35,045 research outputs found
Order restricted inference for comparing the cumulative incidence of a competing risk over several populations
There is a substantial literature on testing for the equality of the
cumulative incidence functions associated with one specific cause in a
competing risks setting across several populations against specific or all
alternatives. In this paper we propose an asymptotically distribution-free test
when the alternative is that the incidence functions are linearly ordered, but
not equal. The motivation stems from the fact that in many examples such a
linear ordering seems reasonable intuitively and is borne out generally from
empirical observations. These tests are more powerful when the ordering is
justified. We also provide estimators of the incidence functions under this
ordering constraint, derive their asymptotic properties for statistical
inference purposes, and show improvements over the unrestricted estimators when
the order restriction holds.Comment: Published in at http://dx.doi.org/10.1214/193940307000000040 the IMS
Collections (http://www.imstat.org/publications/imscollections.htm) by the
Institute of Mathematical Statistics (http://www.imstat.org
Hierarchical Composition of Memristive Networks for Real-Time Computing
Advances in materials science have led to physical instantiations of
self-assembled networks of memristive devices and demonstrations of their
computational capability through reservoir computing. Reservoir computing is an
approach that takes advantage of collective system dynamics for real-time
computing. A dynamical system, called a reservoir, is excited with a
time-varying signal and observations of its states are used to reconstruct a
desired output signal. However, such a monolithic assembly limits the
computational power due to signal interdependency and the resulting correlated
readouts. Here, we introduce an approach that hierarchically composes a set of
interconnected memristive networks into a larger reservoir. We use signal
amplification and restoration to reduce reservoir state correlation, which
improves the feature extraction from the input signals. Using the same number
of output signals, such a hierarchical composition of heterogeneous small
networks outperforms monolithic memristive networks by at least 20% on waveform
generation tasks. On the NARMA-10 task, we reduce the error by up to a factor
of 2 compared to homogeneous reservoirs with sigmoidal neurons, whereas single
memristive networks are unable to produce the correct result. Hierarchical
composition is key for solving more complex tasks with such novel nano-scale
hardware
A New Method for Multi-Bit and Qudit Transfer Based on Commensurate Waveguide Arrays
The faithful state transfer is an important requirement in the construction
of classical and quantum computers. While the high-speed transfer is realized
by optical-fibre interconnects, its implementation in integrated optical
circuits is affected by cross-talk. The cross-talk between densely packed
optical waveguides limits the transfer fidelity and distorts the signal in each
channel, thus severely impeding the parallel transfer of states such as
classical registers, multiple qubits and qudits. Here, we leverage on the
suitably engineered cross-talk between waveguides to achieve the parallel
transfer on optical chip. Waveguide coupling coefficients are designed to yield
commensurate eigenvalues of the array and hence, periodic revivals of the input
state. While, in general, polynomially complex, the inverse eigenvalue problem
permits analytic solutions for small number of waveguides. We present exact
solutions for arrays of up to nine waveguides and use them to design realistic
buses for multi-(qu)bit and qudit transfer. Advantages and limitations of the
proposed solution are discussed in the context of available fabrication
techniques
Context-aware Synthesis for Video Frame Interpolation
Video frame interpolation algorithms typically estimate optical flow or its
variations and then use it to guide the synthesis of an intermediate frame
between two consecutive original frames. To handle challenges like occlusion,
bidirectional flow between the two input frames is often estimated and used to
warp and blend the input frames. However, how to effectively blend the two
warped frames still remains a challenging problem. This paper presents a
context-aware synthesis approach that warps not only the input frames but also
their pixel-wise contextual information and uses them to interpolate a
high-quality intermediate frame. Specifically, we first use a pre-trained
neural network to extract per-pixel contextual information for input frames. We
then employ a state-of-the-art optical flow algorithm to estimate bidirectional
flow between them and pre-warp both input frames and their context maps.
Finally, unlike common approaches that blend the pre-warped frames, our method
feeds them and their context maps to a video frame synthesis neural network to
produce the interpolated frame in a context-aware fashion. Our neural network
is fully convolutional and is trained end to end. Our experiments show that our
method can handle challenging scenarios such as occlusion and large motion and
outperforms representative state-of-the-art approaches.Comment: CVPR 2018, http://graphics.cs.pdx.edu/project/ctxsy
Teachers’ Perspectives on Year Two Implementation of a Kindergarten Readiness Assessment
In this study we examined teachers’ perspectives regarding the second year of implementing a Kindergarten Readiness Assessment (KRA). Using a mixed-methods approach, we focused on the administration process, the perceived benefits of the assessment, and how teachers used the assessment to inform instruction. We also investigated whether these differed by teacher and district characteristics and how KRA experiences were different in the second year of implementation. Research Findings: Teachers generally did not view the KRA as beneficial for instruction or for students, reporting administration difficulties, inadequate KRA content, and limited utility of KRA data for supporting instruction as ongoing barriers to KRA use. Although the administration process seemed to be easier in the second year, teachers still reported it as burdensome, cutting into important beginning of kindergarten activities. Notably, teacher training and experience were associated with perceptions. Practice or Policy: Reasons for perceived lack of utility have important implications for future KRA design and implementation. These include better integration of KRAs into existing assessment systems, recognizing the added burden of KRAs to teachers (particularly at the beginning of kindergarten), and the role that additional training may have in supporting use of KRAs at the local level
Thermal activation between Landau levels in the organic superconductor -(BEDT-TTF)SFCHCFSO
We show that Shubnikov-de Haas oscillations in the interlayer resistivity of
the organic superconductor -(BEDT-TTF)SF
CHCFSO become very pronounced in magnetic fields ~60~T.
