Process for the controlled growth of single-crystal films of silicon carbide polytypes on silicon carbide wafers

A method for the controlled growth of single-crystal semiconductor-device-quality films of SiC polytypes on vicinal (0001) SiC wafers with low tilt angles is presented. Both homoepitaxial and heteroepitaxial SiC films can be produced on the same wafer. In particular, 3C-SiC and 6H-SiC films can be produced within selected areas of the same 6H-SiC wafer

Silicon Carbide Nanotube Synthesized

Carbon nanotubes (CNTs) have generated a great deal of scientific and commercial interest because of the countless envisioned applications that stem from their extraordinary materials properties. Included among these properties are high mechanical strength (tensile and modulus), high thermal conductivity, and electrical properties that make different forms of single-walled CNTs either conducting or semiconducting, and therefore, suitable for making ultraminiature, high-performance CNT-based electronics, sensors, and actuators. Among the limitations for CNTs is their inability to survive in high-temperature, harsh-environment applications. Silicon carbon nanotubes (SiCNTs) are being developed for their superior material properties under such conditions. For example, SiC is stable in regards to oxidation in air to temperatures exceeding 1000 C, whereas carbon-based materials are limited to 600 C. The high-temperature stability of SiCNTs is envisioned to enable high-temperature, harsh-environment nanofiber- and nanotube-reinforced ceramics. In addition, single-crystal SiC-based semiconductors are being developed for hightemperature, high-power electronics, and by analogy to CNTs with silicon semiconductors, SiCNTs with single-crystal SiC-based semiconductors may allow high-temperature harsh-environment nanoelectronics, nanosensors, and nanoactuators to be realized. Another challenge in CNT development is the difficulty of chemically modifying the tube walls, which are composed of chemically stable graphene sheets. The chemical substitution of the CNTs walls will be necessary for nanotube self-assembly and biological- and chemical-sensing applications. SiCNTs are expected to have a different multiple-bilayer wall structure, allowing the surface Si atoms to be functionalized readily with molecules that will allow SiCNTs to undergo self-assembly and be compatible with a variety of materials (for biotechnology applications and high-performance fiber-reinforced ceramics)

The infrared imaging spectrograph (IRIS) for TMT: sensitivities and simulations

We present sensitivity estimates for point and resolved astronomical sources for the current design of the InfraRed Imaging Spectrograph (IRIS) on the future Thirty Meter Telescope (TMT). IRIS, with TMT's adaptive optics system, will achieve unprecedented point source sensitivities in the near-infrared (0.84 - 2.45 {\mu}m) when compared to systems on current 8-10m ground based telescopes. The IRIS imager, in 5 hours of total integration, will be able to perform a few percent photometry on 26 - 29 magnitude (AB) point sources in the near-infrared broadband filters (Z, Y, J, H, K). The integral field spectrograph, with a range of scales and filters, will achieve good signal-to-noise on 22 - 26 magnitude (AB) point sources with a spectral resolution of R=4,000 in 5 hours of total integration time. We also present simulated 3D IRIS data of resolved high-redshift star forming galaxies (1 < z < 5), illustrating the extraordinary potential of this instrument to probe the dynamics, assembly, and chemical abundances of galaxies in the early universe. With its finest spatial scales, IRIS will be able to study luminous, massive, high-redshift star forming galaxies (star formation rates ~ 10 - 100 M yr-1) at ~100 pc resolution. Utilizing the coarsest spatial scales, IRIS will be able to observe fainter, less massive high-redshift galaxies, with integrated star formation rates less than 1 M yr-1, yielding a factor of 3 to 10 gain in sensitivity compared to current integral field spectrographs. The combination of both fine and coarse spatial scales with the diffraction-limit of the TMT will significantly advance our understanding of early galaxy formation processes and their subsequent evolution into presentday galaxies.Comment: SPIE Astronomical Instrumentation 201

Integral Field Spectroscopy of High-Redshift Star Forming Galaxies with Laser Guided Adaptive Optics: Evidence for Dispersion-Dominated Kinematics

We present early results from an ongoing study of the kinematic structure of star-forming galaxies at redshift z ~ 2 - 3 using integral-field spectroscopy of rest-frame optical nebular emission lines in combination with Keck laser guide star adaptive optics (LGSAO). We show kinematic maps of 3 target galaxies Q1623-BX453, Q0449-BX93, and DSF2237a-C2 located at redshifts z = 2.1820, 2.0067, and 3.3172 respectively, each of which is well-resolved with a PSF measuring approximately 0.11 - 0.15 arcsec (~ 900 - 1200 pc at z ~ 2-3) after cosmetic smoothing. Neither galaxy at z ~ 2 exhibits substantial kinematic structure on scales >~ 30 km/s; both are instead consistent with largely dispersion-dominated velocity fields with sigma ~ 80 km/s along any given line of sight into the galaxy. In contrast, DSF2237a-C2 presents a well-resolved gradient in velocity over a distance of ~ 4 kpc with peak-to-peak amplitude of 140 km/s. It is unlikely that DSF2237a-C2 represents a dynamically cold rotating disk of ionized gas as the local velocity dispersion of the galaxy (sigma = 79 km/s) is comparable to the observed shear. Using extant multi-wavelength spectroscopy and photometry we relate these kinematic data to physical properties such as stellar mass, gas fraction, star formation rate, and outflow kinematics and consider the applicability of current galaxy formation models.[Abridged]Comment: 19 pages, 10 figures (5 color); accepted for publication in ApJ. Version with full-resolution figures is available at http://www.astro.caltech.edu/~drlaw/Papers/OSIRIS_data1.pd

