2,470 research outputs found
A fully-integrated 1.8-V, 2.8-W, 1.9-GHz, CMOS power amplifier
This paper demonstrated the first 2-stage, 2.8W, 1.8V, 1.9GHz fully-integrated DAT power amplifier with 50Ω input and output matching using 0.18μm CMOS transistors. It has a small-signal gain of 27dB. The amplifier provides 2.8W of power into a 50Ω load with a PAE of 50%
Millimeter-Wave Diffraction by a Photo-Induced Plasma Grating
Optical gratings are used extensively for beamsteering in the visible and IR range of the spectrum. Change in the dielectric permittivity of a semiconductor medium resulting from the excitation of a nonequilibrium electron-hole plasma makes it possible to extend this technique to MMW frequencies. A photo-induced plasma grating (PIPG) can be easily rewritten by changing the illumination pattern. So this technique can be used in optically controllable MMW antennas. Initial experimental work studied the diffraction of MMW propagating along a dielectric waveguide containing a PIPG. This paper reports on the diffraction of MMW propagating in free space, steered by the PIPG
Coaxial carbon plasma gun deposition of amorphous carbon films
A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented
Gamma-Ray Bursts and the Cosmic Star Formation Rate
We have tested several models of GRB luminosity and redshift distribution
functions for compatibility with the BATSE 4B number versus peak flux relation.
Our results disagree with recent claims that current GRB observations can be
used to strongly constrain the cosmic star formation history. Instead, we find
that relaxing the assumption that GRBs are standard candles renders a very
broad range of models consistent with the BATSE number-flux relation. We
explicitly construct two sample distributions, one tracing the star formation
history and one with a constant comoving density. We show that both
distributions are compatible with the observed fluxes and redshifts of the
bursts GRB970508, GRB971214, and GRB980703, and we discuss the measurements
required to distinguish the two models.Comment: 12 pages, 2 postscript figures, uses AAS LaTex macros v4.0. To be
published in Astrophysical Journal Letters, accepted August 20, 1998. Revised
for publicatio
Field Evaluation of Herbicides on Small Fruit, Vegetable, and Ornamental Crops, 1997
Growers generally use herbicides to efficiently produce high-quality fruit and vegetables for processing or fresh market sales. Due to the smaller acreage of these crops compared to major field crops, fewer herbicides are registered for use in fruit and vegetable crops than for field crops. Each year, new herbicides are evaluated under Arkansas growing conditions with the objective of improving the herbicide technology for the grower, processor, and ultimately the consumer. This report includes studies on the control of many of the more serious weed problems in important crops of this region, including snapbeans, spinach, southern pea, watermelon, cantaloupe, tomato, blackberry, and grape. In addition, the report includes information on the tolerance of selected bedding plants to some effective herbicides
Chandra Observations of 1RXS J141256.0+792204 (Calvera)
We report the results of a 30 ks Chandra ACIS-S observation of the isolated
compact object 1RXS J141256.0+792204 (Calvera). The X-ray spectrum is
adequately described by an absorbed neutron star hydrogen atmosphere model with
an effective temperature at infinity of 88.3 +/- 0.8 eV and radiation radius at
infinity of 4.1 +/- 0.1 km/kpc. The best-fit blackbody spectrum yields
parameters consistent with previous measurements; although the fit itself is
not statistically acceptable, systematic uncertainties in the pile-up
correction may contribute to this. We find marginal evidence for narrow
spectral features in the X-ray spectrum between 0.3 and 1.0 keV. In one
interpretation, we find evidence at 81%-confidence for an absorption edge at
0.64 (+0.08) (-0.06) keV with an equivalent width of ~70 eV; if this feature is
real, it is reminiscent of features seen in the isolated neutron stars RX
J1605.3+3249, RX J0720.4-3125, and 1RXS J130848.6+212708 (RBS 1223). In an
alternative approach, we find evidence at 88%-confidence for an unresolved
emission line at energy 0.53 +/- 0.02 keV, with an equivalent width of ~28 eV;
the interpretation of this feature, if real, is uncertain. We search for
coherent pulsations up to the Nyquist frequency of 1.13 Hz and set an upper
limit of 8.0% rms on the strength of any such modulation. We derive an improved
position for the source and set the most rigorous limits to-date on any
associated extended emission on arcsecond scales. Our analysis confirms the
basic picture of Calvera as the first isolated compact object in the
ROSAT/Bright Source Catalog discovered in six years, the hottest such object
known, and an intriguing target for multiwavelength study.Comment: Submitted to ApJ. AASTeX, 19 pages, 2 figure
Multiresolution analysis in statistical mechanics. I. Using wavelets to calculate thermodynamic properties
The wavelet transform, a family of orthonormal bases, is introduced as a
technique for performing multiresolution analysis in statistical mechanics. The
wavelet transform is a hierarchical technique designed to separate data sets
into sets representing local averages and local differences. Although
one-to-one transformations of data sets are possible, the advantage of the
wavelet transform is as an approximation scheme for the efficient calculation
of thermodynamic and ensemble properties. Even under the most drastic of
approximations, the resulting errors in the values obtained for average
absolute magnetization, free energy, and heat capacity are on the order of 10%,
with a corresponding computational efficiency gain of two orders of magnitude
for a system such as a Ising lattice. In addition, the errors in
the results tend toward zero in the neighborhood of fixed points, as determined
by renormalization group theory.Comment: 13 pages plus 7 figures (PNG
Sputtered coatings for protection of spacecraft polymers
Kapton polyimide oxidizes at significant rates (4.3x10(-24) gram/incident oxygen atom) when exposed in low Earth orbit to the ram atomic oxygen flux. Ion beam sputter deposited thin films of Al2O3 and SiO2 as well as a codeposited mixture of predominantly SiO2 with a small amount of polytetrafluoroethylene were evaluated and found to be effective in protecting Kapton from oxidation in both laboratory plasma ashing tests as well as in space on board shuttle flight STS-8. A protective film of or = 96 percent SiO2 and or = 4 percent polytetrafluoroethylene was found to be very flexible compared to the pure metal oxide coatings and resulted in mass loss rates that were 0.2 percent of that of the unprotected Kapton. The optical properties of Kapton for wavelengths investigated between 0.33 and 2.2 microns were not significantly altered by the presence of the coatings or changed by exposure of the coated Kapton to the low Earth orbital ram environment
Atomic Oxygen Treatment Technique for Removal of Smoke Damage from Paintings
Soot deposits that can accumulate on surfaces of a painting during a fire can be difficult to clean from some types of paintings without damaging the underlying paint layers. A non-contact technique has been developed which can remove the soot by allowing a gas containing atomic oxygen to flow over the surface and chemically react with the soot to form carbon monoxide and carbon dioxide. The reaction is limited to the surface, so the underlying paint is not touched. The process can be controlled so that the cleaning can be stopped once the paint surface is reached. This paper describes the smoke exposure and cleaning of untreated canvas, acrylic gesso, and sections of an oil painting using this technique. The samples were characterized by optical microscopy and reflectance spectroscopy
Flexible fluoropolymer filled protective coatings
Metal oxide films such as SiO2 are known to provide an effective barrier to the transport of moisture as well as gaseous species through polymeric films. Such thin film coatings have a tendency to crack upon flexure of the polymeric substrate. Sputter co-deposition of SiO2 with 4 to 15 percent fluoropolymers was demonstrated to produce thin films with glass-like barrier properties that have significant increases in strain to failure over pure glass films which improves their tolerance to flexure on polymeric substrates. Deposition techniques capable of producing these films on polymeric substrates are suitable for durable food packaging and oxidation/corrosion protection applications
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