1,469 research outputs found
A new code for Fourier-Legendre analysis of large datasets: first results and a comparison with ring-diagram analysis
Fourier-Legendre decomposition (FLD) of solar Doppler imaging data is a
promising method to estimate the sub-surface solar meridional flow. FLD is
sensible to low-degree oscillation modes and thus has the potential to probe
the deep meridional flow. We present a newly developed code to be used for
large scale FLD analysis of helioseismic data as provided by the Global
Oscillation Network Group (GONG), the Michelson Doppler Imager (MDI)
instrument, and the upcoming Helioseismic and Magnetic Imager (HMI) instrument.
First results obtained with the new code are qualitatively comparable to those
obtained from ring-diagram analyis of the same time series.Comment: 4 pages, 2 figures, 4th HELAS International Conference "Seismological
Challenges for Stellar Structure", 1-5 February 2010, Arrecife, Lanzarote
(Canary Islands
The photospheric solar oxygen project: III. Investigation of the centre-to-limb variation of the 630nm [OI]-NiI blend
The solar photospheric abundance of oxygen is still a matter of debate. For
about ten years some determinations have favoured a low oxygen abundance which
is at variance with the value inferred by helioseismology. Among the oxygen
abundance indicators, the forbidden line at 630nm has often been considered the
most reliable even though it is blended with a NiI line. In Papers I and Paper
II of this series we reported a discrepancy in the oxygen abundance derived
from the 630nm and the subordinate [OI] line at 636nm in dwarf stars, including
the Sun. Here we analyse several, in part new, solar observations of the the
centre-to-limb variation of the spectral region including the blend at 630nm in
order to separate the individual contributions of oxygen and nickel. We analyse
intensity spectra observed at different limb angles in comparison with line
formation computations performed on a CO5BOLD 3D hydrodynamical simulation of
the solar atmosphere. The oxygen abundances obtained from the forbidden line at
different limb angles are inconsistent if the commonly adopted nickel abundance
of 6.25 is assumed in our local thermodynamic equilibrium computations. With a
slightly lower nickel abundance, A(Ni)~6.1, we obtain consistent fits
indicating an oxygen abundance of A(O)=8.73+/-0.05. At this value the
discrepancy with the subordinate oxygen line remains. The derived value of the
oxygen abundance supports the notion of a rather low oxygen abundance in the
solar hotosphere. However, it is disconcerting that the forbidden oxygen lines
at 630 and 636nm give noticeably different results, and that the nickel
abundance derived here from the 630nm blend is lower than expected from other
nickel lines.Comment: to appear in A&
Critical properties of the double exchange ferromagnet Nd0.4Pb0.4MnO3
Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3
single crystal in the temperature range around T_C (Curie temperature) which
embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported.
The magnetic data analyzed in the critical region using the Kouvel-Fisher
method give the values for the T_C =156.47 +/- 0.06 K and the critical
exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of
magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of
initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547
+/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical
exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b
f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The
exponent values are very close to those expected for the universality class of
3D Heisenberg ferromagnets with short-range interactions.Comment: 19 pages, including 6 figure
Solitonic spin-liquid state due to the violation of the Lifshitz condition in FeTe
A combination of phenomenological analysis and M\"ossbauer spectroscopy
experiments on the tetragonal FeTe system indicates that the magnetic
ordering transition in compounds with higher Fe-excess, 0.11, is
unconventional. Experimentally, a liquid-like magnetic precursor with
quasi-static spin-order is found from significantly broadened M\"ossbauer
spectra at temperatures above the antiferromagnetic transition. The
incommensurate spin-density wave (SDW) order in FeTe is described by a
magnetic free energy that violates the weak Lifshitz condition in the Landau
theory of second-order transitions. The presence of multiple Lifshitz
invariants provides the mechanism to create multidimensional, twisted, and
modulated solitonic phases.Comment: 5 pages, 2 figure
The Univariate Marginal Distribution Algorithm Copes Well With Deception and Epistasis
In their recent work, Lehre and Nguyen (FOGA 2019) show that the univariate
marginal distribution algorithm (UMDA) needs time exponential in the parent
populations size to optimize the DeceptiveLeadingBlocks (DLB) problem. They
conclude from this result that univariate EDAs have difficulties with deception
and epistasis.
In this work, we show that this negative finding is caused by an unfortunate
choice of the parameters of the UMDA. When the population sizes are chosen
large enough to prevent genetic drift, then the UMDA optimizes the DLB problem
with high probability with at most fitness
evaluations. Since an offspring population size of order
can prevent genetic drift, the UMDA can solve the DLB problem with fitness evaluations. In contrast, for classic evolutionary algorithms no
better run time guarantee than is known (which we prove to be tight
for the EA), so our result rather suggests that the UMDA can cope
well with deception and epistatis.
From a broader perspective, our result shows that the UMDA can cope better
with local optima than evolutionary algorithms; such a result was previously
known only for the compact genetic algorithm. Together with the lower bound of
Lehre and Nguyen, our result for the first time rigorously proves that running
EDAs in the regime with genetic drift can lead to drastic performance losses
Effect of Particle Size on Droplet Infiltration into Hydrophobic Porous Media As a Model of Water Repellent Soil
The wettability of soil is of great importance for plants and soil biota, and in determining the risk for preferential flow, surface runoff, flooding,and soil erosion. The molarity of ethanol droplet (MED) test is widely used for quantifying the severity of water repellency in soils that show reduced wettability and is assumed to be independent of soil particle size. The minimum ethanol concentration at which droplet penetration occurs within a short time (â€10 s) provides an estimate of the initial advancing contact angle at which spontaneous wetting is expected. In this study, we test the assumption of particle size independence using a simple model of soil, represented by layers of small (0.2â2 mm) diameter beads that predict the effect of changing bead radius in the top layer on capillary driven imbibition. Experimental results using a three-layer bead system show broad agreement with the model and demonstrate a dependence of the MED test on particle size. The results show that the critical initial advancing contact angle for penetration can be considerably less than 90° and varies with particle size, demonstrating that a key assumption currently used in the MED testing of soil is not necessarily valid
Ontology: A Linked Data Hub for Mathematics
In this paper, we present an ontology of mathematical knowledge concepts that
covers a wide range of the fields of mathematics and introduces a balanced
representation between comprehensive and sensible models. We demonstrate the
applications of this representation in information extraction, semantic search,
and education. We argue that the ontology can be a core of future integration
of math-aware data sets in the Web of Data and, therefore, provide mappings
onto relevant datasets, such as DBpedia and ScienceWISE.Comment: 15 pages, 6 images, 1 table, Knowledge Engineering and the Semantic
Web - 5th International Conferenc
- âŠ