691 research outputs found
A Framework for Genetic Algorithms Based on Hadoop
Genetic Algorithms (GAs) are powerful metaheuristic techniques mostly used in
many real-world applications. The sequential execution of GAs requires
considerable computational power both in time and resources. Nevertheless, GAs
are naturally parallel and accessing a parallel platform such as Cloud is easy
and cheap. Apache Hadoop is one of the common services that can be used for
parallel applications. However, using Hadoop to develop a parallel version of
GAs is not simple without facing its inner workings. Even though some
sequential frameworks for GAs already exist, there is no framework supporting
the development of GA applications that can be executed in parallel. In this
paper is described a framework for parallel GAs on the Hadoop platform,
following the paradigm of MapReduce. The main purpose of this framework is to
allow the user to focus on the aspects of GA that are specific to the problem
to be addressed, being sure that this task is going to be correctly executed on
the Cloud with a good performance. The framework has been also exploited to
develop an application for Feature Subset Selection problem. A preliminary
analysis of the performance of the developed GA application has been performed
using three datasets and shown very promising performance
Dynamical two-mode squeezing of thermal fluctuations in a cavity opto-mechanical system
We report the experimental observation of two-mode squeezing in the
oscillation quadratures of a thermal micro-oscillator. This effect is obtained
by parametric modulation of the optical spring in a cavity opto-mechanical
system. In addition to stationary variance measurements, we describe the
dynamic behavior in the regime of pulsed parametric excitation, showing
enhanced squeezing effect surpassing the stationary 3dB limit. While the
present experiment is in the classical regime, our technique can be exploited
to produce entangled, macroscopic quantum opto-mechanical modes
Calibrated quantum thermometry in cavity optomechanics
Cavity optomechanics has achieved the major breakthrough of the preparation
and observation of macroscopic mechanical oscillators in peculiarly quantum
states. The development of reliable indicators of the oscillator properties in
these conditions is important also for applications to quantum technologies. We
compare two procedures to infer the oscillator occupation number, minimizing
the necessity of system calibrations. The former starts from homodyne spectra,
the latter is based on the measurement of the motional sidebands asymmetry in
heterodyne spectra. Moreover, we describe and discuss a method to control the
cavity detuning, that is a crucial parameter for the accuracy of the latter,
intrinsically superior procedure
Control of Recoil Losses in Nanomechanical SiN Membrane Resonators
In the context of a recoil damping analysis, we have designed and produced a
membrane resonator equipped with a specific on-chip structure working as a
"loss shield" for a circular membrane. In this device the vibrations of the
membrane, with a quality factor of , reach the limit set by the intrinsic
dissipation in silicon nitride, for all the modes and regardless of the modal
shape, also at low frequency. Guided by our theoretical model of the loss
shield, we describe the design rationale of the device, which can be used as
effective replacement of commercial membrane resonators in advanced
optomechanical setups, also at cryogenic temperatures
Corona-Australis DANCe I. Revisiting the census of stars with Gaia-DR2 data
Context. Corona-Australis is one of the nearest regions to the Sun with recent and ongoing star formation, but the current picture of its stellar (and substellar) content is not complete yet.
Aims. We take advantage of the second data release of the Gaia space mission to revisit the stellar census and search for additional members of the young stellar association in Corona-Australis.
Methods. We applied a probabilistic method to infer membership probabilities based on a multidimensional astrometric and photometric data set over a field of 128 deg(2) around the dark clouds of the region.
Results. We identify 313 high-probability candidate members to the Corona-Australis association, 262 of which had never been reported as members before. Our sample of members covers the magnitude range between G greater than or similar to 5 mag and G less than or similar to 20 mag, and it reveals the existence of two kinematically and spatially distinct subgroups. There is a distributed "off-cloud" population of stars located in the north of the dark clouds that is twice as numerous as the historically known "on-cloud" population that is concentrated around the densest cores. By comparing the location of the stars in the HR-diagram with evolutionary models, we show that these two populations are younger than 10 Myr. Based on their infrared excess emission, we identify 28 Class II and 215 Class III stars among the sources with available infrared photometry, and we conclude that the frequency of Class II stars (i.e. "disc-bearing" stars) in the on-cloud region is twice as large as compared to the off-cloud population. The distance derived for the Corona-Australis region based on this updated census is d = 149.4(-0.4)(+0.4) pc, which exceeds previous estimates by about 20 pc.
Conclusions. In this paper we provide the most complete census of stars in Corona-Australis available to date that can be confirmed with Gaia data. Furthermore, we report on the discovery of an extended and more evolved population of young stars beyond the region of the dark clouds, which was extensively surveyed in the past
Perspectivas para o uso de fungos entomopatogênicos no controle microbiano das pragas do coqueiro.
O controle de insetos-pragas por meio de agentes biológicos como os fungos entomopatogênicos e uma opção desejável para evitar aplicações químicas e aumentar a proteção ambiental.bitstream/item/68752/1/CPATC-CIR.-TEC.-26-01.pd
Optical self-cooling of a membrane oscillator in a cavity optomechanical experiment at room temperature
Thermal noise is a major obstacle to observing quantum behavior in
macroscopic systems. To mitigate its effect, quantum optomechanical experiments
are typically performed in a cryogenic environment. However, this condition
represents a considerable complication in the transition from fundamental
research to quantum technology applications. It is therefore interesting to
explore the possibility of achieving the quantum regime in room temperature
experiments. In this work we test the limits of sideband cooling vibration
modes of a SiN membrane in a cavity optomechanical experiment. We obtain an
effective temperature of a few mK, corresponding to a phononic occupation
number of around 100. We show that further cooling is prevented by the excess
classical noise of our laser source, and we outline the road toward the
achievement of ground state coolin
Customized CMOS wavefront sensor
We report on an integrated Hartmann wavefront sensor (WFS) using passive-pixel architecture and pixels clustered as position-sensitive detectors for dynamic wavefront analysis. This approach substitutes a conventional imager, such as a CCD or CMOS imager, by a customized detector, thus improving the overall speed performance. CMOS (complementary-metal- oxide-semiconductor) technology enables on-chip integration of several analog and digital circuitry. The sensor performance depends on the feature size of the technology, noise levels, photosensitive elements employed, architecture chosen and reconstruction algorithm.(undefined
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