Defenses

Title: Phospholipid Behavior and Dynamics in Curved Biological Membranes

Author: Haoyuan Jing

Date/Time: November 6, 2020 11:00am-1:00pm

Zoom Link: https://umd.zoom.us/j/2663589029

Committee Members
Dr. Siddhartha Das (Chair)
Dr. Silvina Matysiak (Dean’s Represenative)
Dr. Doron Levy
Dr. Amir Riaz
Dr. Peter Chung
Dr. Kumaran Ramamurthi (Special Member)

Abstract: Curvature in biological membranes defines the morphology of cells and organelles and serves key roles in maintaining a variety of cellular functions, enabling trafficking, recruiting and localizing shape-responsive proteins. For example, the bacterial protein SpoVM is a small amphipathic alpha-helical protein that localizes to the outer surface of a forespore, the only convex surface in the mother bacteria. Understanding several of these membrane curvature dependent events rely on a thorough understanding of the properties, energetics, and interactions of the constituent lipid molecules in presence of curvatures.  

In this dissertation, we have used molecular dynamics (MD) simulations to explore how the curvature of the lipid bilayer (LBL), a simplified mimic of the cell membrane, affects the packing fraction and diffusivity of lipid molecules in the LBL, energetics of lipid flip flop in the LBL, and lipid desorption from the LBLs. We have also investigated the interaction between LBLs and a small bacterial protein, SpoVM, which was previously shown to preferentially embed in positively curved membranes. Our work started with simulating convex surface, represented by the nanoparticle supported lipid bilayers (NPSLBLs) in MD. We first quantified the self-assembly, structure, and properties of a NPSLBL with a diameter of 20 nm and showed how the type of the nanoparticle (NP) affects the properties of the NPSLBLs. Second, we studied the energetics of lipid flip flop and desorption from LBLs for the cases of planar substrate supported lipid bilayer (PSSLBL) and NPSLBL. Finally, we investigated the energetics of SpoVM desorption from the PSSLBL and the NPSLBL providing clues to the fundamental driving forces dictating the curvature sensing of SpoVM. 

Title: CERTIFYING AN AUTONOMOUS SYSTEM TO COMPLETE TASKS CURRENTLY RESERVED FOR QUALIFIED PILOTS

Author: Donald “Bucket” Costello

Date/Time: Oct 29, 2020 07:00 PM Eastern Time (US and Canada)

Examining Committee:

• Asst. Prof. Huan Xu, Chair/Advisor
• Prof. Adam Porter, Dean’s Representative
• Prof. Jeffrey Herrmann
• Prof. Miao Yu
• Asst. Prof. Sarah Bergbreiter

Abstract: When naval certification officials issue a safety of flight clearance, they are certifying that when the vehicle is used by a qualified pilot they can safety accomplish their mission. The pilot is ultimately responsible for the vehicle. While the naval safety of flight clearance process is an engineering based risk mitigation process, the qualification process for military pilots is largely a trust process. When a commanding officer designates a pilot as being fully qualified, they are placing their trust in the pilot’s decision making abilities during off nominal conditions. The advent of autonomous systems will shift this established paradigm as there will no longer be a human in the loop who is responsible for the vehicle. Yet, a method for certifying an autonomous vehicle to make decisions currently reserved for qualified pilots does not exist. We propose and exercise a methodology for certifying an autonomous system to complete tasks currently reserved for qualified pilots. First, we decompose the steps currently taken by qualified pilots to the basic requirements. We then develop a specification which defines the envelope where a system can exhibit autonomous behavior. Following a formal methods approach to analyzing the specification, we developed a protocol that software developers can use to ensure the vehicle will remain within the clearance envelope when operating autonomously. Second, we analyze flight test data of an autonomous system completing a task currently re-served for qualified pilots while focusing on legacy test and evaluation methods to determine suitability for obtaining a certification. We found that the system could complete the task under controlled conditions. However, when faced with conditions that were not anticipated (situations where a pilot uses their judgment) the vehicle was unable to complete the task. Third, we highlight an issue with the use of onboard sensors to build the situational awareness of an autonomous system. As those sensors degrade, a point exists where the situational awareness provided is insufficient for sound aeronautical decisions. We demonstrate (through modeling and simulation) an objective measure for adequate situational awareness (subjective end) to complete a task currently reserved for qualified pilots.

