5,747 research outputs found
On the Shapley-like Payoff Mechanisms in Peer-Assisted Services with Multiple Content Providers
This paper studies an incentive structure for cooperation and its stability
in peer-assisted services when there exist multiple content providers, using a
coalition game theoretic approach. We first consider a generalized coalition
structure consisting of multiple providers with many assisting peers, where
peers assist providers to reduce the operational cost in content distribution.
To distribute the profit from cost reduction to players (i.e., providers and
peers), we then establish a generalized formula for individual payoffs when a
"Shapley-like" payoff mechanism is adopted. We show that the grand coalition is
unstable, even when the operational cost functions are concave, which is in
sharp contrast to the recently studied case of a single provider where the
grand coalition is stable. We also show that irrespective of stability of the
grand coalition, there always exist coalition structures which are not
convergent to the grand coalition. Our results give us an important insight
that a provider does not tend to cooperate with other providers in
peer-assisted services, and be separated from them. To further study the case
of the separated providers, three examples are presented; (i) underpaid peers,
(ii) service monopoly, and (iii) oscillatory coalition structure. Our study
opens many new questions such as realistic and efficient incentive structures
and the tradeoffs between fairness and individual providers' competition in
peer-assisted services.Comment: 13 pages, 4 figures, an extended version of the paper to be presented
in ICST GameNets 2011, Shanghai, China, April 201
Detection of Polyps via Shape and Appearance Modeling
Presented at the MICCAI 2008 Workshop on Computational and Visualization Challenges in the New Era of Virtual Colonoscopy, September 6, 2008, New York, USA.This paper describes a CAD system for the detection of colorectal polyps in CT. It is based on stochastic shape and appearance modeling of structures of the colon and rectum, in contrast to the data-driven approaches more commonly found in the literature it derives predictive stochastic models for the features used for classification. The method makes extensive use of medical domain knowledge in the design of the models and in the setting of their parameters. The proposed approach was successfully tested on challenging datasets acquired under a protocol with little colonic preparation; such protocol reduces patient discomfort and potentially improves compliance
Nonequilibrium electron transport using the density matrix renormalization group
We extended the Density Matrix Renormalization Group method to study the real
time dynamics of interacting one dimensional spinless Fermi systems by applying
the full time evolution operator to an initial state. As an example we describe
the propagation of a density excitation in an interacting clean system and the
transport through an interacting nano structure
Measures of Health-Related Quality of Life Outcomes in Pediatric Neurosurgery: Literature Review
Background
Improving value in healthcare means optimizing outcomes and minimizing costs. The emerging pay-for-performance era requires understanding of the effect of healthcare services on health-related quality of life (HRQoL). Pediatric and surgical subspecialties have yet to fully integrate HRQoL measures into practice. The present study reviewed and characterized the HRQoL outcome measures across various pediatric neurosurgical diagnoses.
Methods
A literature review was performed by searching PubMed and Google Scholar with search terms such as “health-related quality of life” and “pediatric neurosurgery” and then including the specific pathologies for which a HRQoL instrument was found (e.g., “health-related quality of life” plus “epilepsy”). Each measurement was evaluated by content and purpose, relative strengths and weaknesses, and validity.
Results
We reviewed 68 reports. Epilepsy, brain tumor, cerebral palsy, spina bifida, hydrocephalus, and scoliosis were diagnoses found in reported studies that had used disease-specific HRQoL instruments. Information using general HRQoL instruments was also reported. Internal, test–retest, and/or interrater reliability varied across the instruments, as did face, content, concurrent, and/or construct validity. Few instruments were tested enough for robust reliability and validity. Significant variability was found in the usage of these instruments in clinical studies within pediatric neurosurgery.
