University of Maine
|Research specialty||Degree type|
(Final degree/Enroute to PhD)
|Atomic, Molecular, & Optical Physics||Both||Both|
|Condensed Matter Physics||Both||Both|
|Energy Sources & Environment||Both||Both|
|Materials Science, Metallurgy||Experimental||Both|
|Medical, Health Physics||Both||Both|
|Physics and other Science Education||Both||Both|
|Relativity & Gravitation||Theoretical||Both|
|Statistical & Thermal Physics||Theoretical||Both|
Polyelectrolyte microgels and microcapsules are microscopic gel particles that are swollen in a solvent. Composed of porous, elastic networks of cross-linked polymers, microgels are soft colloids that can encapsulate dye molecules or drugs. Their sensitive response to environmental conditions (e.g., temperature and pH) and influence on flow properties suit microgels to widespread applications in the chemical, pharmaceutical, food, and consumer care industries. We model microgels and microcapsules using molecular simulations and Poisson-Boltzmann theory.
Lipid membranes surround all living cells, forming a barrier that ensures integrity and function. We are interested in understanding the physical properties of membranes and relating them to biological functions. Among the interesting questions are how different lipids influence the lateral organization of a lipid bilayer and what the role of membrane-associated proteins is. Some of our work also addresses bending of lipid membranes and electrostatic interactions between the lipid bilayer and adsorbed macroions.
Electronic Structure of Nanoparticles from First Principles
The ability to control properties of nanomaterials via size, shape, composition, surface structure, and self-assembly has opened new degrees of freedom inaccessible in conventional device design. At the same time, computational studies of nanostructures have become an attractive alternative to actual experiments, since the ability to explore the vast set of all possible configurations experimentally is limited. In recent years, advances in ab initio electronic structure techniques, such as Density Functional Theory, combined with new computational capabilities have enabled accurate calculations for atomistic models of nanoparticles. The results of these studies often serve as a unique source of insight into nanomaterial properties.
We study properties of photoexcited semiconductor nanoparticles, such as quantum dots, nanowires, nanofilms, and carbon nanotubes. This requires description of electrons, photons, and atomic vibrations (phonons), all of which are interacting quantum mechanical particles. In our work methods of modern quantum field theory, which have been mostly used in theoretical nuclear and particle physics, are combined with advanced computational electronic structure capabilities.
Materials Theory and Design
The key, technology-enabling materials have historically often been discovered through intuition-driven trial-and-error experiments or through lucky accidents. Moving a material after initial discovery to the market can take 20 or more years. Our research is focused on designing and creating new materials with tailored properties, aiming to significantly accelerate the pace of discovery and deployment of advanced material systems. We use quantum mechanical first-principles methods of computational electronic-structure and defect theory, which have provided extremely powerful tools for predicting the electronic, structural, and defect properties of materials. We seek to understand the physical properties of condensed matter and materials, identify the rational structure-property relationships, and discover new materials for experimental realization. Our research covers a broad range of material classes, including but not limited to, complex oxides and their interfaces for next-generation electronics, 2D flexible electronics, photovoltaic materials, transparent conductors, heterogeneous catalysts, and batteries and super-capacitors.
Physics Education Research
We use theories and frameworks drawn from a variety of research areas, including cognitive science and science education as well as disciplined-based education research (e.g., physics and mathematics). Recent investigations have employed dual-process theories of reasoning and decision-making, analysis based on student difficulties, epistemic games, symbolic forms, the resource framework, and gesture analysis and embodied cognition. These frameworks serve as analytical lenses through which we may gain insight into student thinking. In some cases, the knowledge generated is used to guide the development of instructional approaches as well as student-centered instructional resources.
Biophysics of Influenza Virus
Influenza virus continues to cause significant illness in humans. Development of new vaccines takes time, and many of the circulating strains are resistant to available drugs. New strategies for identifying anti-viral targets are needed. The viral glycoprotein hemagglutinin (HA) catalyzes membrane fusion, which is crucial for viral entry, and the clustering of HA is necessary for fusion to occur. We recently discovered an association between HA and several host cell actin binding proteins (ABPs) and actin itself in the absence of other viral components. However, the mechanism for this interaction is unknown. We are using FPALM to examine the nanoscale interactions between HA and the actin cytoskeleton under perturbations of HA, lipid microenvironment, and cell signaling. Results obtained will help determine the mechanism for influenza interactions with host cell actin, improve understanding of membrane cell biology, and identify new host cell targets for anti-viral therapies.
Hyperspectral Remote Sensing Physics
We have pioneered the development of aircraft- and spacecraft-based imaging Fourier transform spectrometers for a wide range of remote sensing applications. Current research is focused on development of tomographic hyperspectral systems, and on application of hyperspectral remote sensing to the transportation infrastructure, particularly applications involving Unmanned Aircraft Systems (UAS).
C. Hess, Samuel Hess
Liquid Crystals and Complex Fluids
Static and dynamic light scattering in liquid crystals and complex fluids, phase transitions.
Physics and other Science Education
Physics Education Research. We investigate the learning and teaching of physics, as well as related topics, from a disciplinary perspective. These include empirical studies of conceptual understanding and student reasoning approaches, development and assessment of instructional materials, identification of both specific student difficulties and productive student resources while learning physics, teacher knowledge of student thinking about physics and physical science, and student metacognitive and reasoning skills in a variety of instructional environments, including upper-division laboratories. One emphasis of our research group is a focus at the upper division and in interdisciplinary studies, including the use and understanding of mathematics in physics as well as the teaching and learning of electronics in both physics and engineering. Another emphasis is the study of K-12 teachers, their knowledge of content and students’ ideas, and their use of formative assessment during classroom interactions with students. Data come from free-response written items, surveys, individual and multi-subject interviews, and classroom video.
MacKenzie Stetzer, John Thompson, Michael Wittmann
Diffraction limits resolution in optical microscopy, but much of biology occurs at the molecular level. The development of localization-based super-resolution microscopy has broken the diffraction limit, resulting in a Nobel Prize in Chemistry in 2014. Our invention, fluorescence photoactivation localization microscopy (FPALM; S.T. Hess et al. Biophysical Journal, 2006) uses a combination of photophysics and fluorescence to sequentially activate sparse subsets of individual molecules (initially in a dark state), image them, determine their positions (localization), convert them back to a dark state, and repeat. Recent development of a combined super-resolution imaging and single molecule spectroscopy instrument (Mlodzianoski et al., PLoS One, 2016) has enabled us to measure emission spectra from individual fluorescent particles while also localizing their positions, to distinguish three different fluorescent proteins within a cell, and to observe changes in the emission spectrum of a single molecule over time. This capability has led to the discovery of spectral wandering in a variety of photoactivatable fluorescent proteins and organic fluorophores we have examined, and suggests a host of new super-resolution imaging methodologies based on changes in single molecule emission spectra.
Thin Film and Sensor Technology
A variety of thin film materials (metal alloys, oxides, borides, nitrides, and oxynitrides) are being developed for application as thin film components in chemical, biological, and physical sensors and MEMS devices. Film synthesis is being carried out using e-beam evaporation, magnetron sputtering, plasma-assisted epitaxy, atomic layer deposition, and other methods to yield thin film nanocomposite structures and novel multilayer films. Film properties are characterized including nanostructure, nanomorphology, chemical composition, electrical response, chemical reactivity, and friction, hardness and wear to optimize the performance of materials and devices. Recent interests focus on thin film sensor materials that can operate in harsh environments up to 1500oC and oxidizing and reducing gases up to 600 psi.