1,397 research outputs found
Semileptonic decays of charmed mesons in the effective action of QCD
Within the framework of phenomenological Lagrangians we construct the
effective action of QCD relevant for the study of semileptonic decays of
charmed mesons. Hence we evaluate the form factors of D -> P(0^-) l^+ nu_l at
leading order in the 1/N_C expansion and, by demanding their QCD-ruled
asymptotic behaviour, we constrain the couplings of the Lagrangian. The
features of the model-independent parameterization of form factors provided and
their relevance for the analysis of experimental data are pointed out.Comment: 1+24 pages, 1 figure. Updated version. Conclusions unchanged.
Accepted for publication in The European Physical Journal
Structural properties and quasiparticule energies of cubic SrO, MgO and SrTiO3
The structural properties and the band structures of the charge-transfer
insulating oxides SrO, MgO and SrTiO3 are computed both within density
functional theory in the local density approximation (LDA) and in the Hedin's
GW scheme for self-energy corrections, by using a model dielectric function,
which approximately includes local field and dynamical effects. The deep
valence states are shifted by the GW method to higher binding energies, in very
good agreement with photoemission spectra. Since in all of these oxides the
direct gaps at high-symmetry points of the Brillouin zone may be very sensitive
to the actual value of the lattice parameter a, already at the LDA level,
self-energy corrections are computed both at the theoretical and the
experimental a. For MgO and SrO, the values of the transition energies between
the valence and the conduction bands are improved by GW corrections, while for
SrTiO3 they are overestimated. The results are discussed in relation to the
importance of local field effects and to the nature of the electronic states in
these insulating oxides.Comment: 3 figures, accepted in J. Phys.: Condens. Matte
Form factors of radiative pion decays in nonlocal chiral quark models
We study the radiative pion decay pi+ -> e+ nu_e gamma within nonlocal chiral
quark models that include wave function renormalization. In this framework we
analyze the momentum dependence of the vector form factor F_V(q^2), and the
slope of the axial-vector form factor F_A(q^2) at threshold. Our results are
compared with available experimental information and with the predictions given
by the NJL model. In addition we calculate the low energy constants l_5 and
l_6, comparing our results with the values obtained in chiral perturbation
theory.Comment: 22 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1011.640
Relativity and constituent quark structure in model calculations of parton distributions
According to recent studies, Parton Distribution Functions (PDFs) and Generalized Parton Distributions (GPDs) can be evaluated in a Constituent Quark Model (CQM) scenario, considering the constituent quarks as composite objects. In here, a fully covariant model for a system of two particles, together with its non relativistic limit, are used to calculate PDFs and GPDs. The analysis permits to realize that by no means the effects of Relativity can be simulated taking into account the structure of the constituent particles, the two effects being independent and necessary for a proper description of available high energy data in terms of CQM
MAXIMALITY OF LOGIC WITHOUT IDENTITY
Lindström’s theorem obviously fails as a characterization of first-order logic without identity ( L
−
ωω
). In this note, we provide a fix: we show that L
−
ωω
is a maximal abstract logic satisfying a weak form of the isomorphism property (suitable for identity-free languages and studied in [11]), the Löwenheim–Skolem property, and compactness. Furthermore, we show that compactness can be replaced by being recursively enumerable for validity under certain conditions. In the proofs, we use a form of strong upwards Löwenheim–Skolem theorem not available in the framework with identity
D^0-D^0(bar) mixing in the weak-gauged U(4)_L x U(4)_R Chiral Lagrangian Model
The D^0-D^0(bar) mixing is analyzed in a weak gauged U(4)_L x U(4)_R chiral
lagrangian model where the electroweak interaction is introduced as a gauge
theory over the meson degrees of freedom. This model allows a particular
realization of the G.I.M. mechanism and then could be useful in the study of
processes where G.I.M. suppression is effective. As a test of the model we have
also analyzed the K^0-K^0(bar) mixing. We find \Delta m_K in good agreement
with the experimental result and we show that the D^0-D^0(bar) mixing is very
much suppressed in agreement with previous estimates in the Heavy Quark
expansion framework.Comment: 14 pages, 2 figures, Latex, minor changes in the writing, final
version to be published in Phys. Lett.
