117 research outputs found
Significance Relations for the Benchmarking of Meta-Heuristic Algorithms
The experimental analysis of meta-heuristic algorithm performance is usually
based on comparing average performance metric values over a set of algorithm
instances. When algorithms getting tight in performance gains, the additional
consideration of significance of a metric improvement comes into play. However,
from this moment the comparison changes from an absolute to a relative mode.
Here the implications of this paradigm shift are investigated. Significance
relations are formally established. Based on this, a trade-off between
increasing cycle-freeness of the relation and small maximum sets can be
identified, allowing for the selection of a proper significance level and
resulting ranking of a set of algorithms. The procedure is exemplified on the
CEC'05 benchmark of real parameter single objective optimization problems. The
significance relation here is based on awarding ranking points for relative
performance gains, similar to the Borda count voting method or the Wilcoxon
signed rank test. In the particular CEC'05 case, five ranks for algorithm
performance can be clearly identified.Comment: 6 pages, 2 figures, 1 tabl
Parallel Evolutionary Peer-to-Peer Networking in Realistic Environments
In the present paper we first conduct simulations of the parallel evolutionary peer-to-peer (P2P) networking technique (referred to as P-EP2P) that we previously proposed using models of realistic environments to examine if P-EP2P is practical. Environments are here represented by what users have and want in the network, and P-EP2P adapts the P2P network topologies to the present environment in an evolutionary manner. The simulation results show that P-EP2P is hard to adapt the network topologies to some realistic environments. Then, based on the discussions of the results, we propose a strategy for better adaptability of P-EP2P to the realistic environments. The strategy first judges if evolutionary adaptation of the network topologies is likely to occur in the present environment, and if it judges so, it actually tries to achieve evolutionary adaptation of the network topologies. Otherwise, it brings random change to the network topologies. The simulation results indicate that P-EP2P with the proposed strategy can better adapt the network topologies to the realistic environments. The main contribution of the study is to present such a promising way to realize an evolvable network in which the evolution direction is given by users
Three-Dimensional Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae
We have studied non-axisymmetric standing accretion shock instability, or
SASI, by 3D hydrodynamical simulations. This is an extention of our previous
study on axisymmetric SASI. We have prepared a spherically symmetric and steady
accretion flow through a standing shock wave onto a proto-neutron star, taking
into account a realistic equation of state and neutrino heating and cooling.
This unperturbed model is supposed to represent approximately the typical
post-bounce phase of core-collapse supernovae. We then have added a small
perturbation (~1%) to the radial velocity and computed the ensuing evolutions.
Not only axisymmetric but non-axisymmetric perturbations have been also
imposed. We have applied mode analysis to the non-spherical deformation of the
shock surface, using the spherical harmonics. We have found that (1) the growth
rates of SASI are degenerate with respect to the azimuthal index m of the
spherical harmonics Y_l^m, just as expected for a spherically symmetric
background, (2) nonlinear mode couplings produce only m=0 modes for the
axisymmetric perturbations, whereas m=!0 modes are also generated in the
non-axisymmetric cases according to the selection rule for the quadratic
couplings, (3) the nonlinear saturation level of each mode is lower in general
for 3D than for 2D because a larger number of modes are contributing to
turbulence in 3D, (4) low l modes are dominant in the nonlinear phase, (5) the
equi-partition is nearly established among different m modes in the nonlinear
phase, (6) the spectra with respect to l obey power laws with a slope slightly
steeper for 3D, and (7) although these features are common to the models with
and without a shock revival at the end of simulation, the dominance of low l
modes is more remarkable in the models with a shock revival.Comment: 37 pages, 16 figures, and 1 table, submitted to Ap
Reaction of acylsilanes with potassium cyanide: Brook rearrangement under phase-transfer catalytic conditions
The reactions of acylsilanes with KCN under liquid–liquid phase-transfer catalytic conditions proceeded smoothly via the Brook rearrangement to produce O-silylated cyanohydrin derivatives in excellent yields. We also found that α-cyano carbanions generated by the Brook rearrangement in the reaction of (β-(trimethylsilyl)acryloyl)silane 7 can undergo alkylation at the γ-position and that in the reaction of β-bromoacylsilane 14 intramolecular alkylation occurs to afford cyclopropanone cyanohydrin derivative 16
Inelastic Neutrino-Helium Scatterings and Standing Accretion Shock Instability in Core-Collapse Supernovae
We present the results of numerical experiments, in which we have
investigated the influence of the inelastic neutrino-helium interactions on the
standing accretion shock instability supposed to occur in the post-bounce
supernova core. The axisymmetric hydrodynamical simulations of accretion flows
through the standing accretion shock wave onto the protoneutron star show that
the interactions are relatively minor and the linear growth of the shock
instability is hardly affected. The extra heating given by the inelastic
reactions becomes important for the shock revival after the instability enters
the non-linear regime, but only when the neutrino luminosity is very close to
the critical value, at which the shock would be revived without the
interactions. We have also studied the dependence of the results on the initial
amplitudes of perturbation and the temperatures of mu and tau neutrinos.Comment: 19 pages, 6 figures, submitted to Ap
