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1,219 results on '"Chen, Chunhua"'

1. Pressure induced nonmonotonic evolution of superconductivity in 6R-TaS2 with a natural bulk van der Waals heterostructure

Author

Wang, Shaopeng, Han, Yuyan, Sun, Sutao, Wang, Shuyang, An, Chao, Chen, Chunhua, Zhang, Lili, Zhou, Yonghui, Zhou, Jian, and Yang, Zhaorong

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

The natural bulk van der Waals heterostructures compound 6R-TaS2 consists of alternate stacking 1T- and 1H-TaS2 monolayers, creating a unique system that incorporates charge-density-wave (CDW) order and superconductivity (SC) in distinct monolayers. Here, after confirming that the 2D nature of the lattice is preserved up to 8 GPa in 6R-TaS2, we documented an unusual evolution of CDW and SC by conducting highpressure electronic transport measurements. Upon compression, we observe a gradual suppression of CDW within the 1T-layers, while the SC exhibits a dome-shaped behavior that terminates at a critical pressure Pc around 2.9 GPa. By taking account of the fact that the substantial suppression of SC is concomitant with the complete collapse of CDW order at Pc, we argue that the 6R-TaS2 behaves like a stack of Josephson junctions and thus the suppressed superconductivity can be attributed to the weakening of Josephson coupling associated with the presence of CDW fluctuations in the 1T-layers. Furthermore, the SC reversely enhances above Pc, implying the development of emergent superconductivity in the 1T-layers after the melting of T-layer CDW orders. These results show that the 6R-TaS2 not only provides a promising platform to explore emergent phenomena but also serves as a model system to study the complex interactions between competing electronic states., Comment: 21 pages,5 figures

Published
2024
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29. Policymaking for long-term care provision for older disabled people in China : a comparative study of Beijing and Shanghai municipalities

Author

Chen, Chunhua, Brown, Sarah, and Jawad, Rana

Subjects
Population ageing, Long-term care, Policymaking, China, Multiple Streams Approach
Abstract

With over 40 million disabled older people, long-term care (LTC) provision has become one of the most critical social, economic, and political issues facing the Chinese government. Yet despite significant state attention, accessible and affordable LTC remains a challenge. This has highlighted problematic policymaking, as local policy responses are neither in line with their central instructions nor relevant to local capabilities or identified LTC needs. This study sought to understand why different or even contradictory LTC policy responses have occurred in two case study sites, Beijing and Shanghai, despite being driven by the same national policies. It addresses the lack of research, which has examined the policymaking process from LTC needs to LTC provision in China and how different geographical locations experience policymaking under the same institutions. The thesis adopted a qualitative methodology, interviewing key policymakers and employing the Multiple Streams Approach (MSA) to analyse the LTC policymaking process in Beijing and Shanghai. The findings demonstrate a highly politicised process of LTC policymaking in China, with ambiguous national strategies of LTC provision and weak national steering on implementation. This has led to divergent approaches. In Beijing, politics-driven policymaking has let path-dependent LTC policies dominate, while in Shanghai issue-focused policymaking has resulted in path-departing LTC policies. Different policy responses in the two sites reflected either symbolic or thorough implementation of national policies. Given the evolving LTC policy system, the findings on the highly politicised LTC policymaking and its specific political processes have policy implications for policymaking, LTC provision and social welfare development in China. The thesis also makes a methodological contribution to the literature, showcasing the value of MSA for analysing policy responses of subordinate organisations to superordinate authorities under ambiguity in China.

Published
2021

35. Persistent Insulator: Avoidance of Metallization at Megabar Pressures in Strongly Spin-Orbit-Coupled Sr2IrO4

Author

Chen, Chunhua, Zhou, Yonghui, Chen, Xuliang, Han, Tao, An, Chao, Zhou, Ying, Yuan, Yifang, Zhang, Bowen, Wang, Shuyang, Zhang, Ranran, Zhang, Lili, Zhang, Changjing, Yang1, Zhaorong, DeLong, Lance E., and Cao, Gang

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

It is commonly anticipated that an insulating state collapses in favor of an emergent metallic state at high pressures as the unit cell shrinks and the electronic bandwidth broadens to fill the insulating energy band gap. Here we report a rare insulating state that persists up to at least 185 GPa in the antiferromagnetic iridate Sr2IrO4, which is the archetypical spin-orbit-driven Jeff = 1/2 insulator. This study shows the electrical resistance of single-crystal Sr2IrO4 initially decreases with applied pressure, reaches a minimum in the range, 32 - 38 GPa, then abruptly rises to fully recover the insulating state with further pressure increases up to 185 GPa. Our synchrotron x-ray diffraction and Raman scattering data show the onset of the rapid increase in resistance is accompanied by a structural phase transition from the native tetragonal I41/acd phase to an orthorhombic Pbca phase (with much reduced symmetry) at 40.6 GPa. The clear-cut correspondence of these two anomalies is key to understanding the stability of the insulating state at megabar pressures: Pressure-induced, severe structural distortions prevent the expected metallization, despite the 26% volume compression attained at the highest pressure accessed in this study. Moreover, the resistance of Sr2IrO4 remains stable while the applied pressure is tripled from 61 GPa to 185 GPa. These results suggest that a novel type of electronic Coulomb correlation compensates the anticipated band broadening in strongly spin-orbit-coupled materials at megabar pressures., Comment: 5 figures

