805 research outputs found
Heliospheric Magnetic Field 1835-2009
We use recently acquired geomagnetic archival data to extend our long-term
reconstruction of the HMF strength. The 1835-2009 HMF series is based on an
updated and substantiated IDV series from 1872-onwards and on Bartels'
extension, by proxy, of his u-series from 1835-1871. The new IDV series, termed
IDV09, has excellent agreement (R^2 = 0.98; RMS = 0.3 nT) with the earlier
IDV05 series, and also with the negative component of Love's extended (to 1905)
Dst series (R^2 = 0.91). Of greatest importance to the community, in an area of
research that has been contentious, comparison of the extended HMF series with
other recent reconstructions of solar wind B for the last ~100 years yields a
strong consensus between series based on geomagnetic data. Differences exist
from ~1900-1910 but they are far smaller than the previous disagreement for
this key interval of low solar wind B values which closely resembles current
solar activity. Equally encouraging, a discrepancy with an HMF reconstruction
based on 10Be data for the first half of the 20th century has largely been
removed by a revised 10Be-based reconstruction published after we submitted
this paper, although a remaining discrepancy for the years ~1885-1905 will need
to be resolved
Errors in Scale Values for Magnetic Elements for Helsinki
Using several lines of evidence we show that the scale values of the
geomagnetic variometers operating in Helsinki in the 19th century were not
constant throughout the years of operation 1844-1897. Specifically, the adopted
scale value of the Horizontal Force variometer appears to be too low by ~30%
during the years 1866-1874.5 and the adopted scale value of the Declination
variometer appears to be too low by a factor of ~2 during the interval
1885.8-1887.5. Reconstructing the Heliospheric Magnetic Field strength from
geomagnetic data has reached a stage where a reliable reconstruction is
possible using even just a single geomagnetic data set of hourly or daily
values. Before such reconstructions can be accepted as reliable, the underlying
data must be calibrated correctly. It is thus mandatory that the Helsinki data
be corrected. Such correction has been satisfactorily carried out and the HMF
strength is now well constrained back to 1845
cwl_eval : An evaluation tool for information retrieval
We present a tool (“cwl_eval”) which unifies many metrics typically used to evaluate information retrieval systems using test collections. In the C/W/L framework metrics are specified via a single function which can be used to derive a number of related measurements: Expected Utility per item, Expected Total Utility, Expected Cost per item, Expected Total Cost, and Expected Depth. The C/W/L framework brings together several independent approaches for measuring the quality of a ranked list, and provides a coherent user model-based framework for developing measures based on utility (gain) and cost.Here we outline the C/W/L measurement framework; describe the cwl_eval architecture; and provide examples of how to use it. We provide implementations of a number of recent metrics, including Time Biased Gain, U-Measure, Bejewelled Measure, and the Information Foraging Based Measure, as well as previous metrics such as Precision, Average Precision, Discounted Cumulative Gain, Rank-Biased Precision, and INST. By providing state-of-the-art and traditional metrics within the same framework, we promote a standardised approach to evaluating search effectiveness
- …