Nernst effect in the vortex-liquid regime of a type-II superconductor

We measure the transverse thermoelectric coefficient $\alpha_{xy}$ in simulations of type-II superconductors in the vortex liquid regime, using the time-dependent Ginzburg-Landau (TDGL) equation with thermal noise. Our results are in reasonably good quantitative agreement with experimental data on cuprate samples, suggesting that this simple model of superconducting fluctuations contains much of the physics behind the large Nernst effect observed in these materials.Comment: 6 pages. Expanded version of text. New Fig.

Sensitivity of composite scarf joints to manufacturing deviation and disbond under tensile load

Scarf joints are an effective method of bonding thick composite laminates for applications such as the repair of composite aircraft structures. However, concerns remain about their damage tolerance characteristics. Typically composite scarf repairs to aircraft structures require use of hand tools or rudimentary jigs. If the scarf is incorrectly prepared, this may cause a profile deviation to the joint, affecting the bond line stresses and in turn, reducing the residual strength of the joint or repair. The subject of this work examined the sensitivity of composite scarf joints to machining profile deviation and artificial disbond, when subject to static tensile load. Tensile test specimens were prepared with two different configurations of scarf for representing an undercut or imprecise scarf typical of a machining error. In addition, sensitivity of the scarf joints in the presence of an artificial disbond was also tested. Results indicated that for the specimens tested, the scarf is relatively insensitive to minor profile deviation, but highly sensitive to an artificial disbond. Experimental results were also compared with finite element analysis

The Infrared Imaging Spectrograph (IRIS) for TMT: the atmospheric dispersion corrector

We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with certain glass combinations. The design decisions are discussed and the performance of the design ADC is described. Alternative options and their performance tradeoffs are also presented.Comment: SPIE Astronomical Instrumentation 201

The infrared imaging spectrograph (IRIS) for TMT: spectrograph design

The Infra-Red Imaging Spectrograph (IRIS) is one of the three first light instruments for the Thirty Meter Telescope (TMT) and is the only one to directly sample the diffraction limit. The instrument consists of a parallel imager and off-axis Integral Field Spectrograph (IFS) for optimum use of the near infrared (0.84um-2.4um) Adaptive Optics corrected focal surface. We present an overview of the IRIS spectrograph that is designed to probe a range of scientific targets from the dynamics and morphology of high-z galaxies to studying the atmospheres and surfaces of solar system objects, the latter requiring a narrow field and high Strehl performance. The IRIS spectrograph is a hybrid system consisting of two state of the art IFS technologies providing four plate scales (4mas, 9mas, 25mas, 50mas spaxel sizes). We present the design of the unique hybrid system that combines the power of a lenslet spectrograph and image slicer spectrograph in a configuration where major hardware is shared. The result is a powerful yet economical solution to what would otherwise require two separate 30m-class instruments.Comment: 15 pages, 11 figure

