1,850 research outputs found
Financial correlations at ultra-high frequency: theoretical models and empirical estimation
A detailed analysis of correlation between stock returns at high frequency is
compared with simple models of random walks. We focus in particular on the
dependence of correlations on time scales - the so-called Epps effect. This
provides a characterization of stochastic models of stock price returns which
is appropriate at very high frequency.Comment: 22 pages, 8 figures, 1 table, version to appear in EPJ
Enhanced thermal stability and spin-lattice relaxation rate of N@C60 inside carbon nanotubes
We studied the temperature stability of the endohedral fullerene molecule,
N@C60, inside single-wall carbon nanotubes using electron spin resonance
spectroscopy. We found that the nitrogen escapes at higher temperatures in the
encapsulated material as compared to its pristine, crystalline form. The
temperature dependent spin-lattice relaxation time, T_1, of the encapsulated
molecule is significantly shorter than that of the crystalline material, which
is explained by the interaction of the nitrogen spin with the conduction
electrons of the nanotubes.Comment: 5 pages, 4 figures, 1 tabl
A nonperturbative study of phase transitions in the multi-frequency sine-Gordon model
The phase spaces of the two- and three-frequency sine-Gordon models are
examined in the framework of truncated conformal space approach. The focus is
mainly on a tricritical point in the phase space of the three-frequency model.
We give substantial evidence that this point exists. We also find the critical
line in the phase space and present TCSA data showing the change of the
spectrum on the critical line as the tricritical endpoint is approached. We
find a few points of the line of first order transition as well.Comment: 26 pages, LaTeX, minor modificatio
Multiscaled Cross-Correlation Dynamics in Financial Time-Series
The cross correlation matrix between equities comprises multiple interactions
between traders with varying strategies and time horizons. In this paper, we
use the Maximum Overlap Discrete Wavelet Transform to calculate correlation
matrices over different timescales and then explore the eigenvalue spectrum
over sliding time windows. The dynamics of the eigenvalue spectrum at different
times and scales provides insight into the interactions between the numerous
constituents involved.
Eigenvalue dynamics are examined for both medium and high-frequency equity
returns, with the associated correlation structure shown to be dependent on
both time and scale. Additionally, the Epps effect is established using this
multivariate method and analyzed at longer scales than previously studied. A
partition of the eigenvalue time-series demonstrates, at very short scales, the
emergence of negative returns when the largest eigenvalue is greatest. Finally,
a portfolio optimization shows the importance of timescale information in the
context of risk management
Fluid/solid transition in a hard-core system
We prove that a system of particles in the plane, interacting only with a
certain hard-core constraint, undergoes a fluid/solid phase transition
Effect of Silybum Marianum (L.) Gaertn. on germination, early growth and nutrient uptake of Zea Mays. L.
Linear parameter-varying subspace identification: A unified framework
In this paper, we establish a unified framework for subspace identification
(SID) of linear parameter-varying (LPV) systems to estimate LPV state-space
(SS) models in innovation form. This framework enables us to derive novel LPV
SID schemes that are extensions of existing linear time-invariant (LTI)
methods. More specifically, we derive the open-loop, closed-loop, and
predictor-based data-equations, an input-output surrogate form of the SS
representation, by systematically establishing an LPV subspace identification
theory. We show the additional challenges of the LPV setting compared to the
LTI case. Based on the data-equations, several methods are proposed to estimate
LPV-SS models based on a maximum-likelihood or a realization based argument.
Furthermore, the established theoretical framework for the LPV subspace
identification problem allows us to lower the number of to-be-estimated
parameters and to overcome dimensionality problems of the involved matrices,
leading to a decrease in the computational complexity of LPV SIDs in general.
To the authors' knowledge, this paper is the first in-depth examination of the
LPV subspace identification problem. The effectiveness of the proposed subspace
identification methods are demonstrated and compared with existing methods in a
Monte Carlo study of identifying a benchmark MIMO LPV system.Comment: 15 pages, 2 figures, 2 table
LUCAS Soil Component: proposal for analysing new physical, chemical and biological soil parameters
Excited Random Walk in One Dimension
We study the excited random walk, in which a walk that is at a site that
contains cookies eats one cookie and then hops to the right with probability p
and to the left with probability q=1-p. If the walk hops onto an empty site,
there is no bias. For the 1-excited walk on the half-line (one cookie initially
at each site), the probability of first returning to the starting point at time
t scales as t^{-(2-p)}. Although the average return time to the origin is
infinite for all p, the walk eats, on average, only a finite number of cookies
until this first return when p<1/2. For the infinite line, the probability
distribution for the 1-excited walk has an unusual anomaly at the origin. The
positions of the leftmost and rightmost uneaten cookies can be accurately
estimated by probabilistic arguments and their corresponding distributions have
power-law singularities near the origin. The 2-excited walk on the infinite
line exhibits peculiar features in the regime p>3/4, where the walk is
transient, including a mean displacement that grows as t^{nu}, with nu>1/2
dependent on p, and a breakdown of scaling for the probability distribution of
the walk.Comment: 14 pages, 13 figures, 2-column revtex4 format, for submission to J.
Phys.
DoOP: Databases of Orthologous Promoters, collections of clusters of orthologous upstream sequences from chordates and plants
DoOP (http://doop.abc.hu/) is a database of eukaryotic promoter sequences (upstream regions) aiming to facilitate the recognition of regulatory sites conserved between species. The annotated first exons of human and Arabidopsis thaliana genes were used as queries in BLAST searches to collect the most closely related orthologous first exon sequences from Chordata and Viridiplantae species. Up to 3000 bp DNA segments upstream from these first exons constitute the clusters in the chordate and plant sections of the Database of Orthologous Promoters. Release 1.0 of DoOP contains 21 061 chordate clusters from 284 different species and 7548 plant clusters from 269 different species. The database can be used to find and retrieve promoter sequences of a given gene from various species and it is also suitable to see the most trivial conserved sequence blocks in the orthologous upstream regions. Users can search DoOP with either sequence or text (annotation) to find promoter clusters of various genes. In addition to the sequence data, the positions of the conserved sequence blocks derived from multiple alignments, the positions of repetitive elements and the positions of transcription start sites known from the Eukaryotic Promoter Database (EPD) can be viewed graphically
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