(updated June 19, 2012)
There are a variety of useful applications in industry for shear thickening non-Newtonian fluids. For certain applications, maintaining shear thickening properties for long periods of time at temperatures below -25 Centigrade is desirable. In this project, such fluids will be identified from patent files and scientific publications, and tests will be conducted to determine the properties of one or more of these fluids at temperatures at or below -25C over an extended period of time. Cost effectiveness will also be determined for the fluids tested.
Crystals are usually thought of as the condensation of density waves. However, in some systems, notably blue phase liquid crystals, and, according to recent results in our group also hard tetrahedra, the formation of a crystal comes from the condensation of an “Orientation Wave” in which the orientation of the constituent parts vary periodically, and this periodic variation condenses. We will analyze results from the Glotzer group at U. Michigan of the computer simulation of the statistical mechanics of by writing a fast running program in “C” that will quickly analyze the formation and condensation of orientation waves. A program that reproduces the results of an earlier Mathematica program will be written and used to analyze configurations from simulations of hard polyhedra. Various such configurations will be analyzed. In addition, a program will be written that will allow the analysis of and display of the angular relationships between various wavevectors that have large orientation waves, probably as an addition to an existing program written by Michael Engel at U. Michigan. These programs will be used to help understand the effects of orientation waves in hard particle systems, particularly particles whose shapes are or are close to tetrahedra.
The past few years of work on discerning the topology of the universe have focused on methods like cosmic crystallography and circles-in-the-sky searches, as well as examinations of the correlation matrix to uncover manifolds with non-trivial topology. While helping to constrain the universe’s possible topologies, these hunts have not discovered the ultimate universal shape. This project aims to extend that investigation to a broader set of topological spaces, including some deformations of known manifolds, and some non-manifolds, using known methods — circles and correlation function comparisons. The ultimate goal is to generalize the existing methods to one that works by detecting the discreteness of the Fourier spectrum in a cosmologically non-trivial space.
A topological insulator is a material that behaves as an insulator in its interior but whose surface contains bound conducting states. The bulk of a topological insulator may be described by a massive Dirac model while the gapless surface states follow the massless Dirac equation. Currently lattice models are needed to give a unified description of the bulk and surface states . In this project we will construct a unified description of the bulk and surface states working with a continuum Dirac description by imposing appropriate boundary conditions on the massive Dirac equation at the insulator surface. These boundary conditions must be consistent with the requirement that the Dirac Hamiltonian operator be hermitian and symmetries such as time-reversal and charge conjugation. The continuum description of topological insulators will be used to analyze insulators with nontrivial topologies and geometries. Electrons on the surface of cylindrical topological insulators have been shown to behave as though the cylinder is threaded by an Aharonov-Bohm flux . In this project we will explore analogous effects on spheres and tori. M.Z. Hasan and C.L. Kane, Reviews of Modern Physics 82, 3045 (2010)  Yi Zhang and Ashvin Vishwanath, Physical Review Letters 105, 206601 (2010)
The equilibrium shape of a dielectric droplet in a uniform electric field is determined by the competition between the effects of surface tension and of the dielectric contribution to the free energy. The surface tension favors a spherical shape for the droplet, as this corresponds to the minimum surface area, while the effects of the electric field are to elongate the droplet into a needle-shaped form. To find the equilibrium shape reached by a droplet in the presence of these two forces is a challenging problem that has been studied for over a century, but has resisted an exact solution. We do, however, know that the droplet develops pointed ends at a certain critical field. In this project we will solve numerically the equations that determine the shape of the droplet in order to investigate the nature of the transition from smooth to pointed ends as the electric field is increased.
Magnetic resonance imaging (MRI) has many applications in our current healthcare system. The MRI group at CWRU has recently introduced a new imaging technique, magnetic resonance fingerprinting (MRF), that presents a new quantitative approach to imaging. In current MRI techniques, it is assumed that each voxel only contains a single species of tissue, and thus has single component relaxation. The purpose of this project is to investigate situations when this assumption is not sufficient, and to see whether MRF can actually separate out the different components. I will be looking into the signal behavior that occurs when there is more than one substance in each voxel, and these substances are in exchange with one another. I will use MATLAB to implement specific models of different scanning situations. I will then compare these results with those obtained from real measurements. By removing the single component relaxation assumption, we believe that a more accurate result can be modeled by accounting for the exchange that occurs within each voxel.
The detection of malaria present in humans has been shown to be possible by measuring the absorption of laser light as a magnetic field is applied to a blood sample containing the paramagnetic malaria hemozoin. However, current systems rely on moving parts and are subject to many sources of noise that prevent detection of low level infection rates. By exploring the response of hemozoin to different powers and wavelengths of light, in addition to using liquid crystal photoshutters as a means to detect hemozoin it may be possible to detect malaria infection at one Plasmodium parasite per picoliter of blood or less.
Recent progress in magnet design and persistent joints using for the magnesium diboride, MgB2, superconductor has made clear the increasingly important role of the persistent switch in magnet quench protection. The persistent switch is used to transform a section MgB2 wire between superconducting and normal conducting states. When used as part of a quench protection circuit, it is important that the switch can transform into the normal state within a second or less. The focus of this work will be designing the persistent switch and modeling the transient thermal response of the switch as it is heated and cooled.
