8,394 research outputs found
Continuous function optimization using hybrid ant colony approach with orthogonal design scheme
A hybrid Orthogonal Scheme Ant Colony Optimization (OSACO) algorithm for continuous function optimization (CFO) is presented in this paper. The methodology integrates the advantages of Ant Colony Optimization (ACO) and Orthogonal Design Scheme (ODS). OSACO is based on the following principles: a) each independent variable space (IVS) of CFO is dispersed into a number of random and movable nodes; b) the carriers of pheromone of ACO are shifted to the nodes; c) solution path can be obtained by choosing one appropriate node from each IVS by ant; d) with the ODS, the best solved path is further improved. The proposed algorithm has been successfully applied to 10 benchmark test functions. The performance and a comparison with CACO and FEP have been studied
Resolved Kinematics of Runaway and Field OB Stars in the Small Magellanic Cloud
We use GAIA DR2 proper motions of the RIOTS4 field OB stars in the Small
Magellanic Cloud (SMC) to study the kinematics of runaway stars. The data
reveal that the SMC Wing has a systemic peculiar motion relative to the SMC Bar
of (v_RA, v_Dec) = (62 +/-7, -18+/-5) km/s and relative radial velocity +4.5
+/- 5.0 km/s. This unambiguously demonstrates that these two regions are
kinematically distinct: the Wing is moving away from the Bar, and towards the
Large Magellanic Cloud with a 3-D velocity of 64 +/- 10 km/s. This is
consistent with models for a recent, direct collision between the Clouds. We
present transverse velocity distributions for our field OB stars, confirming
that unbound runaways comprise on the order of half our sample, possibly more.
Using eclipsing binaries and double-lined spectroscopic binaries as tracers of
dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers
of runaways accelerated by supernova kicks, we find significant contributions
from both populations. The data suggest that HMXBs have lower velocity
dispersion relative to dynamically ejected binaries, consistent with the former
corresponding to less energetic supernova kicks that failed to unbind the
components. Evidence suggests that our fast runaways are dominated by
dynamical, rather than supernova, ejections.Comment: Accepted to ApJ Letters. 10 pages, 4 figure
Solving Optimization Problems by the Public Goods Game
This document is the Accepted Manuscript version of the following article: Marco Alberto Javarone, ‘Solving optimization problems by the public goods game’, The European Physical Journal B, 90:17, September 2017. Under embargo. Embargo end date: 18 September 2018. The final, published version is available online at doi: https://doi.org/10.1140/epjb/e2017-80346-6. Published by Springer Berlin Heidelberg.We introduce a method based on the Public Goods Game for solving optimization tasks. In particular, we focus on the Traveling Salesman Problem, i.e. a NP-hard problem whose search space exponentially grows increasing the number of cities. The proposed method considers a population whose agents are provided with a random solution to the given problem. In doing so, agents interact by playing the Public Goods Game using the fitness of their solution as currency of the game. Notably, agents with better solutions provide higher contributions, while those with lower ones tend to imitate the solution of richer agents for increasing their fitness. Numerical simulations show that the proposed method allows to compute exact solutions, and suboptimal ones, in the considered search spaces. As result, beyond to propose a new heuristic for combinatorial optimization problems, our work aims to highlight the potentiality of evolutionary game theory beyond its current horizons.Peer reviewedFinal Accepted Versio
Runaway OB Stars in the Small Magellanic Cloud: Dynamical Versus Supernova Ejections
Runaway OB stars are ejected from their parent clusters via two mechanisms,
both involving multiple stars: the dynamical ejection scenario (DES) and the
binary supernova scenario (BSS). We constrain the relative contributions from
these two ejection mechanisms in the Small Magellanic Cloud (SMC) using data
for 304 field OB stars from the spatially complete, Runaways and Isolated
O-Type Star Spectroscopic Survey of the SMC (RIOTS4). We obtain stellar masses
and projected rotational velocities for the sample using RIOTS4
spectra, and use transverse velocities from DR2
proper motions. Kinematic analyses of the masses, , non-compact
binaries, high-mass X-ray binaries, and Oe/Be stars largely support predictions
for the statistical properties of the DES and BSS populations. We find that
dynamical ejections dominate over supernova ejections by a factor of
in the SMC, and our results suggest a high frequency of DES runaways and binary
ejections. Objects seen as BSS runaways also include two-step ejections of
