2,035 research outputs found
Roentgenographic correlation in pulmonary venous hypertension : prediction of pulmonary venous pressure from plain chest films
B_c meson rare decays in the light-cone quark model
We investigate the rare decays
and in the framework of the
light-cone quark model (LCQM). The transition form factors are calculated in
the space-like region and then analytically continued to the time-like region
via exponential parametrization. The branching ratios and longitudinal lepton
polarization asymmetries (LPAs) for the two decays are given and compared with
each other. The results are helpful to investigating the structure of
meson and to testing the unitarity of CKM quark mixing matrix. All these
results can be tested in the future experiments at the LHC.Comment: 9 pages, 11 figures, version accepted for publication in EPJ
Rhenium complex as emitting material in highly efficient phosphorescent organic light-emitting diodes
Interest in luminescent materials able to efficiently emit in the solid state is continuously
growing, because in most applications the dyes are used as solid films. This is the case of the
Organic Light Emitting Diodes (OLEDs), where electroluminescent
metal complexes have been widely investigated as dopants, able to
increase their performances [1]. We present here a dinuclear Re(I)
complexes (1, see Scheme 1) whose emission is higher in solid state
and in PMMA matrix than in solution and is used as dopant in
OLEDs.
This complex belong to the family of neutral Re(I) complexes
with general formula [Re2(CO)6(\u3bc-1,2-diazine)(\u3bc-X)2], where X is halogen. Some of them
have recently gained interest for their intense yellow/green emission, occurring from triplet
metal-to-ligand charge transfer (3MLCT) states [2], showing a modulation effect of the
diazine substituents on wavelengths, lifetimes and quantum yields of the emission. \u3a6 up to
0.53 has been measured for the di-chloro complexes containing diazines bearing alkyl groups
in both the \u3b2 positions [3]. At variance with the chloro derivatives, the bromo analogue 1 is
almost not-emitting in solution (\u3a6em 0.002 in deareated toluene). We have now found that in
the solid state 1 shows intense yellow-orange emission (\u3a6em 0.50 in neat powder), blue
shifted with respect to the solution (560 nm vs. 620 nm). The emission is intense also in
PMMA matrix (\u3a6em 0.19 in PMMA at 10% w/w, 556 nm).
This very high aggregated emission here is discussed in terms of the restriction of the
intramolecular roto-vibrational motions of the \u201cRe2(CO)6(\u3bc-Br)2\u201d scaffold imposed by the
rigid environment, as evidenced by the strong decrease of the knr. Moreover a parallel increase
of kr is noticed, which clearly shows the influence of the halides in determining not only the
energy of the excited state, but also the nature of the lowest (emitting) state.
These properties allowed its successful use as a phosphorescent dopant in OLEDs and
here we report the performances of OLED devices prepared both by solution- and vacuumprocessing.
The values of the external quantum efficiency are 1.7% (4.3 cd/A and 1.7 lm/W)
and 10% (29.1 cd/A and 22.1 lm/W) respectively and are the highest ever reported for
rhenium-based devices, comparable to state-of-the-art devices employing Ir(III)- and Pt(II)-
based metal complexes. The combination of synthetic strategy and encouraging results in
potential OLEDs applications should make these dinuclear Re(I) complexes highly attractive
to a broad spectrum of research fields.
1. \u201cHighly efficient OLEDs with Phosphorescent Materials\u201d H. Yersin Ed. Wiley-VCH, (2008).
2. D. Donghi, G. D\u2019Alfonso, M. Mauro, M. Panigati, P. Mercandelli, A. Sironi, P. Mussini, L. D\u2019Alfonso, Inorg.
Chem. 28 (2008) 4243-4255.
