1,103 research outputs found
Violator Spaces: Structure and Algorithms
Sharir and Welzl introduced an abstract framework for optimization problems,
called LP-type problems or also generalized linear programming problems, which
proved useful in algorithm design. We define a new, and as we believe, simpler
and more natural framework: violator spaces, which constitute a proper
generalization of LP-type problems. We show that Clarkson's randomized
algorithms for low-dimensional linear programming work in the context of
violator spaces. For example, in this way we obtain the fastest known algorithm
for the P-matrix generalized linear complementarity problem with a constant
number of blocks. We also give two new characterizations of LP-type problems:
they are equivalent to acyclic violator spaces, as well as to concrete LP-type
problems (informally, the constraints in a concrete LP-type problem are subsets
of a linearly ordered ground set, and the value of a set of constraints is the
minimum of its intersection).Comment: 28 pages, 5 figures, extended abstract was presented at ESA 2006;
author spelling fixe
Space-efficient Feature Maps for String Alignment Kernels
String kernels are attractive data analysis tools for analyzing string data.
Among them, alignment kernels are known for their high prediction accuracies in
string classifications when tested in combination with SVM in various
applications. However, alignment kernels have a crucial drawback in that they
scale poorly due to their quadratic computation complexity in the number of
input strings, which limits large-scale applications in practice. We address
this need by presenting the first approximation for string alignment kernels,
which we call space-efficient feature maps for edit distance with moves
(SFMEDM), by leveraging a metric embedding named edit sensitive parsing (ESP)
and feature maps (FMs) of random Fourier features (RFFs) for large-scale string
analyses. The original FMs for RFFs consume a huge amount of memory
proportional to the dimension d of input vectors and the dimension D of output
vectors, which prohibits its large-scale applications. We present novel
space-efficient feature maps (SFMs) of RFFs for a space reduction from O(dD) of
the original FMs to O(d) of SFMs with a theoretical guarantee with respect to
concentration bounds. We experimentally test SFMEDM on its ability to learn SVM
for large-scale string classifications with various massive string data, and we
demonstrate the superior performance of SFMEDM with respect to prediction
accuracy, scalability and computation efficiency.Comment: Full version for ICDM'19 pape
Reconstruction and actual trends of landslide activities in Bruust–Haltiwald, Horw, canton of Lucerne, Switzerland
A spatiotemporal reconstruction of slope movements on the
edge of Lake Lucerne near the municipality of Horw, canton of Lucerne, is
presented. The reconstruction was realized by analyzing growth reactions of
beech (Fagus sylvatica L.) and fir (Abies alba Mill.) trees growing on this slope. Before
dendrochronological sampling, a detailed geomorphological mapping of the
landslide was conducted with the aim to determine the spatial extent of the
sliding area. For tree-ring analyses, 124 increment cores from 62 trees were
analyzed following standard techniques of dendrogeomorphology. In addition,
long micro-sections were prepared from the entire cores to extend the common
eccentricity analyses by microscopic determination of the onset of reaction
wood in fir and beech. Results clearly show that the area is moving at
least since 1948. A significant concentration of events was observed between
the years 1990 and 2000 as well as after 2006. The definition of a threshold
to define events using an eccentricity index alone is problematic and needs
to be adapted to specific site conditions. For this reason, we recommend always combining the application of an eccentricity index with a detailed
visual (anatomical) inspection to check for the occurrence of reaction wood.</p
Crossover to the KPZ equation
We characterize the crossover regime to the KPZ equation for a class of
one-dimensional weakly asymmetric exclusion processes. The crossover depends on
the strength asymmetry () and it occurs at
. We show that the density field is a solution of an
Ornstein-Uhlenbeck equation if , while for it is
an energy solution of the KPZ equation. The corresponding crossover for the
current of particles is readily obtained.Comment: Published by Annales Henri Poincare Volume 13, Number 4 (2012),
813-82
Исследование зон усталостного разрушения шнеков
Шнек - основной рабочий орган машин для переработки отходов - экструдеров. От качества его изготовления зависит производительность цеха и целостность корпуса машины. При переработке многокомпонентного сырья, которым является Refuse Derived Fuel - это общее название альтернативных видов топлива, получаемых при переработке отходов. В качестве сырья используется практически любой органический материал: целлюлоза, резина, пластик, кожа, дерево, пищевые заменители. В исследовании использован пример на базе работы с RDF-сырьем Мусороперерабатывающего комбината "Янино", Ленинградская область. Именно при работе с такими высокоабразивными отходами возникает необходимость многократно повышать ресурс шнеков за счет использования новых технологий обработки металлов, так как в составе данного сырья могут встречаться металлические компоненты и трудно размалываемые силикаты.Screw - the main working organ of machines for processing waste - extruders. From the quality of its production depends the productivity of the shop and the integrity of the machine body. When refining a multicomponent raw material, which is Refuse Derived Fuel - this is the general name for alternative fuels obtained from recycling. As raw material, almost any organic material is used: cellulose, rubber, plastic, leather, its substitutes. The study used an example based on work with RDF-raw materials of the Janino Refuse Processing Plant. Leningrad region. It is when working with such highly abrasive waste that it becomes necessary to increase the service life of screw augmentedly by using new processing technologies, since metal components and hard-to-break silicates can occur in the composition of this raw material
