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2019

University of Massachusetts Amherst

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Articles 1 - 30 of 111

Full-Text Articles in Engineering

Predictive Simulation Of Human Movement And Applications To Assistive Device Design And Control, Vinh Nguyen Nov 2019

Predictive Simulation Of Human Movement And Applications To Assistive Device Design And Control, Vinh Nguyen

Doctoral Dissertations

Predictive simulation based on dynamic optimization using musculoskeletal models is a powerful approach for studying biomechanics of human gait. Predictive simulation can be used for a variety of applications from designing assistive devices to testing theories of motor controls. However, one of the challenges in formulating the predictive dynamic optimization problem is that the cost function, which represents the underlying goal of the walking task (e.g., minimal energy consumption) is generally unknown and is assumed a priori. While different studies used different cost functions, the qualities of the gaits with those cost functions were often not provided. Therefore, this ...


A Parallel Direct Method For Finite Element Electromagnetic Computations Based On Domain Decomposition, Javad Moshfegh Nov 2019

A Parallel Direct Method For Finite Element Electromagnetic Computations Based On Domain Decomposition, Javad Moshfegh

Doctoral Dissertations

High performance parallel computing and direct (factorization-based) solution methods have been the two main trends in electromagnetic computations in recent years. When time-harmonic (frequency-domain) Maxwell's equation are directly discretized with the Finite Element Method (FEM) or other Partial Differential Equation (PDE) methods, the resulting linear system of equations is sparse and indefinite, thus harder to efficiently factorize serially or in parallel than alternative methods e.g. integral equation solutions, that result in dense linear systems. State-of-the-art sparse matrix direct solvers such as MUMPS and PARDISO don't scale favorably, have low parallel efficiency and high memory footprint. This work ...


Extreme Dynamics Of Nanomaterials Under High-Rate Mechanical Stimuli, Wanting Xie Oct 2019

Extreme Dynamics Of Nanomaterials Under High-Rate Mechanical Stimuli, Wanting Xie

Doctoral Dissertations

Nanomaterials demonstrate novel mechanical properties attributed to the extremely large interfacial area. At quasi-static rates, the interfacial interactions are crucial in mechanical behaviors, however, materials under extreme mechanical stimuli are rarely studied at nanoscale. With an advanced laser-induced projectile impact test, we perform supersonic impact of micro-projectiles on polymer films, multilayer graphene, carbon- based nanocomposites membranes as well as individual micro-fibers, to study the interface interactions in the high-rate regime, and develop a simplified model to characterize the ballistic performance of materials.


Residual Stress Models For Large Eddy Simulation Of Stratified Turbulent Flows, Felipe Augusto Ventura De Bragança Alves Oct 2019

Residual Stress Models For Large Eddy Simulation Of Stratified Turbulent Flows, Felipe Augusto Ventura De Bragança Alves

Doctoral Dissertations

The residual stresses and scalar fluxes are required to close the momentum and scalar transport equations in simulations of turbulence that are not fully resolved in space.

In stratified turbulence, the stress and fluxes are statistically anisotropic unless the smallest resolved length scale is smaller than the Ozmidov scale and the buoyancy Reynolds number is sufficiently high for there to exist a range of scales that is statistically isotropic.

In this work, a tensorial basis set is derived analytically that potentially contains sufficient information about the anisotropic interaction between resolved and residual scales.

The residual stress tensor is evaluated by ...


Service Competition And Data-Centric Protocols For Internet Access, Thiago Teixeira Oct 2019

Service Competition And Data-Centric Protocols For Internet Access, Thiago Teixeira

Doctoral Dissertations

The Internet evolved in many aspects, from the application to the physical layers. However, the evolution of the Internet access technologies, most visible in dense urban scenarios, is not easily noticeable in sparsely populated and rural areas.

In the United States, for example, the FCC identified that 50% of the census blocks have access to up to two broadband providers; however, these providers do not necessarily compete. Additionally, due to the methodology of the study, there is evidence that the number of actual customers without broadband access is higher since the FCC considers the entire block to have broadband if ...