The conductivity minima exhibit thermally-activated behaviour that can be
explained simply by the presence of a Landau gap, with the
quasi-one-dimensional Fermi surface sheets contributing negligibly to the
conductivity. This observation, together with complete suppression of chemical
potential oscillations, is consistent with an incommensurate nesting
instability of the quasi-one-dimensional sheets.Comment: 6 pages, 4 figure
Semantic Image Retrieval via Active Grounding of Visual Situations
We describe a novel architecture for semantic image retrieval---in
particular, retrieval of instances of visual situations. Visual situations are
concepts such as "a boxing match," "walking the dog," "a crowd waiting for a
bus," or "a game of ping-pong," whose instantiations in images are linked more
by their common spatial and semantic structure than by low-level visual
similarity. Given a query situation description, our architecture---called
Situate---learns models capturing the visual features of expected objects as
well the expected spatial configuration of relationships among objects. Given a
new image, Situate uses these models in an attempt to ground (i.e., to create a
bounding box locating) each expected component of the situation in the image
via an active search procedure. Situate uses the resulting grounding to compute
a score indicating the degree to which the new image is judged to contain an
instance of the situation. Such scores can be used to rank images in a
collection as part of a retrieval system. In the preliminary study described
here, we demonstrate the promise of this system by comparing Situate's
performance with that of two baseline methods, as well as with a related
semantic image-retrieval system based on "scene graphs.
Structural identification of cubic iron-oxide nanocrystal mixtures: X-ray powder diffraction versus quasi-kinematic transmission electron microscopy
Two novel (and proprietary) strategies for the structural identification of a
nanocrystal from either a single high-resolution (HR) transmission electron
microscopy (TEM) image or a single precession electron diffraction pattern are
proposed and their advantages discussed in comparison to structural
fingerprinting from powder X-ray diffraction patterns. Simulations for cubic
magnetite and maghemite nanocrystals are used as examples. This is an expanded
and updated version of a conference paper that has been published in Suppl.
Proc. of TMS 2008, 137th Annual Meeting & Exhibition, Volume 1, Materials
Processing and Properties, pp. 25-32.Comment: 7 pages, 3 figures, 1 table, expanded and updated version of a
conference paper that has been published in Suppl. Proc. of TMS 2008, 137th
Annual Meeting & Exhibition, Volume 1, Materials Processing and Properties,
pp. 25-3
The auxiliary space preconditioner for the de Rham complex
We generalize the construction and analysis of auxiliary space
preconditioners to the n-dimensional finite element subcomplex of the de Rham
complex. These preconditioners are based on a generalization of a decomposition
of Sobolev space functions into a regular part and a potential. A discrete
version is easily established using the tools of finite element exterior
calculus. We then discuss the four-dimensional de Rham complex in detail. By
identifying forms in four dimensions (4D) with simple proxies, form operations
are written out in terms of familiar algebraic operations on matrices, vectors,
and scalars. This provides the basis for our implementation of the
preconditioners in 4D. Extensive numerical experiments illustrate their
performance, practical scalability, and parameter robustness, all in accordance
with the theory
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Investigating the impact of remotely sensed precipitation and hydrologic model uncertainties on the ensemble streamflow forecasting
In the past few years sequential data assimilation (SDA) methods have emerged as the best possible method at hand to properly treat all sources of error in hydrological modeling. However, very few studies have actually implemented SDA methods using realistic input error models for precipitation. In this study we use particle filtering as a SDA method to propagate input errors through a conceptual hydrologic model and quantify the state, parameter and streamflow uncertainties. Recent progress in satellite-based precipitation observation techniques offers an attractive option for considering spatiotemporal variation of precipitation. Therefore, we use the PERSIANN-CCS precipitation product to propagate input errors through our hydrologic model. Some uncertainty scenarios are set up to incorporate and investigate the impact of the individual uncertainty sources from precipitation, parameters and also combined error sources on the hydrologic response. Also probabilistic measure are used to quantify the quality of ensemble prediction. Copyright 2006 by the American Geophysical Union
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