1,585 research outputs found
Composite Gaussian process models for emulating expensive functions
A new type of nonstationary Gaussian process model is developed for
approximating computationally expensive functions. The new model is a composite
of two Gaussian processes, where the first one captures the smooth global trend
and the second one models local details. The new predictor also incorporates a
flexible variance model, which makes it more capable of approximating surfaces
with varying volatility. Compared to the commonly used stationary Gaussian
process model, the new predictor is numerically more stable and can more
accurately approximate complex surfaces when the experimental design is sparse.
In addition, the new model can also improve the prediction intervals by
quantifying the change of local variability associated with the response.
Advantages of the new predictor are demonstrated using several examples.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS570 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Towards Optimal Variance Reduction in Online Controlled Experiments
We study optimal variance reduction solutions for count and ratio metrics in
online controlled experiments. Our methods leverage flexible machine learning
tools to incorporate covariates that are independent from the treatment but
have predictive power for the outcomes, and employ the cross-fitting technique
to remove the bias in complex machine learning models. We establish CLT-type
asymptotic inference based on our estimators under mild convergence conditions.
Our procedures are optimal (efficient) for the corresponding targets as long as
the machine learning estimators are consistent, without any requirement for
their convergence rates. In complement to the general optimal procedure, we
also derive a linear adjustment method for ratio metrics as a special case that
is computationally efficient and can flexibly incorporate any pre-treatment
covariates. We evaluate the proposed variance reduction procedures with
comprehensive simulation studies and provide practical suggestions regarding
commonly adopted assumptions in computing ratio metrics. When tested on real
online experiment data from LinkedIn, the proposed optimal procedure for ratio
metrics can reduce up to 80\% of variance compared to the standard
difference-in-mean estimator and also further reduce up to 30\% of variance
compared to the CUPED approach by going beyond linearity and incorporating a
large number of extra covariates
Impacts of a 90 degree twist on lateral web dynamics
Twists are sometimes used to turn or provide passive lateral control for narrow webs in those cases where space for a sufficient twist span length (to avoid a wrinkle) is achievable. This paper uses the finite element method to study the lateral dynamics of a web downstream of a 90 degree twist in response to an upstream lateral disturbance. A designed experiment of 46 different finite element runs was used to study the interactions among different material, geometry, and input variables. Specifically, the frequency response for downstream cross-direction position was modeled as a function of the disturbance frequency, disturbance amplitude, span length, wrap angle and material stiffness. Nominal strain was held constant. A composite Gaussian process model was fit to the resulting data to facilitate a deeper and more holistic interpretation. Excellent attenuation of the disturbance amplitude and interesting interactions with the applied frequency and twist span length were shown
Wrinkling mechanisms of webs with spatially varying material properties
Webs often include variation in caliper or modulus of elasticity as a result of manufacturing variation. Light-weight nonwoven webs are especially prone to these issues because the variation is proportionally more, relative to the average modulus. It is proposed that the length scale variability in fiber orientation and most importantly mass density extends to the mechanical properties of the web, including the degree of orthotropy and Poisson's ratio (neckdown behavior). Finite element simulations show that materials exhibiting this kind of variability (in MD and CMD modulus, and Poisson's ratio), notably with nominally high and low regions alternating in the MD, leads to trough and wrinkle formation. Multiple simulations with varied material properties have led to a greater understanding of the mechanisms and conditions that cause these types of wrinkles
Gate-tuned normal and superconducting transport at the surface of a topological insulator
Three-dimensional topological insulators are characterized by the presence of
a bandgap in their bulk and gapless Dirac fermions at their surfaces. New
physical phenomena originating from the presence of the Dirac fermions are
predicted to occur, and to be experimentally accessible via transport
measurements in suitably designed electronic devices. Here we study transport