Molybdenum disulfide (MoS2) transistors have attracted considerable attention. Molybdenum disulfide (MoS2) transistors on boron nitride (BN) substrates in particular show interesting I-V characteristics. Unfortunately these transistor devices currently exhibit undesirable I-V characteristics at low temperatures due to the degradation of the MoS2 contacts at low temperatures. This project focuses on mastering device fabrication and improving device I-V characteristics at low temperatures. In order to master device fabrication, understanding the techniques of exfoliation and transfer for the MoS2 is necessary, along with other techniques such as annealing of the contacts. After the base device layer is made, a second layer of metal will be added to the contacts of the device. This metal layer will be added by evaporation through a stencil mask, etched using a focused ion beam. The new device will then be brought down to low temperatures and tested in order to evaluate and understand its I-V characteristics.
The project aims to discern the connection between structural, optical, and spin-dependent properties for films of semiconductor nanoparticles. These films are to be created through various methods involving solutions of quantum dots, and will vary in thickness and uniformity. The structural and optical properties of these films are to be measured using atomic force microscopy (AFM) and optical spectroscopy; light/spin interactions are then to be characterized in a pump-probe Faraday rotation experiment. By systematically varying the film deposition parameters, connections between the films’ structural, optical, and spin-dependent properties will be explored. An understanding of how the deposition parameters affect these properties will enable experiments that require high concentrations of quantum dots, and ultimately may find application in integrated spintronic/photonic devices.
Understanding the origin of cosmic rays observed from earth is expected to help answer fundamental questions about the nature of the highest energy processes in the universe. Cosmic rays are charged particles arriving to the Earth from all directions in space. Their nature and origin has remained a persistent puzzle for many years. This project will focus on analyzing data taken from a prototype cosmic ray detector, which was used to collect flashes of Cherenkov light from cosmic ray air showers. Our objective is to characterize the shape of the pulses and compare them to the expected pulse shape of detection of photons as predicted from simulated cosmic ray air showers. Additionally we will be calibrating our prototype detector, which consists of an optical collector and PMTs, so that an observed voltage reading from the PMTs can be converted to the amount of light collected.
Computer simulations of hard tetrahedra show a disordered phase and two dodecagonal quasicrystal phases. The fluctuations in the disordered phase and the order in the ordered phases are examined in terms the irreducible representations of the group of translations and rotations, which are density and orientation waves. We have demonstrated that the ordered phases can be explained in terms of the condensation of orientation waves that have large fluctuations in the disordered phase. The Landau theory of such orientation waves for particles with local tetrahedral will be examined, as will other theories in which there are spatially varying or spatially constant high order tensors. These theories, much more naturally than the Landau theory of density waves, result in a number of crystalline and quasicrystalline phases, including (with appropriate parameters) those observed in hard tetrahedra. Possible use of such order parameters to find other quasicrystalline phases in simulations, explain them in experiment, and to guide synthesis, will be examined.
Hyperspectral imaging is an advanced imaging technique that measures visible and near-infrared light reflecting off a surface. Hyperspectral imagery has a wide range of applications from geospatial sciences to ecology, surveillance and more. A hyperspectral image is a 3D structure with a spectrum of values associated with every pixel corresponding to the image intensity at a fixed spatial location recorded at different wavelengths. These spectra can be compared to known materials, and then classified.
Hyperspectral data processing has been given a lot of attention during the past decade, but the problem of classification is still open. We intend to perform an in-depth study of the existing classification and dimension reduction methods for hyperspectral data. We will attempt to improve those by integrating the most successful existing methods into a joint framework and/or adjusting the methodology for a specific subclass of data with the goal of improving the performance in either the quality of output or the computational efficiency. We will use the publicly available hyperspectral datasets and spectral signatures (SpecTIR® Remote Sensing Division website, NASA).
Simple energy balance models with temperature dependent albedo (reflected fraction of incoming radiation) can exhibit hysteresis and rapid transitions between “warm” and “cold” equilibrium states. Another important factor that affects radiative balance and mean temperature are greenhouse gases (GHG) that control outgoing radiation. They have multiple sources and sinks, natural and anthropogenic (man-made), and temperature could also affect those processes. We will develop and explore a coupled EBM + GHG dynamic model with temperature feedbacks linked to albedo and GHG. Our goal is to study possible tipping points (abrupt transitions) and hysteresis cycles in such systems. We shall also explore different inputs and control parameters that could affect abrupt transitions, like anthropogenic GHG emissions or frozen methane deposits. The models will include globally average (“zero-dimensional”) EBM, and zonally average 1D EBM, and focus on CO2 and methane GHG
Monolayers of transition metal dichalcogenides (TMDCs), such MoS2 and MoSe2 , have been the subject of increased interest due to their promising potential in nanoelectronics, optoelectronics, and other fields. To date, the synthesis of large area high quality monolayer TMCDs has proven difficult, with high quality samples generally being restricted to the micron scale. The intent of this project is to study the growth mechanism of TMDCs on a substrate via the physical vapor deposition method. An increased understanding of the material’s growth process may facilitate the synthesis of single layer wafer-scale, high quality TMDC.