449,633 research outputs found
A COMPUTATIONAL TOOL TO EVALUATE THE SAMPLE SIZE IN MAP POSITIONAL ACCURACY
In many countries, the positional accuracy control by points in Cartography or Spatial data corresponds to the comparison between sets of coordinates of well-defined points in relation to the same set of points from a more accurate source. Usually, each country determines a maximum number of points which could present error values above a pre-established threshold. In many cases, the standards define the sample size as 20 points, with no more consideration, and fix this threshold in 10% of the sample. However, the sampling dimension (n), considering the statistical risk, especially when the percentages of outliers are around 10%, can lead to a producer risk (to reject a good map) and a user risk (to accept a bad map). This article analyzes this issue and allows defining the sampling dimension considering the risk of the producer and of the user. As a tool, a program developed by us allows defining the sample size according to the risk that the producer / user can or wants to assume. This analysis uses 600 control points, each of them with a known error. We performed the simulations with a sample size of 20 points (n) and calculate the associated risk. Then we changed the value of (n), using smaller and larger sizes, calculating for each situation the associated risk both for the user and for the producer. The computer program developed draws the operational curves or risk curves, which considers three parameters: the number of control points; the number of iterations to create the curves; and the percentage of control points above the threshold, that can be the Brazilian standard or other parameters from different countries. Several graphs and tables are presented which were created with different parameters, leading to a better decision both for the user and for the producer, as well as to open possibilities for other simulations and researches in the future
The First Data Release from SweetSpot: 74 Supernovae in 36 Nights on WIYN+WHIRC
SweetSpot is a three-year National Optical Astronomy Observatory (NOAO)
Survey program to observe Type Ia supernovae (SNe Ia) in the smooth Hubble flow
with the WIYN High-resolution Infrared Camera (WHIRC) on the WIYN 3.5-m
telescope. We here present data from the first half of this survey, covering
the 2011B-2013B NOAO semesters, and consisting of 493 calibrated images of 74
SNe Ia observed in the rest-frame near-infrared (NIR) from .
Because many observed supernovae require host galaxy subtraction from templates
taken in later semesters, this release contains only the 186 NIR () data
points for the 33 SNe Ia that do not require host-galaxy subtraction. The
sample includes 4 objects with coverage beginning before the epoch of B-band
maximum and 27 beginning within 20 days of B-band maximum. We also provide
photometric calibration between the WIYN+WHIRC and Two-Micron All Sky Survey
(2MASS) systems along with light curves for 786 2MASS stars observed alongside
the SNe Ia. This work is the first in a planned series of three SweetSpot Data
Releases. Future releases will include the full set of images from all 3 years
of the survey, including host-galaxy reference images and updated data
processing and host-galaxy reference subtraction. SweetSpot will provide a
well-calibrated sample that will help improve our ability to standardize
distance measurements to SNe Ia, examine the intrinsic optical-NIR colors of
SNe Ia at different epochs, explore nature of dust in other galaxies, and act
as a stepping stone for more distant, potentially space-based surveys.Comment: Published in AJ. 10 tables. 11 figures. Lightcurve plots included as
a figureset and available in source tarball. Data online at
http://www.phyast.pitt.edu/~wmwv/SweetSpot/DR1_data
Diversity of Decline-Rate-Corrected Type Ia Supernova Rise Times: One Mode or Two?
B-band light-curve rise times for eight unusually well-observed nearby Type
Ia supernovae (SNe) are fitted by a newly developed template-building
algorithm, using light-curve functions that are smooth, flexible, and free of
potential bias from externally derived templates and other prior assumptions.
From the available literature, photometric BVRI data collected over many
months, including the earliest points, are reconciled, combined, and fitted to
a unique time of explosion for each SN. On average, after they are corrected
for light-curve decline rate, three SNe rise in 18.81 +- 0.36 days, while five
SNe rise in 16.64 +- 0.21 days. If all eight SNe are sampled from a single
parent population (a hypothesis not favored by statistical tests), the rms
intrinsic scatter of the decline-rate-corrected SN rise time is 0.96 +0.52
-0.25 days -- a first measurement of this dispersion. The corresponding global
mean rise time is 17.44 +- 0.39 days, where the uncertainty is dominated by
intrinsic variance. This value is ~2 days shorter than two published averages
that nominally are twice as precise, though also based on small samples. When
comparing high-z to low-z SN luminosities for determining cosmological
parameters, bias can be introduced by use of a light-curve template with an
unrealistic rise time. If the period over which light curves are sampled
depends on z in a manner typical of current search and measurement strategies,
a two-day discrepancy in template rise time can bias the luminosity comparison
by ~0.03 magnitudes.Comment: As accepted by The Astrophysical Journal; 15 pages, 6 figures, 2
tables. Explanatory material rearranged and enhanced; Fig. 4 reformatte
Kummer Covers with Many Points
We give a method for constructing Kummer covers with many points over finite
fields.Comment: Plain Tex, 13 page
Counting curves over finite fields
This is a survey on recent results on counting of curves over finite fields.
It reviews various results on the maximum number of points on a curve of genus
g over a finite field of cardinality q, but the main emphasis is on results on
the Euler characteristic of the cohomology of local systems on moduli spaces of
curves of low genus and its implications for modular forms.Comment: 25 pages, to appear in Finite Fields and their Application
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