through superconducting junctions fabricated on thin Bi2Se3 single crystals,
equipped with a gate electrode. In the presence of perpendicular magnetic field
B, sweeping the gate voltage enables us to observe the filling of the Dirac
fermion Landau levels, whose character evolves continuously from electron- to
hole-like. When B=0, a supercurrent appears, whose magnitude can be gate tuned,
and is minimum at the charge neutrality point determined from the Landau level
filling. Our results demonstrate how gated nano-electronic devices give control
over normal and superconducting transport of Dirac fermions at an individual
surface of a three-dimensional topological insulator.Comment: 28 pages, 5 figure
Modulating signaling networks by CRISPR/Cas9-mediated transposable element insertion
In a recent past, transposable elements (TEs) were referred to as selfish genetic components only capable of copying themselves with the aim of increasing the odds of being inherited. Nonetheless, TEs have been initially proposed as positive control elements acting in synergy with the host. Nowadays, it is well known that TE movement into host genome comprises an important evolutionary mechanism capable of increasing the adaptive fitness. As insights into TE functioning are increasing day to day, the manipulation of transposition has raised an interesting possibility of setting the host functions, although the lack of appropriate genome engineering tools has unpaved it. Fortunately, the emergence of genome editing technologies based on programmable nucleases, and especially the arrival of a multipurpose RNA-guided Cas9 endonuclease system, has made it possible to reconsider this challenge. For such purpose, a particular type of transposons referred to as miniature inverted-repeat transposable elements (MITEs) has shown a series of interesting characteristics for designing functional drivers. Here, recent insights into MITE elements and versatile RNA-guided CRISPR/Cas9 genome engineering system are given to understand how to deploy the potential of TEs for control of the host transcriptional activity.Fil: Vaschetto, Luis Maria Benjamin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Cátedra de Diversidad Animal I; Argentin
Many faces of low mass neutralino dark matter in the unconstrained MSSM, LHC data and new signals
If all strongly interacting sparticles (the squarks and the gluinos) in an
unconstrained minimal supersymmetric standard model (MSSM) are heavier than the
corresponding mass lower limits in the minimal supergravity (mSUGRA) model,
obtained by the current LHC experiments, then the existing data allow a variety
of electroweak (EW) sectors with light sparticles yielding dark matter (DM)
relic density allowed by the WMAP data. Some of the sparticles may lie just
above the existing lower bounds from LEP and lead to many novel DM producing
mechanisms not common in mSUGRA. This is illustrated by revisiting the above
squark-gluino mass limits obtained by the ATLAS Collaboration, with an
unconstrained EW sector with masses not correlated with the strong sector.
Using their selection criteria and the corresponding cross section limits, we
find at the generator level using Pythia, that the changes in the mass limits,
if any, are by at most 10-12% in most scenarios. In some cases, however, the
relaxation of the gluino mass limits are larger (). If a subset of
the strongly interacting sparticles in an unconstrained MSSM are within the
reach of the LHC, then signals sensitive to the EW sector may be obtained. This
is illustrated by simulating the \etslash, , and \etslash signals in i) the light stop scenario and ii) the light
stop-gluino scenario with various light EW sectors allowed by the WMAP data.
Some of the more general models may be realized with non-universal scalar and
gaugino masses.Comment: 27 pages, 1 figure, references added, minor changes in text, to
appear in JHE
Search based software engineering: Trends, techniques and applications
© ACM, 2012. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version is available from the link below.In the past five years there has been a dramatic increase in work on Search-Based Software Engineering (SBSE), an approach to Software Engineering (SE) in which Search-Based Optimization (SBO) algorithms are used to address problems in SE. SBSE has been applied to problems throughout the SE lifecycle, from requirements and project planning to maintenance and reengineering. The approach is attractive because it offers a suite of adaptive automated and semiautomated solutions in situations typified by large complex problem spaces with multiple competing and conflicting objectives.
This article provides a review and classification of literature on SBSE. The work identifies research trends and relationships between the techniques applied and the applications to which they have been applied and highlights gaps in the literature and avenues for further research.EPSRC and E
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