Small perturbations and strong impurity exhaust capability associated with the small grassy ELMs render the grassy-ELM regime a suitable candidate for achieving steady-state H-mode operation with a ...radiative divertor, especially in a metal-wall device, such as the Experimental Advanced Superconducting Tokamak (EAST). As the degradation of pedestal performance with excessive divertor impurity seeding or accumulation tends to be accompanied with significantly increased radiation near the divertor X point, feedback control of the absolute extreme ultraviolet (AXUV) radiation near the X point has been employed to maintain the confinement property in EAST. However, the absolute value of the AXUV radiation at the outer target varies with plasma conditions as during the divertor detachment process. Thus, a new feedback-control scheme has been recently developed and applied to grassy-ELM H-mode plasmas in EAST to achieve stationary partial detachment while maintaining good global energy confinement with H98,y2 >1. In this scheme, electron temperatures (Tet) measured by divertor Langmuir probes are used to identify the onset of detachment, and then the plasma control system (PCS) switches to the feedback control of one channel of AXUV radiation near the X point, where a steep gradient in the radiation profile is present. The feedback is performed through pulse-width-modulated duty cycle of a piezo valve to seed impurities with mixed gas (50% Ne and 50% D2) from the outer target plate near the strike point in the upper tungsten monoblock divertor. Tet near the strike point is maintained in the range of 5-8 eV, and peak surface temperature on the outer target plate (TIR,peak) is suppressed and maintained at ∼180 °C, based on infrared camera measurements. The plasma stored energy maintains nearly constant over the entire feedback-control period. It thus offers a highly promising plasma control scenario suitable for long-pulse high-performance H-mode operation in EAST, which is potentially applicable to future steady-state fusion reactors as an integrated solution for the control of both ELM-induced transient and steady-state divertor heat loads while maintaining good core confinement.
High-temperature superconductivity in iron-arsenic materials (pnictides) near an antiferromagnetic phase raises the possibility of spin-fluctuation-mediated pairing. However, the interplay between ...antiferromagnetic fluctuations and superconductivity remains unclear in the underdoped regime, which is closer to the antiferromagnetic phase. Here we report that the superconducting gap of underdoped pnictides scales linearly with the transition temperature, and that a distinct pseudogap coexisting with the superconducting gap develops on underdoping. This pseudogap occurs on Fermi surface sheets connected by the antiferromagnetic wavevector, where the superconducting pairing is stronger as well, suggesting that antiferromagnetic fluctuations drive both the pseudogap and superconductivity. Interestingly, we found that the pseudogap and the spectral lineshape vary with the Fermi surface quasi-nesting conditions in a fashion that shares similarities with the nodal-antinodal dichotomous behaviour observed in underdoped copper oxide superconductors.
Divertor detachment offers a promising solution to the challenge of plasma-wall interactions for steady-state operation of fusion reactors. Here, we demonstrate the excellent compatibility of ...actively controlled full divertor detachment with a high-performance (β
~ 3, H
~ 1.5) core plasma, using high-β
(poloidal beta, β
> 2) scenario characterized by a sustained core internal transport barrier (ITB) and a modest edge transport barrier (ETB) in DIII-D tokamak. The high-β
high-confinement scenario facilitates divertor detachment which, in turn, promotes the development of an even stronger ITB at large radius with a weaker ETB. This self-organized synergy between ITB and ETB, leads to a net gain in energy confinement, in contrast to the net confinement loss caused by divertor detachment in standard H-modes. These results show the potential of integrating excellent core plasma performance with an efficient divertor solution, an essential step towards steady-state operation of reactor-grade plasmas.
By means of first-principles calculation, we explore the vacancy mechanism of titanium sesquioxide (Ti2O3) and further investigate the influence of vacancy on the electronic properties of Ti2O3. Two ...vacancy models are considered. We find that Ti2O3 prefers to form oxygen vacancy (O-va) in comparison to Ti vacancy (Ti-va) because the removed oxygen atom improves the localized hybridization between Ti and O. The low concentration of vacancies is more thermodynamic stability than that of high concentration of vacancies. In comparison to titanium dioxide (TiO2), Ti2O3 exhibits the metallic behavior due to the band overlap between the conduction band and the valence band. Importantly, we find that those vacancies enhance the electronic transport of Ti2O3 because the removed atom promotes the band overlaps at the Fermi level (EF).
