This paper presents an ultralow-frequency cyclic loading creep test system for rock salt.The system comprises five subsystems:a cyclic load generation system,a triaxial pressure chamber,a pressure and deformation moni...This paper presents an ultralow-frequency cyclic loading creep test system for rock salt.The system comprises five subsystems:a cyclic load generation system,a triaxial pressure chamber,a pressure and deformation monitoring system,a signal acquisition and load control integrated system,and an automatic oil replenishment and discharge system.This test system overcomes the limitations of traditional electrohydraulic servo creep testing machines and gravity loading creep testing machines when conducting low-frequency cyclic load creep tests.This allows for long-term(1-2 years)creep tests under extremely-low-frequency cyclic loading conditions,which simulate the actual operating conditions of salt cavern gas storage.The cyclic load generation system converted constant-weight loads into a continuously variable hydraulic oil pressure and amplified the oil pressure using a pressure intensifier,which provided a stable load source for the test system.Using this test system,creep tests were performed under low-frequency cyclic loading with periods of 1 d and 7 d.The results showed that the test system performed well,as evidenced by the validation of the loading capacity,loading stability,and temperature control stability.Comparing the creep deformation of rock salt samples with the cyclic periods of 1 d and 7 d,it was observed that,within this cyclic period range,the creep deformation of the sample increased with higher loading frequencies,provided that the cyclic loading waveform and stress remained constant.展开更多
Interlayer interactions at the heterointerfaces of van der Waals heterostructures (vdWHs), which consist of vertically stacked two-dimensional materials, play important roles in determining their properties. The inter...Interlayer interactions at the heterointerfaces of van der Waals heterostructures (vdWHs), which consist of vertically stacked two-dimensional materials, play important roles in determining their properties. The interlayer interactions are tunable from noncoupling to strong coupling by controlling the twist angle between adjacent layers. However, the influence of stacking sequence and individual component thickness on the properties of vdWHs has rarely been explored. In this work, the influence of the stacking sequence of WSe2 and graphene in vdWHs of graphene-on-WSe2 (graphene/WSe2) or WSe2-on-graphene (WSe2/graphene), as well as their thickness, on their interlayer interaction was systematically investigated by ultralow-frequency (ULF) Raman spectroscopy. A series of ULF breathing modes of WSe2 nanosheets in these vdWHs were observed with frequencies highly dependent on graphene thickness. Interestingly, the ULF breathing modes of WSe2 red-shifted in graphene/WSe2 and WSe2/graphene configurations, and the amount of shift in the former was much larger than that in the latter. In contrast, no obvious ULF shift was observed by varying the twist angle between WSe2 and graphene. This indicates that the interlayer interaction is more sensitive to the stacking sequence compared with the twist angle. The results provide alternative approaches to modulate the interlayer interaction of vdWHs and, thus, tune their optical and optoelectronic properties.展开更多
The properties of two-dimensional(2D)materials are highly dependent on their phase and thickness.Various phases exist in tin disulfide(SnS_(2)),resulting in promising electronic and optical properties.Hence,accurately...The properties of two-dimensional(2D)materials are highly dependent on their phase and thickness.Various phases exist in tin disulfide(SnS_(2)),resulting in promising electronic and optical properties.Hence,accurately identifying the phase and thickness of SnS_(2)nanosheets is prior to their optoelectronic applications.Herein,layered 2H-SnS_(2)and 4H-SnS_(2)crystals were grown by chemical vapor transportation and the crystalline phase of SnS_(2)was characterized by X-ray diffraction,ultralow frequency(ULF)Raman spectroscopy and high-resolution transmission electron microscope.As-grown crystals were mechanically exfoliated to single-and few-layer nanosheets,which were investigated by optical microscopy,atomic force microscopy and ULF Raman spectroscopy.Although the 2H-SnS_(2)and 4H-SnS_(2)nanosheets have similar optical contrast on SiO_(2)/Si substrates,their ULF Raman spectra obviously show different shear and breathing modes,which are highly dependent on their phases and thicknesses.Interestingly,the SnS_(2)nanosheets have shown phase-dependent electrical properties.The 4H-SnS_(2)nanosheet shows a current on/off ratio of 2.58×10^(5) and excellent photosensitivity,which are much higher than those of the 2H-SnS_(2)nanosheet.Our work not only offers an accurate method for identifying single-and few-layer SnS_(2)nanosheets with different phases,but also paves the way for the application of SnS_(2)nanosheets in highperformance optoelectronic devices.展开更多