Top-Down And Bottom-Up Fabrication Of Key Components In Miniature Energy Storage Devices, Wenhao Li Oct 2019

Top-Down And Bottom-Up Fabrication Of Key Components In Miniature Energy Storage Devices, Wenhao Li

Doctoral Dissertations

The advent of miniature electronic devices demands power sources of commensurate form factors. This spurs the research of micro energy storage devices, e.g., 3D microbatteries. A 3D microbattery contains nonplanar microelectrodes with high aspect ratio and high surface area, separated by a nanoscale electrolyte. The device takes up a total volume as small as 10 mm3, allowing it to serve on a chip and to provide power in-situ. The marriage of nanotechnology and electrochemical energy storage makes microbattery research a fascinating field with both scientific excitement and application prospect. However, successful fabrication of well-functioned key components and the ...


Time-Difference Circuits: Methodology, Design, And Digital Realization, Shuo Li Oct 2019

Time-Difference Circuits: Methodology, Design, And Digital Realization, Shuo Li

Doctoral Dissertations

This thesis presents innovations for a special class of circuits called Time Difference (TD) circuits. We introduce a signal processing methodology with TD signals that alters the target signal from a magnitude perspective to time interval between two time events and systematically organizes the primary TD functions abstracted from existing TD circuits and systems. The TD circuits draw attention from a broad range of application fields. In addition, highly evolved complementary metal-oxide-semiconductor (CMOS) technology suffers from various problems related to voltage and current amplitude signal processing methods. Compared to traditional analog and digital circuits, TD circuits bring several compelling features ...


Software-Defined Infrastructure For Iot-Based Energy Systems, Stephen Lee Oct 2019

Software-Defined Infrastructure For Iot-Based Energy Systems, Stephen Lee

Doctoral Dissertations

Internet of Things (IoT) devices are becoming an essential part of our everyday lives. These physical devices are connected to the internet and can measure or control the environment around us. Further, IoT devices are increasingly being used to monitor buildings, farms, health, and transportation. As these connected devices become more pervasive, these devices will generate vast amounts of data that can be used to gain insights and build intelligence into the system. At the same time, large-scale deployment of these devices will raise new challenges in efficiently managing and controlling them.

In this thesis, I argue that the IoT ...


Controlling Selectivities In Heterogeneously Catalyzed Aldol Reactions, Koushik Ponnuru Oct 2019

Controlling Selectivities In Heterogeneously Catalyzed Aldol Reactions, Koushik Ponnuru

Doctoral Dissertations

Aldol condensation is an important C-C bond formation reaction in chemical synthesis that finds versatile applications in bulk and fine chemical industries and has the potential for upgrading of biomass to fuels. However, aldol reactions pose a challenge for controlling the product selectivity by forming a mixture of desired and undesired self, cross, and poly-condensation products. Furthermore, a side reaction, the fission of aldol products resulting in an olefin and a carboxylic acid, has garnered attention recently as a route to isobutene from acetone. While a high level of selectivity control is achievable by homogeneous catalysis, selective solid catalysts, which ...


Bioinspired Complex Nanoarchitectures By Dna Supramolecular Polymerization, Laura A. Lanier Oct 2019

Bioinspired Complex Nanoarchitectures By Dna Supramolecular Polymerization, Laura A. Lanier

Doctoral Dissertations

Bioinspired nanoarchitectures are of great interest for applications in fields such as nanomedicine, tissue engineering, and biosensing. With this interest, understanding how the physical properties of these complex nanostructures relate to their function is increasingly important. This dissertation describes the creation of complex nanoarchitectures with controlled structure and the investigation of the effect of nanocarrier physical properties on cell uptake for applications in nanomedicine.

DNA self-assembly by supramolecular polymerization was chosen to create complex nanostructures of controlled architectures. We demonstrated that the supramolecular polymerization of DNA known as hybridization chain reaction (HCR) is in fact a living polymerization. The living ...


