9,835 research outputs found
A spectacular nitrogen isotope anomaly in Bencubbin
Results of isotopic measurements on an unusual stony-iron meteorite named Bencubbin, which was found in Western Australia in 1930, are reported. Nitrogen from both the metallic and stony parts of the Bencubbin meteorite was analyzed, and in both materials large excesses of (15)N were found, resulting in values of the (14)N/(15)N abundance ratios as low as 137. That is, (15)N is enriched in Bencubbin by about a factor of two relative to terrestrial nitrogen. This is the largest (15)N enrichment of any known natural material. The effect is so large that chemical processes are probably inadequate to account for it. Nuclear processes which may be responsible for the anomalous isotope abundance are discussed
Variable Winds and Dust Formation in R Coronae Borealis Stars
We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in
the He I 10830 lines of twelve R Coronae Borealis (RCB) stars over short (1
month) and long (3 year) timescales to look for variations linked to their
dust-formation episodes. In almost all cases, the strengths and terminal
velocities of the line vary significantly and are correlated with dust
formation events. Strong absorption features with blue-shifted velocities ~400
km/s appear during declines in visible brightness and persist for about 100
days after recovery to maximum brightness. Small residual winds of somewhat
lower velocity are present outside of the decline and recovery periods. The
correlations support models in which recently formed dust near the star is
propelled outward at high speed by radiation pressure and drags the gas along
with it.Comment: AJ in press, 21 pages, 3 figure
Do Hydrogen-Deficient Carbon Stars Have Winds?
We present high resolution spectra of the five known hydrogen-deficient carbon (HdC) stars in the vicinity of the 10830 angstrom line of neutral helium. In R Coronae Borealis (RCB) stars the He I line is known to be strong and broad, often with a P Cygni profile, and must be formed in the powerful winds of those stars. RCB stars have similar chemical abundances as HdC stars and also share greatly enhanced O-18 abundances with them, indicating a common origin for these two classes of stars, which has been suggested to be white dwarf mergers. A narrow He I absorption line may be present in the hotter HdC stars, but no line is seen in the cooler stars, and no evidence for a wind is found in any of them. The presence of wind lines in the RCB stars is strongly correlated with dust formation episodes so the absence of wind lines in the HdC stars, which do not make dust, is as expected.NSFScience and Technology FacilitiesCouncilthe National Research CouncilCONICYTAustralian Research CouncilMinistᄡerio da Ciᄡencia e TecnologiaSECYTMcDonald Observator
Micromachined submicrometer photodiode for scanning probe microscopy
Journal ArticleA submicrometer photodiode probe with a sub-50 nanometer tip radius has been developed for optical surface characterization on a nanometer scale. The nanoprobe is built to detect subwavelength optical intensity variations in the near field of an illuminated surface. The probe consists of an Al-Si Schottky diode constructed near the end of a micromachined pyramidal silicon tip. The process for batch fabrication of the nanoprobes is described. Electrical and optical characterization measurements of the nanoprobe are presented. The diode has a submicrometer optically sensitive area with a 150 fW sensitivity
Nanometer scale absorption spectroscopy by near-field photodetection optical microscopy
Journal ArticleNear-field photodetection optical microscopy (NPOM) is a fundamentally new approach to near-field optical microscopy. This scanning probe technique uses a nanometer-scale photodiode detector which absorbs optical power directly as it is scanned in the near field of an illuminated sample surface. We have applied NPOM to measure the visible absorption spectrum of dye molecules embedded in a single 300 nm polystyrene sphere. The near-field absorption spectrum is obtained by measuring the NPOM probe photocurrent while the wavelength of the illumination pump beam is scanned from 450 to 800 nm. Peaks are identified at 567, 608, and 657 nm in the near-field spectrum of the single-dyed polystyrene sphere. These peak positions are in good agreement with far-field absorption measurements performed on many dyed polystyrene spheres
Government Policy in Support of Domestic Agriculture: Costs and Benefits, The United States
Agricultural and Food Policy,
Micromachined submicrometer photodiode for scanning probe microscopy
Journal ArticleA submicrometer photodiode probe with a sub-50 nanometer tip radius has been developed for optical surface characterization on a nanometer scale. The nanoprobe is built to detect subwavelength optical intensity variations in the near field of an illuminated surface. The probe consists of an Al-Si Schottky diode constructed near the end of a micromachined pyramidal silicon tip. The process for batch fabrication of the nanoprobes is described. Electrical and optical characterization measurements of the nanoprobe are presented. The diode has a submicrometer optically sensitive area with a 150 fW sensitivity
Atomic scale trap state characterization by dynamic tunneling force microscopy
pre-printDynamic tunneling force microscopy (DTFM) is applied to the study of point defects in an inter-layer dielectric film. A recent development enables simultaneous acquisition of DTFM, surface potential, and topographic images while under active height feedback control. The images show no clear correlation between trap state location and surface potential or topography of the surface. The energy and depth of individual trap states are determined by DTFM images obtained at different probe tip heights and applied voltages and quantitative tunneling and electrostatic models. The measured density of states in these films is found to be approximately 11019cm3eV1 near the dielectric film surface
SPIRAL Phase A: A Prototype Integral Field Spectrograph for the AAT
We present details of a prototype fiber feed for use on the Anglo-Australian
Telescope (AAT) that uses a dedicated fiber-fed medium/high resolution (R >
10000) visible-band spectrograph to give integral field spectroscopy (IFS) of
an extended object. A focal reducer couples light from the telescope to the
close-packed lenslet array and fiber feed, allowing the spectrograph be used on
other telescopes with the change of a single lens. By considering the
properties of the fibers in the design of the spectrograph, an efficient design
can be realised, and we present the first scientific results of a prototype
spectrograph using a fiber feed with 37 spatial elements, namely the detection
of Lithium confirming a brown dwarf candidate and IFS of the supernova remnant
SN1987A.Comment: 41 pages, 15 figures, 3 tables; accepted by PAS
Proceedings: Aquaculture Effluents: Overview of EPA Guidelines and Standards and BMPs for Ponds, Raceways, and Recycle Culture Systems
Aquaculture is the production of aquatic organisms, both plant and animal under controlled or semi-controlled conditions. The “controlled or semi-controlled conditions” distinguishes aquaculture from traditional “hunt-and-capture” fishing of wild stocks of marine and freshwater fish, shrimp, and shellfish. The combination of world aquaculture and commercial catches (wild stocks) have grown from 98.6 million metric tons (mmt) in 1990 to 126.2 mmt in 1999, but in 1990 aquaculture was only 13.2% of the total compared with 26.4% in 1999
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