2,051 research outputs found
Counting Causal Paths in Big Times Series Data on Networks
Graph or network representations are an important foundation for data mining
and machine learning tasks in relational data. Many tools of network analysis,
like centrality measures, information ranking, or cluster detection rest on the
assumption that links capture direct influence, and that paths represent
possible indirect influence. This assumption is invalidated in time-stamped
network data capturing, e.g., dynamic social networks, biological sequences or
financial transactions. In such data, for two time-stamped links (A,B) and
(B,C) the chronological ordering and timing determines whether a causal path
from node A via B to C exists. A number of works has shown that for that reason
network analysis cannot be directly applied to time-stamped network data.
Existing methods to address this issue require statistics on causal paths,
which is computationally challenging for big data sets.
Addressing this problem, we develop an efficient algorithm to count causal
paths in time-stamped network data. Applying it to empirical data, we show that
our method is more efficient than a baseline method implemented in an
OpenSource data analytics package. Our method works efficiently for different
values of the maximum time difference between consecutive links of a causal
path and supports streaming scenarios. With it, we are closing a gap that
hinders an efficient analysis of big time series data on complex networks.Comment: 10 pages, 2 figure
Giant Carrier Mobility in Single Crystals of FeSb2
We report the giant carrier mobility in single crystals of FeSb2. Nonlinear
field dependence of Hall resistivity is well described with the two-carrier
model. Maximum mobility values in high mobility band reach ~10^5 cm^2/Vs at 8
K, and are ~10^2 cm^2/Vs at the room temperature. Our results point to a class
of materials with promising potential for applications in solid state
electronics.Comment: 5 pages, 3 figures. Applied Physics Letters (in press
Optical investigation of the metal-insulator transition in
We present a comprehensive optical study of the narrow gap
semiconductor. From the optical reflectivity, measured from the far infrared up
to the ultraviolet spectral range, we extract the complete absorption spectrum,
represented by the real part of the complex optical
conductivity. With decreasing temperature below 80 K, we find a progressive
depletion of below cm, the
semiconducting optical gap. The suppressed (Drude) spectral weight within the
gap is transferred at energies and also partially piles up over a
continuum of excitations extending in the spectral range between zero and
. Moreover, the interaction of one phonon mode with this continuum leads
to an asymmetric phonon shape. Even though several analogies between
and were claimed and a Kondo-insulator scenario was also invoked for
both systems, our data on differ in several aspects from those of
. The relevance of our findings with respect to the Kondo insulator
description will be addressed.Comment: 17 pages, 5 figure
Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2
We have investigated anisotropy in magnetic and electrical transport
properties of Fe1-xCrxSb2 (0<= x <=1) single crystals. The magnetic ground
state of the system evolves from paramagnetic to antiferromagnetic with gradual
substitution of Fe with Cr. Anisotropy in electrical transport diminishes with
increased Cr substitution and fades away by x=0.5. We find that the variable
range hopping (VRH) conduction mechanism dominates at low temperatures for
0.4<= x <=0.75.Comment: 5 pages, 6 figure
Evidence for electron-phonon interaction in FeMSb (M=Co, Cr) single crystals
We have measured polarized Raman scattering spectra of the
FeCoSb and FeCrSb (00.5)
single crystals in the temperature range between 15 K and 300 K. The highest
energy symmetry mode shows significant line asymmetry due to phonon
mode coupling width electronic background. The coupling constant achieves the
highest value at about 40 K and after that it remains temperature independent.
Origin of additional mode broadening is pure anharmonic. Below 40 K the
coupling is drastically reduced, in agreement with transport properties
measurements. Alloying of FeSb with Co and Cr produces the B mode
narrowing, i.e. weakening of the electron-phonon interaction. In the case of
A symmetry modes we have found a significant mode mixing
Wind Turbine Optimal Control During Storms
This paper proposes a control algorithm that enables wind turbine operation in high winds. With this objective, an online optimization procedure is formulated that, based on the wind turbine state, estimates those extremal wind speed variations that would produce maximal allowable wind turbine loads. Optimization results are compared to the actual wind speed and, if there is a danger of excessive loading, the wind turbine power reference is adjusted to ensure that loads stay within allowed limits. This way, the machine can operate safely even above the cut-out wind speed, thereby realizing a soft envelope-protecting cut-out. The proposed control strategy is tested and verified using a high-fidelity aeroservoelastic simulation model
121,123Sb NQR as a microscopic probe in Te doped correlated semimetal FeSb2 : emergence of electronic Griffith phase, magnetism and metallic behavior %
nuclear quadrupole resonance (NQR) was applied to
in the low doping regime (\emph{x = 0, 0.01} and
\emph{0.05}) as a microscopic zero field probe to study the evolution of
\emph{3d} magnetism and the emergence of metallic behavior. Whereas the NQR
spectra itself reflects the degree of local disorder via the width of the
individual NQR lines, the spin lattice relaxation rate (SLRR) probes
the fluctuations at the - site. The fluctuations originate either from
conduction electrons or from magnetic moments. In contrast to the semi metal
with a clear signature of the charge and spin gap formation in
, the 1\% doped system exhibits
almost metallic conductivity and a almost filled gap. A weak divergence of the
SLRR coefficient points towards the
presence of electronic correlations towards low temperatures wheras the
\textit{5\%} doped sample exhibits a much larger divergence in the SLRR
coefficient showing . According to the specific heat
divergence a power law with is expected for the SLRR.
Furthermore -doped as a disordered paramagnetic metal might be a
platform for the electronic Griffith phase scenario. NQR evidences a
substantial asymmetric broadening of the NQR spectrum for the
\emph{5\%} sample. This has purely electronic origin in agreement with the
electronic Griffith phase and stems probably from an enhanced - bond
polarization and electronic density shift towards the atom inside
- dumbbell
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