ISSN 0253-2778

CN 34-1054/N

2021 Vol. 51, No. 6

Research Reviews
The application of immersive virtual reality technology in geoscience
Luo Ting, Leng Wei
2021, 51(6): 431-440. doi: 10.52396/JUST-2021-0073
In recent years, with the development of science and technology, a large amount of measurement and simulation data in the field of geoscience has emerged,posing challenges to data visualization and real-time analysis. Traditional two-dimensional visualization methods can no longer fully meet the scientific research and teaching needs of geoscience. The new generation of immersive virtual reality technology enables observers to intuitively observe and analyze the scientific data of the three-dimensional earth, and interact with the data to achieve immersive real-time analysis or remote virtual field surveys. This will help researchers in the field of geoscience to understand the three-dimensional geoscience data more quickly and accurately; promote the generation of new scientific discoveries; and help popularize the results of geoscience among the general public. At present, many scholars have carried out related explorations and achieved a series of important results. This article reviews the basic principles of immersive virtual reality technology and various specific applications in the field of geoscience in the past few decades, discusses the advantages and prospects of this technology in the field of geoscience, and the related issues that need to be resolved to further expand the application level.
Research Reviews: Physics
Searching for radio pulsation from SGR 1935+2154 with the Parkes ultra-wideband low receiver
Tang Zhenfan, Zhang Songbo, Dai Shi, Li Ye, Wu Xuefeng
2021, 51(6): 441-446. doi: 10.52396/JUST-2021-0132
Magnetars have been proposed to be the origin of the fast radio bursts (FRBs) soon after its initial discovery. The detection of the first Galactic FRB 200428 from SGR 1935+2154 has made this hypothesis more convincing. In October 2020, this source was supposed to be in an extremely active state again. We then carried out a 1.6-hours follow-up observation of SGR 1935+2154 using the new ultra-wideband low (UWL) receiver of the Parkes 64 m radio telescope covering a frequency range of 704-4032 MHz. However, no convincing signal was detected in either of our single pulse or periodicity searches. We obtained a limit on the flux density of periodic signal of 3.6 μJy using the full 3.3 GHz bandwidth data sets, which is the strictest limit for that of SGR 1935+2154. Our full bandwidth limit on the single pulses fluence is 35 mJy ms, which is well below the brightest single pulses detected by the FAST radio telescope just two days before our observation. Assuming that SGR 1935+2154 is active during our observation, our results suggest that its radio bursts are either intrinsically narrow-band or show a steep spectrum.
Research Reviews: Mathematics
A fourth order linear parabolic equation on conical surfaces
Zhang Fangxu
2021, 51(6): 447-452. doi: 10.52396/JUST-2021-0076
A parabolic equation of fourth order on surfaces with conical singularities is considered. By the analysis of energy and approximations, the existence and uniqueness of the solution of this equation in a special space that has some approximation property are proved. Finally, it's proved that the property is equivalent to the finiteness of energy for some functions when β∈(-1,0).
Research Reviews: Earth and Space Sciences
Transit-time scattering of radiation belt electrons by off-equatorially generated magnetosonic waves
Wu Zhiyong, Su Zhenpeng
2021, 51(6): 453-458. doi: 10.52396/JUST-2021-0123
In the inner magnetosphere, the magnetosonic waves have been proposed to transit-time scatter the radiation belt electrons over a broad range of energy and pitch-angle. Recent observations have shown that magnetosonic waves can be generated in the off-equatorial plasmasphere, whose latitudinal coverage and propagation angle are significantly different from the traditional magnetosonic waves confined near the equator. Using our previously-developed test-particle code, we here investigate the possible transit-time scattering of radiation belt electrons by the off-equatorially generated magnetosonic waves. Our results indicate that the transit-time scattering is primarily related to the perturbation near the edge of the finite wave train. The extending of wave occurrence latitudes causes the shrinking of the equatorial pitch-angle range of the transit-time scattering. Compared to the near-equatorially confined magnetosonic waves, the off-equatorially generated magnetosonic waves produce ignorable pitch-angle perturbations but slightly stronger energy perturbations.
A new high-resolution δ13Ccarb record for the Early-Middle Triassic: Insights from the Tianshengqiao section, South China
Zhang Guijie, Zhang Xiaolin, Zhou Changyong, Huang Jinyuan, Zhang Qiyue, Hu Shixue, Wen Wen, Huang Xiemin
2021, 51(6): 459-467. doi: 10.52396/JUST-2021-0128
Previous studies have documented remarkable changes in the carbon cycle during the Early Triassic. To verify these trends and improve our understanding of carbon cycling during the Early-Middle Triassic, we investigate the new δ13Ccarb record for the Early-Middle Triassic in the Tianshengqiao section of South China. Our study shows that the δ13Ccarb values in the Tianshengqiao section have received minimal diagenetic alterations. The δ13Ccarb profile initially shows a negative excursion of 2.2‰ within the Member I of the Jialingjiang Formation, followed by a positive excursion of 3.8‰ in the lower part of the Member III of the Jialingjiang Formation. After that, δ13Ccarb displays a negative excursion of 2.5‰ in the Member III of the Jialingjiang Formation, followed by a positive excursion with a maximum of +5.0‰ at the base of the Member I of the Guanling Formation. Above the maximum value, the δ13Ccarb profile exhibits a third negative excursion and then recovers and stabilizes around +1‰ to +2‰ through the Member II of the Guanling Formation to the Yangliujing Formation. The observed trend of the δ13Ccarb profile in the Tianshengqiao section can be correlated with the global C-isotopic excursions derived from the coeval sections worldwide. The similarity of the Early-Middle Triassic δ13Ccarb profile to those from other sections worldwide is indicative of the near completeness of the stratigraphic interval of the Tianshengqiao section. Our results suggest that the δ13Ccarb profile in the Tianshengqiao section represents a global carbon cycle perturbation. The stratigraphic coincidence between the carbon cycle perturbation and the limited biotic recovery has been documented in the Tianshengqiao section, suggesting that the physical mechanism of the carbon cycle perturbation may have contributed to the prolonged biotic recovery.