Engineering Nanomaterials For Imaging And Therapy Of Bacteria And Biofilm-Associated Infections, Akash Gupta Oct 2019

Engineering Nanomaterials For Imaging And Therapy Of Bacteria And Biofilm-Associated Infections, Akash Gupta

Doctoral Dissertations

Infections caused by multidrug-resistant (MDR) bacteria pose a serious global burden of mortality, causing thousands of deaths each year. The “superbug” risk is further exacerbated by chronic infections generated from antibiotic-resistant biofilms that are highly resistant to available treatments. Synthetic macromolecules such as polymers and nanoparticles have emerged as promising antimicrobials. Moreover, ability to modulate nanomaterial interaction with bacterial cellular systems plays a pivotal role in improving the efficacy of the strategy.

In the initial studies on engineering nanoparticle surface chemistry, I investigated the role played by surface ligands in determining the antimicrobial activity of the nanoparticles. In further study ...


Structural Control Of Offshore Wind Turbines Using Passive And Semi-Active Control, Semyung Park Oct 2019

Structural Control Of Offshore Wind Turbines Using Passive And Semi-Active Control, Semyung Park

Doctoral Dissertations

Offshore wind energy has the potential to generate substantial electricity production compared to onshore locations, due to the high-quality wind resource. Offshore wind turbines must endure severe offshore environmental conditions and be cost effective, in order to be sustainable. As a result, load mitigation becomes crucial in successfully enabling deployment of offshore wind turbines. A direct approach to reduce loads in offshore wind turbines is the application of structural control techniques. So far, the application of structural control techniques to offshore wind turbines has shown to be effective in reducing fatigue and extreme loads of turbine structures. However, the majority ...


Stealthy Parametric Hardware Trojans In Vlsi Circuits, Samaneh Ghandali Oct 2019

Stealthy Parametric Hardware Trojans In Vlsi Circuits, Samaneh Ghandali

Doctoral Dissertations

Over the last decade, hardware Trojans have gained increasing attention in academia, industry and by government agencies. In order to design reliable countermeasures, it is crucial to understand how hardware Trojans can be built in practice. This is an area that has received relatively scant treatment in the literature. In this thesis, we examine how particularly stealthy parametric Trojans can be introduced to VLSI circuits. Parametric Trojans do not require any additional logic and are purely based on subtle manipulations on the sub-transistor level to modify the parameters of few transistors which makes them very hard to detect.

We introduce ...


Modeling And Simulation Of Driven Nanopatterning Of Bulk-Material And Thin-Film Surfaces, Ashish Kumar Oct 2019

Modeling And Simulation Of Driven Nanopatterning Of Bulk-Material And Thin-Film Surfaces, Ashish Kumar

Doctoral Dissertations

Material nanostructures such as nanowires, quantum dots, and nanorings have a wide variety of applications in electronic and photonic devices among numerous others. Assembling uniformly arranged and consistently sized nanostructure patterns on solid material surfaces is a major challenge for nanotechnology. This dissertation focuses on developing predictive models capable of simulation and analysis of such nanopattern formation on bulk material and strained thin film surfaces.

Single-layer atomic clusters (islands) of sizes larger than a critical size on crystalline conducting substrates undergo morphological instabilities when driven by an externally applied electric field or thermal gradient. We have conducted a systematic and ...


Amorphous-Crystalline Brush Block Copolymers: Phase Behavior, Rheology And Composite Design, Gayathri Kopanati Oct 2019

Amorphous-Crystalline Brush Block Copolymers: Phase Behavior, Rheology And Composite Design, Gayathri Kopanati

Doctoral Dissertations

Bottlebrush block copolymers are polymers with chemically distinct polymer side chains grafted onto a common backbone. The unique architecture induced properties make these materials attractive for applications such as photonic materials, stimuli responsive actuators and drug delivery vehicles to name a few. This dissertation primarily investigates the phase transitions and rheological behavior of amorphous-crystalline bottlebrush brush block copolymers and their composites. The temperature induced phase behavior is investigated using time resolved synchrotron X-ray source. Irrespective of volume fraction and backbone length, the samples display strong segregation even at high temperatures (200 °C) and there is no accessible order-disorder transition in ...


