Repeated Evolution of Digital Adhesion in Geckos: A Reply to Harrington and Reeder

We published a phylogenetic comparative analysis that found geckos had gained and lost adhesive toepads multiple times over their long evolutionary history (Gamble et al., PLoS One, 7, 2012, e39429). This was consistent with decades of morphological studies showing geckos had evolved adhesive toepads on multiple occasions and that the morphology of geckos with ancestrally padless digits can be distinguished from secondarily padless forms. Recently, Harrington & Reeder (J. Evol. Biol., 30, 2017, 313) reanalysed data from Gamble et al. (PLoS One, 7, 2012, e39429) and found little support for the multiple origins hypothesis. Here, we argue that Harrington and Reeder failed to take morphological evidence into account when devising ancestral state reconstruction models and that these biologically unrealistic models led to erroneous conclusions about the evolution of adhesive toepads in geckos

Coming to America: Multiple Origins of New World Geckos

Geckos in the Western Hemisphere provide an excellent model to study faunal assembly at a continental scale. We generated a time-calibrated phylogeny, including exemplars of all New World gecko genera, to produce a biogeographic scenario for the New World geckos. Patterns of New World gecko origins are consistent with almost every biogeographic scenario utilized by a terrestrial vertebrate with different New World lineages showing evidence of vicariance, dispersal via temporary land bridge, overseas dispersal, or anthropogenic introductions. We also recovered a strong relationship between clade age and species diversity, with older New World lineages having more species than more recently arrived lineages. Our data provide the first phylogenetic hypothesis for all New World geckos and highlight the intricate origins and ongoing organization of continental faunas. The phylogenetic and biogeographical hypotheses presented here provide an historical framework to further pursue research on the diversification and assembly of the New World herpetofauna

Elemental boron doping behavior in silicon molecular beam epitaxy

Boron-doped Si epilayers were grown by molecular beam epitaxy (MBE) using an elemental boron source, at levels up to 2×1020 cm−3, to elucidate profile control and electrical activation over the growth temperature range 450–900 °C. Precipitation and surface segregation effects were observed at doping levels of 2×1020 cm−3 for growth temperatures above 600 °C. At growth temperatures below 600 °C, excellent profile control was achieved with complete electrical activation at concentrations of 2×1020 cm−3, corresponding to the optimal MBE growth conditions for a range of Si/SixGe1−x heterostructures

X-Ray Absorption Studies of Strain in Epitaxial (Si-Ge) Atomic Layer Superlattice and Alloy Films

The Si 1s (K-shell) X-ray absorption spectra of a series of strained SixGe100-x alloy thin films and several {(Si)m(Ge)n}p atomic layer superlattices (ALS) grown epitaxially on Si(100) and Ge(100) substrates have been investigated using plane polarized synchrotron radiation. Polarization dependent components of the signal are attributed to anisotropic states associated with strain-induced tetragonal distortions. The sense of the polarization is shown to be identical for all compositions (x = 25 to 92) of SiGe alloys grown on Si(100) substrates. The opposite polarization dependence is found to occur for all SixGe100-x alloys (x = 12 to 50) grown on Ge(100) substrates. The polarization dependence and shape of the near edge spectral features of alloy and ALS samples which have similar (average) chemical composition are remarkably similar. A preliminary comparison of the alloy results with literature band structure calculations is made

Charge Transfer Properties Through Graphene Layers in Gas Detectors

Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical, electrical and optical properties. For the first time graphene layers suspended on copper meshes were installed into a gas detector equipped with a gaseous electron multiplier. Measurements of low energy electron and ion transfer through graphene were conducted. In this paper we describe the sample preparation for suspended graphene layers, the testing procedures and we discuss the preliminary results followed by a prospect of further applications.Comment: 2014 IEEE Nuclear Science Symposium and Medical Imaging Conference with the 21st Symposium on Room-Temperature Semiconductor X-Ray and Gamma-Ray Detectors, 4 pages, 8 figure

