18,537 research outputs found
Structured variable selection in support vector machines
When applying the support vector machine (SVM) to high-dimensional
classification problems, we often impose a sparse structure in the SVM to
eliminate the influences of the irrelevant predictors. The lasso and other
variable selection techniques have been successfully used in the SVM to perform
automatic variable selection. In some problems, there is a natural hierarchical
structure among the variables. Thus, in order to have an interpretable SVM
classifier, it is important to respect the heredity principle when enforcing
the sparsity in the SVM. Many variable selection methods, however, do not
respect the heredity principle. In this paper we enforce both sparsity and the
heredity principle in the SVM by using the so-called structured variable
selection (SVS) framework originally proposed in Yuan, Joseph and Zou (2007).
We minimize the empirical hinge loss under a set of linear inequality
constraints and a lasso-type penalty. The solution always obeys the desired
heredity principle and enjoys sparsity. The new SVM classifier can be
efficiently fitted, because the optimization problem is a linear program.
Another contribution of this work is to present a nonparametric extension of
the SVS framework, and we propose nonparametric heredity SVMs. Simulated and
real data are used to illustrate the merits of the proposed method.Comment: Published in at http://dx.doi.org/10.1214/07-EJS125 the Electronic
Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Searching Signals in Chinese Ancient Records for the C Increases in AD 774-775 and in AD 992-993
According to the analysis of the C content of two Japanese trees over
a period of approximately 3000 years at high time resolution, Miyake (2012)
found a rapid increase at AD 774-775 and later on at AD 992-993 (Miyake 2013).
This corresponds to a high-energy event happened within one year that input
-ray energy about 710erg to the Earth, leaving the
origin a mystery. Such strong event should have an unusual optical counterpart,
and have been recorded in historical literature. We searched Chinese historical
materials around AD 744-775 and AD 992-993, but no remarkable event was found
except a violent thunderstorm in AD 775. However, the possibility of a
thunderstorm containing so much energy is still unlikely. We conclude the event
caused the C increase is still unclear. This event most probably has no
optical counterpart, and short gamma-ray burst, giant flare of a soft gamma-ray
repeater and terrestrial -ray flash may all be the candidates.Comment: 8 pages, 3 figure
Structured variable selection and estimation
In linear regression problems with related predictors, it is desirable to do
variable selection and estimation by maintaining the hierarchical or structural
relationships among predictors. In this paper we propose non-negative garrote
methods that can naturally incorporate such relationships defined through
effect heredity principles or marginality principles. We show that the methods
are very easy to compute and enjoy nice theoretical properties. We also show
that the methods can be easily extended to deal with more general regression
problems such as generalized linear models. Simulations and real examples are
used to illustrate the merits of the proposed methods.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS254 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Expected high energy emission from GRB 080319B and origins of the GeV emission of GRBs 080514B, 080916C and 081024B
We calculate the high energy (sub-GeV to TeV) prompt and afterglow emission
of GRB 080319B that was distinguished by a naked-eye optical flash and by an
unusual strong early X-ray afterglow. There are three possible sources for high
energy emission: the prompt optical and -ray photons IC scattered by
the accelerated electrons, the prompt photons IC scattered by the early
external reverse-forward shock electrons, and the higher band of the
synchrotron and the synchrotron self-Compton emission of the external shock.
There should have been in total {hundreds} high energy photons detectable for
the Large Area Telescope (LAT) onboard the Fermi satellite, and {tens} photons
of those with energy GeV. The GeV emission had a duration about
twice that of the soft -rays. AGILE could have observed these energetic
signals if it was not occulted by the Earth at that moment. The physical
origins of the high energy emission detected in GRB 080514B, GRB 080916C and
GRB 081024B are also discussed. These observations seem to be consistent with
the current high energy emission models.Comment: Accepted for publication in MNRAS, the interpretation of GRB 080916C
has been extended, main conclusions are unchange
Study of Minor Actinides Transmutation in PWR MOX fuel
The management of long-lived radionuclides in spent fuel is a key issue to
achieve the closed nuclear fuel cycle and the sustainable development of
nuclear energy. Partitioning-Transmutation is supposed to be an efficient
method to treat the long-lived radionuclides in spent fuel. Some Minor
Actinides (MAs) have very long half-lives among the radionuclides in the spent
fuel. Accordingly, the study of MAs transmutation is a significant work for the
post-processing of spent fuel.
In the present work, the transmutations in Pressurized Water Reactor (PWR)
mixed oxide (MOX) fuel are investigated through the Monte Carlo based code RMC.
Two kinds of MAs, Np and five MAs (Np, Am, Am,
Cm and Cm) are incorporated homogeneously into the MOX fuel
assembly. The transmutation of MAs is simulated with different initial MOX
concentrations.
The results indicate an overall nice efficiency of transmutation in both
initial MOX concentrations, especially for the two kinds of MAs primarily
generated in the UOX fuel, Np and Am. In addition, the
inclusion of Np in MOX has no large influence for other MAs, while the
transmutation efficiency of Np is excellent. The transmutation of MAs
in MOX fuel depletion is expected to be a new, efficient nuclear spent fuel
management method for the future nuclear power generation
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