4,425 research outputs found
Can Self-Organizing Maps accurately predict photometric redshifts?
We present an unsupervised machine learning approach that can be employed for
estimating photometric redshifts. The proposed method is based on a vector
quantization approach called Self--Organizing Mapping (SOM). A variety of
photometrically derived input values were utilized from the Sloan Digital Sky
Survey's Main Galaxy Sample, Luminous Red Galaxy, and Quasar samples along with
the PHAT0 data set from the PHoto-z Accuracy Testing project. Regression
results obtained with this new approach were evaluated in terms of root mean
square error (RMSE) to estimate the accuracy of the photometric redshift
estimates. The results demonstrate competitive RMSE and outlier percentages
when compared with several other popular approaches such as Artificial Neural
Networks and Gaussian Process Regression. SOM RMSE--results (using
z=z--z) for the Main Galaxy Sample are 0.023, for the
Luminous Red Galaxy sample 0.027, Quasars are 0.418, and PHAT0 synthetic data
are 0.022. The results demonstrate that there are non--unique solutions for
estimating SOM RMSEs. Further research is needed in order to find more robust
estimation techniques using SOMs, but the results herein are a positive
indication of their capabilities when compared with other well-known methods.Comment: 5 pages, 3 figures, submitted to PAS
A Systematic Analysis of Supernova Light in Gamma-Ray Burst Afterglows
We systematically reanalyzed all Gamma-Ray Burst (GRB) afterglow data
published through the end of 2002, in an attempt to detect the predicted
supernova light component and to gain statistical insight on its
phenomenological properties. We fit the observed photometric light curves as
the sum of an afterglow, an underlying host galaxy, and a supernova component.
The latter is modeled using published multi-color light curves of SN 1998bw as
a template. The total sample of afterglows with established redshifts contains
21 bursts (GRB 970228 - GRB 021211). For nine of these GRBs a weak supernova
excess (scaled to SN 1998bw) was found, what makes this to one of the first
samples of high-z core collapse supernovae. Among this sample are all bursts
with redshifts less than ~0.7. These results strongly support the notion that
in fact all afterglows of long-duration GRBs contain light from an associated
supernova. A statistics of the physical parameters of these GRB-supernovae
shows that SN 1998bw was at the bright end of its class, while it was not
special with respect to its light curve shape. Finally, we have searched for a
potential correlation of the supernova luminosities with the properties of the
corresponding bursts and optical afterglows, but we have not found such a
relation.Comment: 25 pages, 7 figures, accepted by ApJ; revised, shortened and updated
compared to version 1; Title slightly changed; all figures showing individual
afterglow light curves removed, as advised by the referee; conclusions
unchange
JCMmode: An Adaptive Finite Element Solver for the Computation of Leaky Modes
We present our simulation tool JCMmode for calculating propagating modes of
an optical waveguide. As ansatz functions we use higher order, vectorial
elements (Nedelec elements, edge elements). Further we construct transparent
boundary conditions to deal with leaky modes even for problems with
inhomogeneous exterior domains as for integrated hollow core Arrow waveguides.
We have implemented an error estimator which steers the adaptive mesh
refinement. This allows the precise computation of singularities near the
metal's corner of a Plasmon-Polariton waveguide even for irregular shaped metal
films on a standard personal computer.Comment: 11 page
The flying fox manual: A new handbook for wildlife carers in Australia
This long-awaited first edition of the ‘flying fox manual’ would certainly have, had it appeared any earlier, created turmoil and debate among both wildlife carers and ecologists in Australia and beyond. Beliefs, myths and own recipes passed on from carer generation to carer generation still dominate flying fox care throughout the continent, where thousands of animals are taken into temporary or permanent care every year. This includes all age classes from orphaned young over injured adults to animals for experimental studies. Through a combination of scientific insight and practical experience, however, the author convincingly takes a long overdue stand against outdated methods and convincingly argues for a release-oriented, wildlife-focussed approach in flying fox care. Extensive research, cooperation with many contributors from all fields of natural sciences and careful review of all aspects of Megachiroptera in care has led to a volume which is capable of finally filling a wide-open gap in available literature, meeting a pressing need amongst volunteer as well as professional carers for accurate and up-to-date information
The prompt optical/near-infrared flare of GRB 050904: the most luminous transient ever detected
With a redshift of z=6.295, GRB 050904 is the most distant gamma-ray burst
ever discovered. It was an energetic event at all wavelengths and the afterglow
was observed in detail in the near-infrared bands. We gathered all available
optical and NIR afterglow photometry of this GRB to construct a composite NIR
light curve spanning several decades in time and flux density. Transforming the
NIR light curve into the optical, we find that the afterglow of GRB 050904 was
more luminous at early times than any other GRB afterglow in the
pre-\emph{Swift} era, making it at these wavelengths the most luminous
transient ever detected. Given the intrinsic properties of GRB 050904 and its
afterglow, we discuss if this burst is markedly different from other GRBs at
lower redshifts.Comment: The Astronomical Journal, in press; revised version, including the
comments of the referee (one figure added, text restructured, all conclusions
unchanged), 7 pages, 3 figure
Evaluating behavioral intention to increase classroom Geotechnology usage following geoinquiry implementation
As educational practices include foundational and cutting-edge preparation, the value of problem-based instruction employing industry-standard technologies increases. Geospatial technologies (GST), are a group of professional technologies, including GIS (Geographic Information Systems), used by industries to make informed decisions with spatial data. This study investigated educator behavioral intention to use GIS/GST in classroom practice, and the moderating effect, if any, of the GeoInquiry, a curricular resource. The UTAUT framework was employed to evaluate and quantify the factors impacting behavioral intention (performance expectancy, effort expectancy, social influence, and facilitating conditions). These data were examined to identify moderation by GeoInquiry usage. One hundred and two surveys were completed by educators in 27 states. The survey results indicate a moderate statistically significant relationship between each of the factors and behavioral intention. An increase in any factor will increase behavioral intention. The mean response increased for the group that used GeoInquiries in classroom instruction, indicating correlation between each factor and GeoInquiry usage. Statistically significant differences related to using GeoInquiries in classroom instruction were identified for effort expectancy, facilitating conditions, and behavioral intention. Similar results related to the degree of GeoInquiry usage were not found. Implications include professional development for both educators and administrators, the continued development of curricular resources, and an alignment of both professional development and curricular resources to high yield instructional strategies, standards, and student engagement. Recommendations for future research include expanding the number of survey respondents, modifying items, conducting structured interviews, social network analysis, and developing curricular resources, which could impact student learning with digital mapping technology
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