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131.
Genetic algorithms are commonly used metaheuristics for global optimization, but there has been very little research done
on the generation of their initial population. In this paper, we look for an answer to the question whether the initial population
plays a role in the performance of genetic algorithms and if so, how it should be generated. We show with a simple example
that initial populations may have an effect on the best objective function value found for several generations. Traditionally,
initial populations are generated using pseudo random numbers, but there are many alternative ways. We study the properties
of different point generators using four main criteria: the uniform coverage and the genetic diversity of the points as well
as the speed and the usability of the generator. We use the point generators to generate initial populations for a genetic
algorithm and study what effects the uniform coverage and the genetic diversity have on the convergence and on the final objective
function values. For our tests, we have selected one pseudo and one quasi random sequence generator and two spatial point
processes: simple sequential inhibition process and nonaligned systematic sampling. In numerical experiments, we solve a set
of 52 continuous test functions from 16 different function families, and analyze and discuss the results. 相似文献
132.
133.
Photoluminescence enhancement by localized surface plasmons in AlGaN/GaN/AlGaN double heterostructures
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Alexander Y. Polyakov Jin‐Hyeon Yun Haeng‐Keun Ahn Alexander S. Usikov Eugene B. Yakimov Sergey A. Tarelkin Nikolai B. Smirnov Kirill D. Shcherbachev Heikki Helava Yuri N. Makarov Sergey Yu Kurin Sergey I. Didenko Boris P. Papchenko In‐Hwan Lee 《固体物理学:研究快报》2015,9(10):575-579
Double heterostructures AlGaN/GaN/AlGaN grown by hydride vapor phase epitaxy and designed for use as light emitting diodes for 360 nm wavelength were patterned by shallow nanoholes and injected with Ag/SiO2 or Al nanoparticles. A 1.8 times increase in the photoluminescence and microcathodoluminescence signal from the GaN active region was observed for 100 nm diameter Al nanoparticles, the efficiency decreased compared to the reference planar samples for small Al nanoparticles of 30–40 nm diameter, and a moderate increase of 1.2 times was detected for Ag/SiO2 nanoparticles. The observed phenomena are explained by the GaN emitter coupling with localized surface plasmons produced by metallic nanoparticles. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
134.
135.
Toni Andersson Susanna Holappa Vladimir Aseyev Heikki Tenhu 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):1904-1914
The interactions between oppositely charged polyelectrolytes were studied in saline aqueous solutions as functions of the temperature and the salt and polymer concentrations. The polyanion was a diblock copolymer composed of a poly(ethylene oxide) block and a poly(sodium methacrylate) block. Two polycations were used, the homopolymer poly(methacryl oxyethyl trimethylammonium chloride) and its poly(ethylene oxide)‐grafted analogue. By dynamic light scattering and turbidity measurements, it was observed that the salt concentration, temperature, and counterion size had a significant effect on the formation of the polymer complexes in aqueous solutions. At a fixed salt concentration and a fixed temperature, it was possible to form completely soluble complexes of an ionic polymer in aqueous solutions between poly(ethylene oxide)‐grafted poly(methacryl oxyethyl trimethylammonium chloride)and the polyanion with a poly(ethylene oxide) block at a 1:1 anion/cation ratio. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1904–1914, 2003 相似文献
136.
Ly HV Moilanen J Tuononen HM Parvez M Roesler R 《Chemical communications (Cambridge, England)》2011,47(29):8391-8393
Ruthenium and iron sandwich complexes incorporating cyclopentadienyl analogs with CB(2)N(2)(-) skeletons were characterized. Electrochemical measurements supported by computational studies revealed that in combination with larger metal ions such as Ru the CB(2)N(2)(-) ligand can be more electron-rich than its organic counterpart. 相似文献
137.
