1,362 research outputs found
Constraint-based sequence mining using constraint programming
The goal of constraint-based sequence mining is to find sequences of symbols
that are included in a large number of input sequences and that satisfy some
constraints specified by the user. Many constraints have been proposed in the
literature, but a general framework is still missing. We investigate the use of
constraint programming as general framework for this task. We first identify
four categories of constraints that are applicable to sequence mining. We then
propose two constraint programming formulations. The first formulation
introduces a new global constraint called exists-embedding. This formulation is
the most efficient but does not support one type of constraint. To support such
constraints, we develop a second formulation that is more general but incurs
more overhead. Both formulations can use the projected database technique used
in specialised algorithms. Experiments demonstrate the flexibility towards
constraint-based settings and compare the approach to existing methods.Comment: In Integration of AI and OR Techniques in Constraint Programming
(CPAIOR), 201
The role of structural evolution on the quantum conductance behavior of gold nanowires during stretching
Gold nanowires generated by mechanical stretching have been shown to adopt
only three kinds of configurations where their atomic arrangements adjust such
that either the [100], [111] or [110] zone axes lie parallel to the elongation
direction. We have analyzed the relationship between structural rearrangements
and electronic transport behavior during the elongation of Au nanowires for
each of the three possibilities. We have used two independent experiments to
tackle this problem, high resolution transmission high resolution electron
microscopy to observe the atomic structure and a mechanically controlled break
junction to measure the transport properties. We have estimated the conductance
of nanowires using a theoretical method based on the extended H\"uckel theory
that takes into account the atom species and their positions. Aided by these
calculations, we have consistently connected both sets of experimental results
and modeled the evolution process of gold nanowires whose conductance lies
within the first and third conductance quanta. We have also presented evidence
that carbon acts as a contaminant, lowering the conductance of one-atom-thick
wires.Comment: 10 page
Hinode EUV Imaging Spectrometer Observations of Solar Active Region Dynamics
The EUV Imaging Spectrometer (EIS) on the Hinode satellite is capable of
measuring emission line center positions for Gaussian line profiles to a
fraction of a spectral pixel, resulting in relative solar Doppler-shift
measurements with an accuracy of less than a km/s for strong lines. We show an
example of the application of that capability to an active region sit-and-stare
observation in which the EIS slit is placed at one location on the Sun and many
exposures are taken while the spacecraft tracking keeps the same solar location
within the slit. For the active region examined (NOAA 10930), we find that
significant intensity and Doppler-shift fluctuations as a function of time are
present at a number of locations. These fluctuations appear to be similar to
those observed in high-temperature emission lines with other space-borne
spectroscopic instruments. With its increased sensitivity over earlier
spectrometers and its ability to image many emission lines simultaneously, EIS
should provide significant new constraints on Doppler-shift oscillations in the
corona.Comment: 7 Pages, 7 figure
Observations of Transient Active Region Heating with Hinode
We present observations of transient active region heating events observed
with the Extreme Ultraviolet Imaging Spectrometer (EIS) and X-ray Telescope
(XRT) on Hinode. This initial investigation focuses on NOAA active region 10940
as observed by Hinode on February 1, 2007 between 12 and 19 UT. In these
observations we find numerous examples of transient heating events within the
active region. The high spatial resolution and broad temperature coverage of
these instruments allows us to track the evolution of coronal plasma. The
evolution of the emission observed with XRT and EIS during these events is
generally consistent with loops that have been heated and are cooling. We have
analyzed the most energetic heating event observed during this period, a small
GOES B-class flare, in some detail and present some of the spectral signatures
of the event, such as relative Doppler shifts at one of the loop footpoints and
enhanced line widths during the rise phase of the event. While the analysis of
these transient events has the potential to yield insights into the coronal
heating mechanism, these observations do not rule out the possibility that
there is a strong steady heating level in the active region. Detailed
statistical analysis will be required to address this question definitively
Constructing a Toolkit to Evaluate Quality of State and Local Administrative Data
State and local agencies administering programs have in their administrative data a powerful resource for policy analysis to inform evaluation and guide improvement of their programs. Understanding different aspects of their administrative data quality is critical for agencies to conduct such analyses and to improve their data for future use. However, state and local agencies often lack the resources and training for staff to conduct rigorous evaluations of data quality. We describe our efforts developing tools that can be used to assess data quality as well as the challenges encountered in constructing these tools. The toolkit focuses on critical dimensions of quality for analyzing an administrative dataset, including checks on data accuracy, the completeness of the records, and the comparability of the data over time and among subgroups of interest. State and local administrative databases often include a longitudinal component which our toolkit also aims to exploit to help evaluate data quality. While we seek to develop general tools for common data quality analyses, most administrative datasets have particularities that can benefit from a customized analysis building on our toolkit. In addition, we incorporate data visualization to draw attention to sets of records or variables that contain outliers or for which quality may be a concern
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