Three Essays On Data-Driven Optimization For Scheduling In Manufacturing And Healthcare, Ekin Koker Oct 2019

Three Essays On Data-Driven Optimization For Scheduling In Manufacturing And Healthcare, Ekin Koker

Doctoral Dissertations

This dissertation consists of three essays on data-driven optimization for scheduling in manufacturing and healthcare. In Chapter 1, we briefly introduce the optimization problems tackled in these essays. The first of these essays deals with machine scheduling problems. In Chapter 2, we compare the effectiveness of direct positional variables against relative positional variables computationally in a variety of machine scheduling problems and we present our results. The second essay deals with a scheduling problem in healthcare: the team primary care practice. In Chapter 3, we build upon the two-stage stochastic integer programming model introduced by Alvarez Oh (2015) to solve ...


Function And Dissipation In Finite State Automata - From Computing To Intelligence And Back, Natesh Ganesh Oct 2019

Function And Dissipation In Finite State Automata - From Computing To Intelligence And Back, Natesh Ganesh

Doctoral Dissertations

Society has benefited from the technological revolution and the tremendous growth in computing powered by Moore's law. However, we are fast approaching the ultimate physical limits in terms of both device sizes and the associated energy dissipation. It is important to characterize these limits in a physically grounded and implementation-agnostic manner, in order to capture the fundamental energy dissipation costs associated with performing computing operations with classical information in nano-scale quantum systems. It is also necessary to identify and understand the effect of quantum in-distinguishability, noise, and device variability on these dissipation limits. Identifying these parameters is crucial to ...


A Synthetic Human Brain Ecm Hydrogel For Tight Control Of Astrocyte Activation, Sualyneth Galarza Oct 2019

A Synthetic Human Brain Ecm Hydrogel For Tight Control Of Astrocyte Activation, Sualyneth Galarza

Doctoral Dissertations

Bioengineers have aimed to design instructive extracellular matrix (ECM) models that can tailor the protein composition and biomechanics of the brain in vitro in order to study how astrocytes remodel the brain during trauma and inflammation. However, these parameters cannot be independently controlled in protein-based models, and although tunable in synthetic systems, current astrocyte cultures fail to retain their characteristic stellate morphology without becoming activated. To this date, there is no biomaterial model that can retain astrocyte quiescence in vitro. This dissertation sought to develop such an in vitro model that would enable the study of specific ECM factors that ...


Polymeric Impulsive Actuation Mechanisms: Development, Characterization, And Modeling, Yongjin Kim Oct 2019

Polymeric Impulsive Actuation Mechanisms: Development, Characterization, And Modeling, Yongjin Kim

Doctoral Dissertations

Recent advances in the field of biomedical and life-sciences are increasingly demanding more life-like actuation with higher degrees of freedom in motion at small scales. Many researchers have developed various solutions to satisfy these emerging requirements. In many cases, new solutions are made possible with the development of novel polymeric actuators. Advances in polymeric actuation not only addressed problems concerning low degree of freedom in motion, large system size, and bio-incompatibility associated with conventional actuators, but also led to the discovery of novel applications, which were previously unattainable with conventional engineered systems.

This dissertation focuses on developing novel actuation mechanisms ...


Self-Exfoliating And Reactive Polymer (Serp) As A Protection Against Chemical Warfare Agents (Cwas), Soeun Kim Oct 2019

Self-Exfoliating And Reactive Polymer (Serp) As A Protection Against Chemical Warfare Agents (Cwas), Soeun Kim

Doctoral Dissertations

According to the US army report, there are still significant numbers of stockpiles of chemical warfare agents (CWAs) produced during the Second World War. CWAs production and stockpiling were officially outlawed by the Chemical Weapons Convention of 1993. Nevertheless, some fanatics around the world use CWA as a weapon of mass destruction, such as the Sarin gas attack in Syria in 2013. Since the discovery that toxic pentavalent organophosphorus (OP) compounds has facilitated the development of CWAs as well as insecticides, research on developing protective materials against those toxins have become a priority. Simply, those poisonous molecules are referred to ...


