1,033 research outputs found
Mashing up Visual Languages and Web Mash-ups
Research on web mashups and visual languages
share an interest in human-centered computing. Both
research communities are concerned with supporting
programming by everyday, technically inexpert users.
Visual programming environments have been a focus for
both communities, and we believe that there is much to
be gained by further discussion between these research
communities. In this paper we explore some connections
between web mashups and visual languages, and try to
identify what each might be able to learn from the other.
Our goal is to establish a framework for a dialog
between the communities, and to promote the exchange
of ideas and our respective understandings of humancentered
computing.published or submitted for publicationis peer reviewe
Coordinated and robust aviation network resource allocation
In the United States, flight operators may schedule flights to most airports at whatever time best achieves their objectives. However, during some time periods, both at airports and in the airspace, these freely-developed schedules may become infeasible because weather or other factors reduce capacity. A plan must then be implemented to mitigate this congestion safely, efficiently, and equitably. Current planning processes treat each congested resource independently, applying various rules to increase interoperation times sufficiently to match the reduced capacity. However, several resources are occasionally congested simultaneously, and ignoring possible dependencies may yield infeasible allocations for flights using multiple resources.
In this dissertation, this problem of developing coordinated flight-slot allocations for multiple congested resources is considered from several perspectives. First, a linear optimization model is developed. It is demonstrated that optimally minimizing flight arrival delays induces an increasing bias against flights using multiple resources. However, the resulting allocations reduce overall arrival delay, as compared to the infeasible independent allocations, and to current operational practice. The analytic properties of the model are used to develop a rule-based heuristic for allocating capacity that achieves comparable aggregate results. Alternatively, minimizing delay assigned at all resources is considered, and this objective is shown to mimic the flights' original schedule order.
Recognizing that minimizing arrival delays is attractive because of its tangible impact on system performance, variations to the original optimization model are proposed that constrain the worst-case performance of any individual user. Several different constraints and cost-based approaches are considered, all of which are successful to varying degrees in limiting inequities.
Finally, the model is reformulated to consider uncertainty in capacity. This adds considerable complexity to the formulation, and introduces practical difficulties in identifying joint probability distributions for the capacity outcomes at each resource. However, this new model is successful in developing more robust flight-slot allocations that enable quick responses to capacity variations.
Each of the optimization models and heuristics presented here are tested on a realistic case study. The problem studied and the approaches employed represent an important middle ground in air traffic flow management research between single resource models and comprehensive ones
Halo gas cross sections and covering fractions of MgII absorption selected galaxies
We examine halo gas cross sections and covering fractions, fc, of intermediate-redshift Mg II absorption selected galaxies. We computed statistical absorber halo radii, Rx, using current values of dN/dz and Schechter luminosity function parameters, and have compared these values to the distribution of impact parameters and luminosities from a sample of 37 galaxies. For equivalent widths Wr(2796) ≥ 0.3 Å, we find 43 ≤ Rx ≤ 88 kpc, depending on the lower luminosity cutoff and the slope, β, of the Holmberg-like luminosity scaling, R ∝ α L^β . The observed distribution of impact parameters, D, are such that several absorbing galaxies lie at D > Rx and several non-absorbing galaxies lie at D ~ 0.5 for our sample. Moreover, the data suggest that halo radii of Mg II absorbing galaxies do not follow a luminosity scaling with β in the range of 0.2–0.28, if fc = 1 as previously reported. However, provided fc ~ 0.5, we find that halo radii can remain consistent with a Holmberg-like luminosity relation with β ≃ 0.2 and R∗ = Rx/√(fc) ~ 110 kpc. No luminosity scaling (β = 0) is also consistent with the observed distribution of impact parameters if fc ≤ 0.37. The data support a scenario in which gaseous halos are patchy and likely have non-symmetric geometric distributions about the galaxies. We suggest that halo gas distributions may not be governed primarily by galaxy mass/luminosity but also by stochastic processes local to the galaxy
MAGIICAT V. Orientation of Outflows and Accretion Determine the Kinematics and Column Densities of the Circumgalactic Medium
We investigate the dependence of gas kinematics and column densities in the
MgII-absorbing circumgalactic medium on galaxy color, azimuthal angle, and
inclination to trace baryon cycle processes. Our sample of 30 foreground
isolated galaxies at , imaged with the Hubble Space
Telescope, are probed by background quasars within a projected distance of
kpc. From the high-resolution ( km s)
quasar spectra, we quantify the extent of the absorber velocity structure with
pixel-velocity two-point correlation functions. Absorbers with the largest
velocity dispersions are associated with blue, face-on ()
galaxies probed along the projected minor axis (), while
those with the smallest velocity dispersions belong to red, face-on galaxies
along the minor axis. The velocity structure is similar for edge-on () galaxies regardless of galaxy color or azimuthal angle, for red
galaxies with azimuthal angle, and for blue and red galaxies probed along the
projected major axis (). The cloud column densities for
face-on galaxies and red galaxies are smaller than for edge-on galaxies and
blue galaxies, respectively. These results are consistent with biconical
outflows along the minor axis for star-forming galaxies and accreting and/or
rotating gas, which is most easily observed in edge-on galaxies probed along
the major axis. Gas entrained in outflows may be fragmented with large velocity
dispersions, while gas accreting onto or rotating around galaxies may be more
coherent due to large path lengths and smaller velocity dispersions. Quiescent
galaxies may exhibit little-to-no outflows along the minor axis, while
accretion/rotation may exist along the major axis.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in Ap
Towards Real-Time Detection and Tracking of Spatio-Temporal Features: Blob-Filaments in Fusion Plasma
A novel algorithm and implementation of real-time identification and tracking
of blob-filaments in fusion reactor data is presented. Similar spatio-temporal
features are important in many other applications, for example, ignition
kernels in combustion and tumor cells in a medical image. This work presents an
approach for extracting these features by dividing the overall task into three
steps: local identification of feature cells, grouping feature cells into
extended feature, and tracking movement of feature through overlapping in
space. Through our extensive work in parallelization, we demonstrate that this
approach can effectively make use of a large number of compute nodes to detect
and track blob-filaments in real time in fusion plasma. On a set of 30GB fusion
simulation data, we observed linear speedup on 1024 processes and completed
blob detection in less than three milliseconds using Edison, a Cray XC30 system
at NERSC.Comment: 14 pages, 40 figure
Determining the Number of Slots to Submit to a Market Mechanism at a Single Airport
In this thesis, several stochastic optimization models are presented to determine the number of airport arrival slots that should be made available for distribution via a market mechanism. Considerable attention is paid to the structure and mathematical properties of each of these models, with regards to obtaining integer-valued solutions. Calibration of the various parameters is undertaken using historical data. In addition, an analysis of the average pecuniary valuations assigned to each slot is presented, as this is an essential input to these models. Several methods are suggested by which each of these values can be estimated. The models are intended to be taken in a general context, but extensive computational examples making use of data for LaGuardia Airport are provided as a case study in the application of the various techniques presented herein
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