Conclusions
The HRQoL instruments used in pediatric neurosurgery are currently without standardized guidelines and thus exhibit high variability in use. Clinicians should support the development and application of these methods to optimize these instruments, promote standardization of research, improve performance measures to reflect clinically modifiable and meaningful outcomes, and, ultimately, lead the national discussion in healthcare quality and patient-centered care
Linear response strength functions with iterative Arnoldi diagonalization
We report on an implementation of a new method to calculate RPA strength
functions with iterative non-hermitian Arnoldi diagonalization method, which
does not explicitly calculate and store the RPA matrix. We discuss the
treatment of spurious modes, numerical stability, and how the method scales as
the used model space is enlarged. We perform the particle-hole RPA benchmark
calculations for double magic nucleus 132Sn and compare the resulting
electromagnetic strength functions against those obtained within the standard
RPA.Comment: 9 RevTeX pages, 11 figures, submitted to Physical Review
Statistical Mechanics of Nonlinear On-line Learning for Ensemble Teachers
We analyze the generalization performance of a student in a model composed of
nonlinear perceptrons: a true teacher, ensemble teachers, and the student. We
calculate the generalization error of the student analytically or numerically
using statistical mechanics in the framework of on-line learning. We treat two
well-known learning rules: Hebbian learning and perceptron learning. As a
result, it is proven that the nonlinear model shows qualitatively different
behaviors from the linear model. Moreover, it is clarified that Hebbian
learning and perceptron learning show qualitatively different behaviors from
each other. In Hebbian learning, we can analytically obtain the solutions. In
this case, the generalization error monotonically decreases. The steady value
of the generalization error is independent of the learning rate. The larger the
number of teachers is and the more variety the ensemble teachers have, the
smaller the generalization error is. In perceptron learning, we have to
numerically obtain the solutions. In this case, the dynamical behaviors of the
generalization error are non-monotonic. The smaller the learning rate is, the
larger the number of teachers is; and the more variety the ensemble teachers
have, the smaller the minimum value of the generalization error is.Comment: 13 pages, 9 figure
On-line Learning of an Unlearnable True Teacher through Mobile Ensemble Teachers
On-line learning of a hierarchical learning model is studied by a method from
statistical mechanics. In our model a student of a simple perceptron learns
from not a true teacher directly, but ensemble teachers who learn from the true
teacher with a perceptron learning rule. Since the true teacher and the
ensemble teachers are expressed as non-monotonic perceptron and simple ones,
respectively, the ensemble teachers go around the unlearnable true teacher with
the distance between them fixed in an asymptotic steady state. The
generalization performance of the student is shown to exceed that of the
ensemble teachers in a transient state, as was shown in similar
ensemble-teachers models. Further, it is found that moving the ensemble
teachers even in the steady state, in contrast to the fixed ensemble teachers,
is efficient for the performance of the student.Comment: 18 pages, 8 figure
On the Prospects for Laser Cooling of TlF
We measure the upper state lifetime and two ratios of vibrational branching
fractions f_{v'v} on the B^{3}\Pi_{1}(v') - X^{1}\Sigma^{+}(v) transition of
TlF. We find the B state lifetime to be 99(9) ns. We also determine that the
off-diagonal vibrational decays are highly suppressed: f_{01}/f_{00} <
2x10^{-4} and f_{02}/f_{00} = 1.10(6)%, in excellent agreement with their
predicted values of f_{01}/f_{00} < 8x10^{-4} and f_{02}/f_{00} = 1.0(2)% based
on Franck-Condon factors calculated using Morse and RKR potentials. The
implications of these results for the possible laser cooling of TlF and
fundamental symmetries experiments are discussed.Comment: 5 pages, 2 figure
Optimization of the Asymptotic Property of Mutual Learning Involving an Integration Mechanism of Ensemble Learning
We propose an optimization method of mutual learning which converges into the
identical state of optimum ensemble learning within the framework of on-line
learning, and have analyzed its asymptotic property through the statistical
mechanics method.The proposed model consists of two learning steps: two
students independently learn from a teacher, and then the students learn from
each other through the mutual learning. In mutual learning, students learn from
each other and the generalization error is improved even if the teacher has not
taken part in the mutual learning. However, in the case of different initial
overlaps(direction cosine) between teacher and students, a student with a
larger initial overlap tends to have a larger generalization error than that of
before the mutual learning. To overcome this problem, our proposed optimization
method of mutual learning optimizes the step sizes of two students to minimize
the asymptotic property of the generalization error. Consequently, the
optimized mutual learning converges to a generalization error identical to that
of the optimal ensemble learning. In addition, we show the relationship between
the optimum step size of the mutual learning and the integration mechanism of
the ensemble learning.Comment: 13 pages, 3 figures, submitted to Journal of Physical Society of
Japa
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