5,469 research outputs found
On the approximate maximum likelihood estimation for diffusion processes
The transition density of a diffusion process does not admit an explicit
expression in general, which prevents the full maximum likelihood estimation
(MLE) based on discretely observed sample paths. A\"{\i}t-Sahalia [J. Finance
54 (1999) 1361--1395; Econometrica 70 (2002) 223--262] proposed asymptotic
expansions to the transition densities of diffusion processes, which lead to an
approximate maximum likelihood estimation (AMLE) for parameters. Built on
A\"{\i}t-Sahalia's [Econometrica 70 (2002) 223--262; Ann. Statist. 36 (2008)
906--937] proposal and analysis on the AMLE, we establish the consistency and
convergence rate of the AMLE, which reveal the roles played by the number of
terms used in the asymptotic density expansions and the sampling interval
between successive observations. We find conditions under which the AMLE has
the same asymptotic distribution as that of the full MLE. A first order
approximation to the Fisher information matrix is proposed.Comment: Published in at http://dx.doi.org/10.1214/11-AOS922 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Abnormality Detection in Mammography using Deep Convolutional Neural Networks
Breast cancer is the most common cancer in women worldwide. The most common
screening technology is mammography. To reduce the cost and workload of
radiologists, we propose a computer aided detection approach for classifying
and localizing calcifications and masses in mammogram images. To improve on
conventional approaches, we apply deep convolutional neural networks (CNN) for
automatic feature learning and classifier building. In computer-aided
mammography, deep CNN classifiers cannot be trained directly on full mammogram
images because of the loss of image details from resizing at input layers.
Instead, our classifiers are trained on labelled image patches and then adapted
to work on full mammogram images for localizing the abnormalities.
State-of-the-art deep convolutional neural networks are compared on their
performance of classifying the abnormalities. Experimental results indicate
that VGGNet receives the best overall accuracy at 92.53\% in classifications.
For localizing abnormalities, ResNet is selected for computing class activation
maps because it is ready to be deployed without structural change or further
training. Our approach demonstrates that deep convolutional neural network
classifiers have remarkable localization capabilities despite no supervision on
the location of abnormalities is provided.Comment: 6 page
Hidden force opposing ice compression
Coulomb repulsion between the unevenly-bound bonding and nonbonding electron
pairs in the O:H-O hydrogen-bond is shown to originate the anomalies of ice
under compression. Consistency between experimental observations, density
functional theory and molecular dynamics calculations confirmed that the
resultant force of the compression, the repulsion, and the recovery of
electron-pair dislocations differentiates ice from other materials in response
to pressure. The compression shortens and strengthens the longer-and-softer
intermolecular O:H lone-pair virtual-bond; the repulsion pushes the bonding
electron pair away from the H+/p and hence lengthens and weakens the
intramolecular H-O real-bond. The virtual-bond compression and the real-bond
elongation symmetrize the O:H-O as observed at ~60 GPa and result in the
abnormally low compressibility of ice. The virtual-bond stretching phonons (<
400 cm-1) are thus stiffened and the real-bond stretching phonons (> 3000 cm-1)
softened upon compression. The cohesive energy of the real-bond dominates and
its loss lowers the critical temperature for the VIII-VII phase transition. The
polarization of the lone electron pairs and the entrapment of the bonding
electron pairs by compression expand the band gap consequently. Findings should
form striking impact to understanding the physical anomalies of H2O.Comment: arXiv admin note: text overlap with arXiv:1110.007
The dependence of tidal stripping efficiency on the satellite and host galaxy morphology
In this paper we study the tidal stripping process for satellite galaxies
orbiting around a massive host galaxy, and focus on its dependence on the
morphology of both satellite and host galaxy. For this purpose, we use three
different morphologies for the satellites: pure disc, pure bulge and a mixture
bulge+disc. Two morphologies are used for the host galaxies: bulge+disc and
pure bulge. We find that while the spheroidal stellar component experiences a
constant power-law like mass removal, the disc is exposed to an exponential
mass loss when the tidal radius of the satellite is of the same order of the
disc scale length. This dramatic mass loss is able to completely remove the
stellar component on time scale of 100 Myears. As a consequence two satellites
with the same stellar and dark matter masses, on the same orbit could either
retain considerable fraction of their stellar mass after 10 Gyrs or being
completely destroyed, depending on their initial stellar morphology. We find
that there are two characteristic time scales describing the beginning and the
end of the disc removal, whose values are related to the size of the disc. This
result can be easily incorporated in semi-analytical models. We also find that
the host morphology and the orbital parameters also have an effect on the
determining the mass removal, but they are of secondary importance with respect
to satellite morphology. We conclude that satellite morphology has a very
strong effect on the efficiency of stellar stripping and should be taken into
account in modeling galaxy formation and evolution.Comment: 11 pages, 9 figures; accepted for publication in MNRA
High dimensional generalized empirical likelihood for moment restrictions with dependent data
This paper considers the maximum generalized empirical likelihood (GEL)
estimation and inference on parameters identified by high dimensional moment
restrictions with weakly dependent data when the dimensions of the moment
restrictions and the parameters diverge along with the sample size. The
consistency with rates and the asymptotic normality of the GEL estimator are
obtained by properly restricting the growth rates of the dimensions of the
parameters and the moment restrictions, as well as the degree of data
dependence. It is shown that even in the high dimensional time series setting,
the GEL ratio can still behave like a chi-square random variable
asymptotically. A consistent test for the over-identification is proposed. A
penalized GEL method is also provided for estimation under sparsity setting
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