WOOD THRUSH MOVEMENTS AND HABITAT USE: EFFECTS OF FOREST MANAGEMENT FOR RED-COCKADED WOODPECKERS

We monitored adult and juvenile breeding-season movements and habitat use of radio-tagged Wood Thrushes (Hylocichla mustelina) at the Piedmont National Wildlife Refuge, central Georgia, USA. We investigated the effects that management for Red-cockaded Woodpeckers (Picoides borealis), thinning and burning \u3e30 year old loblolly pine (Pinus taeda) habitat, had on Wood Thrushes, a ground-foraging and midstory-nesting species. Adult Wood Thrush pairs regularly moved long distances between nesting attempts (range 1 to 17,388 m). The only experimental effect we found on adult movements was a decrease in weekly emigration rates (AP) from thinned and burned compartments after silvicultural management. Adult males preferred riparian hardwoods with sparse to moderate cover and those preferences increased following management. Juveniles remained near their nest site (x = 177 m, SE = 113) for an average 24 days (SE = 6.3), and then dispersed a mean 2,189 m (SE = 342). Before dispersal, juveniles preferred upland hardwood-pine mixed habitat (P \u3c 0.05) with moderate overstory cover (P \u3c 0.05). We found no management effects on dispersal distances or predispersal habitat use. However, juveniles from thinned and burned compartments dispersed to hardwood habitats with dense cover, whereas birds from control compartments dispersed to pine-dominated habitats with sparse cover. All juveniles dispersed to areas with habitat similar to what they used before dispersal. Small-scale thinning and burning for Red-cockaded Woodpeckers may have had little effect on Wood Thrush habitat use and movements because typical movements were often larger than the scale (stand or compartment) targeted for management. Monitoreamos con radio-telemetria los movimientos y el uso de habitat durante la 6poca reproductiva de adultos y juveniles de Hylocichla mustelina en el Refugio Nacional de Vida Silvestre Piedmont, en Georgia central, EEUU. Investigamos los efectos que tiene el manejo del bosque (entresaca y quema de hibitat de Pinus taeda con mas de 30 anios de edad) orientado a la conservaci6n de Picoides borealis sobre H. mustelina, una especie que se alimenta en el suelo y que nidifica a media altura del bosque. Las parejas adultas de H. mustelina por lo general se movieron largas distancias entre los intentos de nidificaci6n (rango 1 a 17,388 m). El uanico efecto experimental que encontramos en los movimientos de adultos fue una disminuci6n en las tasas semanales de emigraci6n (T) desde los sectores entresacados y quemados luego del manejo silvicultural. Los machos adultos prefirieron los bosques riberefios con poca a moderada cobertura, y estas preferencias incrementaron luego del manejo. Los juveniles permanecieron cercanos al sitio de nidificaci6n (x = 177 m, ES = 113) por un promedio de 24 dias (ES = 6.3) y luego se dispersaron una media de 2,189 m (ES = 342). Antes de la dispersi6n los juveniles prefirieron habitat no-ribereiio mixto de bosque y pino (P \u3c 0.05) con moderada cobertura del dosel (P \u3c 0.05). No encontramo

WOOD THRUSH MOVEMENTS AND HABITAT USE: EFFECTS OF FOREST MANAGEMENT FOR RED-COCKADED WOODPECKERS

We monitored adult and juvenile breeding-season movements and habitat use of radio-tagged Wood Thrushes (Hylocichla mustelina) at the Piedmont National Wildlife Refuge, central Georgia, USA. We investigated the effects that management for Red-cockaded Woodpeckers (Picoides borealis), thinning and burning \u3e30 year old loblolly pine (Pinus taeda) habitat, had on Wood Thrushes, a ground-foraging and midstory-nesting species. Adult Wood Thrush pairs regularly moved long distances between nesting attempts (range 1 to 17,388 m). The only experimental effect we found on adult movements was a decrease in weekly emigration rates (AP) from thinned and burned compartments after silvicultural management. Adult males preferred riparian hardwoods with sparse to moderate cover and those preferences increased following management. Juveniles remained near their nest site (x = 177 m, SE = 113) for an average 24 days (SE = 6.3), and then dispersed a mean 2,189 m (SE = 342). Before dispersal, juveniles preferred upland hardwood-pine mixed habitat (P \u3c 0.05) with moderate overstory cover (P \u3c 0.05). We found no management effects on dispersal distances or predispersal habitat use. However, juveniles from thinned and burned compartments dispersed to hardwood habitats with dense cover, whereas birds from control compartments dispersed to pine-dominated habitats with sparse cover. All juveniles dispersed to areas with habitat similar to what they used before dispersal. Small-scale thinning and burning for Red-cockaded Woodpeckers may have had little effect on Wood Thrush habitat use and movements because typical movements were often larger than the scale (stand or compartment) targeted for management. Monitoreamos con radio-telemetria los movimientos y el uso de habitat durante la 6poca reproductiva de adultos y juveniles de Hylocichla mustelina en el Refugio Nacional de Vida Silvestre Piedmont, en Georgia central, EEUU. Investigamos los efectos que tiene el manejo del bosque (entresaca y quema de hibitat de Pinus taeda con mas de 30 anios de edad) orientado a la conservaci6n de Picoides borealis sobre H. mustelina, una especie que se alimenta en el suelo y que nidifica a media altura del bosque. Las parejas adultas de H. mustelina por lo general se movieron largas distancias entre los intentos de nidificaci6n (rango 1 a 17,388 m). El uanico efecto experimental que encontramos en los movimientos de adultos fue una disminuci6n en las tasas semanales de emigraci6n (T) desde los sectores entresacados y quemados luego del manejo silvicultural. Los machos adultos prefirieron los bosques riberefios con poca a moderada cobertura, y estas preferencias incrementaron luego del manejo. Los juveniles permanecieron cercanos al sitio de nidificaci6n (x = 177 m, ES = 113) por un promedio de 24 dias (ES = 6.3) y luego se dispersaron una media de 2,189 m (ES = 342). Antes de la dispersi6n los juveniles prefirieron habitat no-ribereiio mixto de bosque y pino (P \u3c 0.05) con moderada cobertura del dosel (P \u3c 0.05). No encontramo