Cranial Ontogeny in Stegoceras validum (Dinosauria: Pachycephalosauria): A Quantitative Model of Pachycephalosaur Dome Growth and Variation

Historically, studies of pachycephalosaurs have recognized plesiomorphically flat-headed taxa and apomorphically domed taxa. More recently, it has been suggested that the expression of the frontoparietal dome is ontogenetic and derived from a flat-headed juvenile morphology. However, strong evidence to support this hypothesis has been lacking. Here we test this hypothesis in a large, stratigraphically constrained sample of specimens assigned to Stegoceras validum, the best known pachycephalosaur, using multiple independent lines of evidence including conserved morphology of ornamentation, landmark-based allometric analyses of frontoparietal shape, and cranial bone histology. New specimens show that the diagnostic ornamentation of the parietosquamosal bar is conserved throughout the size range of the sample, which links flat-headed specimens to domed S. validum. High-resolution CT scans of three frontoparietals reveal that vascularity decreases with size and document a pattern that is consistent with previously proposed histological changes during growth. Furthermore, aspects of dome shape and size are strongly correlated and indicative of ontogenetic growth. These results are complementary and strongly support the hypothesis that the sample represents a growth series of a single taxon. Cranial dome growth is positively allometric, proceeds from a flat-headed to a domed state, and confirms the synonymy of Ornatotholus browni as a juvenile Stegoceras. This dataset serves as the first detailed model of growth and variation in a pachycephalosaur. Flat-headed juveniles possess three characters (externally open cranial sutures, tuberculate dorsal surface texture, and open supratemporal fenestrae) that are reduced or eliminated during ontogeny. These characters also occur in putative flat-headed taxa, suggesting that they may also represent juveniles of domed taxa. However, open cranial sutures and supratemporal fenestrae are plesiomorphic within Ornithischia, and thus should be expected in the adult stage of a primitive pachycephalosaur. Additional lines of evidence will be needed to resolve the taxonomic validity of flat-headed pachycephalosaur taxa

Electroabsorption measurements of polysquaraine

We report an electroabsorption signal for the main IR-Vis absorption peak in thin films of polysquaraine. Spectra from 1.0 to 2.0 eV at a temperature of 10 K show a positive peak at 1.29 eV, followed by a negative peak at 1.35 eV with vibronic structure on the high energy wing. The results are discussed in terms of a Stark effect on molecular states. Using the results a Stark shift of about 1 meV is calculated, consistent with values for other pi-conjugated polymer systems

Electroabsorption measurements of the emeraldine base form of polyaniline

Electroabsorption measurements have been performed on the polymeric emeraldine base form of polyaniline and a related phenyl-capped tetramer. The spectra run from the near infrared to the UV, encompassing the main low energy absorption peaks of the materials. The lineshapes of the spectra closely resemble each other, indicating that the electronic structure of the two are similar. The results also indicate that the state produced upon 2 eV photoexcitation is, to some degree, spatially extended. The data for the phenyl-capped tetramer show a small signal below the main peak in the electroabsorption which could possibly be assigned to a transition of oscillator strength to a normally optically forbidden transition

Conductivity studies of polyaniline doped with CSA

Polyaniline films prepared via the camphorsulphonic acid (CSA)m-cresol solution processing route have been synthesized with doping levels in the range of 10-90%. The electrical conductivity of these films has been measured as a function of temperature between 10 and 300 K. At a doping level of 30% the onset of metallic transport is observed, and at 60% the films are found to exhibit metallic transport down to 135 K, and have a maximum room-temperature conductivity of 300 +/- 30 S cm(-1). The results are modelled in terms of a heterogeneous model of fluctuation induced tunnelling (FIT) and metallic transport

Thermal studies of doped polyaniline

The thermal behaviour of camphorsulphonic acid doped polyaniline was studied using T.G.A, D.S.C. and D.M.T.A methods in an attempt to find the best processing conditions

Electroabsorption studies of polyaniline

We present the results of electroabsorption measurements of emeraldine base and a related phenyl capped tetramer, both spun from NMP. A comparison of the data of the two materials shows many similarities, indicating that the electronic structures are similar. Kramers-Kronig analysis has been used to calculate the third order non-linear susceptibility chi((3))(-omega;omega,0,0) as a function of energy. The values of chi((3)) are at a maximum around 1.6 eV with values of the order 3 x 10(-11) esu

Studies of stretched predoped polyaniline films

The electrical conductivity of two isotropic 50% CSA doped polyaniline films were measured to be (300+/-30) S/cm. Four samples were cut from one isotropic film and drawn to various extensions at 150C. An additional four samples were cut from the other film and similarly drawn at 155C. The conductivity's parallel (sigma(parallel to)) and perpendicular (sigma(perpendicular to)) to the draw direction were then measured using a four-in-line probe. The most highly drawn film had an extension of 120% and gave sigma(parallel to) of(967+/-30) S/cm and sigma(perpendicular to) of (100+/-20) S/cm, an anisotropy of 9.67, the different draw temperatures had no effect on the conductivity measured. The conductivity enhancement is attributed to orientation of both the crystal and amorphous phases

Conducting Polymer Fibers

Organic fibers that can function as electronic components such as batteries, sensors, and actuators are exciting prospects for new textile technologies known as smart fabrics or e-textiles. Conducting polymer materials are ideal candidates for such fibers as a result of their good electronic conductivity and mechanical properties and their electrochemical activity. The latter allows the polymer to act as a battery or supercapacitor electrode, to respond to its chemical surroundings as a sensor and to change properties (e.g., color, conductivity, and stiffness) and size when oxidized or reduced. Developing these useful materials into fiber forms has involved wet spinning of soluble forms of polyaniline, polypyrrole, and polythiophene. Both structural modification to the base monomer and the use of solubilizing dopants have been used to render the polymer soluble. In some cases, the addition of carbon nanotubes to the spinning solution has been used to produce composite fibers with improved mechanical and electrical properties. These fibers have been evaluated for applications including biomechanical sensors and artificial muscles. The main current limitation in the further development of conducting polymer fibers for textiles processing is their low toughness