Ozone Depletion from Nearby Supernovae

Estimates made in the 1970's indicated that a supernova occurring within tens of parsecs of Earth could have significant effects on the ozone layer. Since that time, improved tools for detailed modeling of atmospheric chemistry have been developed to calculate ozone depletion, and advances have been made in theoretical modeling of supernovae and of the resultant gamma-ray spectra. In addition, one now has better knowledge of the occurrence rate of supernovae in the galaxy, and of the spatial distribution of progenitors to core-collapse supernovae. We report here the results of two-dimensional atmospheric model calculations that take as input the spectral energy distribution of a supernova, adopting various distances from Earth and various latitude impact angles. In separate simulations we calculate the ozone depletion due to both gamma-rays and cosmic rays. We find that for the combined ozone depletion roughly to double the ``biologically active'' UV flux received at the surface of the Earth, the supernova must occur at <8 pc. Based on the latest data, the time-averaged galactic rate of core-collapse supernovae occurring within 8 pc is ~1.5/Gyr. In comparing our calculated ozone depletions with those of previous studies, we find them to be significantly less severe than found by Ruderman (1974), and consistent with Whitten et al. (1976). In summary, given the amplitude of the effect, the rate of nearby supernovae, and the ~Gyr time scale for multicellular organisms on Earth, this particular pathway for mass extinctions may be less important than previously thought.Comment: 24 pages, 4 Postscript figures, to appear in The Astrophysical Journal, 2003 March 10, vol. 58

Ethical and compliance-competence evaluation: a key element of sound corporate governance

Motivated by the ongoing post-Enron refocusing on corporate governance and the shift by the Financial Services Authority (FSA) in the UK to promoting compliance- competence within the financial services sector, this paper demonstrates how template analysis can be used as a tool for evaluating compliance-competence. Focusing on the ethical dimension of compliance-competence, we illustrate how this can be subjectively appraised. We propose that this evaluation technique could be utilised as a starting point in informing senior management of corporate governance issues and be used to monitor and demonstrate key compliance and ethical aspects of an institution to external stakeholders and regulators

Normally-off Diamond Reverse Blocking MESFET

Schottky contacts have been used to fabricate normally-off lateral reverse-blocking MESFETs on p-type (boron-doped) O-terminated monocrystalline diamond. The devices utilized an ohmic source contact but both gate and drain contacts were Schottky in nature. Boron-doped p-channel diamond MESFETs reported to date display the less attractive normally-on characteristics. Here, the normally-off transistor delivered a current level of ~1.5 μAmm⁻¹ at a negative VGS of 0.8 V and a transconductance (gₘ) of 16 μSmm⁻¹, measured at room temperature (RT); at a temperature of 425 K, these values rose to ~70 μAmm⁻¹ for IDS and a gₘ value of 260 μSmm⁻¹. In both cases, a negligible gate leakage current was measured with no breakdown apparent at the maximum field investigated here (3.7 x 10⁵ V/m⁻¹). The Schottky gate demonstrates a well-behaved control of the channel even at higher temperatures. The high-temperature operation, normally-off behavior, and diamond's inherent radiation hardness make this transistor promising for harsh environment applications

Charge Transfer Properties Through Graphene for Applications in Gaseous Detectors

Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical and electrical properties. Regarded as the thinnest and narrowest conductive mesh, it has drastically different transmission behaviours when bombarded with electrons and ions in vacuum. This property, if confirmed in gas, may be a definitive solution for the ion back-flow problem in gaseous detectors. In order to ascertain this aspect, graphene layers of dimensions of about 2x2cm$^2$, grown on a copper substrate, are transferred onto a flat metal surface with holes, so that the graphene layer is freely suspended. The graphene and the support are installed into a gaseous detector equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency properties to electrons and ions are studied in gas as a function of the electric fields. The techniques to produce the graphene samples are described, and we report on preliminary tests of graphene-coated GEMs.Comment: 4pages, 3figures, 13th Pisa Meeting on Advanced Detector

Influence of Annealing on the Interface Structure and Strain Relief in Si/Ge Heterostructures on (100) Si

Research work on the general problem of the nature and thermal stability of the Si/Ge semiconductor interface is reviewed. We report on our recent studies of the interface structure in [(Si)m(Ge)n]p superlattices and (Ge)n layers buried in Si as revealed by Raman scattering, extended X-ray absorption fine structure, and X-ray techniques. Strain relaxation and interdiffusion in the superlattices caused by annealing have been investigated, and it is found that considerable strain-enhanced intermixing together with partial relaxation of Ge-Ge bonds occurs even for very short anneal times at 700°C. Further annealing leads to diffusion at a much slower rate and to the eventual formation of an alloy layer. The Ge-Ge bond lengths in as-grown samples are that expected for a fully strained Ge layer. Similar studies of the (Ge)n layers reveal that two-dimensional pseudomorphic growth proceeds up to n = 5, probably mediated by a Si-Ge interface interdiffusion over one or two monolayers of approximately 20%. A n = 12 layer gave evidence of strain relaxation by the introduction of dislocations and clustering. Interdiffusion proceeds rapidly on annealing at 750°C