This study reports the rare ultralow-frequency(ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17(Geostationary Operational Environmental Satel...This study reports the rare ultralow-frequency(ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17(Geostationary Operational Environmental Satellite) in the magnetosphere, the CSES(China Seismo-Electromagnetic Satellite) in the ionosphere, and the THEMIS ground-based observatories(GBO) GAKO and EAGL in the Earth's polar region during the main phase of an intense storm on 4 November 2021. Along with the enhanced-pressure solar wind moving tailward, the geomagnetic field structure experienced a large-scale change. From dawn/dusk sides to midnight, the GAKO, EAGL, and GOES-17 sequentially observed the ULF waves in a frequency range of0.04–0.36 Hz at L shells of ~5.07, 6.29, and 5.67, respectively. CSES also observed the ULF wave event with the same frequency ranges at wide L-shells of 2.52–6.22 in the nightside ionosphere. The analysis results show that the ULF waves at ionospheric altitude were mixed toroidal-poloidal mode waves. Comparing the ULF waves observed in different regions, we infer that the nightside ULF waves were directly or indirectly excited by the solar wind dynamic pressure increase: in the area of L-shells~2.52–6.29, the magnetic field line resonances(FLRs) driven by the solar wind dynamic pressure increase is an essential excitation source;on the other hand, around L~3.29, the ULF waves can also be excited by the outward expansion of the plasmapause owing to the decrease of the magnetospheric convection, and in the region of L-shells ~5.19–6.29, the ULF waves are also likely excited by the ion cyclotron instabilities driven by the solar wind dynamic pressure increase.展开更多
基金funding support from the General Program of the National Natural Science Foundation of China(Grant No.52374069)the Excellent Young Scientists Fund Program of the National Natural Science Foundation of China(Grant No.52122403)the Youth Innovation Promotion Association CAS(Grant No.Y2023089).
文摘This paper presents an ultralow-frequency cyclic loading creep test system for rock salt.The system comprises five subsystems:a cyclic load generation system,a triaxial pressure chamber,a pressure and deformation monitoring system,a signal acquisition and load control integrated system,and an automatic oil replenishment and discharge system.This test system overcomes the limitations of traditional electrohydraulic servo creep testing machines and gravity loading creep testing machines when conducting low-frequency cyclic load creep tests.This allows for long-term(1-2 years)creep tests under extremely-low-frequency cyclic loading conditions,which simulate the actual operating conditions of salt cavern gas storage.The cyclic load generation system converted constant-weight loads into a continuously variable hydraulic oil pressure and amplified the oil pressure using a pressure intensifier,which provided a stable load source for the test system.Using this test system,creep tests were performed under low-frequency cyclic loading with periods of 1 d and 7 d.The results showed that the test system performed well,as evidenced by the validation of the loading capacity,loading stability,and temperature control stability.Comparing the creep deformation of rock salt samples with the cyclic periods of 1 d and 7 d,it was observed that,within this cyclic period range,the creep deformation of the sample increased with higher loading frequencies,provided that the cyclic loading waveform and stress remained constant.
基金supported by the National Natural Science Foundation of China (Grant Nos. 21571101 and 51322202)the Natural Science Foundation of Jiangsu Province in China (Grant Nos. BK20161543 and BK20130927)+1 种基金the Joint Research Fund for Overseas Chinese, Hong Kong and Macao Scholars (Grant No. 51528201)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 15KJB430016).
