ISSN 0253-2778

CN 34-1054/N

2020 Vol. 50, No. 12

Research Letter
Holographic preheating
CAI Yifu, LIN Shu, LIU Junyu, SUN Jiarui
2020, 50(12): 1447-1452. doi: 10.3969/j.issn.0253-2778.2020.12.001
We propose a holographic description of cosmic preheating at strong coupling. In this scenario the energy transfer between the inflation and matter field is mimicked by a model of holographic superconductor. An exponential amplification of the matter field during preheating can be described by the quasi-normal modes of a metastable " black hole" in the bulk spacetime with an expanding boundary. Our results reveal that the matter field can be produced continuously at strong coupling in contrast to the case of weak coupling with a discontinuous matter growth as inflaton oscillates. Furthermore, the amplification of matter field has an enhanced dependence on the vacuum expectation value of the inflaton at strong coupling. By virtue of the proposed mechanism, physics of the very early universe at an extremely high temperature right after inflaton may become accessible.
Review Article
Progress in the research of trace elements in sapropelic coal of China
GUI Lin, LIU Guijian, LIU Yuan
2020, 50(12): 1453-1459. doi: 10.3969/j.issn.0253-2778.2020.12.002
Coal is the main energy source in China whose extensive use will cause a series of environmental problems, especially the migration and precipitation of its harmful trace elements. Although there is already a relatively complete research system of trace elements in coal, its trace element geochemistry research is far less developed than that of humic coal, due to the secondary economic status of sapropel. The extensive and thick distribution of sapropelic coal gives it a certain industrial value, and the content characteristics of trace elements in sapropelic coal have been partially reported. However, the modes of occurrence, enrichment mechanism and geological origin of trace elements in sapropelic coal need to be systematically studied. Therefore, based on the comprehensive analysis of domestic and foreign research on sapropel, this paper elaborates the hot issues, key contents and development direction of trace element geochemistry of sapropel. The geochemical research on sapropel is a supplement and improvement of coal geology and coal geochemistry theory, which has important scientific significance, It is also of great practical significance as its beneficial to the theoretical system of coal formation and resource development of special coal in China.
Research Article
Anisotropic surface meshing using locally isometric embedding
LI Huicong, FU Xiaoming
2020, 50(12): 1460-1471. doi: 10.3969/j.issn.0253-2778.2020.12.003
A novel method for anisotropic surface meshing was proposed. Different from the previous methods using globally conformal embeddings or high-dimensional isometric embeddings, our algorithm is based on the idea of locally isometric embedding. In order to achieve isometric embeddings, the input surface was partitioned into a set of cone patches that are remeshed one by one. First, a patch was parameterized bijectively into a plane, then an anisotropic mesh was generated in the parameterized domain, and finally, the remeshed patch was mapped back to the input surface. To deal with the stitching problem between different patches, the cone patch was made containing the previously unprocessed boundary. Therefore, the triangles near the boundary could be remeshed. The robustness of our method was demonstrated on various complex meshes. Compared to the existing methods, our method is more robust, and contains a smaller approximation error to the input mesh.
A novel linear iteration method for M-matrix algebraic Riccati equations
GUAN Jinrui, FENG Yuehua
2020, 50(12): 1472-1477. doi: 10.3969/j.issn.0253-2778.2020.12.004
Numerical solutions of the M-matrix algebraic Riccati equation (MARE) were studied, which has become a hot topic in recent years due to its broad applications. A novel linear iteration method for computing the minimal nonnegative solution of MARE was proposed, in which only matrix multiplications are needed at each iteration. Convergence of the new method was proved by choosing proper parameters for the MARE associated with a nonsingular M-matrix or an irreducible singular M- matrix. Theoretical analysis and numerical experiments show that the new method is feasible and is effective than some existing methods under certain conditions.
Lp quantile regression with realized measure
2020, 50(12): 1478-1487. doi: 10.3969/j.issn.0253-2778.2020.12.005
A new financial risk model named Lp quantile regression with a realized measure (realized Lp quantile) was proposed. The realized measure and Lp quantiles were combined and Lp quantile were added to the measurement equation. The realized Lp quantile model is a generic model that includes realized quantile model and expectile model. An asymmetric exponential power distribution (AExpPow) was proposed to derive the formula of log-likelihood. And a simulation was conducted to justify the validity of the log-likelihood. Finally an empirical study was conducted to justify the validity of the realized Lp quantile. And some conclusions were drawn as follows: differfent power indices suit different data and different time-frequencies suit different realized measures, and higher frequency is not always better.
