
Tel: (951) 827-1012

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Bourns College of Engineering
446 Winston Chung Hall

Tel: (951) 827-5190
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