Archaeological Investigations at the Belmont Site, Henry County, Virginia

Research Report No. 15, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

Systematic evaluation of techniques for the study of the supramolecular architecture of rhodopsin

The eye is outstanding in its sensitivity: it can react to single photons due to the rod photoreceptor, in particular its outer segment. This thesis investigates experimental approaches to study the higher-order structure of the outer segment’s crucial constituent: rhodopsin. The oligomeric state and organization of rhodopsin within disk membranes has been discussed intensively due to its fundamental meaning. The method of choice to analyze rhodopsin in its close-to-native state so far has been cryo-electron microscopy of vitreous sections (CEMOVIS). To analyze one illumination state of rhodopsin (dark state), CEMOVIS was sufficient. However, CEMOVIS has the disadvantage to be time-consuming and error-prone. To analyze different illumination states, CEMOVIS is not efficient enough. The main part of this thesis treats alternative techniques to overcome the disadvantages of CEMOVIS. Additionally, studies of rhodopsin’s temporal bleaching behaviour were carried out. In more detail: First, we aim to analyze the bleaching of intact retinas. This was done quantitatively via UV-VIS-spectroscopy. We could see an exponential bleaching within the short time scale (in the range of ms). Second, alternative techniques to substitute CEMOVIS were considered and their applicability investigated and evaluated. Dual-axis tomography for tomogram acquisition of samples produced via CEMOVIS turned out to be suboptimal. A ROS solubilization prior to cryo-fixation was accompanied by the same disadvantages like CEMOVIS of high-pressure-frozen retinas. The retinal misplacement and thereby the oblique fractioning of ROS during freeze-fracture experiments with retinal cryo-samples impeded direct imaging of exposed ROS disk membranes. Samples for cryo-ET can also be produced with the focused-ion beam (FIB). Tomography is sped up by using the Fib , due to superior sample quality. However, this way to produce samples is again suboptimal and time-consuming at the present. The most promising approach was to reduce dimensionality of the sample via isolation of ROS disks. ROS disks can subsequently be used for vitrification (plunge-freezing) and subsequent cryo-ET or analyzed via atomic force microscopy (AFM). AFM however, does not allow the investigaion of close-to-native state samples. Nevertheless, it has the advantage of being a technique with a greater effectiveness – what we aimed for. A future optimization of this technique will allow for further investigations of, for example, rhodopsin’s supramolecular structure upon illumination. Finally, a tomogram was simulated and compared to real data

STRETCHABLE CONDUCTIVE COMPOSITES FOR USE IN SOFT DEVICES

An elastically-deformable, conductive composite using elastomers and conductive fibers and simple fabrication procedures is provided. Conductive elastomeric composites offer low resistance to electrical current and are elastic over large (\u3e25%) extensional strains. They can be easily interfaced/built into structures fabricated from elastomeric polymers

Skeleton Structures and Origami Design

In this dissertation we study problems related to polygonal skeleton structures that have applications to computational origami. The two main structures studied are the straight skeleton of a simple polygon (and its generalizations to planar straight line graphs) and the universal molecule of a Lang polygon. This work builds on results completed jointly with my advisor Ileana Streinu. Skeleton structures are used in many computational geometry algorithms. Examples include the medial axis, which has applications including shape analysis, optical character recognition, and surface reconstruction; and the Voronoi diagram, which has a wide array of applications including geographic information systems (GIS), point location data structures, motion planning, etc. The straight skeleton, studied in this work, has applications in origami design, polygon interpolation, biomedical imaging, and terrain modeling, to name just a few. Though the straight skeleton has been well studied in the computational geometry literature for over 20 years, there still exists a significant gap between the fastest algorithms for constructing it and the known lower bounds. One contribution of this thesis is an efficient algorithm for computing the straight skeleton of a polygon, polygon with holes, or a planar straight-line graph given a secondary structure called the induced motorcycle graph. The universal molecule is a generalization of the straight skeleton to certain convex polygons that have a particular relationship to a metric tree. It is used in Robert Lang\u27s seminal TreeMaker method for origami design. Informally, the universal molecule is a subdivision of a polygon (or polygonal sheet of paper) that allows the polygon to be ``folded\u27\u27 into a particular 3D shape with certain tree-like properties. One open problem is whether the universal molecule can be rigidly folded: given the initial flat state and a particular desired final ``folded\u27\u27 state, is there a continuous motion between the two states that maintains the faces of the subdivision as rigid panels? A partial characterization is known: for a certain measure zero class of universal molecules there always exists such a folding motion. Another open problem is to remove the restriction of the universal molecule to convex polygons. This is of practical importance since the TreeMaker method sometimes fails to produce an output on valid input due the convexity restriction and extending the universal molecule to non-convex polygons would allow TreeMaker to work on all valid inputs. One further interesting problem is the development of faster algorithms for computing the universal molecule. In this thesis we make the following contributions to the study of the universal molecule. We first characterize the tree-like family of surfaces that are foldable from universal molecules. In order to do this we define a new family of surfaces we call Lang surfaces and prove that a restricted class of these surfaces are equivalent to the universal molecules. Next, we develop and compare efficient implementations for computing the universal molecule. Then, by investigating properties of broader classes of Lang surfaces, we arrive at a generalization of the universal molecule from convex polygons in the plane to non-convex polygons in arbitrary flat surfaces. This is of both practical and theoretical interest. The practical interest is that this work removes the case from Lang\u27s TreeMaker method that causes TreeMaker to fail to produce output in the presence of non-convex polygons. The theoretical interest comes from the fact that our generalization encompasses more than just those surfaces that can be cut out of a sheet of paper, and pertains to polygons that cannot be lied flat in the plane without self-intersections. Finally, we identify a large class of universal molecules that are not foldable by rigid folding motions. This makes progress towards a complete characterization of the foldability of the universal molecule

Preparation and Properties of Isolated Z-disks

Z-disks form the boundaries of the sarcomeres, the basic contractile units of muscle cells. Within the Z-line thin filaments containing mainly actin interdigitate and are crosslinked by α-actinin. Ends of the giant proteins titin and nebulin are also anchored in the Z-disk. The Z-line was originally thought to have the purely mechanical function of transmitting contractile force along the myofibrils. However, more recently, the Z-disk has emerged as a highly dynamic structure involved in stress sensing and important signaling pathways that govern muscle homeostasis. In order to fully understand how the Z-disk functions a detailed description of its molecular organization is essential. Even though the structure the structure of the Z-disk has been studied by electron microscopy techniques its molecular organization is known only in outline to a resolution of about 5 nm, whereas at least 3 nm is required to begin distinguishing protein shapes and to accurately dock crystal structure. Reports describing the isolation of intact Z-disks from insect indirect flight muscle date from 30-40 years ago, but these preparations have not been subjected to modern electron microscopy techniques. We improved the existing methods for the isolation of the Z-disk from honeybee flight muscle and investigated its structure using cryo-electron tomography and subtomogram averaging. The preliminary data indicate that the resolution was improved when compared with past studies of plastic sectioned muscle. We have also investigated the protein composition of the preparations to monitor the components that are washed away during preparation. Methods for the isolation of intact Z-disks from vertebrate muscle are not available. We explored strategies for isolating Z-disks from skeletal and cardiac muscle. Even though such a preparation has not been achieved we present promising approaches that, with optimization, should enable isolation of Z-disks from vertebrate muscle