Heterogeneous causal inference of corporate profitability using two-scale distributional nearest neighbor estimation
HE Yu, WU Yue, ZHENG Zemin, WU Jie
2020, 50(12): 1488-1497. doi: 10.3969/j.issn.0253-2778.2020.12.006
The heterogeneous treatment effect is the center of gravity in modern causal inference and is also widely used in the financial field. Studying the heterogeneous effect of improving solvency on the profitability of listed companies with different operational capabilities can eliminate the impact of individual differences in listed companies and make the estimation results more accurate. The two-scale distributional nearest neighbor (DNN) is able to eliminate the first-order finite sample bias in the estimate, and it is asymptotically unbiased and asymptotically normal under regularization conditions. Therefore, an empirical analysis was conducted of the financial indicators of Chinese listed companies in the CSMAR financial statement database by using the two-scale distributional nearest neighbor estimation. And a study was carried out on that whether there is heterogeneity in the impact of corporate solvency reduction on corporate profitability under different operating capabilities. Corresponding suggestions were given for optimizing the financial structure and improving the profitability of listed companies.
Quasi-normal modes and holographic renormalization of holographic preheating
CAI Yifu, LIN Shu, LIU Junyu, SUN Jiarui
2020, 50(12): 1498-1506. doi: 10.3969/j.issn.0253-2778.2020.12.007
In the holographic description of cosmic preheating, the energy transfer between the inflaton and matter field at strong coupling is suggested to be mimicked by superfluid and normal components of a superconductor on Friedmann-Robertson-Walker (FRW) boundary in an asymptotically Anti-de Sitter (AdS) spacetime. In this paper we investigated two aspects of the scenario of holographic preheating that are not included in the accompanied work. Firstly, we study in detail the evolution of the quasi- normal modes ( QNMs) surrounding a metastable hairy black hole. This analysis can quantitatively describe the preheating process of the matter field that is produced continuously in the case of strong coupling. Secondly, we present a detailed analysis of the holographic renormalization for the AdS-FRW background, which allows us to extract operator expectation values for studying cosmological implications.
Quantum algorithms for ranking nodes of network
LU Binhan, HAN Yongjian, WU Yuchun, LI Ye, AN Ningbo, DOU Menghan, ZHAO Dongyi, GUO Guoping
2020, 50(12): 1507-1515. doi: 10.3969/j.issn.0253-2778.2020.12.008
Ranking the node of a network is one of the central problems in a complex network. Here, An improved SpringRank method was proposed that builds an adaptive physical model with variable-spring connected between nodes and a novel penalty function. By minimizing the penalty function, the method can rank the nodes of a directed and weighted complex network. To decrease the computation complexity which increases too fast with the number of nodes, quantum algorithms were used to speed up the process of minimizing the penalty functions. The convexity enables us to find the minimum by solving a linear system. When the linear system has the properties of sparsity and a small conditional number, we use the HHL algorithm to find the minimum of the penalty function by solving the linear equation. And we use the QITE algorithm to find the minimum by updating the parameters iteratively when the linear system doesn’ t have those properties. Lastly, using the quantum simulator QPanda, we implemented the algorithms for several networks and gave the right ranking results.
Modified Stoney formula for in-situ lithiation stress measurement in thin-film Si electrode
LIU Peilin, LU Yuyang, ZHENG Dongchang, HE Linghui, NI Yong
2020, 50(12): 1516-1524. doi: 10.3969/j.issn.0253-2778.2020.12.009
The multi-beam optical stress sensor method combined with Stoney equation is an effective approach to measure in-situ average stress in thin film electrodes upon lithiation / delithiation. However, the classic Stoney formula is applicable only at low stress states. A modified Stoney formula for stress measurement in thin-film Si electrodes was applied to account for the combined effects of the Li concentration-dependent material properties and large substrate curvature change. The numerical results based on three-dimensional non-linear finite element model for the full coupling of large deformation and Li diffusion confirm the accuracy of the modified Stoney equation. Further, a critical condition for the curvature bifurcation was discussed, which should be avoid when using the modified Stoney equation.