149,382 research outputs found
Hadronic B Decays to Charmed Baryons
We study exclusive B decays to final states containing a charmed baryon
within the pole model framework. Since the strong coupling for is larger than that for , the two-body charmful decay
has a rate larger than
as the former proceeds via the pole while the latter via the
pole. By the same token, the three-body decay receives less baryon-pole contribution than
. However, because the important charmed-meson
pole diagrams contribute constructively to the former and destructively to the
latter, has a rate slightly larger than
. It is found that one quarter of the rate comes from the resonant contributions. We discuss
the decays and
and stress that they are not color suppressed even though they can only proceed
via an internal W emission.Comment: 25 pages, 6 figure
Parity-even and Parity-odd Mesons in Covariant Light-front Approach
Decay constants and form factors for parity-even (s-wave) and parity-odd
(p-wave) mesons are studied within a covariant light-front approach. The three
universal Isgur-Wise functions for heavy-to-heavy meson transitions are
obtained.Comment: 3 pages, talk given at the 2004 DPF Meeting, Riverside, CA. Aug
26-31, 200
AIS-BN: An Adaptive Importance Sampling Algorithm for Evidential Reasoning in Large Bayesian Networks
Stochastic sampling algorithms, while an attractive alternative to exact
algorithms in very large Bayesian network models, have been observed to perform
poorly in evidential reasoning with extremely unlikely evidence. To address
this problem, we propose an adaptive importance sampling algorithm, AIS-BN,
that shows promising convergence rates even under extreme conditions and seems
to outperform the existing sampling algorithms consistently. Three sources of
this performance improvement are (1) two heuristics for initialization of the
importance function that are based on the theoretical properties of importance
sampling in finite-dimensional integrals and the structural advantages of
Bayesian networks, (2) a smooth learning method for the importance function,
and (3) a dynamic weighting function for combining samples from different
stages of the algorithm. We tested the performance of the AIS-BN algorithm
along with two state of the art general purpose sampling algorithms, likelihood
weighting (Fung and Chang, 1989; Shachter and Peot, 1989) and self-importance
sampling (Shachter and Peot, 1989). We used in our tests three large real
Bayesian network models available to the scientific community: the CPCS network
(Pradhan et al., 1994), the PathFinder network (Heckerman, Horvitz, and
Nathwani, 1990), and the ANDES network (Conati, Gertner, VanLehn, and Druzdzel,
1997), with evidence as unlikely as 10^-41. While the AIS-BN algorithm always
performed better than the other two algorithms, in the majority of the test
cases it achieved orders of magnitude improvement in precision of the results.
Improvement in speed given a desired precision is even more dramatic, although
we are unable to report numerical results here, as the other algorithms almost
never achieved the precision reached even by the first few iterations of the
AIS-BN algorithm
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