Author: John McGahagan

Advisory Committee:
Professor Michel Cukier, Chair
Professor Jennifer Golbeck, Dean’s Representative
Associate Professor Katrina Groth
Professor Jeffrey Herrmann
Professor Mohammad Modarres 

Date/Time: October 23rd 1pm-3pm ET

Abstract: Although the internet enables many important functions of modern life, it is also a ground for nefarious activity by malicious actors and cybercriminals. For example, malicious websites facilitate phishing attacks, malware infections, data theft, and disruption. A major component of cybersecurity is to detect and mitigate attacks enabled by malicious websites. Although prior researchers have presented promising results – specifically in the use of website features to detect malicious websites – malicious website detection continues to pose major challenges. This dissertation presents an investigation into feature-based malicious website detection. We conducted six studies on malicious website detection, with a focus on discovering new features for malicious website detection, challenging assumptions of features from prior research, comparing the importance of the features for malicious website detection, building and evaluating detection models over various scenarios, and evaluating malicious website detection models across different datasets and over time. We evaluated this approach on various datasets, including: a dataset composed of several threats from industry; a dataset derived from the Alexa top one million domains and supplemented with open source threat intelligence information; and a dataset consisting of websites gathered repeatedly over time. Results led us to postulate that new, unstudied, features could be incorporated to improve malicious website detection models, since, in many cases, models built with new features outperformed models built from features used in prior research and did so with fewer features. We also found that features discovered using feature selection could be applied to other datasets with minor adjustments. In addition: we demonstrated that the performance of detection models decreased over time; we measured the change of websites in relation to our detection model; and we demonstrated the benefit of re-training in various scenarios.

Title: Phase Change Materials For Vehicle And Electronic Transient Thermal Systems

Advisory Committee
Professor F. Patrick McCluskey, Chair
Professor Neil Goldsman (Dean’s Representative)
Professor Hugh Bruck
Professor Michael Ohadi
Professor Jungho Kim

Date & Time: November 5, 2020; 3:00-5:00pm 

Zoom Link: https://umd.zoom.us/j/91690449959?pwd=cUpZejJPOXdEdlJvMzhURVJ0c2U1dz09

Abstract:  Most vehicle operating environments are transient in
nature, yet traditional subsystem thermal management addresses peak
load conditions with steady-state designs.  The large, overdesigned
systems that result are increasingly unable to meet target system
size, weight and power demands.  Phase change thermal energy storage
is a promising technique for buffering thermal transients while
providing a functional thermal energy reservoir.  Despite significant
research over the half century, few phase change material (PCM) based
solutions have transitioned out of the research laboratory.  This work
explores the state of phase change materials research for vehicle and
electronics applications and develops design tool compatible modeling
approaches for applying these materials to electronics packaging.

This thesis begins with a comprehensive PCM review, including over 700
candidate materials across more than a dozen material classes, and
follows with a thorough analysis of transient vehicle thermal systems.
After identifying promising materials for each system with potential
for improvement in emissions reduction, energy efficiency, or thermal
protection, future material research recommendations are made
including improved data collection, alternative metrics, and increased
focus on metallic and solid-state PCMs for high-speed applications.

Following the material and application review, the transient
electronics heat transfer problem is specifically addressed.
Electronics packages are shown using finite element based thermal
circuits to exhibit both worsened response and extreme convective
insensitivity under pulsed conditions.  Both characteristics are
quantified using analytical and numerical transfer function models,
including both clarification of apparently nonphysical thermal
capacitance and demonstration that the convective insensitivity can be
quantified using a package thermal Elmore delay metric.

Finally, in order to develop design level PCM models, an energy
conservative polynomial smoothing function is developed for Enthalpy
and Apparent Capacity Method phase change models.  Two case studies
using this approach examine the incorporation of PCMs into electronics
packages: substrate integrated Thermal Buffer Heat Sinks using
standard finite element modeling, and direct on-die PCM integration
using a new phase change thermal circuit model.  Both show
effectiveness in buffering thermal transients, but the metallic phase
change materials exhibit the best performance with significant
sub-millisecond temperature suppression, something improved cooling or package integration alone were unable to address.

Author: Xie Zheng

Advisory Committee:
Professor Balakumar Balachandran, Chair
Professor Amp Baz
Professor Nikhil Chopra
Associate Professor Jin-Oh Hahn
Associate Professor Maria Cameron

Date & Time: October 2, 2020 1pm-3pm

Abstract: Drill strings are flexible, slender structures, which are many kilometers long, and used to transmit the rotary motion to the drill bit in the process of drilling a borehole. Due to the flexibility of the drill string and nonlinear interactions between the drill bit and rock, these systems often experience severe vibrations, and these vibrations may cause excessive wear of drill bit and equipment damage. The aim of this dissertation effort is to further the understanding of the underlying mechanism leading to the undesired vibratory motions of drill strings, as well as to develop a viable control strategy that is applicable for mitigation of harmful vibrations.

 A reduced-order drill-string model with coupled axial and torsional dynamics is constructed. Nonlinear effects associated with dry friction, loss of contact, and the state-dependent delay, which all arise from cutting mechanics are considered. For the sake of analyses, a non-dimensionalized form of the governing equations is provided. Next, in order to study the local stability of the drill-string system, a linear system associated with the state-dependent delay is derived. The stability analysis of this linearized system is carried out analytically by using the D-subdivision scheme. The obtained results are illustrated in the terms of stability crossing curves, which are presented in the plane of non-dimensional rotation speed and non-dimensional cutting depth; non-dimensional rotation speed, and cutting coefficient, respectively. As to nonlinear analysis, a numerical continuation method is developed and used to follow periodic orbits of systems with friction, loss of contact, and state-dependent delay. Bifurcation diagrams are constructed to capture the possible routes from either a nominal stable operational state or a stable limit-cycle motion without stick-slip to a limit-cycle motion with stick-slip. It is shown that the system can experience subcritical Hopf bifurcations of equilibrium solutions and cyclic fold bifurcations. Furthermore, with the preceding work, an observer-based on controller design is proposed by using a continuous pole placement method for time delay systems. The effectiveness of the controller in suppressing stick-slip behavior is shown through simulations. 