Effects of Rotation on Standing Accretion Shock Instability in Nonlinear Phase for Core-Collapse Supernovae
We studied the effects of rotation on standing accretion shock instability
(SASI) by performing three-dimensional hydrodynamics simulations. Taking into
account a realistic equation of state and neutrino heating/cooling, we prepared
a spherically symmmetric and steady accretion flow through a standing shock
wave onto a proto-neutron star (PNS). When the SASI entered the nonlinear
phase, we imposed uniform rotation on the flow advecting from the outer
boundary of the iron core, whose specific angular momentum was assumed to agree
with recent stellar evolution models. Using spherical harmonics in space and
Fourier decompositions in time, we performed mode analysis of the nonspherical
deformed shock wave to observe rotational effects on the SASI in the nonlinear
phase. We found that rotation imposed on the axisymmetric SASI did not make any
spiral modes and hardly affected sloshing modes, except for steady l=2, m=0
modes. In contrast, rotation imposed on the non-axisymmetric flow increased the
amplitude of spiral modes so that some spiral flows accreting on the PNS were
more clearly formed inside the shock wave than without rotation. The amplitudes
of spiral modes increased significantly with rotation in the progressive
direction.Comment: 27 pages, 11 figures, Submitted to Ap
Explosive nucleosynthesis in the neutrino-driven aspherical supernova explosion of a non-rotating 15 star with solar metallicity
We investigate explosive nucleosynthesis in a non-rotating 15 star
with solar metallicity that explodes by a neutrino-heating supernova (SN)
mechanism aided by both standing accretion shock instability (SASI) and
convection. To trigger explosions in our two-dimensional hydrodynamic
simulations, we approximate the neutrino transport with a simple light-bulb
scheme and systematically change the neutrino fluxes emitted from the
protoneutron star. By a post-processing calculation, we evaluate abundances and
masses of the SN ejecta for nuclei with the mass number employing a
large nuclear reaction network. Aspherical abundance distributions, which are
observed in nearby core-collapse SN remnants, are obtained for the non-rotating
spherically-symmetric progenitor, due to the growth of low-mode SASI. Abundance
pattern of the supernova ejecta is similar to that of the solar system for
models whose masses ranges (0.4-0.5) \Ms of the ejecta from the inner region
(\le 10,000\km) of the precollapse core. For the models, the explosion
energies and the \nuc{Ni}{56} masses are and
(0.05-0.06) \Ms, respectively; their estimated baryonic masses of the neutron
star are comparable to the ones observed in neutron-star binaries. These
findings may have little uncertainty because most of the ejecta is composed by
matter that is heated via the shock wave and has relatively definite
abundances. The abundance ratios for Ne, Mg, Si and Fe observed in Cygnus loop
are well reproduced with the SN ejecta from an inner region of the 15\Ms
progenitor.Comment: 15 pages, 1 table, 17 figures, accepted for publication in
Astrophyscal Journa
Dynamic and Decentralized Storage Load Balancing with Analogy to Thermal Diffusion for P2P File Sharing
In this paper we propose a file replication scheme inspired by a thermal diffusion phenomenon for storage load balancing in unstructured peer-to-peer (P2P) file sharing networks. The proposed scheme is designed such that the storage utilization ratios of peers will be uniform, in the same way that the temperature in a field becomes uniform in a thermal diffusion phenomenon. The proposed scheme creates replicas of files in peers probabilistically, where the probability is controlled by using parameters that can be used to find the trade-off between storage load balancing and search performance in unstructured P2P file sharing networks. First, we show through theoretical analysis that the statistical behavior of the storage load balancing controlled by the proposed scheme has an analogy with the thermal diffusion phenomenon. We then show through simulation that the proposed scheme not only has superior performance with respect to balancing the storage load among peers (the primary objective of the present proposal) but also allows the performance trade-off to be widely found. Finally, we qualitatively discuss a guideline for setting the parameter values in order to widely find the performance trade-off from the simulation results
Effects of Rotation on Stochasticity of Gravitational Waves in Nonlinear Phase of Core-Collapse Supernovae
By performing three-dimensional (3D) simulations that demonstrate the
neutrino-driven core-collapse supernovae aided by the standing accretion shock
instability (SASI), we study how the spiral modes of the SASI can have impacts
on the properties of the gravitational-wave (GW) emission. To see the effects
of rotation in the non-linear postbounce phase, we give a uniform rotation on
the flow advecting from the outer boundary of the iron core, whose specific
angular momentum is assumed to agree with recent stellar evolution models. We
compute fifteen 3D models in which the initial angular momentum as well as the
input neutrino luminosities from the protoneutron star are changed in a
systematic manner. By performing a ray-tracing analysis, we accurately estimate
the GW amplitudes generated by anisotropic neutrino emission. Our results show
that the gravitational waveforms from neutrinos in models that include rotation
exhibit a common feature otherwise they vary much more stochastically in the
absence of rotation. The breaking of the stochasticity stems from the excess of
the neutrino emission parallel to the spin axis. This is because the
compression of matter is more enhanced in the vicinity of the equatorial plane
due to the growth of the spiral SASI modes, leading to the formation of spiral
flows circulating around the spin axis with higher temperatures. We point out
that a recently proposed future space interferometers like Fabry-Perot type
DECIGO would permit detection of these signals for a Galactic supernova.Comment: 13 Figures, ApJ in pres
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