Comparing Three Water Quality Sampling Techniques for Measuring Non-Point Source Pollution in Forest Streams

Coshocton wheel samplers, ISCO pumping samplers, and single stage samplers were compared on each of three small (5-6 ha), forested watersheds in the Ouachita Mountains of central Arkansas. The objective of the comparisons was to evaluate the performance of each sampling method in providing reliable samples for measuring concentrations of total suspended solids (TSS). H-flumes and water level recorders provided stream discharge data; a network of recording and non-recording raingages provided preciptation measurements. Rainfall and storm discharges during the study period were unusually low. No samples were collected by the single stage samplers. They appear unsuited for use on small ephemeral headwater streams in the ~achita Mountains because only unusually large storms will provide the depth of flow required to fill the sample bottles. A few of the Coshocton Wheel samples provided eradic and unpredictable measurements of TSS; however, there was generally good agreement between the Coshoston and pumped samples. The ISCO pumping samplers provided data that were more consistent and predictable than that of the Coshocton wheel. The small number of storm events during the study precludes a definite conclusion as to which sampling method is best . Measurements are continuing

Design and Performance of a Practical Variable-Temperature Scanning Tunneling Potentiometry System

We have constructed a scanning tunneling potentiometry system capable of simultaneously mapping the transport-related electrochemical potential of a biased sample along with its surface topography. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit - the Johnson noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining angstrom scale STM imaging, all at scan sizes of up to 15 um. A mm-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. By performing studies of several model systems, we discuss the implications of various types of surface morphology for potentiometric measurements.Comment: 16 pages, 17 figures, accepted to Review of Scientific Instruments v2 - minor changes: cleaned up figures/figure caption

Spectroscopy of Globular Clusters in the Sculptor Group Galaxies NGC 253 and NGC 55

We have obtained spectra for 103 published globular cluster candidates in the Sculptor Group galaxies NGC 253 and NGC 55. On the basis of radial velocities and digitized plate images, 14 globular clusters are identified in NGC 253 and one probable globular cluster is identified in NGC 55. The majority of the objects in the sample appear to be background galaxies. We have obtained and analysed COSMOS plate scans of NGC 253 and NGC 55 and use these along with the spectroscopically identified clusters to define new samples of globular cluster candidates in the two galaxies which should have reduced contamination.Comment: 11 pages, 9 postscript figures, accepted for publication in MNRA

Toric Duality Is Seiberg Duality

We study four N=1 SU(N)^6 gauge theories, with bi-fundamental chiral matter and a superpotential. In the infrared, these gauge theories all realize the low-energy world-volume description of N coincident D3-branes transverse to the complex cone over a del Pezzo surface dP_3 which is the blowup of P^2 at three generic points. Therefore, the four gauge theories are expected to fall into the same universality class--an example of a phenomenon that has been termed "toric duality." However, little independent evidence has been given that such theories are infrared-equivalent. In fact, we show that the four gauge theories are related by the N=1 duality of Seiberg, vindicating this expectation. We also study holographic aspects of these gauge theories. In particular we relate the spectrum of chiral operators in the gauge theories to wrapped D3-brane states in the AdS dual description. We finally demonstrate that the other known examples of toric duality are related by N=1 duality, a fact which we conjecture holds generally.Comment: 46 pages, 2 figures, harvma

The Atacama Large Millimeter/submillimeter Array: Overview & status

The Atacama Large Millimeter/submillimeter Array (ALMA) is an international radio telescope under construction in the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key observing components: an array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging in size from 0.15 to ~14 km, and a set of four 12-m and twelve 7-m antennas operating in closely-packed configurations ~50m in diameter (known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two flexible digital correlators

An Exploratory Investigation of the Effects of a Thin Plastic Film Cover on the Profile Drag of an Aircraft Wing Panel

Exploratory wind tunnel tests were conducted on a large chord aircraft wing panel to evaluate the potential for drag reduction resulting from the application of a thin plastic film cover. The tests were conducted at a Mach number of 0.15 over a Reynolds number range from about 7 x 10 to the 6th power to 63 x 10 to the 6th power