Animal Agriculture in South Carolina

Livestock Production/Industries,

Animal Agriculture in South Carolina: A Fact Book

Livestock Production/Industries,

Single ultrafast diffusive conduction based optoelectronic switch for multi-channel operation

For multi-channel optical switching, we report single ultrafast diffusive conduction based optoelectronic switches that accommodate >100 optical channels (with 2,000mm-2 channel density and <10% crosstalk), on 300μm×300μm devices with switching bandwidths of >50GHz. © 2005 IEEE

Self-aligned via and trench for metal contact in III-V semiconductor devices

A semiconductor processing method for the formation of self-aligned via and trench structures in III-V semiconductor devices (in particular, on InP platform) is presented, together with fabrication results. As a template for such self-aligned via and trench formations in a surrounding polymer layer on a semiconductor device, we make use of a sacrificial layer that consists of either a Si O2 dielectric hard mask layer deposited on the device layers or a sacrificial semiconductor layer grown on top of the device epitaxial layers (e.g., InP on an InGaAs etch stop), both laid down on the device layers before patterning the device geometry. During the semiconductor device etching, the sacrificial layer is kept as a part of the patterned structures and is, therefore, perfectly self-aligned. By selectively removing the sacrificial layer surrounded by the polymer that is etched back within the thickness of the sacrificial layer, an opening such as a via and a trench is formed perfectly self-aligned on the device top area in the place of the sacrificial layer. This process yields a pristine semiconductor surface for metal contacts and fully utilizes the contact area available on the device top, no matter how small the device area is. This approach thus provides as low an Ohmic contact resistance as possible upon filling the via and the trench with metal deposition. The additional use of a thin Si3 N4 protecting layer surrounding the device sidewalls improves the robustness of the process without any undesired impact on the device electrical passivation (or on the optical mode characteristics if the device also includes a waveguide). This method offers metal contacts scalable to the device size, being limited only by the feasible device size itself. This method is also applicable to the fabrication of other III-V based integrated devices. © 2006 American Vacuum Society

Electrically-reconfigurable integrated photonic switches

We report remotely electrically reconfigurable photonic switches that intimately integrate waveguide electroabsorption modulators with surface-normal photodiodes, avoiding conventional electronics. These switches exhibit full C-band wavelength conversion at 5 Gb/s and are remotely reconfigurable within tens of nanoseconds

Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models

Both community ecology and conservation biology seek further understanding of factors governing the advance of an invasive species. We model biological invasion as an individual-based, stochastic process on a two-dimensional landscape. An ecologically superior invader and a resident species compete for space preemptively. Our general model includes the basic contact process and a variant of the Eden model as special cases. We employ the concept of a "roughened" front to quantify effects of discreteness and stochasticity on invasion; we emphasize the probability distribution of the front-runner's relative position. That is, we analyze the location of the most advanced invader as the extreme deviation about the front's mean position. We find that a class of models with different assumptions about neighborhood interactions exhibit universal characteristics. That is, key features of the invasion dynamics span a class of models, independently of locally detailed demographic rules. Our results integrate theories of invasive spatial growth and generate novel hypotheses linking habitat or landscape size (length of the invading front) to invasion velocity, and to the relative position of the most advanced invader.Comment: The original publication is available at www.springerlink.com/content/8528v8563r7u2742

Entangled-Photon Generation from Parametric Down-Conversion in Media with Inhomogeneous Nonlinearity

We develop and experimentally verify a theory of Type-II spontaneous parametric down-conversion (SPDC) in media with inhomogeneous distributions of second-order nonlinearity. As a special case, we explore interference effects from SPDC generated in a cascade of two bulk crystals separated by an air gap. The polarization quantum-interference pattern is found to vary strongly with the spacing between the two crystals. This is found to be a cooperative effect due to two mechanisms: the chromatic dispersion of the medium separating the crystals and spatiotemporal effects which arise from the inclusion of transverse wave vectors. These effects provide two concomitant avenues for controlling the quantum state generated in SPDC. We expect these results to be of interest for the development of quantum technologies and the generation of SPDC in periodically varying nonlinear materials.Comment: submitted to Physical Review

The Planetary Nebula Luminosity Function at the Dawn of Gaia

The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent extragalactic standard candle. In theory, the PNLF method should not work at all, since the luminosities of the brightest planetary nebulae (PNe) should be highly sensitive to the age of their host stellar population. Yet the method appears robust, as it consistently produces < 10% distances to galaxies of all Hubble types, from the earliest ellipticals to the latest-type spirals and irregulars. It is therefore uniquely suited for cross-checking the results of other techniques and finding small offsets between the Population I and Population II distance ladders. We review the calibration of the method and show that the zero points provided by Cepheids and the Tip of the Red Giant Branch are in excellent agreement. We then compare the results of the PNLF with those from Surface Brightness Fluctuation measurements, and show that, although both techniques agree in a relative sense, the latter method yields distances that are ~15% larger than those from the PNLF. We trace this discrepancy back to the calibration galaxies and argue that, due to a small systematic error associated with internal reddening, the true distance scale likely falls between the extremes of the two methods. We also demonstrate how PNLF measurements in the early-type galaxies that have hosted Type Ia supernovae can help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally, we discuss how the results from space missions such as Kepler and Gaia can help our understanding of the PNLF phenomenon and improve our knowledge of the physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic Distance Scale: State of the Art and Gaia Perspective", to appear in Astrophysics and Space Scienc