Bogdan A Molina MJ Tenhu H Loerting T 《Physical chemistry chemical physics : PCCP》2011,13(44):19704-19706
Atmospheric aerosol droplets containing NH(4)(+) and SO(4)(2-) ions are precursors of cirrus ice clouds. However, the low-temperature phase transformation of such droplets is not understood yet. Here we show for the first time that micrometre-scaled (NH(4))(2)SO(4)/H(2)O droplets produce one freezing event but three melting events which are the melting of (i) pure ice, (ii) eutectic ice/(NH(4))(2)SO(4), and (iii) eutectic ice/(NH(4))(3)H(SO(4))(2). We also find that the melting of ice/(NH(4))(3)H(SO(4))(2) consists of two eutectic melting events, presumably ice/letovicite-II and ice/letovicite-III. 相似文献
138.
We consider the dimensional crossover in the topological matter, which involves the transformation of different types of topologically
protected zeroes in the fermionic spectrum. In the considered case, the multiple Dirac (Fermi) point in quasi 2-dimensional
system evolves into the flat band on the surface of the 3-dimensional system when the number of atomic layers increases. This
is accompanied by formation of the spiral nodal lines in the bulk. We also discuss the topological quantum phase transition
at which the surface flat band shrinks and changes its chirality, while the nodal spiral changes its helicity. 相似文献
139.
Heikki Hakkarainen Nageswari Shanmugalingam 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(16):5525-5543
We study relations between the variational Sobolev 1-capacity and versions of variational BV-capacity in a complete metric space equipped with a doubling measure and supporting a weak (1,1)-Poincaré inequality. We prove the equality of 1-modulus and the continuous 1-capacity, extending the known results for 1<p<∞ to also cover the more geometric case p=1. Then we give alternative definitions for variational BV-capacities and obtain equivalence results between them. Finally we study relations between total 1-capacity and versions of BV-capacity. 相似文献
140.
Konu J Chivers T Tuononen HM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(42):11844-11856
The metathetical reactions of a) [Li(tmeda)]2[(S)C(PPh2S)2] (Li2? 3 c ) with CuCl2 and b) [Li(tmeda)]2[(SPh2P)2CSSC(PPh2S)2] (Li2? 4 c ) with two equivalents of CuCl both afford the binuclear CuI complex {Cu2[(SPh2P)2CSSC(PPh2S)2]} ( 5 c ). The elongated (C)S? S(C) bond (ca. 2.54 and 2.72 Å) of the dianionic ligand observed in the solid‐state structure of 5 c indicate the presence of diradical character as supported by theoretical analyses. The treatment of [Li(tmeda)]2[(SPh2P)2CSeSeC(PPh2S)2] (Li2? 4 b ) and Li2? 4 c with AgOSO2CF3 produce the analogous AgI derivatives, {Ag2[(SPh2P)2CEEC(PPh2S)2]} ( 6 b , E=Se; 6 c , E=S), respectively. The diselenide complex 6 b exhibits notably weaker Ag? Se(C) bonds than the corresponding contacts in the CuI congeners, and the 31P NMR data suggest a possible isomerization in solution. In contrast to the metathesis observed for CuI and AgI reagents, the reactions of Li2? 4 b and Li2? 4 c with Au(CO)Cl involve a redox process in which the dimeric dichalcogenide ligands are reduced to the corresponding monomeric dianions, [(E)C(PPh2S)2]2? ( 3 b , E=Se; 3 c , E=S), and one of the gold centers is oxidized to generate the mixed‐valent AuI/AuIII complexes, {Au[(E)C(PPh2S)2]}2 ( 7 b , E=Se; 7 c , E=S), with relatively strong aurophilic AuI???AuIII interactions. The new compounds 5 c , 6 b , c and 7 b , c are characterized in solution by NMR spectroscopy and in the solid state by X‐ray crystallography ( 5 c , 6 b , 7 b and 7 c ) and by Raman spectroscopy ( 5 c and 6 c ). The UV‐visible spectra of coinage metal complexes of the type 5 , 6 and 7 are discussed in the light of results from theoretical analyses using time‐dependent density functional theory. 相似文献