Title:  DETERMINING MEASUREMENT REQUIREMENTS FOR WHOLE BUILDING ENERGY MODEL CALIBRATION

Committee:

• Professor Jelena Srebric, Ph.D., Chair
• Professor Reinhard Radermacher, Ph.D.
• Professor Yunho Hwang, Ph.D.
• Professor Bao Yang, Ph.D.
• Professor Donald Milton, MD, DrPH, Dean’s Representative

Date/Time: Friday, August 28th 2:00-4:00pm EDT

Abstract: 
Energy retrofits of existing buildings reduce grid requirements for new generation and reduce greenhouse gas emissions.  However, it is difficult to estimate energy savings both at the individual building and entire building stock level because building energy models are poorly calibrated to actual building performance.  This uncertainty has made it difficult to prioritize research & development and incentive programs for building technologies at the utility, state, and federal level.  This research seeks to make it easier to generate building energy models for existing buildings, and to calibrate buildings at the stock level to create accurate commercial building load forecasts.  Once calibrated, these building models can be used as seeds to other building energy model calibration approaches and to help utility, state, and federal actors to identify promising energy savings technologies in commercial buildings.  This research details the economics of a building energy retrofit at a singular building, contributes significantly to the development of ComStock, a model of the commercial building stock in the U.S., identifies important parameters for calibrating ComStock, and calibrates ComStock for an example utility region of Fort Collins, CO against individual commercial building interval data.  A study of retrofit costs finds that measure cost and model uncertainty are the most significant sources of variation in retrofit financial performance, followed by capital cost.  A wide range of greenhouse gas pricing scenarios shows they have little impact on the financial performance of whole building retrofits.  A sensitivity analysis of ComStock model inputs across an exhaustive range of models identifies 19 parameters that explain 80% of energy use and 25 parameters explain 90% of energy use.  Building floor area alone explains 41% of energy use.  Finally, a comparison of ComStock to Fort Collins, CO interval meter data shows a -12.6% normalized mean bias error and 23.5% coefficient of variation of root mean square error.  Improvements in meter classification and ComStock model variability will further improve model fit and provide an accurate means of modeling the commercial building stock. 

Department of Mechanical and Aerospace Engineering

North Carolina State University

Raleigh, NC 27695

The DEPARTMENT OF MECHANICAL AND AEROSPACE ENGINEERING at North Carolina State University invites outstanding applicants for two open rank full-time faculty positions in all areas of Mechanical Engineering. Candidates in emerging areas of Mechanical Engineering, including but not limited to autonomous systems and robotics, cyberphysical systems, energy storage, additive manufacturing, renewable energies and industrial IOT, are encouraged to apply.

Successful applicants should demonstrate interest and capabilities for developing active, internationally visible, externally sponsored research programs. The candidates should demonstrate a commitment to effective teaching at both undergraduate and graduate levels. Applicants are expected to have a doctoral degree in Mechanical Engineering or other closely related fields before the start date of the position. The expected start date is as early as Spring 2020

Potential applicants can access the position description and submit their application at the following site: Applicants should submit 1) a cover letter, 2) their curriculum vitae, 3) names and contact information for four references, and 4) their research and teaching statements. Applications received before September 1 will be given priority revie

NC State University is an equal opportunity and affirmative action employer. All qualified applicants will receive consideration for employment without regard to race, color, national origin, religion, sex, gender identity, age, sexual orientation, genetic information, status as an individual with a disability, or status as a protected

About the Department:

The Department of Mechanical and Aerospace Engineering at North Carolina State University (Raleigh, NC) is among the largest and most prominent in the nation. The department offers separate B.S., M.S. and Ph.D. degrees in both Mechanical Engineering (ME) and Aerospace Engineering (AE). The MAE department currently boasts 47 highly recognized tenure-track faculty, 6 non-tenure-track teaching faculty and 15 staff

The Department has an enrollment of over 1,200 undergraduates and 400 graduate students. The department is housed in Engineering Building III, a four-story, 250,000-square foot facility built in 2010. NC State’s location on Centennial Campus, combined with its proximity to the Research Triangle Park and neighboring universities, provides extensive opportunities for academic and industrial interaction and collaboration. The College of Engineering is ranked overall #24 and #9 in research expenditures among all engineering colleges

Further information on the department can be found at: http://www.mae.ncsu.edu.