832 research outputs found
Chernoff Index for Cox Test of Separate Parametric Families
The asymptotic efficiency of a generalized likelihood ratio test proposed by
Cox is studied under the large deviations framework for error probabilities
developed by Chernoff. In particular, two separate parametric families of
hypotheses are considered [Cox, 1961, 1962]. The significance level is set such
that the maximal type I and type II error probabilities for the generalized
likelihood ratio test decay exponentially fast with the same rate. We derive
the analytic form of such a rate that is also known as the Chernoff index
[Chernoff, 1952], a relative efficiency measure when there is no preference
between the null and the alternative hypotheses. We further extend the analysis
to approximate error probabilities when the two families are not completely
separated. Discussions are provided concerning the implications of the present
result on model selection
On the Identifiability of Diagnostic Classification Models
This paper establishes fundamental results for statistical inference of
diagnostic classification models (DCM). The results are developed at a high
level of generality, applicable to essentially all diagnostic classification
models. In particular, we establish identifiability results of various modeling
parameters, notably item response probabilities, attribute distribution, and
Q-matrix-induced partial information structure. Consistent estimators are
constructed. Simulation results show that these estimators perform well under
various modeling settings. We also use a real example to illustrate the new
method. The results are stated under the setting of general latent class
models. For DCM with a specific parameterization, the conditions may be adapted
accordingly
A Fused Latent and Graphical Model for Multivariate Binary Data
We consider modeling, inference, and computation for analyzing multivariate
binary data. We propose a new model that consists of a low dimensional latent
variable component and a sparse graphical component. Our study is motivated by
analysis of item response data in cognitive assessment and has applications to
many disciplines where item response data are collected. Standard approaches to
item response data in cognitive assessment adopt the multidimensional item
response theory (IRT) models. However, human cognition is typically a
complicated process and thus may not be adequately described by just a few
factors. Consequently, a low-dimensional latent factor model, such as the
multidimensional IRT models, is often insufficient to capture the structure of
the data. The proposed model adds a sparse graphical component that captures
the remaining ad hoc dependence. It reduces to a multidimensional IRT model
when the graphical component becomes degenerate. Model selection and parameter
estimation are carried out simultaneously through construction of a
pseudo-likelihood function and properly chosen penalty terms. The convexity of
the pseudo-likelihood function allows us to develop an efficient algorithm,
while the penalty terms generate a low-dimensional latent component and a
sparse graphical structure. Desirable theoretical properties are established
under suitable regularity conditions. The method is applied to the revised
Eysenck's personality questionnaire, revealing its usefulness in item analysis.
Simulation results are reported that show the new method works well in
practical situations.Comment: 49 pages, 6 figures, and 5 table
Guaranteed-cost consensus for multiagent networks with Lipschitz nonlinear dynamics and switching topologies
Guaranteed-cost consensus for high-order nonlinear multi-agent networks with
switching topologies is investigated. By constructing a time-varying
nonsingular matrix with a specific structure, the whole dynamics of multi-agent
networks is decomposed into the consensus and disagreement parts with nonlinear
terms, which is the key challenge to be dealt with. An explicit expression of
the consensus dynamics, which contains the nonlinear term, is given and its
initial state is determined. Furthermore, by the structure property of the
time-varying nonsingular transformation matrix and the Lipschitz condition, the
impacts of the nonlinear term on the disagreement dynamics are linearized and
the gain matrix of the consensus protocol is determined on the basis of the
Riccati equation. Moreover, an approach to minimize the guaranteed cost is
given in terms of linear matrix inequalities. Finally, the numerical simulation
is shown to demonstrate the effectiveness of theoretical results.Comment: 16 page
Control of Surface Wettability via Strain Engineering
Reversible control of surface wettability has wide applications in
lab-on-chip systems, tunable optical lenses, and microfluidic tools. Using a
graphene sheet as a sample material and molecular dynamic (MD) simulations, we
demonstrate that strain engineering can serve as an effective way to control
the surface wettability. The contact angles of water droplets on a
graphene vary from 72.5 to 106 under biaxial strains ranging
from -10% to 10% that are applied on the graphene layer. For an intrinsic
hydrophilic surface (at zero strain), the variation of upon the
applied strains is more sensitive, i.e., from 0 to 74.8.
