Physics Commons^™

Assembly Of Particles Onto Rigid Cylinders And Flexible Membranes: Probing Effects Of Surface Curvature And Deformation, Derek Wood

Doctoral Dissertations

In this thesis we explore two specific topics within the broad field of particle adhesion. First, we examine the effect of substrate shape and geometry on the self assembly of adsorbed particles, by performing molecular dynamics simulations of interacting particles constrained to the surface of cylinders of varying diameters. We find the diameter of the cylinder imposes a constraint on the shape and crystallographic orientation of the self-assembled lattice, essentially determining the optimal arrangement of particles a priori. We propose a simple one-dimensional model to explain the optimal arrangement of particles as a function of the particle interaction potential …

Analyses Of Densely Crosslinked Phenolic Systems Using Low Field Nmr, Jigneshkumar Patel

Doctoral Dissertations

A uniform dispersion of reactants is necessary to achieve a complete reaction involving multi-components, especially for the crosslinking of rigid high-performance materials. In these reactions, miscibility is crucial for curing efficiency. This miscibility is typically enhanced by adding a third component, a plasticizer. For the reaction of the highly crystalline crosslinking agent hexamethylenetetramine (HMTA) with a strongly hydrogen-bonded phenol formaldehyde resin, furfural has been traditionally used as the plasticizer. However, the reason for its effectiveness is not clear. In this doctoral thesis work, miscibility and crosslinking efficiency of plasticizers in phenolic curing reactions are studied by thermal analysis and spectroscopic …

Conducting Polyelectrolyte Complexes: Assembly, Structure, And Transport, Michael A. Leaf

Doctoral Dissertations

Decades of progress have yielded a tremendous variety of organic electronics, with great strides in the development of photovoltaics, thermoelectrics and other flexible devices. Ubiquitous in these research areas are films of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT: PSS), a complex of oppositely-charged polyelectrolytes initially suspended in water before film formation. This material has high electronic conductivity and good water processability. Pristine film conductivity is somewhat low, but is dramatically enhanced through simple treatments like ionic liquid addition or shear. Can this enhancement be understood so that further optimization might render PEDOT: PSS commercially viable? PEDOT: PSS is a complicated material, with …

Production Of Cosmological Observables During The Inflationary Epoch, Cody Goolsby-Cole

Doctoral Dissertations

This dissertation proposal explores the production of present day cosmological observables which might have been produced during the inflationary era. The first observable is the current net electric charge of our observable universe produced by charge fluctuations during inflation. Next, we examine the possibility of a signal in the primordial gravitational wave power spectrum produced by a scalar field with a time dependent mass. Finally, we examine primordial magnetic fields produced during inflation through the Ratra model coupling with the Schwinger effect.

Interface Driven Dynamics And Assembly, Wei Hong

Doctoral Dissertations

Interfaces between two substances (e.g., gas / liquid, liquid / liquid) are ubiquitous in nature and industry. In this project, we study two important aspects of interface: interface driven dynamics and assembly. In the area of interface driven dynamics, we conduct experiments to study how interfacial capillarity drives flow of wax inside paper under controlled temperature and pressure. The findings lead to the ability to manufacture high-resolution paper-based microfluidic devices. In the area of interface driven assembly, we study how to tune interfacial electrostatic potential and how this potential can enhance or suppress colloidal particle assembly to the interface. We …

Problems In Graph-Structured Modeling And Learning, James Atwood

Doctoral Dissertations

This thesis investigates three problems in graph-structured modeling and learning. We first present a method for efficiently generating large instances from nonlinear preferential attachment models of network structure. This is followed by a description of diffusion-convolutional neural networks, a new model for graph-structured data which is able to outperform probabilistic relational models and kernel-on-graph methods at node classification tasks. We conclude with an optimal privacy-protection method for users of online services that remains effective when users have poor knowledge of an adversary's behavior.

Morphology Of Thin Sheets In The Lame Setup And Beyond, Zhanlong Qiu

Doctoral Dissertations

We present a general analytical approach to study the wrinkling phenomena in the Lame, sheet on drop, drop on sheet, and twisted ribbon setups. In the partially single-mode wrinkle pattern, we employ the boundary layer analysis to regularize the divergence in the energy and obtain the optimal wavenumber. In the multi-mode wrinkle pattern scenario, we consider the effects of the boundary condition, meniscus, and the geometry of the setup separately on the energies and obtain scaling results for the wavenumber of the multi-mode pattern due to each effect. Lastly, a wrinkle-to-fold transition is discussed in the Lame setup, with our …

A Search For Double Beta Decay Of Xenon To Excited States Of Barium With Exo-200, Sereres Johnston

Doctoral Dissertations

This thesis presents searches for several modes of double beta decays of 136Xe to two low-lying excited levels of 136Ba. For each final level, both 2ν and 0ν double beta decay processes are considered. The data and general techniques developed by the EXO-200 collaboration are used, including a Machine Learning process to improve sensitivity in multivariate space. EXO-200 is an experimental program searching for 0νββ decay in a time projection chamber filled with 175 kg of liquid Xenon enriched to 80% 136Xe, functioning as both source and detector. Experimental searches of double beta decay with 136Xe and other isotopes are …

