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61.
62.
A heavy quark antiquark potential is suggested connecting asymptotic freedom and quark confinement in a unified way. Theα
g
(q
2) calculated using Borel summation technique with three loop agrees with the two loopβ-function up tog
2/4π≅ 1.1 but changes appreciably afterg
2/4π=1.5. The potential so derived satisfactorily explains the
and
spectrum. 相似文献
63.
T.K. Kundu S. Mishra N. Karak P. Barik 《Journal of Physics and Chemistry of Solids》2012,73(4):579-583
Nanostructured nickel ferrites (NiFe2O4) were prepared by doping with Ti4+ ions using solid-state reaction route. Lowest grain size of 55 nm was achieved in the specimens with 20 mole% TiO2 doping. Magnetization in the specimens decreases with decreasing grain sizes. Lower volume fractions of ferrite phase due to dissociation of the magnetic phase into smaller particles by the disruption of super exchange interaction by the titanium substitution results a decrease in magnetizations. Coercivity showed an increasing trend. This was explained as arising due to multidomain/monodomain magnetic behavior of magnetic nanoparticles. Small polaron hopping conduction between Fe2+ and Fe3+ sites controls the dc electrical properties of the specimens. The presence of an interfacial amorphous phase between the sites is evident from Mott's analysis. Specimens containing 10 mole or more TiO2 and sintered at 1350 °C contain NiTiO3 as a secondary phase and show unusual dc conductivity. 相似文献
64.
Suman Kumar Saha Rajib Kar Durbadal Mandal Sakti Prasad Ghoshal 《Memetic Computing》2013,5(4):311-321
In this paper, a new optimization method named gravitational search algorithm (GSA) is adopted for designing optimal linear phase finite impulse response band pass (BP) and band stop (BS) digital filters. Other various population based evolutionary algorithms like real coded genetic algorithm, conventional particle swarm optimization, differential evolution (DE), bee swarm optimization have also been applied for the sake of comparative study of the same optimal designs. In GSA, particles are considered as objects and their performances are measured by their masses. All these objects attract each other by gravity forces, and these forces produce global movements of all objects towards the objects with heavier masses. GSA guarantees the exploitation step of the algorithm and it is apparently free from premature convergence. Extensive simulation results justify superior optimization capability of GSA over the afore-mentioned optimization techniques for the solution of the multimodal, non-differentiable, highly non-linear, and constrained filter design problems. 相似文献
65.
66.
Sangeeta Mondal Sakti Prasad Ghoshal Rajib Kar Durbadal Mandal 《Journal of Optimization Theory and Applications》2012,155(1):315-324
This paper proposes one novel algorithm called differential evolution with wavelet mutation for the optimal design of linear phase finite impulse response filters. For comparative performance study, the Parks–McClellan algorithm and some evolutionary algorithms like the real coded genetic algorithm, conventional particle swarm optimization, and conventional differential evolution have also been applied. 相似文献
67.
68.
S.K. Barik P.K. Mahapatra R.N.P. Choudhary 《Applied Physics A: Materials Science & Processing》2006,85(2):199-203
Na1/2La1/2TiO3 (NLT) ceramic was prepared by a high-temperature solid-state reaction technique. A preliminary structural analysis (XRD) suggested the formation of a single-phase orthorhombic structure. SEM micrograph of the material showed uniform grain distribution on the surface of the sample. The dielectric permittivity and the loss tangent of the sample were measured in a frequency range from 1 kHz to 1 MHz and a temperature range 28 °C to 525 °C. Electrical properties of the material were studied using an ac impedance spectroscopic technique. Detailed analysis of the impedance spectrum suggested that the electrical properties of the material are strongly temperature dependant. The Nyquist plots clearly showed the presence of both bulk and grain boundary effect in the compound. The activation energy was estimated to be 1.1 eV from the temperature variation of dc conductivity. The a.c. conductivity spectrum suggests a typical signature of ion conducting system. PACS 77.22.Ch; 77.22.Gm; 77.80.Bh; 77.22.Ej 相似文献
69.
70.
Sodium perborate tetrahydrate has been utilized as a nucleophilic catalyst for facile conversion of 2′-hydroxychalcones to flavanones in warm aqueous acetonitrile, and then these chalcones, upon oxidative cyclization in warm acetic acid with an excess of the same reagent, afforded flavones in acceptable yields. One-pot synthesis of 3′,5′-diiodoflavone has been accomplished by diacetoxyiodobenzene-catalyzed iodination of 2′-hydroxychalcone with tetra-n-butylammonium iodide in acetic acid in the presence of sodium perborate as a terminal oxidant. 相似文献