25,127 research outputs found
Efficiency versus Convergence of Boolean Kernels for On-Line Learning Algorithms
The paper studies machine learning problems where each example is described
using a set of Boolean features and where hypotheses are represented by linear
threshold elements. One method of increasing the expressiveness of learned
hypotheses in this context is to expand the feature set to include conjunctions
of basic features. This can be done explicitly or where possible by using a
kernel function. Focusing on the well known Perceptron and Winnow algorithms,
the paper demonstrates a tradeoff between the computational efficiency with
which the algorithm can be run over the expanded feature space and the
generalization ability of the corresponding learning algorithm. We first
describe several kernel functions which capture either limited forms of
conjunctions or all conjunctions. We show that these kernels can be used to
efficiently run the Perceptron algorithm over a feature space of exponentially
many conjunctions; however we also show that using such kernels, the Perceptron
algorithm can provably make an exponential number of mistakes even when
learning simple functions. We then consider the question of whether kernel
functions can analogously be used to run the multiplicative-update Winnow
algorithm over an expanded feature space of exponentially many conjunctions.
Known upper bounds imply that the Winnow algorithm can learn Disjunctive Normal
Form (DNF) formulae with a polynomial mistake bound in this setting. However,
we prove that it is computationally hard to simulate Winnows behavior for
learning DNF over such a feature set. This implies that the kernel functions
which correspond to running Winnow for this problem are not efficiently
computable, and that there is no general construction that can run Winnow with
kernels
Advanced passive communication satellite systems comparison studies. Volume 1 - Summary Final report
Passive communication satellites feasibility for Comsat system - Vol.
Advanced passive communication satellite systems comparison studies. Volume 2 - Technical discussion Final report
Passive communication satellites feasibility for Comsat system - Vol.
Quantitative flaw characterization with scanning laser acoustic microscopy
Surface roughness and diffraction are two factors that have been observed to affect the accuracy of flaw characterization with scanning laser acoustic microscopy. In accuracies can arise when the surface of the test sample is acoustically rough. It is shown that, in this case, Snell's law is no longer valid for determining the direction of sound propagation within the sample. The relationship between the direction of sound propagation within the sample, the apparent flaw depth, and the sample's surface roughness is investigated. Diffraction effects can mask the acoustic images of minute flaws and make it difficult to establish their size, depth, and other characteristics. It is shown that for Fraunhofer diffraction conditions the acoustic image of a subsurface defect corresponds to a two-dimensional Fourier transform. Transforms based on simulated flaws are used to infer the size and shape of the actual flaw
No-Core Shell Model for Nuclear Systems with Strangeness
We report on a novel ab initio approach for nuclear few- and many-body
systems with strangeness. Recently, we developed a relevant no-core shell model
technique which we successfully applied in first calculations of lightest
hypernuclei. The use of a translationally invariant finite harmonic
oscillator basis allows us to employ large model spaces, compared to
traditional shell model calculations, and use realistic nucleon-nucleon and
nucleon-hyperon interactions (such as those derived from EFT). We discuss
formal aspects of the methodology, show first demonstrative results for
H, H and He, and give outlook.Comment: 4 pages, 3 figures; Proceedings of the 22nd European Conference on
Few Body Problems in Physics, 9 - 13 September, 2013, Cracow, Polan
Di-boson Production beyond NLO QCD and Anomalous Couplings
In these proceedings, we review results for several di-boson production
processes beyond NLO QCD at high transverse momenta using the VBFNLO
Monte-Carlo program together with the LOOPSIM method. Additionally, we show for
the WZ production process how higher order QCD corrections can resemble
anomalous coupling effects.Comment: Conference Proceedings:C15-05-25.
Quantum phases of atomic boson-fermion mixtures in optical lattices
The zero-temperature phase diagram of a binary mixture of bosonic and
fermionic atoms in an one-dimensional optical lattice is studied in the
framework of the Bose-Fermi-Hubbard model. By exact numerical solution of the
associated eigenvalue problems, ground state observables and the response to an
external phase twist are evaluated. The stiffnesses under phase variations
provide measures for the boson superfluid fraction and the fermionic Drude
weight. Several distinct quantum phases are identified as function of the
strength of the repulsive boson-boson and the boson-fermion interaction.
Besides the bosonic Mott-insulator phase, two other insulating phases are
found, where both the bosonic superfluid fraction and the fermionic Drude
weight vanish simultaneously. One of these double-insulator phases exhibits a
crystalline diagonal long-range order, while the other is characterized by
spatial separation of the two species.Comment: 4 pages, 3 figures, using REVTEX
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