1,419 research outputs found
Evolutionary Algorithms with Self-adjusting Asymmetric Mutation
Evolutionary Algorithms (EAs) and other randomized search heuristics are
often considered as unbiased algorithms that are invariant with respect to
different transformations of the underlying search space. However, if a certain
amount of domain knowledge is available the use of biased search operators in
EAs becomes viable. We consider a simple (1+1) EA for binary search spaces and
analyze an asymmetric mutation operator that can treat zero- and one-bits
differently. This operator extends previous work by Jansen and Sudholt (ECJ
18(1), 2010) by allowing the operator asymmetry to vary according to the
success rate of the algorithm. Using a self-adjusting scheme that learns an
appropriate degree of asymmetry, we show improved runtime results on the class
of functions OneMax describing the number of matching bits with a fixed
target .Comment: 16 pages. An extended abstract of this paper will be published in the
proceedings of PPSN 202
Absolute velocity measurements in sunspot umbrae
In sunspot umbrae, convection is largely suppressed by the strong magnetic
field. Previous measurements reported on negligible convective flows in umbral
cores. Based on this, numerous studies have taken the umbra as zero reference
to calculate Doppler velocities of the ambient active region. To clarify the
amount of convective motion in the darkest part of umbrae, we directly measured
Doppler velocities with an unprecedented accuracy and precision. We performed
spectroscopic observations of sunspot umbrae with the Laser Absolute Reference
Spectrograph (LARS) at the German Vacuum Tower Telescope. A laser frequency
comb enabled the calibration of the high-resolution spectrograph and absolute
wavelength positions. A thorough spectral calibration, including the
measurement of the reference wavelength, yielded Doppler shifts of the spectral
line Ti i 5713.9 {\AA} with an uncertainty of around 5 m s-1. The measured
Doppler shifts are a composition of umbral convection and magneto-acoustic
waves. For the analysis of convective shifts, we temporally average each
sequence to reduce the superimposed wave signal. Compared to convective
blueshifts of up to -350 m s-1 in the quiet Sun, sunspot umbrae yield a
strongly reduced convective blueshifts around -30 m s-1. {W}e find that the
velocity in a sunspot umbra correlates significantly with the magnetic field
strength, but also with the umbral temperature defining the depth of the
titanium line. The vertical upward motion decreases with increasing field
strength. Extrapolating the linear approximation to zero magnetic field
reproduces the measured quiet Sun blueshift. Simply taking the sunspot umbra as
a zero velocity reference for the calculation of photospheric Dopplergrams can
imply a systematic velocity error.Comment: 10 pages, 7 figures, 2 tables, Appendix with 5 figure
Searching for Radio Pulsars in 3EG Sources at Urumqi Observatory
Since mid-2005, a pulsar searching system has been operating at 18 cm on the
25-m radio telescope of Urumqi Observatory. Test observations on known pulsars
show that the system can perform the intended task. The prospect of using this
system to observe 3EG sources and other target searching tasks is discussed.Comment: a training project about MSc thesi
Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel
We investigate a new scheme for astronomical spectrograph calibration using
the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our
concept is based upon a single-mode fiber channel, that simultaneously feeds
the spectrograph with comb light and sunlight. This yields nearly perfect
spatial mode matching between the two sources. In combination with the absolute
calibration provided by the frequency comb, this method enables extremely
robust and accurate spectroscopic measurements. The performance of this scheme
is compared to a sequence of alternating comb and sunlight, and to absorption
lines from Earth's atmosphere. We also show how the method can be used for
radial-velocity detection by measuring the well-explored 5-minute oscillations
averaged over the full solar disk. Our method is currently restricted to solar
spectroscopy, but with further evolving fiber-injection techniques it could
become an option even for faint astronomical targets.Comment: 21 pages, 11 figures. A video abstract for this paper is available on
youtube. For watching the video, please follow
https://www.youtube.com/watch?v=oshdZgrt89I . The video abstract is also
available for streaming and download on the related article website of New
Journal of Physic
Particulate emissions from large North American wildfires estimated using a new top-down method
Particulate matter emissions from wildfires affect climate, weather
and air quality. However, existing global and regional aerosol emission
estimates differ by a factor of up to 4 between different methods. Using
a novel approach, we estimate daily total particulate matter (TPM) emissions
from large wildfires in North American boreal and temperate regions. Moderate
Resolution Imaging Spectroradiometer (MODIS) fire location and aerosol
optical thickness (AOT) data sets are coupled with HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) atmospheric
dispersion simulations, attributing identified smoke plumes to sources.
Unlike previous approaches, the method (i)Â combines information from both
satellite and AERONET (AErosol RObotic NETwork) observations to take into account aerosol water uptake
and plume specific mass extinction efficiency when converting smoke AOT to
TPM, and (ii)Â does not depend on instantaneous emission rates observed during
individual satellite overpasses, which do not sample night-time emissions.
The method also allows multiple independent estimates for the same emission
period from imagery taken on consecutive days.
<br><br>
Repeated fire-emitted AOT estimates for the same emission period over 2 to 3
days of plume evolution show increases in plume optical thickness by
approximately 10 % for boreal events and by 40 % for
temperate emissions. Inferred median water volume fractions for aged
boreal and temperate smoke observations are 0.15 and 0.47 respectively,
indicating that the increased AOT is partly explained by aerosol water
uptake. TPM emission estimates for boreal events, which predominantly
burn during daytime, agree closely with bottom-up Global
Fire Emission Database (GFEDv4) and Global Fire Assimilation System
(GFASv1.0) inventories, but are lower by approximately 30 % compared
to Quick Fire Emission Dataset (QFEDv2) PM<sub>2. 5</sub>,
and are higher by approximately a factor of 2 compared to Fire Energetics and
Emissions Research (FEERv1) TPM estimates. The discrepancies are
larger for temperate fires, which are characterized by lower median
fire radiative power values and more significant night-time combustion. The TPM
estimates for this study for the biome are lower than QFED PM<sub>2. 5</sub> by
35 %, and are larger by factors of 2.4, 3.2 and 4
compared with FEER, GFED and GFAS inventories respectively. A large
underestimation of TPM emission by bottom-up GFED and GFAS indicates
low biases in emission factors or consumed biomass estimates for temperate
fires
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
Ring Migration Topology Helps Bypassing Local Optima
Running several evolutionary algorithms in parallel and occasionally
exchanging good solutions is referred to as island models. The idea is that the
independence of the different islands leads to diversity, thus possibly
exploring the search space better. Many theoretical analyses so far have found
a complete (or sufficiently quickly expanding) topology as underlying migration
graph most efficient for optimization, even though a quick dissemination of
individuals leads to a loss of diversity. We suggest a simple fitness function
FORK with two local optima parametrized by and a scheme for
composite fitness functions. We show that, while the (1+1) EA gets stuck in a
bad local optimum and incurs a run time of fitness evaluations
on FORK, island models with a complete topology can achieve a run time of
by making use of rare migrations in order to explore the
search space more effectively. Finally, the ring topology, making use of rare
migrations and a large diameter, can achieve a run time of
, the black box complexity of FORK. This shows that the
ring topology can be preferable over the complete topology in order to maintain
diversity.Comment: 12 page
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