30,292 research outputs found
Reverse engineering of CAD models via clustering and approximate implicitization
In applications like computer aided design, geometric models are often
represented numerically as polynomial splines or NURBS, even when they
originate from primitive geometry. For purposes such as redesign and
isogeometric analysis, it is of interest to extract information about the
underlying geometry through reverse engineering. In this work we develop a
novel method to determine these primitive shapes by combining clustering
analysis with approximate implicitization. The proposed method is automatic and
can recover algebraic hypersurfaces of any degree in any dimension. In exact
arithmetic, the algorithm returns exact results. All the required parameters,
such as the implicit degree of the patches and the number of clusters of the
model, are inferred using numerical approaches in order to obtain an algorithm
that requires as little manual input as possible. The effectiveness, efficiency
and robustness of the method are shown both in a theoretical analysis and in
numerical examples implemented in Python
Some Physics And System Issues In The Security Analysis Of Quantum Key Distribution Protocols
In this paper we review a number of issues on the security of quantum key
distribution (QKD) protocols that bear directly on the relevant physics or
mathematical representation of the QKD cryptosystem. It is shown that the
cryptosystem representation itself may miss out many possible attacks which are
not accounted for in the security analysis and proofs. Hence the final security
claims drawn from such analysis are not reliable, apart from foundational
issues about the security criteria that are discussed elsewhere. The cases of
continuous-variable QKD and multi-photon sources are elaborated upon
Geometric symmetry in the quadratic Fisher discriminant operating on image pixels
This article examines the design of Quadratic Fisher Discriminants (QFDs)
that operate directly on image pixels, when image ensembles are taken to
comprise all rotated and reflected versions of distinct sample images. A
procedure based on group theory is devised to identify and discard QFD
coefficients made redundant by symmetry, for arbitrary sampling lattices. This
procedure introduces the concept of a degeneracy matrix. Tensor representations
are established for the square lattice point group (8-fold symmetry) and
hexagonal lattice point group (12-fold symmetry). The analysis is largely
applicable to the symmetrisation of any quadratic filter, and generalises to
higher order polynomial (Volterra) filters. Experiments on square lattice
sampled synthetic aperture radar (SAR) imagery verify that symmetrisation of
QFDs can improve their generalisation and discrimination ability.Comment: Accepted for publication in IEEE Transactions on Information Theor
Beyond the Born-Oppenheimer approximation: high-resolution overtone spectroscopy of H2D+ and D2H+
Transitions to overtone 2v2 and 2v3, and combination v2 + v3 vibrations in jet-cooled H2D+ and D2H+ molecular ions have been measured for the first time by high-resolution IR spectroscopy. The source of these ions is a pulsed slit jet supersonic discharge, which allows for efficient generation, rotational cooling, and high frequency (100 KHz) concentration modulation for detection via sensitive lock-in detection methods. Isotopic substitution and high-resolution overtone spectroscopy in this fundamental molecular ion permit a systematic, first principles investigation of BornâOppenheimer "breakdown" effects due to large amplitude vibrational motion as well as provide rigorous tests of approximate theoretical methods beyond the BornâOppenheimer level. The observed overtone transitions are in remarkably good agreement (<0.1 cmâ1) with non-BornâOppenheimer ab initio theoretical predictions, with small but systematic deviations for 2v2, 2v + 3v, and 2v3 excited states indicating directions for further improvement in such treatments. Spectroscopic assignment and analysis of the isotopomeric transitions reveals strong Coriolis mixing between near resonant 2v3 and 2v + 3v vibrations in D2H+. Population-independent line intensity ratios for transitions from common lower states indicate excellent overall agreement with theoretical predictions for D2H+, but with statistically significant discrepancies noted for H2D+. Finally, H2D+ versus D2H+ isotopomer populations are analyzed as a function of D2/H2 mixing ratio and can be well described by steady state kinetics in the slit discharge expansion
BIGMAC : breaking inaccurate genomes and merging assembled contigs for long read metagenomic assembly.
BackgroundThe problem of de-novo assembly for metagenomes using only long reads is gaining attention. We study whether post-processing metagenomic assemblies with the original input long reads can result in quality improvement. Previous approaches have focused on pre-processing reads and optimizing assemblers. BIGMAC takes an alternative perspective to focus on the post-processing step.ResultsUsing both the assembled contigs and original long reads as input, BIGMAC first breaks the contigs at potentially mis-assembled locations and subsequently scaffolds contigs. Our experiments on metagenomes assembled from long reads show that BIGMAC can improve assembly quality by reducing the number of mis-assemblies while maintaining or increasing N50 and N75. Moreover, BIGMAC shows the largest N75 to number of mis-assemblies ratio on all tested datasets when compared to other post-processing tools.ConclusionsBIGMAC demonstrates the effectiveness of the post-processing approach in improving the quality of metagenomic assemblies
Continuous-variable entanglement distillation over a pure loss channel with multiple quantum scissors
Entanglement distillation is a key primitive for distributing high-quality
entanglement between remote locations. Probabilistic noiseless linear
amplification based on the quantum scissors is a candidate for entanglement
distillation from noisy continuous-variable (CV) entangled states. Being a
non-Gaussian operation, quantum scissors is challenging to analyze. We present
a derivation of the non-Gaussian state heralded by multiple quantum scissors in
a pure loss channel with two-mode squeezed vacuum input. We choose the reverse
coherent information (RCI)---a proven lower bound on the distillable
entanglement of a quantum state under one-way local operations and classical
communication (LOCC), as our figure of merit. We evaluate a Gaussian lower
bound on the RCI of the heralded state. We show that it can exceed the
unlimited two-way LOCCassisted direct transmission entanglement distillation
capacity of the pure loss channel. The optimal heralded Gaussian RCI with two
quantum scissors is found to be significantly more than that with a single
quantum scissors, albeit at the cost of decreased success probability. Our
results fortify the possibility of a quantum repeater scheme for CV quantum
states using the quantum scissors.Comment: accepted for publication in Physical Review
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