binaries that are reaccelerated by SN kicks. We find that two-step runaways
likely dominate the BSS runaway population. Our results further imply that any
contribution from field OB star formation is small. Finally, our
data strongly support the post-mass-transfer model for the origin of classical
Oe/Be stars, providing a simple explanation for the bimodality in the distribution and high, near-critical, Oe/Be rotation velocities. The close
correspondence of Oe/Be stars with BSS predictions implies that the
emission-line disks are long-lived.Comment: 20 pages, 7 figures, 3 tables. Accepted by Ap
Neuronal assembly dynamics in supervised and unsupervised learning scenarios
The dynamic formation of groups of neurons—neuronal assemblies—is believed to mediate cognitive phenomena at many levels, but their detailed operation and mechanisms of interaction are still to be uncovered. One hypothesis suggests that synchronized oscillations underpin their formation and functioning, with a focus on the temporal structure of neuronal signals. In this context, we investigate neuronal assembly dynamics in two complementary scenarios: the first, a supervised spike pattern classification task, in which noisy variations of a collection of spikes have to be correctly labeled; the second, an unsupervised, minimally cognitive evolutionary robotics tasks, in which an evolved agent has to cope with multiple, possibly conflicting, objectives. In both cases, the more traditional dynamical analysis of the system’s variables is paired with information-theoretic techniques in order to get a broader picture of the ongoing interactions with and within the network. The neural network model is inspired by the Kuramoto model of coupled phase oscillators and allows one to fine-tune the network synchronization dynamics and assembly configuration. The experiments explore the computational power, redundancy, and generalization capability of neuronal circuits, demonstrating that performance depends nonlinearly on the number of assemblies and neurons in the network and showing that the framework can be exploited to generate minimally cognitive behaviors, with dynamic assembly formation accounting for varying degrees of stimuli modulation of the sensorimotor interactions
Response Ant Colony Optimization of End Milling Surface Roughness
Metal cutting processes are important due to increased consumer demands for quality metal cutting related products (more precise tolerances and better product surface roughness) that has driven the metal cutting industry to continuously improve quality control of metal cutting processes. This paper presents optimum surface roughness by using milling mould aluminium alloys (AA6061-T6) with Response Ant Colony Optimization (RACO). The approach is based on Response Surface Method (RSM) and Ant Colony Optimization (ACO). The main objectives to find the optimized parameters and the most dominant variables (cutting speed, feedrate, axial depth and radial depth). The first order model indicates that the feedrate is the most significant factor affecting surface roughness
Alternative hybrid reconstruction for bilateral common and internal iliac artery aneurysms associated with external iliac artery occlusion
Purpose: To describe an alternative reconstruction for bilateral common (CIA) and internal
(IIA) iliac artery aneurysms associated with external iliac artery (EIA) occlusion in a patient
unfit for open surgery.
Case Report: A high-risk 81-year-old man presented with contained rupture of a left CIA
aneurysm in the presence of bilateral CIA and IIA aneurysms associated with complete
occlusion of the left EIA and normal patency of both common femoral arteries. In an
emergent procedure, the left EIA was recanalized subintimally, and the right IIA was
embolized with a 14-mm Amplatzer Plug. The main body of a standard Excluder endograft
was deployed just distal to the origin of the left renal artery, and the ipsilateral leg was
extended into the proximal right EIA. On the contralateral side, a short 10-mm-diameter
limb was inserted through a 12-F sheath and deployed in the CIA, proximal to the iliac
bifurcation. Via a percutaneous left brachial artery access, 3 covered stents (9359 mm,
10359 mm, 10359 mm) were deployed from the distal IIA to the endograft contralateral
limb. A right-to-left femorofemoral crossover bypass graft concluded the operation. The
patient was discharged on the 5th postoperative day without complications; follow-up
imaging at 6 months showed patency of the stent-graft and crossover bypass, with
complete exclusion of the aneurysms and no evidence of endoleak.
Conclusion: This case demonstrates an effective solution for complex aortoiliac lesions
using commercially available devices, underlining how an accurate knowledge of
alternative endovascular techniques and materials is crucial in the management of
complex cases
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