206 research outputs found
Comparison of SIVmac239(352–382) and SIVsmmPBj41(360–390) enterotoxic synthetic peptides
AbstractTo characterize the active domain of the simian immunodeficiency virus (SIV) surface unit (SU) enterotoxin, peptides corresponding to the V3 loop of SIVmac239 (SIVmac) and SIVsmmPBj41 (SIVpbj) were synthesized and examined for enterotoxic activity, α-helical structure, and interaction(s) with model membranes. SIVmac and SIVpbj induced a dose-dependent diarrhea in 6–8-day-old mouse pups similar to full-length SU. The peptides mobilized [Ca2+]i in HT-29 cells with distinct oscillations and elevated inositol triphosphate levels. Circular dichroism analyses showed the peptides were predominantly random coil in buffer, but increased in α-helical content when placed in a hydrophobic environment or with cholesterol-containing membrane vesicles that are rich in anionic phospholipids. None of the peptides underwent significant secondary structural changes in the presence of neutral vesicles indicating ionic interactions were important. These data show that the SIV SU enterotoxic domain localizes in part to the V3 loop region and interacts with anionic membrane domains on the host cell surface
B -> J/psi K^* Decays in QCD Factorization
The hadronic decay B -> J K^* is analyzed within the framework of QCD
factorization. The spin amplitudes A_0, A_\parallel and A_\perp in the
transversity basis and their relative phases are studied using various
different form-factor models for B-K^* transition. The effective parameters
a_2^h for helicity h=0,+,- states receive different nonfactorizable
contributions and hence they are helicity dependent, contrary to naive
factorization where a_2^h are universal and polarization independent. QCD
factorization breaks down even at the twist-2 level for transverse hard
spectator interactions. Although a nontrivial strong phase for the A_\parallel
amplitude can be achieved by adjusting the phase of an infrared divergent
contribution, the present QCD factorization calculation cannot say anything
definite about the phase phi_\parallel. Unlike B -> J/psi K decays, the
longitudinal parameter a_2^0 for B -> J/psi K^* does not receive twist-3
corrections and is not large enough to account for the observed branching ratio
and the fraction of longitudinal polarization. Possible enhancement mechanisms
for a_2^0 are discussed.Comment: 21 pages, 1 figure, a table and a reference added, some typos
correcte
An updated analysis of NN elastic scattering data to 1.6 GeV
An energy-dependent and set of single-energy partial-wave analyses of
elastic scattering data have been completed. The fit to 1.6~GeV has been
supplemented with a low-energy analysis to 400 MeV. Using the low-energy fit,
we study the sensitivity of our analysis to the choice of coupling
constant. We also comment on the possibility of fitting data alone. These
results are compared with those found in the recent Nijmegen analyses. (Figures
may be obtained from the authors upon request.)Comment: 17 pages of text, VPI-CAPS-7/
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
Charmless Exclusive Baryonic B Decays
We present a systematical study of two-body and three-body charmless baryonic
B decays. Branching ratios for two-body modes are in general very small,
typically less than , except that \B(B^-\to p \bar\Delta^{--})\sim
1\times 10^{-6}. In general, due to
the large coupling constant for . For three-body modes we
focus on octet baryon final states. The leading three-dominated modes are with a branching ratio of
order for and
for . The penguin-dominated decays with strangeness
in the meson, e.g., and , have appreciable rates and the mass
spectrum peaks at low mass. The penguin-dominated modes containing a strange
baryon, e.g., , have
branching ratios of order . In contrast, the decay
rate of is smaller. We explain why some of
charmless three-body final states in which baryon-antibaryon pair production is
accompanied by a meson have a larger rate than their two-body counterparts:
either the pole diagrams for the former have an anti-triplet bottom baryon
intermediate state, which has a large coupling to the meson and the
nucleon, or they are dominated by the factorizable external -emission
process.Comment: 46 pages and 3 figures, to appear in Phys. Rev. D. Major changes are:
(i) Calculations of two-body baryonic B decays involving a Delta resonance
are modified, and (ii) Penguin-dominated modes B-> Sigma+N(bar)+p are
discusse
Radiative decays of light vector mesons in a quark level linear sigma model
We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma
decays in the framework of a U(3)xU(3) linear sigma model which includes
constituent quarks. For the first two decays this approach improves results
based on the anomalous Wess-Zumino term, with contributions due to SU(3)
symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays
are dominated by resonant eta' exchange . Our calculation for the later decays
improves and update similar calculations in the -closely related- framework of
vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x10^{-5} and
BR(phi to omega gamma gamma)=2.8x10^{-6} within the scope of the
high-luminosity phi factories.Comment: 8 pages, submitted to Phys. Rev.
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
Charmless Two-body Baryonic B Decays
We study charmless two-body baryonic B decays in a diagramatic approach.
Relations on decay amplitudes are obtained. In general there are more than one
tree and more than one penguin amplitudes. The number of independent amplitudes
can be reduced in the large m_B limit. It leads to more predictive results.
Some prominent modes for experimental searches are pointed out.Comment: 15 pages, 2 figures. To appear in Phys. Rev.
On Counting the Number of Consistent Genotype Assignments for Pedigrees
Consistency checking of genotype information in pedigrees plays an important role in genetic analysis and for complex pedigrees the computational complexity is critical. We present here a detailed complexity analysis for the problem of counting the number of complete consistent genotype assignments. Our main result is a polynomial time algorithm for counting the number of complete consistent assignments for non-looping pedigrees. We further classify pedigrees according to a number of natural parameters like the number of generations, the number of children per individual and the cardinality of the set of alleles. We show that even if we assume all these parameters as bounded by reasonably small constants, the counting problem becomes computationally hard (#P-complete) for looping pedigrees. The border line for counting problems computable in polynomial time (i.e. belonging to the class FP) and #P-hard problems is completed by showing that even for general pedigrees with unlimited number of generations and alleles but with at most one child per individual and for pedigrees with at most two generations and two children per individual the counting problem is in FP
J/psi->VP decays and the quark and gluon content of the eta and eta'
The - pseudoscalar mixing angle and the gluonium content
of the meson are deduced from an updated phenomenological
analysis of decays into a vector and a pseudoscalar meson. In absence
of gluonium, the value of the mixing angle in the quark-flavour basis is found
to be . In presence of gluonium, the values for the
mixing angle and the gluonic content of the wave function are
and ,
respectively. The newly reported values of by the BABAR
and BES Collaborations are crucial to get a consistent description of data.Comment: 7 pages, 1 figure, uses svjour style. Comments on the relationship
between J/psi to VP and V to Pgamma decays and on the neglected contributions
together with an asymmetric treatment of errors are include
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