766 research outputs found
Comment on " a unified scheme for flavored mesons and baryons"
We would comment on the results of the paper "a unified scheme for flavored
mesons and baryons" (P.C.Vinodkumar, J.N.Panandya, V.M.Bannur, and
S.B.Khadkikar Eur. Phys. J. A4(1999)83), and point out some inconsistencies and
mistakes in the work for solving the Dirac equation. In terms of an example for
a single particle we investigate the reliability of the perturbative method for
computing the Coulomb energy and discuss the contribution to the wavefunction
at origin from the Coulomb potential. We conclude that the accuracy of their
numerical results needs to be reconsidered.Comment: Latex file, 11page
Microstructures and mechanical properties of pure tantalum processed by high-pressure torsion
A body-centred cubic (BCC) structure metal, tantalum, was processed by high- pressure torsion (HPT) at room temperature with different numbers of rotations. The microstructural evolution was studied by electron backscatter diffraction (EBSD). The grain sizes were significantly refined at the disk edge area in the early stages of deformation (N = 0.5) but tended to attain saturation after the numbers of rotations was increased to N = 5. As the deformation continued, some coarse grains appeared in the disk edge areas and it appeared that there was structural recovery at the expense of grain boundary migration in the tantalum during HPT processing. Microhardness measurements showed the hardness gradually evolved towards a more homogenized level across the disk surfaces as the numbers of rotations increased. The hardness level after N = 10 turns was slightly lower than after N = 5 turns, thereby indicating the occurrence of a recovery process after 5 turn
The significance of self-annealing in two-phase alloys processed by high-pressure torsion
The Zn-22% Al eutectoid alloy and the Pb-62% Sn eutectic alloy were processed by high-pressure torsion (HPT) over a range of experimental conditions. Both alloys exhibit similar characteristics with significant grain refinement after processing by HPT but with a reduction in the hardness values by comparison with the initial unprocessed conditions. After storage at room temperature for a period of time, it is shown that the microhardness of both alloys gradually recovers to close to the initial unprocessed values. Electron backscatter diffraction (EBSD) measurements on the Pb-Sn alloy suggest that the self-recovery behaviour is correlated with the fraction of high-angle grain boundaries (HAGBs) after HPT processing. Thus, high fractions of HAGBs occur immediately after processing and this favours grain boundary migration and sliding which is important in the self-annealing and recovery process. Conversely, the relatively lower fractions of HAGBs occurring after annealing at room temperature are not so conducive to easy migration and slidin
Continuous-variable controlled-Z gate using an atomic ensemble
The continuous-variable controlled-Z gate is a canonical two-mode gate for
universal continuous-variable quantum computation. It is considered as one of
the most fundamental continuous-variable quantum gates. Here we present a
scheme for realizing continuous-variable controlled-Z gate between two optical
beams using an atomic ensemble. The gate is performed by simply sending the two
beams propagating in two orthogonal directions twice through a spin-squeezed
atomic medium. Its fidelity can run up to one if the input atomic state is
infinitely squeezed. Considering the noise effects due to atomic decoherence
and light losses, we show that the observed fidelities of the scheme are still
quite high within presently available techniques.Comment: 7 pages, 3 figures, to appear in Physical Review
An expectation-maximization algorithm for probabilistic reconstructions of full-length isoforms from splice graphs.
Reconstructing full-length transcript isoforms from sequence fragments (such as ESTs) is a major interest and challenge for bioinformatic analysis of pre-mRNA alternative splicing. This problem has been formulated as finding traversals across the splice graph, which is a directed acyclic graph (DAG) representation of gene structure and alternative splicing. In this manuscript we introduce a probabilistic formulation of the isoform reconstruction problem, and provide an expectation-maximization (EM) algorithm for its maximum likelihood solution. Using a series of simulated data and expressed sequences from real human genes, we demonstrate that our EM algorithm can correctly handle various situations of fragmentation and coupling in the input data. Our work establishes a general probabilistic framework for splice graph-based reconstructions of full-length isoforms
Simplified Optimization Model for Low-Thrust Perturbed Rendezvous Between Low-Eccentricity Orbits
Trajectory optimization of low-thrust perturbed orbit rendezvous is a crucial
technology for space missions in low Earth orbits, which is difficult to solve
due to its initial value sensitivity, especially when the transfer trajectory
has many revolutions. This paper investigated the time-fixed perturbed orbit
rendezvous between low-eccentricity orbits and proposed a priori quasi-optimal
thrust strategy to simplify the problem into a parametric optimization problem,
which significantly reduces the complexity. The optimal trajectory is divided
into three stages including transfer to a certain intermediate orbit,
thrust-off drifting and transfer from intermediate orbit to the target orbit.
In the two transfer stages, the spacecraft is assumed to use a parametric law
of thrust. Then, the optimization model can be then obtained using very few
unknowns. Finally, a differential evolution algorithm is adopted to solve the
simplified optimization model and an analytical correction process is proposed
to eliminate the numerical errors. Simulation results and comparisons with
previous methods proved this new method's efficiency and high precision for
low-eccentricity orbits. The method can be well applied to premilitary analysis
and high-precision trajectory optimization of missions such as in-orbit service
and active debris removal in low Earth orbits
In-Process Global Interpretation for Graph Learning via Distribution Matching
Graphs neural networks (GNNs) have emerged as a powerful graph learning model
due to their superior capacity in capturing critical graph patterns. To gain
insights about the model mechanism for interpretable graph learning, previous
efforts focus on post-hoc local interpretation by extracting the data pattern
that a pre-trained GNN model uses to make an individual prediction. However,
recent works show that post-hoc methods are highly sensitive to model
initialization and local interpretation can only explain the model prediction
specific to a particular instance. In this work, we address these limitations
by answering an important question that is not yet studied: how to provide
global interpretation of the model training procedure? We formulate this
problem as in-process global interpretation, which targets on distilling
high-level and human-intelligible patterns that dominate the training procedure
of GNNs. We further propose Graph Distribution Matching (GDM) to synthesize
interpretive graphs by matching the distribution of the original and
interpretive graphs in the feature space of the GNN as its training proceeds.
These few interpretive graphs demonstrate the most informative patterns the
model captures during training. Extensive experiments on graph classification
datasets demonstrate multiple advantages of the proposed method, including high
explanation accuracy, time efficiency and the ability to reveal class-relevant
structure.Comment: Under Revie
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