L'Estany des Cibollar
Des que l'any 1983 es va detectar una situació meromiòtica a l'Estany des Cibollar, s'han succeït diversos estudis que han permés conèixer el seu funcionament. Aquà es presenta breument la informació que en l'actualitat es té d'aquesta llacuna costanera, de la seva dinà mica i de les comunitats planctòniques que s'hi desenvolupen. La meromixi eclogènica de l'Estany des Cibollar determina les seves principals caracterÃstiques. L'estratificació de la columna d'aigua dificulta la mescla vertical provocant una anòxia permanent en el monimolimnion, una inversió tèrmica durant l'hivern i un mà xim d'oxigen dissolt en el metalimnion
Contribución al conocimiento de los complejos de Cu(I) con el bromuro bromhidrato del 2-aminoetilisotiouronio (AET)
Se han estudiado los quelatos 2 mercaptoetilguanidina-Cu. Se han determinado las constantes ácidas por el método de Bjerrum y los valores son pKl 9,45 y pK2 7,17. El coeficiente de extinción es E330 = 560 M1-1 cm-1.The chelates 2-mercaptoethyIguanidine-Cu have been studied. The acid constants have been determined by Bjerum method and the values are pK1, 9,45 and pK2 7,17. The extinction coefficient is E330= 560 MJ-1 cm1
Acute promyelocytic Leukemia: Update on the mechanisms of leukemogenesis, resistance and on innovative treatment strategies
This review highlights new findings that have deepened our understanding of the mechanisms of leukemogenesis, therapy and resistance in acute promyelocytic leukemia (APL). Promyelocytic leukemia-retinoic acid receptor alpha (PML-RARa) sets the cellular landscape of acute promyelocytic leukemia (APL) by repressing the transcription of RARa target genes and disrupting PML-NBs. The RAR receptors control the homeostasis of tissue growth, modeling and regeneration, and PML-NBs are involved in self-renewal of normal and cancer stem cells, DNA damage response, senescence and stress response. The additional somatic mutations in APL mainly involve FLT3, WT1, NRAS, KRAS, ARID1B and ARID1A genes. The treatment outcomes in patients with newly diagnosed APL improved dramatically since the advent of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). ATRA activates the transcription of blocked genes and degrades PML-RAR alpha, while ATO degrades PML-RARa by promoting apoptosis and has a pro-oxidant effect. The resistance to ATRA and ATO may derive from the mutations in the RARa ligand binding domain (LBD) and in the PML-B2 domain of PML-RARa, but such mutations cannot explain the majority of resistances experienced in the clinic, globally accounting for 5-10% of cases. Several studies are ongoing to unravel clonal evolution and resistance, suggesting the therapeutic potential of new retinoid molecules and combinatorial treatments of ATRA or ATO with different drugs acting through alternative mechanisms of action, which may lead to synergistic effects on growth control or the induction of apoptosis in APL cells
Oxide nanotemplates for self-assembling "solid" building blocks
It is widely accepted that self-assembling building blocks is one of the
promising ways for engineering new materials. Recent years reveal substantial
progress in fabricating colloidal particles, polymer blocks and supramolecular
aggregates of organic molecules. Despite of substantial progress in molecular
self-assembly there is still a lack of simple blocks made of "solid matter"
(e.g. metals, oxides etc.) with well-defined crystal structure and spatial
order. Here we demonstrate that ordered arrays of metal nanoclusters can be
fabricated by self-assembly on a wide range of oxide templates. These
nano-templates are produced either by depositing an alien oxide film or by
oxidizing a metal/metal oxide substrate.Comment: 11 pages, 2 figures added DFT calculations and Fig.
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