Published
2019
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37. Pressure-tunable large anomalous Hall effect of the ferromagnetic kagome-lattice Weyl semimetal Co3Sn2S2

Author

Chen, Xuliang, Wang, Maoyuan, Gu, Chuanchuan, Wang, Shuyang, Zhou, Yonghui, An, Chao, Zhou, Ying, Zhang, Bowen, Chen, Chunhua, Yuan, Yifang, Qi, Mengyao, Zhang, Lili, Zhou, Haidong, Zhou, Jianhui, Yao, Yugui, and Yang, Zhaorong

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

We investigate the pressure evolution of the anomalous Hall effect in magnetic topological semimetal Co3Sn2S2 in diamond anvil cells with pressures up to 44.9-50.9 GPa. No evident trace of structural phase transition is detected through synchrotron x-ray diffraction over the measured pressure range of 0.2-50.9 GPa. We find that the anomalous Hall resistivity and the ferromagnetism are monotonically suppressed as increasing pressure and almost vanish around 22 GPa. The anomalous Hall conductivity varies non-monotonically against pressure at low temperatures, involving competition between original and emergent Weyl nodes. Combined with first-principle calculations, we reveal that the intrinsic mechanism due to the Berry curvature dominates the anomalous Hall effect under high pressure., Comment: 6 pages, 4 figures. Under review

Published
2019
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45. Correlation between degenerative lumbar scoliosis and multifidus muscle degeneration

Author

YU Xueke, CHEN Can, LI Kai, CHEN Chunhua, and HU Chenbo

Subjects
degenerative lumbar scoliosis, multifidus muscle, functional cross sectional area, fat infiltration rate, Medicine (General), R5-920
Abstract

Objective To evaluate the lumbar multifidus muscle in patients with degenerative lumbar scoliosis (DLS) by magnetic resonance imaging (MRI), and to analyze the degeneration features of lumbar multifidus muscle in the convex and concave sides of different lumbar segments and the correlation with severity of spinal deformity. Methods A cross-sectional trial was performed on 45 DLS subjects (DLS group) and 42 healthy individual (control group) who were recruited among the public by our hospital from March 2019 to June 2021. Image J software was employed to measure and calculate the cross-sectional area (CSA), functional cross-sectional area (FCSA) and fat infiltration rate (FIR) of the multifidus muscles beside the central planes of the intervertebral discs of 5 lumbar segments, L1-L2 and L5-S1, on T2WI images. The Cobb angle of lumbar coronal scoliosis in DLS group was measured by full-length spinal X-ray series. The degeneration features of multifidus muscle in each segment of lumbar vertebrae in DLS group and their correlation with Cobb angle of lumbar scoliosis were analyzed. Results The FCSA of the convex and concave multifidus muscles at L4-L5 and L5-S1 levels were significantly smaller in the DLS group than the control group (P < 0.05). The FIR of the convex and concave multifidus muscles at L1-S1 levels were obviously higher in the DLS group than the control group (P < 0.05). The DLS group had statistically smaller FCSA in the concave side than the convex multifidus muscles at L3-L4, L4-L5 and L5-S1 levels (P < 0.05). In the DLS group, the Cobb angle was positively correlated with FCSA difference index of L4-L5 and L5-S1 levels (r=0.310, 0.559, P < 0.05). Conclusion In DLS patients, degeneration of multifidus muscle corresponding to the lower lumbar levels (L4-L5 and L5-S1) is positively correlated with the severity of scoliosis, and the condition is more serious in the concave side than the convex side. It is suggested that the degeneration of multidus muscle is not an initiating factor of DLS, but may be a compensatory factor.

Published
2022
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46. Research on source term inversion and uncertainty analysis based on particle filter algorithm

Author

ZHENG Zihao, CHEN Chunhua, ZHU Jingxian, CHEN Liwei, and WANG Shipeng

Subjects
source term inversion, particle filter, gaussian puff dispersion model, Nuclear and particle physics. Atomic energy. Radioactivity, QC770-798, Medical physics. Medical radiology. Nuclear medicine, R895-920
Abstract

Considering the special circumstances after nuclear accidents, such as continuous change of source term release rate, limited monitoring data, and variable observed noise, a source term inversion method based on the Gaussian puff dispersion model and particle filter is proposed in this paper. When there are only two sets of effective monitoring data, these data, based on 20% monitoring relative error, superimpose monitoring noise caused by particulate deposition. A particle filter was used to invert the source term release rate from the monitoring data considering stable, linearly increasing, and sinusoidally changing release rates. The error in the results relative to the true value is about 5%, and the maximum error is less than 10%.

Published
2022
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