3,462 research outputs found
Auto-tuning Distributed Stream Processing Systems using Reinforcement Learning
Fine tuning distributed systems is considered to be a craftsmanship, relying
on intuition and experience. This becomes even more challenging when the
systems need to react in near real time, as streaming engines have to do to
maintain pre-agreed service quality metrics. In this article, we present an
automated approach that builds on a combination of supervised and reinforcement
learning methods to recommend the most appropriate lever configurations based
on previous load. With this, streaming engines can be automatically tuned
without requiring a human to determine the right way and proper time to deploy
them. This opens the door to new configurations that are not being applied
today since the complexity of managing these systems has surpassed the
abilities of human experts. We show how reinforcement learning systems can find
substantially better configurations in less time than their human counterparts
and adapt to changing workloads
The use of geographic information systems for the optimal location of biomass power plants in the Madrid Community (Spain)
This article has been extracted from the results of a thesis entitled âPotential bioelectricity production of the
Madrid Community Agricultural Regions based on rye and triticale biomass.â The aim was, first, to quantify the potential of rye (Secale Cereale L.) and triticale (
Triticosecale Aestivum L.) biomass in each of the Madrid Community agricultural regions, and second, to locate the
most suitable areas for the installation of power plants using biomass. At least 17,339.9 t d.m. of rye and triticale would be required to satisfy the biomass needs of a 2.2 MW power plant, (considering an efficiency of 21.5%, 8,000 expected operating hours/year and a biomass LCP of 4,060 kcal/kg for both crops), and 2,577 ha would be used (which represent 2.79% of the Madrid Community fallow dry land surface). Biomass yields that could be achieved in Madrid Community using 50% of the fallow dry land surface (46,150 ha representing 5.75% of the Community area), based on rye and triticale crops, are estimated at 84,855, 74,906, 70,109, 50,791, 13,481, and 943 t annually for the Campiña, Vegas, Sur Occidental, Ărea Metropolitana, Lozoya-Somosierra, and Guadarrama regions. The latter represents a bioelectricity potential of 10.77, 9.5, 8.9, 6.44, 1.71, and 0.12 MW, respectively
Discovery of kilogauss magnetic fields in three DA white dwarfs
We have detected longitudinal magnetic fields between 2 and 4 kG in three (WD
0446790, WD 1105048, WD 2359434) out of a sample of 12 normal DA white
dwarfs by using optical spectropolarimetry done with the VLT Antu 8 m telescope
equipped with FORS1. With the exception of 40 Eri B (4 kG) these are the first
positive detections of magnetic fields in white dwarfs below 30 kG. Although
suspected, it was not clear whether a significant fraction of white dwarfs
contain magnetic fields at this level. These fields may be explained as fossil
relics from magnetic fields in the main-sequence progenitors considerably
enhanced by magnetic flux conservation during the shrinkage of the core. A
detection rate of 25 % (3/12) may indicate now for the first time that a
substantial fraction of white dwarfs have a weak magnetic field. This result,
if confirmed by future observations, would form a cornerstone for our
understanding on the evolution of stellar magnetic fields.
Keywords: stars: white dwarfs - stars: magnetic fields - stars: individual:
WD0446-790, WD1105-048, WD2359-434Comment: 15 pages, 7 figures, Astronomy and Astrophysics, in pres
The swastika as representation of the Sun of Helios and Mithras
At the 20th International Conference of the European Society for Astronomy in Cul- ture, held in Slovenia in 2012, Reza Assasi (2013) presented the paper âSwastika: The For- gotten Constellation Representing the Chariot of Mithrasâ, in which he identified Mithras and his quadriga with the constellation Draco, centre of the zodiac in the map of the stars. Thus he proposed a new interpretation that contradicted that accepted by researchers of the Mithraic religion who associate Mithras with the sun.
This article aims to show that, contrary to this new interpretation, Mithras should still be identified with the solar deity. Mithraic iconography and liturgy is analysed in the present work, paying special attention to the relationship between the two solar deities Helios and Mithras. The context in which the swastika is depicted is analysed, demon- strating that it never represented a constellation but instead represented the sun. We fol- low the theory of David Ulansey (1994), which asserts that Mithras should be identified with the âhypercosmic sunâ, the sphere of fire which Greek philosophers located beyond the starry heavens
Analyzing online search patterns of music festival tourists
Music festivals, as cultural events that induce tourism flows, intermediate both the cultural and travel experience. The present study analyzes online search behavior of potential attenders to a music festival. We hypothesize that the search process reveals latent patterns of behavior of cultural tourists planning to attend music festivals. To this end, information from Google Trends on queries related to three popular music festivals is used to build a network of search topics. Based on it, alternative exponential random graph model specifications are estimated. Findings support the general result of mediated information flows: music festivals induce planning and traveling queries. However, differences relating to the specificities of the cultural event are also found, in particular those regarding what nodes or queries supply the network with more useful information
Direct estimation of electron density in the Orion Bar PDR from mm-wave carbon recombination lines
A significant fraction of the molecular gas in star-forming regions is
irradiated by stellar UV photons. In these environments, the electron density
(n_e) plays a critical role in the gas dynamics, chemistry, and collisional
excitation of certain molecules. We determine n_e in the prototypical strongly
irradiated photodissociation region (PDR), the Orion Bar, from the detection of
new millimeter-wave carbon recombination lines (mmCRLs) and existing far-IR
[13CII] hyperfine line observations. We detect 12 mmCRLs (including alpha,
beta, and gamma transitions) observed with the IRAM 30m telescope, at ~25''
angular resolution, toward the H/H2 dissociation front (DF) of the Bar. We also
present a mmCRL emission cut across the PDR. These lines trace the C+/C/CO gas
transition layer. As the much lower frequency carbon radio recombination lines,
mmCRLs arise from neutral PDR gas and not from ionized gas in the adjacent HII
region. This is readily seen from their narrow line profiles (dv=2.6+/-0.4
km/s) and line peak LSR velocities (v_LSR=+10.7+/-0.2 km/s). Optically thin
[13CII] hyperfine lines and molecular lines - emitted close to the DF by trace
species such as reactive ions CO+ and HOC+ - show the same line profiles. We
use non-LTE excitation models of [13CII] and mmCRLs and derive n_e = 60-100
cm^-3 and T_e = 500-600 K toward the DF. The inferred electron densities are
high, up to an order of magnitude higher than previously thought. They provide
a lower limit to the gas thermal pressure at the PDR edge without using
molecular tracers. We obtain P_th > (2-4)x10^8 cm^-3 K assuming that the
electron abundance is equal or lower than the gas-phase elemental abundance of
carbon. Such elevated thermal pressures leave little room for magnetic pressure
support and agree with a scenario in which the PDR photoevaporates.Comment: Accepted for publication in A&A Letters (includes language editor
corrections
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