40,725 research outputs found
Nonparametric Methods in Astronomy: Think, Regress, Observe -- Pick Any Three
Telescopes are much more expensive than astronomers, so it is essential to
minimize required sample sizes by using the most data-efficient statistical
methods possible. However, the most commonly used model-independent techniques
for finding the relationship between two variables in astronomy are flawed. In
the worst case they can lead without warning to subtly yet catastrophically
wrong results, and even in the best case they require more data than necessary.
Unfortunately, there is no single best technique for nonparametric regression.
Instead, we provide a guide for how astronomers can choose the best method for
their specific problem and provide a python library with both wrappers for the
most useful existing algorithms and implementations of two new algorithms
developed here.Comment: 19 pages, PAS
A Relativistic Quaternionic Wave Equation
We study a one-component quaternionic wave equation which is relativistically
covariant. Bi-linear forms include a conserved 4-current and an antisymmetric
second rank tensor. Waves propagate within the light-cone and there is a
conserved quantity which looks like helicity. The principle of superposition is
retained in a slightly altered manner. External potentials can be introduced in
a way that allows for gauge invariance. There are some results for scattering
theory and for two-particle wavefunctions as well as the beginnings of second
quantization. However, we are unable to find a suitable Lagrangian or an
energy-momentum tensor.Comment: 19 pages; minor corrections in Section 11 and Appendix
630-mV open circuit voltage, 12% efficient n-Si liquid junction
We report the first experimental observation of a semiconductor/liquid junction whose open circuit voltage Voc is controlled by bulk diffusion/recombination processes. Variation in temperature, minority-carrier diffusion length, and/or in majority-carrier concentration produces changes in the Voc of the n-Si/CH3OH interface in accord with bulk recombination/diffusion theory. Under AM2 irradiation conditions, the extrapolated intercept at 0 K of Voc vs T plots yields activation energies for the dominant recombination process of 1.1–1.2 eV, in accord with the 1.12-eV band gap of Si. A crucial factor in achieving optimum performance of the n-Si/CH3OH interface is assigned to photoelectrochemical oxide formation, which passivates surface recombination sites at the n-Si/CH3OH interface and minimizes deleterious effects of pinning of the Fermi level at the Si/CH3OH junction. Controlled Si oxide growth, combined with optimization of bulk crystal parameters in accord with diffusion theory, is found to yield improved photoelectrode output parameters, with 12.0±1.5% AM2 efficiencies and AM1 Voc values of 632–640 mV for 0.2-Ω cm Si materials
Higher Dimensional Lattice Chains and Delannoy Numbers
Fix nonnegative integers n1 , . . ., nd, and let L denote the lattice of points (a1 , . . ., ad) ∈ ℤd that satisfy 0 ≤ ai ≤ ni for 1 ≤ i ≤ d. Let L be partially ordered by the usual dominance ordering. In this paper we use elementary combinatorial arguments to derive new expressions for the number of chains and the number of Delannoy paths in L. Setting ni = n (for all i) in these expressions yields a new proof of a recent result of Duichi and Sulanke [9] relating the total number of chains to the central Delannoy numbers. We also give a novel derivation of the generating functions for these numbers in arbitrary dimension
A checklist of the Limnichidae and the Lutrochidae (Coleoptera) of the world
A checklist of the world species of Limnichidae (35 genera, 345 species) and Lutrochidae (1 genus, 11 species) is presented. The author, year of publication and page number, synonyms, distribution by country, and a terminal bibliography are given for each genus and species. Biological information is also reviewed
A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6
Using a compilation of 25 studies from the literature, we investigate the
evolution of the star-forming galaxy (SFG) Main Sequence (MS) in stellar mass
and star formation rate (SFR) out to . After converting all
observations to a common set of calibrations, we find a remarkable consensus
among MS observations ( dex 1 interpublication scatter). By
fitting for time evolution of the MS in bins of constant mass, we deconvolve
the observed scatter about the MS within each observed redshift bins. After
accounting for observed scatter between different SFR indicators, we find the
width of the MS distribution is dex and remains constant over cosmic
time. Our best fits indicate the slope of the MS is likely time-dependent, with
our best fit , with the age of the Universe in Gyr. We use our fits to create
empirical evolutionary tracks in order to constrain MS galaxy star formation
histories (SFHs), finding that (1) the most accurate representations of MS SFHs
are given by delayed- models, (2) the decline in fractional stellar mass
growth for a "typical" MS galaxy today is approximately linear for most of its
lifetime, and (3) scatter about the MS can be generated by galaxies evolving
along identical evolutionary tracks assuming an initial spread in
formation times of Gyr.Comment: 59 pages, 10 tables, 12 figures, accepted to ApJS; v2, slight changes
to text, added new figure and fit
The Cosmic Microwave Background and the Stellar Initial Mass Function
We argue that an increased temperature in star-forming clouds alters the
stellar initial mass function to be more bottom-light than in the Milky Way. At
redshifts , heating from the cosmic microwave background radiation
produces this effect in all galaxies, and it is also present at lower redshifts
in galaxies with very high star formation rates (SFRs). A failure to account
for it means that at present, photometric template fitting likely overestimates
stellar masses and star formation rates for the highest-redshift and
highest-SFR galaxies. In addition this may resolve several outstanding problems
in the chemical evolution of galactic halos.Comment: 9 pages, 5 figures. Published in MNRAS. Added further reference
The Minnesota Species of Aeshna with Notes on their Habits and Distribution (Odonata: Aeshnidae)
Apart from the well-known green darner, Anax junius, the species of Aeshna are the most familiar Minnesota Aeshnidae. These species are remarkably uniform in appearance. The basic body color is brown with blue, green, or yellow stripes on the thorax and with marks of similar color on the abdomen. Usually the spots of male specimens are blue, whereas green of various shades appears on most females. The individual species are not readily discernible to the novice collector
Population assessment of the vermilion snapper, Rhomboplites aurorubens, from the Southeastern United States
Changes in the age structure and population size of
vermilion snapper, Rhornboplites aurorubens, from North Carolina through the Florida Keys were examined using records of landings and size frequencies of fish from commercial, recreational, and headboat fisheries from 1986-1996. Population size in numbers at age was estimated for each year by applying separable virtual population analysis (SVPA) to the landings in numbers at age. SVPA was used to estimate annual, age-specific fishing mortality (F) for four levels of natural mortality (M = 0.20, 0.25, 0.30,
and 0.35). Although landings of vermilion snapper for the three fisheries have declined, minimum fish size regulations have resulted in an increase in the mean size of fish landed. Age at entry and age at full recruitment were age-1 andage-3 fDr 1986-1991, compared with age-1 and age-4, respectively, for 1992-1996. Levels of mortality from fishing (F) ranged from 0.38 - 0.61 for the entire period. Current spawning potential ratio (SPR) is 21%
or 27% depending on the natural mortality estimate. SPR could be raised to 30% or 40% with a reduction in F, or by increasing the age at entry to the fisheries. The latter could be enhanced now if fishermen, particularly recreational, comply with minimum size regulations. However, released fish mortality, modeled in the assessment at 27%, will continue to make the achievement of 30%
and 40% SPR more difficult. (PDF contains 63 pages
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