773 research outputs found
Thermal modeling of Anchorage driveway culvert with addition of insulation to prevent frost heaving
A predominate problem in cold regions, and specifically in Anchorage, Alaska, is frost heaving
pavement above culverts in residential driveways. The culvert increases heat loss in the subgrade
materials during winter months and allows the soils below the culvert to freeze, which is not an
issue if the underlying soils are non-frost susceptible material. However, there are numerous
locations in Anchorage and other parts of Alaska where the underlying soils are frost susceptible
which result in frost heaving culverts under driveways that cause damaged pavement and culvert
inverts that are too high. The seasonal heave and settlement of culverts under driveways
accelerates pavement deterioration. A model of this scenario was developed and several
insulation configurations were considered to determine a suitable alternative for preventing
pavement damage from heaving culverts. The model used material properties for typical
Anchorage area silty sand. The model showed that insulation could be used below culverts to
prevent differential frost heave at the culvert. In addition, this technique uses typical construction
materials and is reasonable for a typical residential dwelling contractor to complete during the
construction of the home.Title Page / Abstract / Table of Contents / List of Figures / List of Tables / Introduction / Literature Review / Driveway Pavement Section / Driveway Pavement Section Design Method / Driveway Pavement Section / Thermal Analysis / TEMP/W (GeoStudio 2012) / Model Configuration / Model Materials and Boundary Conditions / Analysis Procedure / Results / Steady State Model and Temperature Gradient / Thermal Analysis with Pavement and Culvert without Insulation / Thermal Analysis with Pavement, Culvert, and Insulation / Discussion / Conclusions / Recommendations / References / Appendi
Evaluation of a Tree-based Pipeline Optimization Tool for Automating Data Science
As the field of data science continues to grow, there will be an
ever-increasing demand for tools that make machine learning accessible to
non-experts. In this paper, we introduce the concept of tree-based pipeline
optimization for automating one of the most tedious parts of machine
learning---pipeline design. We implement an open source Tree-based Pipeline
Optimization Tool (TPOT) in Python and demonstrate its effectiveness on a
series of simulated and real-world benchmark data sets. In particular, we show
that TPOT can design machine learning pipelines that provide a significant
improvement over a basic machine learning analysis while requiring little to no
input nor prior knowledge from the user. We also address the tendency for TPOT
to design overly complex pipelines by integrating Pareto optimization, which
produces compact pipelines without sacrificing classification accuracy. As
such, this work represents an important step toward fully automating machine
learning pipeline design.Comment: 8 pages, 5 figures, preprint to appear in GECCO 2016, edits not yet
made from reviewer comment
The Inverse Shapley Value Problem
For a weighted voting scheme used by voters to choose between two
candidates, the \emph{Shapley-Shubik Indices} (or {\em Shapley values}) of
provide a measure of how much control each voter can exert over the overall
outcome of the vote. Shapley-Shubik indices were introduced by Lloyd Shapley
and Martin Shubik in 1954 \cite{SS54} and are widely studied in social choice
theory as a measure of the "influence" of voters. The \emph{Inverse Shapley
Value Problem} is the problem of designing a weighted voting scheme which
(approximately) achieves a desired input vector of values for the
Shapley-Shubik indices. Despite much interest in this problem no provably
correct and efficient algorithm was known prior to our work.
We give the first efficient algorithm with provable performance guarantees
for the Inverse Shapley Value Problem. For any constant \eps > 0 our
algorithm runs in fixed poly time (the degree of the polynomial is
independent of \eps) and has the following performance guarantee: given as
input a vector of desired Shapley values, if any "reasonable" weighted voting
scheme (roughly, one in which the threshold is not too skewed) approximately
matches the desired vector of values to within some small error, then our
algorithm explicitly outputs a weighted voting scheme that achieves this vector
of Shapley values to within error \eps. If there is a "reasonable" voting
scheme in which all voting weights are integers at most \poly(n) that
approximately achieves the desired Shapley values, then our algorithm runs in
time \poly(n) and outputs a weighted voting scheme that achieves the target
vector of Shapley values to within error $\eps=n^{-1/8}.
Media outlets and their moguls: why concentrated individual or family ownership is bad for editorial independence
This article investigates the levels of owner influence in 211 different print and broadcast outlets in 32 different European media markets. Drawing on the literature from industrial organisation, it sets out reasons why we should expect greater levels of influence where ownership of individual outlets is concentrated; where it is concentrated in the hands of individuals or families; and where ownership groups own multiple outlets in the same media market. Conversely, we should expect lower levels of influence where ownership is dispersed between transnational companies. The articles uses original data on the ownership structures of these outlets, and combines it with reliable expert judgments as to the level of owner influence in each of the outlets. These hypotheses are tested and confirmed in a multilevel regression model of owner influence. The findings are relevant for policy on ownership limits in the media, and for the debate over transnational versus local control of media
A Dispersion Operator for Geometric Semantic Genetic Programming
Recent advances in geometric semantic genetic programming (GSGP) have shown that the results obtained by these methods can outperform those obtained by classical genetic programming algorithms, in particular in the context of symbolic regression. However, there are still many open issues on how to improve their search mechanism. One of these issues is how to get around the fact that the GSGP crossover operator cannot generate solutions that are placed outside the convex hull formed by the individuals of the current population. Although the mutation operator alleviates this problem, we cannot guarantee it will find promising regions of the search space within feasible computational time. In this direction, this paper proposes a new geometric dispersion operator that uses multiplicative factors to move individuals to less dense areas of the search space around the target solution before applying semantic genetic operators. Experiments in sixteen datasets show that the results obtained by the proposed operator are statistically significantly better than those produced by GSGP and that the operator does indeed spread the solutions around the target solution
Optimal transport on supply-demand networks
Previously, transport networks are usually treated as homogeneous networks,
that is, every node has the same function, simultaneously providing and
requiring resources. However, some real networks, such as power grid and supply
chain networks, show a far different scenario in which the nodes are classified
into two categories: the supply nodes provide some kinds of services, while the
demand nodes require them. In this paper, we propose a general transport model
for those supply-demand networks, associated with a criterion to quantify their
transport capacities. In a supply-demand network with heterogenous degree
distribution, its transport capacity strongly depends on the locations of
supply nodes. We therefore design a simulated annealing algorithm to find the
optimal configuration of supply nodes, which remarkably enhances the transport
capacity, and outperforms the degree target algorithm, the betweenness target
algorithm, and the greedy method. This work provides a start point for
systematically analyzing and optimizing transport dynamics on supply-demand
networks.Comment: 5 pages, 1 table and 4 figure
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