279 research outputs found
Coupled-channels effects in elastic scattering and near-barrier fusion induced by weakly bound nuclei and exotic halo nuclei
The influence on fusion of coupling to the breakup process is investigated
for reactions where at least one of the colliding nuclei has a sufficiently low
binding energy for breakup to become an important process. Elastic scattering,
excitation functions for sub-and near-barrier fusion cross sections, and
breakup yields are analyzed for Li+Co. Continuum-Discretized
Coupled-Channels (CDCC) calculations describe well the data at and above the
barrier. Elastic scattering with Li (as compared to Li) indicates
the significant role of breakup for weakly bound projectiles. A study of
He induced fusion reactions with a three-body CDCC method for the
He halo nucleus is presented. The relative importance of breakup and
bound-state structure effects on total fusion is discussed.Comment: 29 pages, 9 figure
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
Next-to-leading-order temperature corrections to correlators in QCD
Corrections of order to vector and axial current correlators in QCD at
a finite temperature are obtained using dispersion relations for the
amplitudes of deep inelastic scattering on pions. Their relation with the
operator product expansion is presented. An interpretation of the results in
terms of -dependent meson masses is given: masses of and start
to move with temperature in order .Comment: 13 pages, no figures, CERN-TH.7215/94, BUTP-94/
QCD sum rules and thermal properties of Charmonium in the vector channel
The thermal evolution of the hadronic parameters of charmonium in the vector
channel, i.e. the J/psi resonance mass, coupling (leptonic decay constant),
total width, and continuum threshold is analyzed in the framework of thermal
Hilbert moment QCD sum rules. The continuum threshold , as in other
hadronic channels, decreases with increasing temperature until the PQCD
threshold s_0 = 4, m_Q^2 is reached at T \simeq 1.22T_c (m_Q is the charm quark
mass) and the J/psi mass is essentially constant in a wide range of
temperatures. The other hadronic parameters behave in a very different way from
those of light-light and heavy-light quark systems. The total width grows with
temperature up to T \simeq 1.04T_c beyond which it decreases sharply with
increasing T. The resonance coupling is also initially constant beginning to
increase monotonically around T \simeq T_c. This behavior strongly suggests
that the J/psi resonance might survive beyond the critical temperature for
deconfinement, in agreement with lattice QCD results.Comment: 4 pages, two figures, contribution to QCD 10, Montpellier 28th
June-2nd July 201
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
X-ray Emission from Wind Blown Bubbles. III. ASCA SIS Observations of NGC6888
We present ASCA SIS observations of the wind-blown bubble NGC6888. Owing to
the higher sensitivity of the SIS for higher energy photons compared to the
ROSAT PSPC, we are able to detect a T ~ 8x10^6 K plasma component in addition
to the T ~ 1.3x10^6 K component previously detected in PSPC observations. No
significant temperature variations are detected within NGC6888. Garcia-Segura &
Mac Low's (1995) analytical models of WR bubbles constrained by the observed
size, expansion velocity, and mass of the nebular shell under-predict the
stellar wind luminosity, and cannot reproduce simultaneously the observed X-ray
luminosity, spectrum, surface brightness profile, and SIS count rate of
NGC6888's bubble interior. The agreement between observations and expectations
from models can be improved if one or more of the following ad hoc assumptions
are made: (1) the stellar wind luminosity was weaker in the past, (2) the
bubble is at a special evolutionary stage and the nebular shell has recently
been decelerated to 1/2 of its previous expansion velocity, and (3) the heat
conduction between the hot interior and the cool nebular shell is suppressed.
Chandra and XMM-Newton observations with high spatial resolution and high
sensitivity are needed to determine accurately the physical conditions
NGC6888's interior hot gas for critical comparisons with bubble models.Comment: 24 pages, 6 figures; accepted for Astrophysical Journal, Nov 1, 2005
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Membranes in the two-Higgs standard model
We present some non-topological static wall solutions in two-Higgs extensions
of the standard model. They are classically stable in a large region of
parameter space, compatible with perturbative unitarity and with present
phenomenological bounds.Comment: 7 pages, latex, 3 figures available upon reques
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
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