Designing Ion-Containing Polymers With Controlled Structure And Dynamics, Joshua Enokida Oct 2019

Designing Ion-Containing Polymers With Controlled Structure And Dynamics, Joshua Enokida

Doctoral Dissertations

Ion-containing polymers are a unique class of materials for which strong electrostatic interactions dictate physical properties. By altering molecular parameters, such as the backbone chemical structure, the ion content, and the ion-pair identity, the structure and dynamics of these polymers can be altered. Further investigation of the molecular parameters that govern their structure-property relationships is critical for the future development of these polymeric materials. Particularly, the incorporation of ammonium-based counterions into these polymers offers a facile method to tune their electrostatic interactions and hydrophobicity. Applying this concept, a bulky dimethyloctylammonium (DMOA) counterion was used to modify the organic solubility of ...


Capillary Wrinkling And Mechanical Properties: Single Layers, Bilayers, And Composites, Jooyoung Chang Oct 2019

Capillary Wrinkling And Mechanical Properties: Single Layers, Bilayers, And Composites, Jooyoung Chang

Doctoral Dissertations

In this dissertation, we aim to understand the mechanical properties of thin films and classes of wrinkle patterns of polymer films using capillary wrinkling. We discuss four independent research subjects.

In the first project, we measure the thickness (t) dependence of Young’s modulus (E) of polymer thin films. Thin films were measured from bulk thicknesses down to thickness less than the radius of gyration (6 nm). E does not show any systematic change with t, although an increase in modulus was found for the thinnest poly(styrene) (PS) film.

The second topic is stretching (Y) and bending (B) moduli ...


Cold Spray Deposition Of Polymers – Characterization And Optimization, Zahra Khalkhali Oct 2019

Cold Spray Deposition Of Polymers – Characterization And Optimization, Zahra Khalkhali

Doctoral Dissertations

Abstract

The use of a cool supersonic gas flow to accelerate solid particles to form bonding upon impact on a substrate is known as cold spray deposition. The kinetic energy of the impacting particle dissipates resulting in the thermal softening and plastic deformation of the particle which leads to a strong bonding between the particle and the surface. The cold spray process has been commercialized for some metallic materials, but further research is required to unlock the exciting potential material properties possible with polymeric particles. In this research, a laboratory-scale cold spray system with the capability of accelerating 10 – 100µm ...


Combining Human Factors And Data Science Methods To Evaluate The Use Of Free Text Communication Orders In Electronic Health Records, Swaminathan Kandaswamy Oct 2019

Combining Human Factors And Data Science Methods To Evaluate The Use Of Free Text Communication Orders In Electronic Health Records, Swaminathan Kandaswamy

Doctoral Dissertations

Medication errors are a leading cause of death in the United States. Electronic Health Records (EHR) along with Computerized Provider Order Entry (CPOE) are considered promising ways to reduce these errors. However, EHR systems have not eliminated medication errors. Moreover, in some cases they have facilitated errors due to issues such as poor usability and negative effects on clinical workflows. The use of unexpected free text within a CPOE system can serve as a marker that the system does not adequately support clinical workflow. Prior studies have looked at the use of free text within medication orders, but the inclusion ...


Calculation Of Scalar Isosurface Area And Applications, Kedar Prashant Shete Oct 2019

Calculation Of Scalar Isosurface Area And Applications, Kedar Prashant Shete

Masters Theses

The problem of calculating iso-surface statistics in turbulent flows is interesting for a number of reasons, some of them being combustion modeling, entrainment through turbulent/non-turbulent interfaces, calculating mass flux through iso-scalar surfaces and mapping of scalar fields. A fundamental effect of fuid turbulence is to wrinkle scalar iso-surfaces. A review of the literature shows that iso-surface calculations have primarily been done with geometric methods, which have challenges when used to calculate surfaces that have high complexity, such as in turbulent flows. In this thesis, we propose an alternative integral method and test it against analytical solutions. We present a ...


