277 research outputs found
Synthesis, characterization and photophysical properties of new cyclometallated platinum(II) complexes with pyrazolonate ancillary ligand
New cyclometalated platinum(II) complexes with pyrazolonate ancillary ligand (ppy)Pt(pmip) (1) and (dfppy)Pt(pmip) (2) (ppy = 2-phenylpyridine, dfppy = (4,6-difluorophenyl)pyridine, Hpmip = 1-phenyl-3-methyl-4-isobutyryl-5- pyrazolone) were synthesized and structurally characterized. Both compounds revealed square-planar geometry. The crystal cell of 1 was found to contain the monomer molecules of platinum compound whereas dimer molecules of 2 with short Pt⋯Pt contacts of 3.2217(3) were observed in the crystal cell of 2. Photophysical properties of 1 and 2 were investigated in detail. The highly resolved photoluminesence spectra of the platinum complexes in solution contain emission bands in the region of 470-550 nm attributed to monomer compounds 1 and 2. The triplet-state energies of 1 and 2 obtained from DFT calculations agree very well with the experimental data. In the crystalline state complex 2 revealed excimer emission as a structureless broad band at ca. 584 nm related to dimer molecules of platinum compound presented in the crystals. © 2013 Elsevier B.V. All rights reserved
Thermally stable composite system Al2O3-Ce 0.75Zr0.25O2 for automotive three-way catalysts
Present-day three-way catalysts operate in contact with exhaust gases whose temperature is as high as >1000 C, so the problem of developing thermally stable catalytic compositions is still topical. A series of Al2O 3-Ce0.75Zr0.25O2 composites containing 0, 10, 25, and 50 wt % Al2O3 has been synthesized by direct precipitation. The as-prepared composites and those calcined in air at 1000 and 1100 C have been characterized by BET, X-ray diffraction, transmission electron microscopy, and temperature-programmed reduction methods. The composites aged at 1050 C in a 2% O2 + 10% H2O + 88% N2 atmosphere have been used to prepare monolith catalysts, and the oxygen storage capacity (OSC) of the latter has been measured using a gas analysis setup. As the proportion of Al2O 3 in the composite is raised, the mixing uniformity and degree of dispersion of Ce x Zr1-x O2-δ particles increase, their chemical composition becomes homogeneous, and the amount of cerium involved in oxidation and reduction increases. The composite containing 50 wt % Al2O3 is a mixture of Ce x Zr 1-x O2-δ and Al2O3 crystallites, whose size is practically unaffected by calcination. The (Pt/Al2O3 + Al2O3-Ce 0.75Zr0.25O2) based on this composite has the highest OSC and is the most active. For this reason, full-scale testing of this catalyst is recommended. © 2013 Pleiades Publishing, Ltd
Spectral representation and QCD sum rules for nucleon at finite temperature
We examine the problem of constructing spectral representations for two point
correlation functions, needed to write down the QCD sum rules in the medium. We
suggest constructing them from the Feynman diagrams for the correlation
functions. As an example we use this procedure to write the QCD sum rules for
the nucleon current at finite temperature
Test of local Lorenz invariance using a double-cavity laser system
We report the results of testing the local Lorentz invariance during five-month operation of a double-cavity laser system, where one cavity operates in a free generation mode while the frequency of the second cavity is stabilized with a nonlinear ultra-narrow absorption resonance of the methane molecule. An interpretation of the experimental results is given on the basis of the Robertson-Mansouri-Sexl formalism. © 2012 Pleiades Publishing, Ltd
Skyrmion Multi-Walls
Skyrmion walls are topologically-nontrivial solutions of the Skyrme system
which are periodic in two spatial directions. We report numerical
investigations which show that solutions representing parallel multi-walls
exist. The most stable configuration is that of the square -wall, which in
the limit becomes the cubically-symmetric Skyrme crystal. There is
also a solution resembling parallel hexagonal walls, but this is less stable.Comment: 7 pages, 1 figur
Hot Nucleons in Chiral Soliton Models
Chiral lagrangians as effective field theories of QCD are most suitable for
the study of nucleons in a hot pion gas because they contain pions and also
baryons as solitons of the same action. The semiclassical treatment of the
soliton solutions must be augmented by pionic fluctuations which requires
renormalisation to 1-loop, and finite temperatures do not introduce new
ultraviolet divergencies and may easily be considered. Alternatively, a
renormalisation scheme based on the renormalisation group equation at finite
temperature comprises and extends the rigorous results of chiral perturbation
theory and renders the low energy constants temperature-dependent which allows
the construction of temperature-dependent solitons below the critical
temperature. The temperature-dependence of the baryon energy and the
pion-nucleon coupling is studied. There is no simple scaling law for the
temperature-dependence of these quantities.Comment: 17 pages (RevTeX), 5 figure
Synthesis, crystal structures and luminescent properties of the copper(I) pyrazolonate complexes
© 2014 Elsevier B.V. All rights reserved. New copper(I) complexes with pyrazolonate ligands [Cu(Pri-PMP)(DPEphos)] (1) and [Cu(But-PMP)(DPEphos)] (2) (Pri-PMP = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolonato, But-PMP = 1-phenyl-3-methyl-(2,2-dimethylpropan-1-oyl)-5-pyrazolonato; DPEphos = bis[2-(diphenylphosphino)-pheny]ether) were synthesized and structurally characterized. An unusual η1 coordination of pyrazolonate ligand to the copper atom was found in complex 2. Photo- and electroluminescent properties of the synthesized compounds were investigated. In crystalline form compounds 1 and 2 revealed dual emission consisting of the bands at 445-450 and 485-488 nm which were assigned to transitions from the S1 and T1 states. DFT and TD DFT calculations as well as electrochemical studies correlate with the photophysical data. Synthesized copper(I) complexes generated electroluminescence of yellowish-orange (1) and yellow (2) colors with the maximum luminance of 286 and 39 cd/m2, respectively
Computation of the winding number diffusion rate due to the cosmological sphaleron
A detailed quantitative analysis of the transition process mediated by a
sphaleron type non-Abelian gauge field configuration in a static Einstein
universe is carried out. By examining spectra of the fluctuation operators and
applying the zeta function regularization scheme, a closed analytical
expression for the transition rate at the one-loop level is derived. This is a
unique example of an exact solution for a sphaleron model in spacetime
dimensions.Comment: Some style corrections suggested by the referee are introduced
(mainly in Sec.II), one reference added. To appear in Phys.Rev.D 29 pages,
LaTeX, 3 Postscript figures, uses epsf.st
Sphalerons and the Electroweak Phase Transition in Models with Higher Scalar Representations
In this work we investigate the sphaleron solution in a
gauge theory, which also encompasses the Standard Model, with higher scalar
representation(s) (). We show that the field profiles
describing the sphaleron in higher scalar multiplet, have similar trends like
the doublet case with respect to the radial distance. We compute the sphaleron
energy and find that it scales linearly with the vacuum expectation value of
the scalar field and its slope depends on the representation. We also
investigate the effect of gauge field and find that it is small for the
physical value of the mixing angle, and resembles the case for the
doublet. For higher representations, we show that the criterion for strong
first order phase transition, , is relaxed with respect to
the doublet case, i.e. .Comment: 20 pages, 5 figures & 1 table, published versio
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