56,510 research outputs found
Why not Merge the International Monetary Fund (IMF) with the International Bank for Reconstruction and Development (World Bank)
Motivation: Cellular Electron CryoTomography (CECT) is an emerging 3D imaging technique that visualizes subcellular organization of single cells at sub-molecular resolution and in near-native state. CECT captures large numbers of macromolecular complexes of highly diverse structures and abundances. However, the structural complexity and imaging limits complicate the systematic de novo structural recovery and recognition of these macromolecular complexes. Efficient and accurate reference-free subtomogram averaging and classification represent the most critical tasks for such analysis. Existing subtomogram alignment based methods are prone to the missing wedge effects and low signal-to-noise ratio (SNR). Moreover, existing maximum-likelihood based methods rely on integration operations, which are in principle computationally infeasible for accurate calculation. Results: Built on existing works, we propose an integrated method, Fast Alignment Maximum Likelihood method (FAML), which uses fast subtomogram alignment to sample sub-optimal rigid transformations. The transformations are then used to approximate integrals for maximum-likelihood update of subtomogram averages through expectation-maximization algorithm. Our tests on simulated and experimental subtomograms showed that, compared to our previously developed fast alignment method (FA), FAML is significantly more robust to noise and missing wedge effects with moderate increases of computation cost. Besides, FAML performs well with significantly fewer input subtomograms when the FA method fails. Therefore, FAML can serve as a key component for improved construction of initial structuralmodels frommacromolecules captured by CECT
Role of nucleon resonance excitation in meson photoproduction
The resonance effects are investigated in the meson photoproduction
near threshold through a quark model approach with an effective Lagrangian. The
diffractive contribution is consistently estimated by the {\it t}-channel
Pomeron exchange. Another non-diffractive process, {\it t}-channel
exchange is also included. The numerical result shows that the Pomeron exchange
plays dominant role in the meson photoproduction, while the cross
sections of the non-diffractive processes, i.e. {\it s}- and {\it u}-channel
excitations, and {\it t}-channel exchange, are quite small. In the
polarization observables, we find that large asymmetries are produced in the
backward direction by the interferences from the {\it s}- and {\it u}-channel
resonances, while in the forward direction, only very small asymmetries are
generated. Meanwhile, we find that the effects from the exchange are
generally negligible.Comment: Contribution to "2nd International Conference on Perspectives in
Hadronic Physics", Trieste, ICTP, 10-14 May 1999, to appear in Few-body
Syste
Hawking Radiation of an Arbitrarily Accelerating Kinnersley Black Hole: Spin-Acceleration Coupling Effect
The Hawking radiation of Weyl neutrinos in an arbitrarily accelerating
Kinnersley black hole is investigated by using a method of the generalized
tortoise coordinate transformation. Both the location and temperature of the
event horizon depend on the time and on the angles. They coincide with previous
results, but the thermal radiation spectrum of massless spinor particles
displays a kind of spin-acceleration coupling effect.Comment: 8 pages, no figure, revtex 4.0, revisted version with typesetting
errors and misprint correcte
Non-existence of New Quantum Ergosphere Effect of a Vaidya-type Black Hole
Hawking evaporation of Dirac particles and scalar fields in a Vaidya-type
black hole is investigated by the method of generalized tortoise coordinate
transformation. It is shown that Hawking radiation of Dirac particles does not
exist for components but for components in any
Vaidya-type black holes. Both the location and the temperature of the event
horizon change with time. The thermal radiation spectrum of Dirac particles is
the same as that of Klein-Gordon particles. We demonstrates that there is no
new quantum ergosphere effect in the thermal radiation of Dirac particles in
any spherically symmetry black holes.Comment: Latex, 9 pages, no figure, submitted to Mod. Phys. Lett.
Isospin breaking in scalar and pseudoscalar channels of radiative -decays
In the framework of simple assumption on factorizing a mixing of vector state
with isoscalar components in effective amplitudes of isospin breaking caused by
the electromagnetic quark current, a branching fraction of radiative transition is evaluated at the level of .Comment: 3 pages, revtex4 class, 2 eps-figures; reference, comment and
acknowledgement adde
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