Z. X. Liu

ELMy H-mode confinement and threshold power by low hybrid wave on the EAST tokamak

Stationary type-III ELMy H-mode plasmas were achieved on Experimental Advanced Superconducting Tokamak (EAST) by low hybrid wave in 2010. The threshold power increases with plasma density, and a significant reduction in the H-mode occurs by decreasing the distance between the X-point and the strike point at the outside lower divertor on EAST. A series of statistics for the H-mode confinement such as the dependence of energy confinement time (τE) on plasma density and loss power is experimentally studied in detail.

Vitamin C alleviates aging defects in a stem cell model for Werner syndrome

ABSTRACTWerner syndrome (WS) is a premature aging disorder that mainly affects tissues derived from mesoderm. We have recently developed a novel human WS model using WRN-deficient human mesenchymal stem cells (MSCs). This model recapitulates many phenotypic features of WS. Based on a screen of a number of chemicals, here we found that Vitamin C exerts most efficient rescue for many features in premature aging as shown in WRN-deficient MSCs, including cell growth arrest, increased reactive oxygen species levels, telomere attrition, excessive secretion of inflammatory factors, as well as disorganization of nuclear lamina and heterochromatin. Moreover, Vitamin C restores in vivo viability of MSCs in a mouse model. RNA sequencing analysis indicates that Vitamin C alters the expression of a series of genes involved in chromatin condensation, cell cycle regulation, DNA replication, and DNA damage repair pathways in WRN-deficient MSCs. Our results identify Vitamin C as a rejuvenating factor for WS MSCs, which holds the potential of being applied as a novel type of treatment of WS.

H-mode power threshold and confinement in a molybdenum wall with different magnetic configurations on the EAST tokamak

A series of ELMy H-mode discharges were achieved on Experimental Advanced Superconducting Tokamak (EAST) with low hybrid wave (PLHWxa0=xa00.5–1.7xa0MW at 2.45xa0GHz) and ion cyclotron resonance frequencies (PICRFxa0=xa00.5–2xa0MW) as the auxiliary heating power in 2012. In double-null (DN) configurations, the experimental power threshold with a molybdenum wall (2012) appears to be lower than that with a graphite wall (2010). For lower single null (LSN) plasmas, the lower X-point configuration has a lower power threshold, and a significant reduction (∼25%) in the H-mode power threshold with 3.4xa0cm X-point movement is achieved. The lower X-point configuration on EAST has higher dRsep below zero (closer to the DN configuration). Better energy confinement is observed in DN compared with single null (SN) at the same power loss. For reasons not understood, when the ion grad-B drift is in a favourable direction for H-mode access (towards the X-point) for EASTs LSN configuration, H-mode is achieved in upper single null (USN) configurations, but not in LSN.

Tearing mode with strong flow shear in the viscosity-dominated limit

Using a standard boundary layer approach, the tearing mode with shear flow comparable with shear magnetic field and fluid viscosity much larger than resistivity has been studied analytically. The results show that, the growth rate in this case scales as ν2/3ν, where νν is the normalized viscosity, in agreement with the numerical results of Einaudi and Rubini [Phys. Fluids B 1, 2224 (1989)]. It is found analytically that large viscosity may have a destabilizing effect on the instability.

Coercivity enhancement of sintered Nd14.4Fe78.4Co1.3B5.9 magnets by dysprosium diffusion in grain boundaries of rapidly solidified strips

A new coercivity enhancement process using dysprosium diffusion in grain boundaries of rapidly solidified strips was developed. The effects of the dysprosium diffusion on microstructure and magnetic properties of sintered Nd14.4Fe78.4Co1.3B5.9 magnets have been investigated. The transmission electron microscope observation showed that the intergranular phases of rapidly solidified strips were optimized through the grain boundary diffusion process of strips. From the mapping distribution of dysprosium atoms in sintered magnets and the fact that remanence almost kept constant, one could suppose that dysprosium element preferred the interface of the matrix grains, which was probably a reason of coercivity enhancement. The coercivity of the magnets made from diffusion heat treatment strips was increased by 1100 Oe, while the remanence was almost kept constant. Reduction in remanence is from 14.1 to 13.92 kG. The energy product of the magnets was slightly increased from 46.4 to 47.4 MGOe.

