445 research outputs found
Stability of RungeâKutta methods for the alternately advanced and retarded differential equations with piecewise continuous arguments
AbstractThis paper deals with the numerical properties of RungeâKutta methods for the solution of uâ˛(t)=au(t)+a0u([t+12]). It is shown that the RungeâKutta method can preserve the convergence order. The necessary and sufficient conditions under which the analytical stability region is contained in the numerical stability region are obtained. It is interesting that the θ-methods with 0⊽θ<12 are asymptotically stable. Some numerical experiments are given
Charmless Decays in QCD Factorization
The two body charmless decays of meson to light vector mesons are
analyzed within the framework of QCD factorization. This approach implies that
the nonfactorizable corrections to different helicity amplitudes are not the
same. The effective parameters for helicity states receive
different nonfactorizable contributions and hence are helicity dependent,
contrary to naive factorization approach where are universal and
polarization independent. The branching ratios for decays are
calculated and we find that branching ratios of some channels are of order
, which are measurable at future experiments. The transverse to total
decay rate is also evaluated and found to be very small for
most decay modes, so, in charmless decays, both light vector
mesons tend to have zero helicity.Comment: 16pages. Typos and mistakes fixed. Numerical results change
Phenomenological Analysis of B->PP Decays with QCD Factorization
In this paper, we study nonleptonic charmless B decays to two light
pseudoscalar mesons within the frame of QCD factorization, including the
contributions from the chirally enhanced power corrections and weak
annihilation. Predictions for the CP-averaged branching ratios and CP-violating
asymmetries are given. Within the reasonable range of the parameters, we find
that our predictions for the branching ratios of B -> PP are consistent with
the present experimental data. But because of the logarithmic divergences at
the endpoints in the hard spectator scatterings and weak annihilation, there
are still large uncertainties in these predictions.Comment: 34 pages, 5 figures. to appear in PR
Patterns Of Chronic Graft-Vs-Host Disease And Associated Mortality After Myeloablative Conditioning Incorporating Fludarabine, Busulfan And ATG
The transition form factors for semi-leptonic weak decays of in QCD sum rules
Within the Standard Model, we investigate the semi-leptonic weak decays of
. The various form factors of transiting to a single charmed
meson () are studied in the framework of the QCD sum rules.
These form factors fully determine the rates of the weak semi-leptonic decays
of and provide valuable information about the non-perturbative QCD
effects. Our results indicate that the decay rate of the semi-leptonic weak
decay mode is at order of .Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.
Charming penguin contributions to charmless B decays into two pseudoscalar mesons
We present estimates of the charming penguin contribution to B => K pi, pi
pi,K eta, K eta' decays due to intermediate charmed meson states. We find that
this contribution is indeed significant for B => K pi decays, and its
inclusion, together with the tree and penguin terms, produces large branching
ratios in agreement with data, though the analysis is affected by large
theoretical uncertainties. On the other hand, for B => pi pi, K eta, K eta'
decays, the effect of the charming penguin contribution is more modest. We also
compute CP asymmetries for B => K pi, pi pi decays and we obtain rather large
results.Comment: 12 pages, 4 figures, LaTeX2e with epsfig. Minor changes in the text,
this version will appear in Phys. Rev.
Semi-inclusive B Decays and Direct CP Violation in QCD Factorization
We have systematically investigated the semi-inclusive B decays B->MX, which
are manifestations of the quark decay b->Mq, within the framework of
QCD-improved factorization. These decays are theoretically clean and have
distinctive experimental signatures. We focus on a class of these that do not
require any form factor information and therefore may be especially suitable
for extracting information on the angles and of the unitarity
triangle. The nonfactorizable effects, such as vertex-type and penguin-type
corrections to the two-body b decay and hard spectator corrections to the
3-body decay are calculable in the heavy quark limit. QCD factorization is
applicable when the emitted meson is a light meson or a charmonium. We discuss
the issue of the CPT constraint on partial rate asymmetries. The strong phase
coming from final-state rescattering due to hard gluon exchange between the
final states can induce large rate asymmetries for tree-dominated
color-suppressed modes . The nonfactorizable
hard spectator interactions in the 3-body decay, though phase-space suppressed,
are extremely important for the tree-dominated modes
, and the
penguin-dominated mode . In fact, they are dominated by the
hard spectator corrections. Our result for is in
agreement with experiment. The semi-inclusive decay modes: , ,
and are the most promising ones in searching for
direct CP violation. In fact, they have branching ratios of order
and CP rate asymmetries of order .Comment: 28 page
FAM46B is a prokaryotic-like cytoplasmic poly(A) polymerase essential in human embryonic stem cells
Family with sequence similarity (FAM46) proteins are newly identified metazoan-specific poly(A) polymerases (PAPs). Although predicted as Gld-2-like eukaryotic non-canonical PAPs, the detailed architecture of FAM46 proteins is still unclear. Exact biological functions for most of FAM46 proteins also remain largely unknown. Here, we report the first crystal structure of a FAM46 protein, FAM46B. FAM46B is composed of a prominently larger N-terminal catalytic domain as compared to known eukaryotic PAPs, and a C-terminal helical domain. FAM46B resembles prokaryotic PAP/CCA-adding enzymes in overall folding as well as certain inter-domain connections, which distinguishes FAM46B from other eukaryotic non-canonical PAPs. Biochemical analysis reveals that FAM46B is an active PAP, and prefers adenosine-rich substrate RNAs. FAM46B is uniquely and highly expressed in human pre-implantation embryos and pluripotent stem cells, but sharply down-regulated following differentiation. FAM46B is localized to both cell nucleus and cytosol, and is indispensable for the viability of human embryonic stem cells. Knock-out of FAM46B is lethal. Knock-down of FAM46B induces apoptosis and restricts protein synthesis. The identification of the bacterial-like FAM46B, as a pluripotent stem cell-specific PAP involved in the maintenance of translational efficiency, provides important clues for further functional studies of this PAP in the early embryonic development of high eukaryotes
Mass measurements of neutron-deficient Y, Zr, and Nb isotopes and their impact on rp and νp nucleosynthesis processes
Š 2018 The Authors. Published by Elsevier B.V. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). For further details please see: https://creativecommons.org/licenses/by-nc-nd/4.0/Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of âź10 keV, and the masses of 79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low Îą separation energies for neutron-deficient Mo and Tc isotopes, making the formation of ZrâNb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.Peer reviewe
within and beyond the Standard Model
We revisit (with and ) within
the Standard Model (SM). The electro-magnetic contributions are given in
color-singlet model with non-vanishing lepton masses at the leading order of
. Numerically, the branching ratios of
predicted within the SM are so small that such decays are barely possible to be
detected at future BESIII and SuperB experiments, but may be possible to be
observed at the LHC. We investigate in Type-II 2HDM
with large , and in the Randall-Sundrum
model, to see their chance to be observed in future experiments.Comment: 11 pages, 8 figures. To match the published versio
- âŚ