5,147 research outputs found
Abstracts of Papers Presented at the Sixth Biennial Scientific Meeting of the Asia Pacific Paediatric Endocrine Society
A note on the time evolution of the fission decay width under the influence of dissipation
The claim put forward in a recent paper by B. Jurado, K.-H. Schmidt and J.
Benlliure that the transient effect of nuclear fission may be described simply
as a relaxation process in the upright oscillator around the potential minimum
is refuted. Some critical remarks on the relevance of this effect in general
are added.Comment: 6 pages, LaTex, no figures; final, shorter version, to appear in PL
The Estimation of Item Response Models with the lmer Function from the lme4 Package in R
In this paper we elaborate on the potential of the lmer function from the lme4 package in R for item response (IRT) modeling. In line with the package, an IRT framework is described based on generalized linear mixed modeling. The aspects of the framework refer to (a) the kind of covariates -- their mode (person, item, person-by-item), and their being external vs. internal to responses, and (b) the kind of effects the covariates have -- fixed vs. random, and if random, the mode across which the effects are random (persons, items). Based on this framework, three broad categories of models are described: Item covariate models, person covariate models, and person-by-item covariate models, and within each category three types of more specific models are discussed. The models in question are explained and the associated lmer code is given. Examples of models are the linear logistic test model with an error term, differential item functioning models, and local item dependency models. Because the lme4 package is for univariate generalized linear mixed models, neither the two-parameter, and three-parameter models, nor the item response models for polytomous response data, can be estimated with the lmer function.
Detection superiority of 7 T MRI protocol in patients with epilepsy and suspected focal cortical dysplasia
In 11 adult patients with suspicion of Focal cortical dysplasia (FCD) on 1.5 T (n = 1) or 3 T (n = 10) magnetic resonance imaging (MRI), 7 T MRI was performed. Visibility, extent, morphological features and delineation were independently rated and subsequently discussed by three observers. Additionally, head-to-head comparisons with corresponding 3 T images were made in the eight patients with a previous 3 T MRI and sustained suspicion of FCD. Comparison with histopathology was done in the five patients that underwent surgery. All lesions, seen at 1.5 and 3 T, were also recognized on 7 T. At 7 T FLAIR highlighted the FCD-like lesions best, whereas T2 and T2* were deemed better suited to review structure and extent of the lesion. Image quality with the used 7 T MRI setup was higher than the quality with the used 3 T MRI setup. In 2 out of 11 patients diagnosis changed, in one after re-evaluation of the images, and in the other based on histopathology. With the used 7 T MRI setup, FCD-like lesions can be detected with more confidence and detail as compared to lower field strength. However, concordance between radiologic diagnosis and final diagnosis seems to be lower than expected
Conformal Prediction with Partially Labeled Data
While the predictions produced by conformal prediction are set-valued, the
data used for training and calibration is supposed to be precise. In the
setting of superset learning or learning from partial labels, a variant of
weakly supervised learning, it is exactly the other way around: training data
is possibly imprecise (set-valued), but the model induced from this data yields
precise predictions. In this paper, we combine the two settings by making
conformal prediction amenable to set-valued training data. We propose a
generalization of the conformal prediction procedure that can be applied to
set-valued training and calibration data. We prove the validity of the proposed
method and present experimental studies in which it compares favorably to
natural baselines
A Study of the Problems of Cost Analysis in the Petroleum Industry
The significance of the subject of the present study-the cost of finding, developing and producing petroleum-can be better understood by placing it against a summary view of the supply situation in the postwar world. The most striking fact is the appearance of vast new reserves of oil in various parts of the world. Earlier concern over conservation was aroused by the fear of depletion of the available supply. Taking a long view, this possibility is not to be dismissed. But in recent years the practical problems of the industry, and of public policy toward it, are of a different sort. The capacity of the industry to produce in the countries of the free world greatly exceeds the current rates of consumption. From the sellers\u27 point of view, at least, it seems self-evident that too much oil exists today
Second-Order Uncertainty Quantification: Variance-Based Measures
Uncertainty quantification is a critical aspect of machine learning models,
providing important insights into the reliability of predictions and aiding the
decision-making process in real-world applications. This paper proposes a novel
way to use variance-based measures to quantify uncertainty on the basis of
second-order distributions in classification problems. A distinctive feature of
the measures is the ability to reason about uncertainties on a class-based
level, which is useful in situations where nuanced decision-making is required.
Recalling some properties from the literature, we highlight that the
variance-based measures satisfy important (axiomatic) properties. In addition
to this axiomatic approach, we present empirical results showing the measures
to be effective and competitive to commonly used entropy-based measures.Comment: 22 pages, 10 figure
An Integrated View on the Future of Logistics and Information Technology
In this position paper, we present our vision on the future of the logistics
business domain and the use of information technology (IT) in this domain. The
vision is based on extensive experience with Dutch and European logistics in
various contexts and from various perspectives. We expect that the vision also
holds for logistics outside Europe. We build our vision in a number of steps.
First, we make an inventory of the most important trends in the logistics
domain - we call these mega-trends. Next, we do the same for the information
technology domain, restricted to technologies that have relevance for
logistics. Then, we introduce logistics meta-concepts that we use to describe
our vision and relate them to business engineering. We use these three
ingredients to analyze leading concepts that we currently observe in the
logistics domain. Next, we consolidate all elements into a model that
represents our vision of the integrated future of logistics and IT. We
elaborate on the role of data platforms and open standards in this integrated
vision.Comment: 22 pages, 7 figures, 3 table
A numerical framework for simulating progressive failure in composite laminates under high-cycle fatigue loading
In this work, a recently proposed high-cycle fatigue cohesive zone model,
which covers crack initiation and propagation with limited input parameters, is
embedded in a robust and efficient numerical framework for simulating
progressive failure in composite laminates under fatigue loading. The fatigue
cohesive zone model is enhanced with an implicit time integration scheme of the
fatigue damage variable which allows for larger cycle increments and more
efficient analyses. The method is combined with an adaptive strategy for
determining the cycle increment based on global convergence rates. Moreover, a
consistent material tangent stiffness matrix has been derived by fully
linearizing the underlying mixed-mode quasi-static model and the fatigue damage
update. The enhanced fatigue cohesive zone model is used to describe matrix
cracking and delamination in laminates. In order to allow for matrix cracks to
initiate at arbitrary locations and to avoid complex and costly mesh
generation, the phantom node version of the eXtended finite element method
(XFEM) is employed. For the insertion of new crack segments, an XFEM fatigue
crack insertion criterion is presented, which is consistent with the fatigue
cohesive zone formulation. It is shown with numerical examples that the
improved fatigue damage update enhances the accuracy, efficiency and robustness
of the numerical simulations significantly. The numerical framework is applied
to the simulation of progressive fatigue failure in an open-hole
[45]-laminate. It is demonstrated that the numerical model is capable of
accurately and efficiently simulating the complete failure process from
distributed damage to localized failure.Comment: 40 pages, 21 figure
Mean first passage time for fission potentials having structure
A schematic model of over-damped motion is presented which permits one to
calculate the mean first passage time for nuclear fission. Its asymptotic value
may exceed considerably the lifetime suggested by Kramers rate formula, which
applies only to very special, favorable potentials and temperatures. The
additional time obtained in the more general case is seen to allow for a
considerable increment in the emission of light particles.Comment: 7 pages, LaTex, 7 postscript figures; Keywords: Decay rate, mean
first passage tim
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