2,482 research outputs found
On the bilateral preconditioning for an L2-type all-at-once system arising from time-space fractional Bloch-Torrey equations
Time-space fractional Bloch-Torrey equations (TSFBTEs) are developed by some
researchers to investigate the relationship between diffusion and
fractional-order dynamics. In this paper, we first propose a second-order
implicit difference scheme for TSFBTEs by employing the recently proposed
L2-type formula [A. A. Alikhanov, C. Huang, Appl. Math. Comput. (2021) 126545].
Then, we prove the stability and the convergence of the proposed scheme. Based
on such a numerical scheme, an L2-type all-at-once system is derived. In order
to solve this system in a parallel-in-time pattern, a bilateral preconditioning
technique is designed to accelerate the convergence of Krylov subspace solvers
according to the special structure of the coefficient matrix of the system. We
theoretically show that the condition number of the preconditioned matrix is
uniformly bounded by a constant for the time fractional order . Numerical results are reported to show the efficiency of our
method.Comment: 24 pages, 6 tables, 4 figure
On the Generation of Medical Question-Answer Pairs
Question answering (QA) has achieved promising progress recently. However,
answering a question in real-world scenarios like the medical domain is still
challenging, due to the requirement of external knowledge and the insufficient
quantity of high-quality training data. In the light of these challenges, we
study the task of generating medical QA pairs in this paper. With the insight
that each medical question can be considered as a sample from the latent
distribution of questions given answers, we propose an automated medical QA
pair generation framework, consisting of an unsupervised key phrase detector
that explores unstructured material for validity, and a generator that involves
a multi-pass decoder to integrate structural knowledge for diversity. A series
of experiments have been conducted on a real-world dataset collected from the
National Medical Licensing Examination of China. Both automatic evaluation and
human annotation demonstrate the effectiveness of the proposed method. Further
investigation shows that, by incorporating the generated QA pairs for training,
significant improvement in terms of accuracy can be achieved for the
examination QA system.Comment: AAAI 202
Diaquabis(2-methyl-1H-imidazol-3-ium-4,5-dicarboxylato-κ2 O,O′)magnesium
The title compound, [Mg(C6H5N2O4)2(H2O)2], was prepared by reaction of Mg(NO3)2 and 2-methyl-1H-imidazole-4,5-dicarboxylic acid under hydrothermal conditions. The MgII atom lies on an inversion centre and displays a distorted octahedral coordination geometry. An extended three-dimensional network of intermolecular O—H⋯O and N—H⋯O hydrogen bonds stabilizes the crystal structure
Tris{2-methoxy-6-[(4-methylphenyl)iminiomethyl]phenolato-κ2 O,O′}tris(thiocyanato-κN)cerium(III)
The asymmetric unit of the title compound, [Ce(NCS)3(C15H15NO2)3], contains three Schiff base 2-methoxy-6-[(4-methylphenyl)iminomethyl]phenol (HL) ligands and three independent thiocyanate ions that coordinate the cerium ion via their N atoms. The protonated imine N atoms are involved in an intramolecular hydrogen bond with the respective phenoxide group. The Ce(III) ion exhibits a coordination number of nine
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