Research Reviews: Management Science and Engineering
Application of network vector autoregression model in volatility spillover analysis
Gai Wei, Hu Jie
2021, 51(6): 468-474. doi: 10.52396/JUST-2021-0097
Measuring the network connectedness of the financial system is of great importance in systemic risk analysis, and has drawn great attention in recent years. In this paper, we apply the transfer entropy method to analyze the volatility spillover network connectedness of the U.S. stock market. Based on the network structure, we apply the network vector autoregression model (NVAM) and are interested in identifying the influential firms in volatility spillover network of the financial system. In addition, by using rolling windows, the dynamics of total volatility spillover network connectedness indices are obtained, which shows a sharp rise at the beginning of the financial crisis, while it only fluctuates within a controllable range in the steady economic period. The results show that transfer entropy has great potential for understanding the correlation and information flow of financial markets.
Measuring systemic risk contribution with CoGVaR approach
Zhang Ping, Wang Yashi, Wu Qinyu
2021, 51(6): 475-484. doi: 10.52396/JUST-2021-0140
We propose a new conditional risk measure, conditional generalized value-at-risk (CoGVaR), from the perspective of measuring systemic risk. The new class of risk measures is a natural generalization of the conditional quantiles including the classic CoVaR. Compared with the classic conditional value-at-risk (CoVaR) and conditional expectile (CoExpectile), it has more potential application in reality as it takes the risk attitude of the decision maker into consideration, which has not been the focus of much study to date. Using generalized quantile regression approach with state variables added, some calculation results are presented in the Dow Jones U.S. Financials Index case, and it is shown that it provides a new perspective on systemic risk contribution. In addition, the result shows that our risk measure can capture the tail risk by using more convex disutility function.
Research Reviews: Chemistry
Hydrogen activation over stoichiometric and defective CeO2 surfaces: A first-principles study
Chen Zihui, Zhao Chuanlin, Liu Jinxun, Li Weixue
2021, 51(6): 485-493. doi: 10.52396/JUST-2021-0084
Hydrogen activation plays a pivotal role in hydrogenation reactions over transition metal oxide catalysts. Clarifying hydrogen activation over ceria oxide (CeO2) is an important issue in the acetylene hydrogenation reaction. Employing density functional theory (DFT) calculations, we studied hydrogen activation over stoichiometric and defective CeO2(111), (110), and (100) surfaces. Hydrogen dissociates on the stoichiometric CeO2 surfaces only forming hydroxyl groups. The presence of oxygen vacancies can promote the H2 activation over the defective CeO2 surfaces. Both H+ and H- species can be found on the defective CeO2(111) and (100) surfaces, whereas only H+ species can be observed on the defective CeO2(110) surface. The structure sensitivity of the H2 activation over the stoichiometric and defective CeO2 surfaces is correlated with H+ and H- adsorption energies determined by the ability of the surface oxygen vacancy formation and charge distributions of Ce and O ions. Our work provides more insight into H2 activation on CeO2-based catalysts which will guide better catalyst design for hydrogenation reactions.
Preparation of hollow silica microsphere and its effect on the thermal conductivity of polymer composites
SHU Jingjing, CHEN Jian, CHEN Yawei, ZHAO Chu, WANG Mozhen, GE Xuewu
2021, 51(6): 494-504. doi: 10.52396/JUST-2021-0072
The thermal conductivity of polymer composites filled with hollow microspheres is closely related to the content and structure of hollow microspheres. In this paper, micron-sized monodisperse polystyrene (PS) microspheres are synthesized as the sacrificial template to prepare a series of hollow SiO2 (H-SiO2) microspheres with different inner and outer radius ratios (r/R).The r/R value is controlled by the relative content of PS microspheres and tetraethyl orthosilicate (TEOS). The chemical composition and morphology of H-SiO2 microspheres are characterized by infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Further, H-SiO2 microspheres are blended with polydimethylsiloxane (PDMS) at a certain content to obtain H-SiO2/PDMS composite rubbers. The effect of the content and the r/R value of H-SiO2 microspheres on the thermal conductivity of the composite rubber are investigated.Combined with the theoretical model calculation on the thermal conductivity of the silicone rubber,it can be concluded that the addition of H-SiO2 microspheres with a complete hollow structure and an r/R value higher than 0.963 can reduce the thermal conductivity of H-SiO2/PDMS composite rubbers.The more the H-SiO2 microspheres, the smaller the thermal conductivity of the composite rubber.At the same time, when the mass fraction of H-SiO2 microspheres is no more than 5%, the mechanical properties of the H-SiO2/PDMS composite rubber are also enhanced with the increase of the weight content of H-SiO2 microspheres. This work provides theoretical and experimental guidance for the design and preparation of high-performance hollow microspheres filled with polymer thermal insulation materials.