Reducing The Size Sale Of The Block Copolymer Microdomains And Morphology Study Of Brush Block Copolymers Containing Homopolymer, Gajin Jeong

Doctoral Dissertations

Block copolymers (BCPs), due to their ability to self-assemble into periodic nanoscale morphologies, have been extensively studied over the past few decades. The thermodynamic parameters governing self-assembly of BCPs generally leads to periodic morphologies with characteristic length scales ranging from 10 to 100 nm. Several applications have been demonstrated utilizing BCPs as a template for the fabrication of nanostructured materials. Fabricating structures beyond the 10-100 nm range, remains a challenge and constitutes one of the goals of the proposed research. This dissertation is divided into two parts. The first focuses on the sub 10 nm length scale, when by chemically …

Deformation And Adhesion Of Soft Composite Systems For Bio-Inspired Adhesives And Wrinkled Surface Fabrication, Michael Imburgia

Doctoral Dissertations

The study of soft material deformation and adhesion has broad applicability to industries ranging from automobile tires to medical prosthetics and implants. When a mechanical load is imposed on a soft material system, a variety of issues can arise, including non-linear deformations at interfaces between soft and rigid components. The work presented in this dissertation embraces the occurrence of these non-linear deformations, leading to the design of functional systems that incorporate a soft elastomer layer with application to bio-inspired adhesives and wrinkled surface fabrication. Understanding the deformation of a soft elastomer layer and how the system loading and geometry influence …

Tunneling Assisted Forbidden Transitions In The Single Molecule Magnet Ni4, Yiming Chen

Doctoral Dissertations

This dissertation presents work in exploring novel quantum phenomena in singlemolecule magnets (SMMs) and superconducting circuits. The degree of the freedom studied is the magnetic moment of a single molecule and the flux quantum trapped in a superconducting ring. These phenomena provide us with new insights into some basic questions of physics and may also find their application in quantum computing. The molecule we studied is Ni4 ([Ni4(hmp)(dmp)Cl]4) which can be treated as a spin-4 magnet. The large magnetic anisotropy of the molecule leads to bistability of the magnetic moment at low temperatures, with spin-up and spin-down states separated by …

Investigating Patterns Using Analyzing Digital Images (Adi) Software, Jennifer Welborn, Wayne Kermenski

Patterns Around Us

The mean and variation of a population are easily seen by graphing the number of individuals that have a trait of a given value. In this experiment, we will investigate color variation found in a mealworm population using ADI.

In this investigation, we will use digital images and ADI to measure the increased surface area created by villi located in the small intestines.

Wrinkling Of A Floating Sheet, Narayanan Menon

Patterns Around Us

The objective of today’s work will be to generate wrinkle patterns on very thin polymer films using the forces generated by the surface tension of a water drop. You’ll do a few sizes of water drop and we’ll give you a couple of thicknesses of film. Digital images of the pattern will allow us to make observations of the number and size of the wrinkles generated. We will try to develop an understanding of the dependence of the pattern on the materials used and the forces applied

Branching In Nature, Jennifer Welborn, Wayne Kermenski

Patterns Around Us

No abstract provided.

Wrinkling In Nature, Jennifer Welborn, Wayne Kermenski

Patterns Around Us

This lab experience is separated into four investigative segments:

1. Human saliva and enzymes

2. Osmosis and Dialysis Tubing

3. Analyzing dry and imbibed weights of wrinkled and smooth pea seeds

4. Putting it All Together, What makes Wrinkled Peas?

Overview, Benjamin Davidovitch, Narayanan Menon, Jennifer Welborn, Wayne Kermenski

Patterns Around Us

No abstract provided.

Physics 131: Forces, Energy And Entropy, Brokk Toggerson, David Nguyen

Physics Educational Materials

An openly licensed physics textbook localized for use in Physics 131: Forces, Energy, and Entropy at the University of Massachusetts Amherst. This book is adapted from the OpenStax College Physics textbook, the University of Maryland NEXUS Physics wikibook, the OpenStax Chemistry textbook and the statistics work of John S. Denker.

Superhero Robotics, Frank Sup, Brian Umberger, Nick Sawyer

Science and Engineering Saturday Seminars

No abstract provided.

Gapless Symmetry-Protected Topological Order, Thomas Scaffidi, Daniel E. Parker, Romain Vasseur

Physics Department Faculty Publication Series

We introduce exactly solvable gapless quantum systems in d dimensions that support symmetry-protected topological (SPT) edge modes. Our construction leads to long-range entangled, critical points or phases that can be interpreted as critical condensates of domain walls “decorated” with dimension (d−1) SPT systems. Using a combination of field theory and exact lattice results, we argue that such gapless SPT systems have symmetry-protected topological edge modes that can be either gapless or symmetry broken, leading to unusual surface critical properties. Despite the absence of a bulk gap, these edge modes are robust against arbitrary symmetry-preserving local perturbations near the …