Behavior Of Prestressed Concrete Bridges With Closure Pour Connections And Diaphragms, Gercelino Ramos Oct 2019

Behavior Of Prestressed Concrete Bridges With Closure Pour Connections And Diaphragms, Gercelino Ramos

Masters Theses

Accelerated Bridge Construction (ABC) has gained substantial popularity in new bridge construction and bridge deck replacement because it offers innovative construction techniques that result in time and cost savings when compared to traditional bridge construction practice. One technology commonly implemented in ABC to effectively execute its projects is the use of prefabricated bridge components (precast/prestressed bridge components). Precast/prestressed bridge components are fabricated offsite or near the site and then connected on-site using small volume closure pour connections. Diaphragms are also commonly used to strengthen the connection between certain prefabricated components used in ABC, such as beam elements. Bridges ...


A Study On Controlling Power Supply Ramp-Up Time In Sram Pufs, Harshavardhan Ramanna Oct 2019

A Study On Controlling Power Supply Ramp-Up Time In Sram Pufs, Harshavardhan Ramanna

Masters Theses

With growing connectivity in the modern era, the risk of encrypted data stored in hardware being exposed to third-party adversaries is higher than ever. The security of encrypted data depends on the secrecy of the stored key. Conventional methods of storing keys in Non-Volatile Memory have been shown to be susceptible to physical attacks. Physically Unclonable Functions provide a unique alternative to conventional key storage. SRAM PUFs utilize inherent process variation caused during manufacturing to derive secret keys from the power-up values of SRAM memory cells.

This thesis analyzes the effect of supply ramp-up times on the reliability of SRAM ...


The Promise Of Vr Headsets: Validation Of A Virtual Reality Headset-Based Driving Simulator For Measuring Drivers’ Hazard Anticipation Performance, Ganesh Pai Mangalore Oct 2019

The Promise Of Vr Headsets: Validation Of A Virtual Reality Headset-Based Driving Simulator For Measuring Drivers’ Hazard Anticipation Performance, Ganesh Pai Mangalore

Masters Theses

The objective of the current study is to evaluate the use of virtual reality (VR) headsets to measure driving performance. This is desirable because they are several orders of magnitude less expensive and, if validated, could greatly extend the powers of simulation. Out of several possible measures of performance that could be considered for evaluating VR headsets, the current study specifically examines drivers’ latent hazard anticipation behavior both because it has been linked to crashes and because it has been shown to be significantly poorer in young drivers compared to their experienced counterparts in traditional driving simulators and in open ...


Topology Network Optimization Of Facility Planning And Design Problems, Ravi Ratan Raj Monga Oct 2019

Topology Network Optimization Of Facility Planning And Design Problems, Ravi Ratan Raj Monga

Masters Theses

The research attempts to provide a graphical theory-based approach to solve the facility layout problem. Which has generally been approached using Quadratic Assignment Problem (QAP) in the past, an algebraic method. It is a very complex problem and is part of the NP-Hard optimization class, because of the nonlinear quadratic objective function and (0,1) binary variables. The research is divided into three phases which together provide an optimal facility layout, block plan solution consisting of MHS (material handling solution) projected onto the block plan. In phase one, we solve for the position of departments in a facility based on ...


On The Fuel Spray Applications Of Multi-Phase Eulerian Cfd Techniques, Gabriel Lev Jacobsohn Oct 2019

On The Fuel Spray Applications Of Multi-Phase Eulerian Cfd Techniques, Gabriel Lev Jacobsohn

Masters Theses

Eulerian-Eulerian Computational Fluid Dynamics (CFD) techniques continue to show promise for characterizing the internal flow and near-field spray for various fuel injection systems. These regions are difficult to observe experimentally, and simulations of such regions are limited by computational expense or reliance on empiricism using other methods. The physics governing spray atomization are first introduced. Impinging jet sprays and Gasoline Direct Injection (GDI) are selected as applications, and modern computational/experimental approaches to their study are reviewed. Two in-house CFD solvers are described and subsequently applied in several case studies. Accurate prediction of the liquid distribution in a like-doublet impinging ...