文摘Interlayer interactions at the heterointerfaces of van der Waals heterostructures (vdWHs), which consist of vertically stacked two-dimensional materials, play important roles in determining their properties. The interlayer interactions are tunable from noncoupling to strong coupling by controlling the twist angle between adjacent layers. However, the influence of stacking sequence and individual component thickness on the properties of vdWHs has rarely been explored. In this work, the influence of the stacking sequence of WSe2 and graphene in vdWHs of graphene-on-WSe2 (graphene/WSe2) or WSe2-on-graphene (WSe2/graphene), as well as their thickness, on their interlayer interaction was systematically investigated by ultralow-frequency (ULF) Raman spectroscopy. A series of ULF breathing modes of WSe2 nanosheets in these vdWHs were observed with frequencies highly dependent on graphene thickness. Interestingly, the ULF breathing modes of WSe2 red-shifted in graphene/WSe2 and WSe2/graphene configurations, and the amount of shift in the former was much larger than that in the latter. In contrast, no obvious ULF shift was observed by varying the twist angle between WSe2 and graphene. This indicates that the interlayer interaction is more sensitive to the stacking sequence compared with the twist angle. The results provide alternative approaches to modulate the interlayer interaction of vdWHs and, thus, tune their optical and optoelectronic properties.
基金supported by the National Natural Science Foun-dation of China(Nos.51832001,21571101 and 51322202)the Natural Science Foundation of Jiangsu Province in China(No.BK20161543)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(No.15KJB430016).
文摘The properties of two-dimensional(2D)materials are highly dependent on their phase and thickness.Various phases exist in tin disulfide(SnS_(2)),resulting in promising electronic and optical properties.Hence,accurately identifying the phase and thickness of SnS_(2)nanosheets is prior to their optoelectronic applications.Herein,layered 2H-SnS_(2)and 4H-SnS_(2)crystals were grown by chemical vapor transportation and the crystalline phase of SnS_(2)was characterized by X-ray diffraction,ultralow frequency(ULF)Raman spectroscopy and high-resolution transmission electron microscope.As-grown crystals were mechanically exfoliated to single-and few-layer nanosheets,which were investigated by optical microscopy,atomic force microscopy and ULF Raman spectroscopy.Although the 2H-SnS_(2)and 4H-SnS_(2)nanosheets have similar optical contrast on SiO_(2)/Si substrates,their ULF Raman spectra obviously show different shear and breathing modes,which are highly dependent on their phases and thicknesses.Interestingly,the SnS_(2)nanosheets have shown phase-dependent electrical properties.The 4H-SnS_(2)nanosheet shows a current on/off ratio of 2.58×10^(5) and excellent photosensitivity,which are much higher than those of the 2H-SnS_(2)nanosheet.Our work not only offers an accurate method for identifying single-and few-layer SnS_(2)nanosheets with different phases,but also paves the way for the application of SnS_(2)nanosheets in highperformance optoelectronic devices.
基金supported by the National Key Research and Development Program of China (Grant No. 2023YFE0117300)the National Natural Science Foundation of China (Grant No. 4187417)the APSCO Earthquake Research Project Phase Ⅱ, and the Dragon 5 Cooperation 2020-2024 (Grant No. 59236)。
文摘This study reports the rare ultralow-frequency(ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17(Geostationary Operational Environmental Satellite) in the magnetosphere, the CSES(China Seismo-Electromagnetic Satellite) in the ionosphere, and the THEMIS ground-based observatories(GBO) GAKO and EAGL in the Earth's polar region during the main phase of an intense storm on 4 November 2021. Along with the enhanced-pressure solar wind moving tailward, the geomagnetic field structure experienced a large-scale change. From dawn/dusk sides to midnight, the GAKO, EAGL, and GOES-17 sequentially observed the ULF waves in a frequency range of0.04–0.36 Hz at L shells of ~5.07, 6.29, and 5.67, respectively. CSES also observed the ULF wave event with the same frequency ranges at wide L-shells of 2.52–6.22 in the nightside ionosphere. The analysis results show that the ULF waves at ionospheric altitude were mixed toroidal-poloidal mode waves. Comparing the ULF waves observed in different regions, we infer that the nightside ULF waves were directly or indirectly excited by the solar wind dynamic pressure increase: in the area of L-shells~2.52–6.29, the magnetic field line resonances(FLRs) driven by the solar wind dynamic pressure increase is an essential excitation source;on the other hand, around L~3.29, the ULF waves can also be excited by the outward expansion of the plasmapause owing to the decrease of the magnetospheric convection, and in the region of L-shells ~5.19–6.29, the ULF waves are also likely excited by the ion cyclotron instabilities driven by the solar wind dynamic pressure increase.