3. M. Mauro, E. Quartapelle Procopio, Y. Sun, C. H. Chien, D. Donghi, M. Panigati, P. Mercandelli, P. Mussini,
G. D\u2019Alfonso, L. De Cola, Adv. Funct. Mater. 19 (2009) 2607-2614
Perturbative QCD analysis of decays
We study the first observed charmless modes, the
decays, in perturbative QCD formalism. The obtained branching ratios
are larger than
from QCD factorization. The comparison of the predicted magnitudes and phases
of the different helicity amplitudes, and branching ratios with experimental
data can test the power counting rules, the evaluation of annihilation
contributions, and the mechanism of dynamical penguin enhancement in
perturbative QCD, respectively.Comment: 14 pages, 2 tables, brief disscussion on hard sacle added, version to
appear in PR
Spectra of Free Diquark in the Bethe-Salpeter Approach
In this work, we employ the Bethe-Salpeter (B-S) equation to investigate the
spectra of free diquarks and their B-S wave functions. We find that the B-S
approach can be consistently applied to study the diqaurks with two heavy
quarks or one heavy and one light quarks, but for two light-quark systems, the
results are not reliable. There are a few free parameters in the whole scenario
which can only be fixed phenomenologically. Thus, to determine them, one has to
study baryons which are composed of quarks and diquarks.Comment: 16 pages, no figure
Study of Bc --> J/psi pi, etac pi decays with perturbative QCD approach
The Bc --> J/psi pi, etac pi decays are studied with the perturbative QCD
approach. It is found that form factors and branching ratios are sensitive to
the parameters w, v, f_J/psi and f_etac, where w and v are the parameters of
the charmonium wave functions for Coulomb potential and harmonic oscillator
potential, respectively, f_J/psi and f_etac are the decay constants of the
J/psi and etac mesons, respectively. The large branching ratios and the clear
signals of the final states make the Bc --> J/psi pi, etac pi decays to be the
prospective channels for measurements at the hadron collidersComment: 21 pages, revtex
Analysis of the vector and axialvector mesons with QCD sum rules
In this article, we study the vector and axialvector mesons with the
QCD sum rules, and make reasonable predictions for the masses and decay
constants, then calculate the leptonic decay widths. The present predictions
for the masses and decay constants can be confronted with the experimental data
in the future. We can also take the masses and decay constants as basic input
parameters and study other phenomenological quantities with the three-point
vacuum correlation functions via the QCD sum rules.Comment: 14 pages, 16 figure
Characterization of 13 multi-drug resistant Salmonella serovars from different broiler chickens associated with those of human isolates
<p>Abstract</p> <p>Background</p> <p><it>Salmonella </it>are frequently isolated from chickens and their products. Prevalent serogroups and serovars of <it>Salmonella </it>as well as their genotypes and antibiograms were determined for cloacal samples from 1595 chickens. To understand the possible serovar and H antigens for transmission between chicken and human, serovars and their H antigens of 164 chicken and 5314 human isolates were compared.</p> <p>Results</p> <p>Prevalence of <it>Salmonella </it>differed among chicken lines and ages. Chicken and human isolates belonged mainly to serogroup B, C1, C2-C3, D, and E. 13 serovars and 66 serovars were identified for chicken and human isolates respectively. The common serovars for chicken and human isolates were <it>S</it>. Typhimurium, <it>S</it>. Enteritidis, <it>S</it>. Albany, <it>S</it>. Derby, and <it>S</it>. Anatum and shared common H1 antigens "g complex; i; e,h; and z4,z24" and H2 antigens "1 complex and -". In human isolates, H1 antigen "i" and H2 antigen "-" were common in all serogroups. In chicken, antimicrobial susceptibility differed among serogroups, serovars and three counties. All isolates were susceptible to cefazolin and ceftriaxone, but highly resistant to ampicillin, chloramphenicol, flumequine, streptomycin, sulfamethoxazole-trimethoprim, and tetracycline. Except those isolates of serogroup C1 of Chick group and serogroup G, all isolates were multi-drug resistance. Only <it>S</it>. Kubacha, <it>S</it>. Typhimurium, <it>S</it>. Grampian, and <it>S</it>. Mons were resistant to ciprofloxacin and/or enrofloxacin.</p> <p>Conclusion</p> <p>In chicken, prevalent serogroups and serovars were associated with chicken ages, lines and regions; and flouroquinolone-resistant and MDR isolates emerged. H1 antigens "g complex and i" and H2 antigens "1 complex and -" might be important for transmission of <it>Salmonella </it>between chicken and human.</p
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