914 research outputs found
Two-Scale Homogenization of Non-Linear Degenerate Evolution Equations
AbstractUsing the notion of two-scale convergence developed by Allaire, the homogenization of a degenerate non-linear evolution equation with periodically oscillating coefficients is presented. A two-scale homogenized system is obtained as the limit of the periodic problem. Monotone operator methods and two-scale convergence are employed to show that the solutions of the periodic problem converge to the unique solution of the homogenized system. Homogenized initial conditions are also obtained and the sense in which they hold for the homogenized initial value problem is made specific
Preceding rule induction with instance reduction methods
A new prepruning technique for rule induction is presented which applies instance reduction before rule induction. An empirical evaluation records the predictive accuracy and size of rule-sets generated from 24 datasets from the UCI Machine Learning Repository. Three instance reduction algorithms (Edited Nearest Neighbour, AllKnn and DROP5) are compared. Each one is used to reduce the size of the training set, prior to inducing a set of rules using Clark and Boswell's modification of CN2. A hybrid instance reduction algorithm (comprised of AllKnn and DROP5) is also tested. For most of the datasets, pruning the training set using ENN, AllKnn or the hybrid significantly reduces the number of rules generated by CN2, without adversely affecting the predictive performance. The hybrid achieves the highest average predictive accuracy
Numerical simulations of a kilometre-thick Arctic ice shelf consistent with ice grounding observations
Recently obtained geophysical data show sets of parallel erosional features on the Lomonosov
Ridge in the central Arctic Basin, indicative of ice grounding in water depths up to 1280
m. These features have been interpreted as being formed by an ice shelf—either restricted to
the Amerasian Basin (the “minimum model”) or extending across the entire Arctic Basin.
Here, we use a numerical ice sheet-shelf model to explore how such an ice shelf could form.
We rule out the “minimum model” and suggest that grounding on the Lomonosov Ridge
requires complete Arctic ice shelf cover; this places a minimum estimate on its volume, which
would have exceeded that of the modern Greenland Ice Sheet. Buttressing provided by an
Arctic ice shelf would have increased volumes of the peripheral terrestrial ice sheets. An
Arctic ice shelf could have formed even in the absence of a hypothesised East Siberian Ice
Sheet
A Dodecalogue of Basic Didactics from Applications of Abstract Differential Geometry to Quantum Gravity
We summarize the twelve most important in our view novel concepts that have
arisen, based on results that have been obtained, from various applications of
Abstract Differential Geometry (ADG) to Quantum Gravity (QG). The present
document may be used as a concise, yet informal, discursive and peripatetic
conceptual guide-cum-terminological glossary to the voluminous technical
research literature on the subject. In a bonus section at the end, we dwell on
the significance of introducing new conceptual terminology in future QG
research by means of `poetic language'Comment: 16 pages, preliminary versio
Bessel Process and Conformal Quantum Mechanics
Different aspects of the connection between the Bessel process and the
conformal quantum mechanics (CQM) are discussed. The meaning of the possible
generalizations of both models is investigated with respect to the other model,
including self adjoint extension of the CQM. Some other generalizations such as
the Bessel process in the wide sense and radial Ornstein- Uhlenbeck process are
discussed with respect to the underlying conformal group structure.Comment: 28 Page
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
Search for Neutral Q-balls in Super-Kamiokande II
A search for Q-balls induced groups of successive contained events has been
carried out in Super-Kamiokande II with 541.7 days of live time.
Neutral Q-balls would emit pions when colliding with nuclei, generating a
signal of successive contained pion events along a track. No candidate for
successive contained event groups has been found in Super-Kamiokande II, so
upper limits on the possible flux of such Q-balls have been obtained.Comment: 5 pages, 5 figures, Submitted to Phys. Lett.
All-particle cosmic ray energy spectrum measured with 26 IceTop stations
We report on a measurement of the cosmic ray energy spectrum with the IceTop
air shower array, the surface component of the IceCube Neutrino Observatory at
the South Pole. The data used in this analysis were taken between June and
October, 2007, with 26 surface stations operational at that time, corresponding
to about one third of the final array. The fiducial area used in this analysis
was 0.122 km^2. The analysis investigated the energy spectrum from 1 to 100 PeV
measured for three different zenith angle ranges between 0{\deg} and 46{\deg}.
Because of the isotropy of cosmic rays in this energy range the spectra from
all zenith angle intervals have to agree. The cosmic-ray energy spectrum was
determined under different assumptions on the primary mass composition. Good
agreement of spectra in the three zenith angle ranges was found for the
assumption of pure proton and a simple two-component model. For zenith angles
{\theta} < 30{\deg}, where the mass dependence is smallest, the knee in the
cosmic ray energy spectrum was observed between 3.5 and 4.32 PeV, depending on
composition assumption. Spectral indices above the knee range from -3.08 to
-3.11 depending on primary mass composition assumption. Moreover, an indication
of a flattening of the spectrum above 22 PeV were observed.Comment: 38 pages, 17 figure
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
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