1,118 research outputs found
Saha Equation Normalized to Total Atomic Number
The Saha equation describes the relative number density of consecutive ionization levels of a given atomic species under conditions of thermodynamic equilibrium in an ionized gas. Because the number density in the denominator may be very small, special steps must be taken to ensure numerical stability. In this paper we recast the equation into a form in which each ionization fraction is normalized by the total number density of the atomic species, analogous to the Boltzmann equation describing the distribution of excitation states for a given ion
Accuracy and Precision of Insect Density and Impact Estimates
In estimating insect density and impact, entomologists are understandably interested in accuracy of estimation, but they almost always are dealing with precision because of bias due to an invalid estimator, probability sampling, or nonsampling errors. Definitions related to statistical estimation are reviewed and the concepts of accuracy and precision examined.
Interval estimation and optimum sample size determination related to accuracy and precision, using the concept of allowable error, are examined. Criteria for selecting the best estimator in tenns of accuracy and precision are presented, and the distortion of probability statements due to bias is discussed. Accuracy and precision are compared and contrasted using two examples: (I) estimating insect density and (2) estimating insect impact. Adjusted and more accurate estimators can be obtained if the bias of an estimator can be estimated from a preliminary sample
Development of Empirical Models to Rate Spruce-Fir Stands in Michigan\u27s Upper Peninsula for Hazard From the Spruce Budworm (Lepidoptera: Tortricidae): A Case History
The procedure used to develop empirical models which estimate potential spruce budworm impact to spruce-fir stands in Michigan\u27s Upper Peninsula is reviewed. Criteria used to select independent variables, to select the best of alternative multiple linear regression models. and to validate final models are discussed. Preliminary, intermediate, and final results demonstrate a cyclic pattern to the development procedure. Validation is emphasized as an important step in the procedure. Implications of using the hazard-rating system as a pest management tool in the stand management process are discussed
Optimal merging of point sources extracted from Spitzer Space Telescope data in multiple infrared passbands versus simple general source association
For collating point-source flux measurements derived from multiple infrared passbands of Spitzer-Space-Telescope data – e.g., channels 1-4 of the
Infrared Array Camera (IRAC) and channels 1-3 of the Multiband Imaging Pho-
tometer for Spitzer (MIPS) – it is best to use the ‘bandmerge’ software developed
at the Spitzer Science Center rather than the relatively simple method of general
source association (GSA). The former method uses both source positions and
positional uncertainties to form a chi-squared statistic that can be thresholded
for optimal matching, while the latter method finds nearest neighbors across
bands that fall within a user-specified radius of the primary source. Our assertion is supported by our study of completeness (C) vs. reliability (R) for the
two methods, which involved MIPS-24/IRAC-1 matches in the SWIRE Chandra
Deep Field South. Both methods can achieve C = 98%, but with R = 92.7%
for GSA vs. R = 97.4% for bandmerge. With almost a factor of three lower in
unreliability (1 − R), bandmerge is the clear winner of this comparison
Dürer polyhedra: the dark side of Melancholia
Dürer's engraving Melencolia I famously includes a perspective view of a solid polyhedral block of which the visible portion is an 8-circuit bounding a pentagon-triple+triangle patch. The polyhedron is usually taken to be a cube truncated on antipodal corners, but an infinity of others are compatible with the visible patch. Construction of all cubic polyhedra compatible with the visible portion (i.e., Dürer Polyhedra) is discussed, explicit graphs and symmetries are listed for small cases ( ≤ 18 vertices) and total counts are given for 10 ≤ vertices ≤ 26
AWAIC: A WISE Astronomical Image Co-adder
We describe a new image co-addition tool, AWAIC, to support the creation of a
digital Image Atlas from the multiple frame exposures acquired with the
Wide-field Infrared Survey Explorer (WISE). AWAIC includes preparatory steps
such as frame background matching and outlier detection using robust
frame-stack statistics. Frame co-addition is based on using the detector's
Point Response Function (PRF) as an interpolation kernel. This kernel reduces
the impact of prior-masked pixels; enables the creation of an optimal matched
filtered product for point source detection; and most important, it allows for
resolution enhancement (HiRes) to yield a model of the sky that is consistent
with the observations to within measurement error. The HiRes functionality
allows for non-isoplanatic PRFs, prior noise-variance weighting, uncertainty
estimation, and includes a ringing-suppression algorithm. AWAIC also supports
the popular overlap-area weighted interpolation method, and is generic enough
for use on any astronomical image data that supports the FITS and WCS
standards.Comment: 16 pages, 6 figures. Invited paper to appear in Proceedings of ADASS
XVIII Conferenc
The bandmerged Planck Early Release Compact Source Catalogue: Probing sub-structure in the molecular gas at high Galactic latitude
The Planck Early Release Compact Source Catalogue (ERCSC) includes nine lists
of highly reliable sources, individually extracted at each of the nine Planck
frequency channels. To facilitate the study of the Planck sources, especially
their spectral behaviour across the radio/infrared frequencies, we provide a
"bandmerged" catalogue of the ERCSC sources. This catalogue consists of 15191
entries, with 79 sources detected in all nine frequency channels of Planck and
6818 sources detected in only one channel. We describe the bandmerging
algorithm, including the various steps used to disentangle sources in confused
regions. The multi-frequency matching allows us to develop spectral energy
distributions of sources between 30 and 857 GHz, in particular across the 100
GHz band, where the energetically important CO J=1->0 line enters the Planck
bandpass. We find ~3-5sigma evidence for contribution to the 100 GHz intensity
from foreground CO along the line of sight to 147 sources with |b|>30 deg. The
median excess contribution is 4.5+/-0.9 percent of their measured 100 GHz flux
density which cannot be explained by calibration or beam uncertainties. This
translates to 0.5+/-0.1 K km s^{-1} of CO which must be clumped on the scale of
the Planck 100 GHz beam, i.e., ~10 arcmin. If this is due to a population of
low mass (~15 Msun) molecular gas clumps, the total mass in these clumps may be
more than 2000 Msun. Further, high-spatial-resolution, ground-based
observations of the high-latitude sky will help shed light on the origin of
this diffuse, clumpy CO emission.Comment: 15 pages, 15 figures, MNRAS in pres
Hires and beyond
The High-Resolution image construction program (HiRes) used at IPAC is based on the Maximum Correlation Method. After HiRes intensity images are constructed from IRAS data, additional images are needed to aid in scientific interpretation. Some of the images that are available for this purpose show the fitting noise, estimates of the achieved resolution, and detector track maps. Two methods have been developed for creating color maps without discarding any more spatial information than absolutely necessary: the 'cross-band simulation' and 'prior-knowledge' methods. These maps are demonstrated using the survey observations of a 2 x 2 degree field centered on M31. Prior knowledge may also be used to achieve super-resolution and to suppress ringing around bright point sources observed against background emission. Tools to suppress noise spikes and for accelerating convergence are also described
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