Overall the cosines of the contact angles exhibit a linear relation with
respect to the strains. In light of the inherent dependence of the contact
angle on liquid-solid interfacial energy, we develop an analytic model to show
the as a linear function of the adsorption energy of a
single water molecule over the substrate surface. This model agrees with our MD
results very well. Together with the linear dependence of on biaxial
strains, we can thus understand the effect of strains on the surface
wettability. Thanks to the ease of reversibly applying mechanical strains in
micro/nano-electromechanical systems (MEMS/NEMS), we believe that strain
engineering can be a promising means to achieve the reversibly control of
surface wettability.Comment: Submitted to Physical Review E on September 17, 2012, manuscript ID:
EW1084
Optimal Stopping and Worker Selection in Crowdsourcing: an Adaptive Sequential Probability Ratio Test Framework
In this paper, we aim at solving a class of multiple testing problems under
the Bayesian sequential decision framework. Our motivating application comes
from binary labeling tasks in crowdsourcing, where the requestor needs to
simultaneously decide which worker to choose to provide the label and when to
stop collecting labels under a certain budget constraint. We start with the
binary hypothesis testing problem to determine the true label of a single
object, and provide an optimal solution by casting it under the adaptive
sequential probability ratio test (Ada-SPRT) framework. We characterize the
structure of the optimal solution, i.e., optimal adaptive sequential design,
which minimizes the Bayes risk through log-likelihood ratio statistic. We also
develop a dynamic programming algorithm that can efficiently approximate the
optimal solution. For the multiple testing problem, we further propose to adopt
an empirical Bayes approach for estimating class priors and show that our
method has an averaged loss that converges to the minimal Bayes risk under the
true model. The experiments on both simulated and real data show the robustness
of our method and its superiority in labeling accuracy as compared to several
other recently proposed approaches
Latent Feature Extraction for Process Data via Multidimensional Scaling
Computer-based interactive items have become prevalent in recent educational
assessments. In such items, the entire human-computer interactive process is
recorded in a log file and is known as the response process. This paper aims at
extracting useful information from response processes. In particular, we
consider an exploratory latent variable analysis for process data. Latent
variables are extracted through a multidimensional scaling framework and can be
empirically proved to contain more information than classic binary responses in
terms of out-of-sample prediction of many variables.Comment: 26 pages, 11 figure
The Application of Situational Experiential Teaching in English Reading Teaching in Senior Middle School
The National English Curriculum Standards for General Senior Middle School (2017 ed., 2020 rev.) promotes the establishment of an environment for students to experience English teaching, letting students enter the English world and improve their core literacy to meet teaching expectations. This paper analyzes the connotation of situational experiential teaching mode, then combines teaching examples, thus first creating multi-modal situation, enhancing real sense of students’ experience; secondly basing on the situation task, training students’ problem-solving ability; and thirdly applying situational role and cultivating students’ ability of transfer and innovation, which explores the application of situational experiential teaching method in English reading teaching in senior middle schools from the three aspects.
Analysis on President Xi Jinping’s Expressions in Publicity Translation
In order to make China and Chinese stories better heard, publicity translation has a long way to go and shoulders an arduous task. Although there are some studies about publicity translation, yet only a few have been done on speeches by Chinese leaders. This paper studies several problems as follows: features of President Xi Jinping’s stylistic expressions and analysis on them; the application of publicity translation theories and factors considered while translating, including the translation techniques employed
Tuning of Interlayer Coupling in Large-Area Graphene/WSe2 van der Waals Heterostructure via Ion Irradiation: Optical Evidences and Photonic Applications
Van der Waals (vdW) heterostructures are receiving great attentions due to
their intriguing properties and potentials in many research fields. The flow of
charge carriers in vdW heterostructures can be efficiently rectified by the
inter-layer coupling between neighboring layers, offering a rich collection of
functionalities and a mechanism for designing atomically thin devices.
Nevertheless, non-uniform contact in larger-area heterostructures reduces the
device efficiency. In this work, ion irradiation had been verified as an
efficient technique to enhance the contact and interlayer coupling in the newly
developed graphene/WSe2 hetero-structure with a large area of 10 mm x 10 mm.
During the ion irradiation process, the morphology of monolayer graphene had
been modified, promoting the contact with WSe2. Experimental evidences of the
tunable interlayer electron transfer are displayed by investigation of
photoluminescence and ultrafast absorption of the irradiated heterostructure.
Besides, we have found that in graphene/WSe2 heterostructure, graphene serves
as a fast channel for the photo-excited carriers to relax in WSe2, and the
nonlinear absorption of WSe2 could be effectively tuned by the carrier transfer
process in graphene, enabling specific optical absorption of the
heterostructure in comparison with separated graphene or WSe2. On the basis of
these new findings, by applying the ion beam modified graphene/WSe2
heterostructure as a saturable absorber, Q-switched pulsed lasing with
optimized performance has been realized in a Nd:YAG waveguide cavity. This work
paves the way towards developing novel devices based on large-area
heterostructures by using ion beam irradiation
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