Dynamical aspects of mean field plane rotators and the Kuramoto model
The Kuramoto model has been introduced in order to describe synchronization
phenomena observed in groups of cells, individuals, circuits, etc... We look at
the Kuramoto model with white noise forces: in mathematical terms it is a set
of N oscillators, each driven by an independent Brownian motion with a constant
drift, that is each oscillator has its own frequency, which, in general,
changes from one oscillator to another (these frequencies are usually taken to
be random and they may be viewed as a quenched disorder). The interactions
between oscillators are of long range type (mean field). We review some results
on the Kuramoto model from a statistical mechanics standpoint: we give in
particular necessary and sufficient conditions for reversibility and we point
out a formal analogy, in the N to infinity limit, with local mean field models
with conservative dynamics (an analogy that is exploited to identify in
particular a Lyapunov functional in the reversible set-up). We then focus on
the reversible Kuramoto model with sinusoidal interactions in the N to infinity
limit and analyze the stability of the non-trivial stationary profiles arising
when the interaction parameter K is larger than its critical value K_c. We
provide an analysis of the linear operator describing the time evolution in a
neighborhood of the synchronized profile: we exhibit a Hilbert space in which
this operator has a self-adjoint extension and we establish, as our main
result, a spectral gap inequality for every K>K_c.Comment: 18 pages, 1 figur
Evidence for structural and electronic instabilities at intermediate temperatures in -(BEDT-TTF)X for X=Cu[N(CN)]Cl, Cu[N(CN)]Br and Cu(NCS): Implications for the phase diagram of these quasi-2D organic superconductors
We present high-resolution measurements of the coefficient of thermal
expansion of the quasi-twodimensional
(quasi-2D) salts -(BEDT-TTF)X with X = Cu(NCS), Cu[N(CN)]Br
and Cu[N(CN)]Cl. At intermediate temperatures (B), distinct anomalies
reminiscent of second-order phase transitions have been found at
K and 45 K for the superconducting X = Cu(NCS) and Cu[N(CN)]Br salts,
respectively. Most interestingly, we find that the signs of the uniaxial
pressure coefficients of are strictly anticorrelated with those of
. We propose that marks the transition to a spin-density-wave
(SDW) state forming on minor, quasi-1D parts of the Fermi surface. Our results
are compatible with two competing order parameters that form on disjunct
portions of the Fermi surface. At elevated temperatures (C), all compounds show
anomalies that can be identified with a kinetic, glass-like
transition where, below a characteristic temperature , disorder in the
orientational degrees of freedom of the terminal ethylene groups becomes frozen
in. We argue that the degree of disorder increases on going from the X =
Cu(NCS) to Cu[N(CN)]Br and the Cu[N(CN)]Cl salt. Our results
provide a natural explanation for the unusual time- and cooling-rate
dependencies of the ground-state properties in the hydrogenated and deuterated
Cu[N(CN)]Br salts reported in the literature.Comment: 22 pages, 7 figure
Green coloring of GaN single crystals introduced by Cr impurity
In this study unintentionally doped GaN grown by hydride vapor phase epitaxy that exhibits a sharply delimited region of green color was investigated. Optical analysis was performed by absorption and photoluminescence spectroscopy. An absorption band between 1.5 and 2.0 eV was found to be responsible for the green color and was related to a sharp emission at 1.193 eV by luminescence and excitation spectroscopy. The appearance of both optical signatures in the region of green color was related to an increase of Cr contamination detected by secondary ion mass spectrometry. We propose that the origin of green color as well as the emission line at 1.193 eV is attributed to internal transitions of Cr⁴⁺
Positive Semidefiniteness and Positive Definiteness of a Linear Parametric Interval Matrix
We consider a symmetric matrix, the entries of which depend linearly on some
parameters. The domains of the parameters are compact real intervals. We
investigate the problem of checking whether for each (or some) setting of the
parameters, the matrix is positive definite (or positive semidefinite). We
state a characterization in the form of equivalent conditions, and also propose
some computationally cheap sufficient\,/\,necessary conditions. Our results
extend the classical results on positive (semi-)definiteness of interval
matrices. They may be useful for checking convexity or non-convexity in global
optimization methods based on branch and bound framework and using interval
techniques
- …