Enhanced magnetoresistance of La2/3Ca1/3MnO3/CeO2 nanocystalline composites synthesized by polymer-network gel method

Using a dispersing particle polymer-network gel method, we prepared xLa2∕3Ca1∕3MnO3∕(1−x)CeO2 nanocystalline composites, where the average grain sizes of La2∕3Ca1∕3MnO3 and CeO2 are about 30nm and less than 10nm, respectively. The magnetoresistance of the sintered composites is explored as a function of the ratio of metal/insulator, temperature, and magnetic field. The system exhibits metallic percolation threshold at x=xp∼35%, around which the high field magnetoresistance has a maximum (∼70%) at 50K and 5T, and the low field magnetoresistance value is close to 16% at 5K and 0.05T.

Different respiration metabolism between mycorrhizal and non-mycorrhizal rice under low-temperature stress: a cry for help from the host

Low-temperature stress is an important environmental factor that severely disrupts plant respiration but can be alleviated by symbiotic arbuscular mycorrhizal fungi (AMF). In the current study, a pot experiment was performed to determine changes in the respiratory metabolic capacity of mycorrhizal rice ( Oryza sativa ) under low-temperature stress. The results demonstrated that low temperature might accelerate the biosynthesis of strigolactone in mycorrhizal rice roots by triggering the expression of genes for the synthesis of strigolactone, which acted as a host stress response signal. In addition, AMF prompted the host tricarboxylic acid (TCA) cycle by enhancing pyruvate metabolism, up-regulating the expression of genes of the TCA cycle under low-temperature stress and affecting the electron transport chain. The alternative oxidase pathway might be the main electron transport pathway in non-mycorrhizal rice under stress, while the cytochrome c oxidase (COX) pathway might be the predominant pathway in arbuscular mycorrhizal symbiosis. Mycorrhizal rice also had higher adenosine triphosphate production to maintain the natural status of respiration under stress conditions, which resulted in improved root growth status and alleviated low-temperature stress.

Magnetic Properties and Microstructure of Melt-Spun Ce–Fe–B Magnets

A series of Ce_xFe_balB₆ (x = 12, 14, 17, 19, and 23 wt%) ternary ribbons was prepared by melt-spinning. Magnetic properties and the microstructure of the Ce-Fe-B ribbons with different Ce contents were investigated. The X-ray diffraction results indicated that multiphase coexisted in the as-spun Ce-Fe-B ribbons, which contained Ce₂Fe₁₇, CeFe₂, Ce-rich phase, Fe-rich phase, cerium oxide, and iron oxide. The magnetic properties, microstructure, and phase composition of the ribbons were directly affected by the cerium content. The magnetic properties could be obtained by exchange coupling between the hard and soft magnetic phases in the pure ternary Ce-Fe-B ribbons. Furthermore, by heat treatment, the magnetic properties of the as-spun Ce-Fe-B ribbons could be optimized. The highest magnetic properties of H_cj = 6.2 kOe, B_r = 6.9 kGs, and (BH)_m = 8.6 MGOe were obtained in Ce₁₇FebalB₆ magnets.

Observation of ion-cyclotron-frequency mode conversion plasma rotation on HT-7

In this paper, we present a study on D?H (7Li) plasmas with moderate hydrogen concentration (?15%) on the HT-7 tokamak. Enhanced density fluctuation induced by ion cyclotron range of frequencies (ICRF) at the centre of the plasma is observed by a continuous wave CO2 (??=?10.6??m) collective scattering system. At the same time, the Doppler shift VD due to plasma rotation in the mode-converted ICRF D?H (7Li) plasmas is observed experimentally for the first time on the HT-7 tokamak, and the Doppler shift VD is approximately linear versus the change in plasma stored energy ?W.

ELMy H-mode linear simulation with 3-field model on experimental advanced superconducting tokamak using BOUT++

H-mode plasmas with ELM (edge localized mode) have been realized on experimental advanced superconducting tokamak (EAST) with 2.45u2009GHz low hybrid wave at PLHW∼1u2009MW in 2010. Data from EAST experiments including magnetic geometry, measured pressure profiles, and calculated current profiles are used to investigate the physics of ELM utilizing the BOUT++ code. Results from linear simulations show that the ELMs in EAST are dominated by resistive ballooning modes. When the Lundquist number (dimensionless ratio of the resistive diffusion time to the Alfven time) is equal to or less than 107, the resistive ballooning modes are found to become unstable in the ELMy H-mode plasma. For a fixed pedestal pressure profile, increasing plasma current generates more activities of low-n ELMs.