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•Vacancy mechanism of Titanium Sesquioxide is studied by first-principles calculations.•Ti2O3 exhibits the semiconductor-to-metal transition compared to the TiO2.•Ti2O3 prefers to form the O vacancy due to the strong localized hybridization between Ti and O.•Those vacancies enhance the electronic transport of Ti2O3.
We present a general model study of surface-enhanced resonant Raman scattering and fluorescence focusing on the interplay between electromagnetic effects and the molecular dynamics. Our model ...molecule is placed close to two Ag nanoparticles and has two electronic levels. A Franck-Condon mechanism provides electron-vibration coupling. Using realistic parameter values for the molecule we find that an electromagnetic enhancement by 10 orders of magnitude can yield Raman cross sections sigma(R) of the order 10(-14) cm(2). We also discuss the dependence of sigma(R) on incident laser intensity.
Growth of high-quality single-crystalline InSb layers remains challenging in material science. Such layered InSb materials are highly desired for searching for and manipulation of Majorana Fermions ...in solid state, a fundamental research task in physics today, and for development of novel high-speed nanoelectronic and infrared optoelectronic devices. Here, we report on a new route toward growth of single-crystalline, layered InSb materials. We demonstrate the successful growth of free-standing, two-dimensional InSb nanosheets on one-dimensional InAs nanowires by molecular-beam epitaxy. The grown InSb nanosheets are pure zinc-blende single crystals. The length and width of the InSb nanosheets are up to several micrometers and the thickness is down to ∼10 nm. The InSb nanosheets show a clear ambipolar behavior and a high electron mobility. Our work will open up new technology routes toward the development of InSb-based devices for applications in nanoelectronics, optoelectronics, and quantum electronics and for the study of fundamental physical phenomena.
Hemodynamics have been shown to play an important role in the initiation and progress of intracranial aneurysms, and are considered well-related to vascular configuration. The purpose of this study ...was to quantify the vascular geometry change due to intracranial stent placement and to discuss its potential effects on hemodynamics.
Imaging data of patients with wide-neck AcomA aneurysms, treated with stent-assisted coiling between January 2005 and January 2010, were retrospectively analyzed. The angle between the afferent vessels (A1 segment) and the efferent vessels (ipsilateral or contralateral A2 segment) was calculated to determine the exact change in the angle after stent placement.
In all 20 patients, the stent caused a distinct change in the geometry of the parent vessel. Stent-related vascular angle change ranged from 7.60 to 74.88°, with an average of 29.95°. In 10 cases, the angle changed by >30°. In the 12 patients with the distal segment of the stent placed in the ipsilateral A2 segment, the mean postoperative A1-A2 angle increased by 27.71 ± 13.17° (from 7.60° to 48.29°). In the other 8 patients with the distal segment of the stent placed in the contralateral A2 segment, the mean postoperative A1-AcomA-A2 angle increased by 33.29 ± 21.89°(from 15.49° to 74.88°).
In addition to serving as a scaffold to contain coils, stent placement for AcomA aneurysms has a substantial effect on the vascular geometry, which may result in local hemodynamic changes.
A critical challenge facing the basic long-pulse high-confinement operation scenario (H mode) for ITER is to control a magnetohydrodynamic (MHD) instability, known as the edge localized mode (ELM), ...which leads to cyclical high peak heat and particle fluxes at the plasma facing components. A breakthrough is made in the Experimental Advanced Superconducting Tokamak in achieving a new steady-state H mode without the presence of ELMs for a duration exceeding hundreds of energy confinement times, by using a novel technique of continuous real-time injection of a lithium (Li) aerosol into the edge plasma. The steady-state ELM-free H mode is accompanied by a strong edge coherent MHD mode (ECM) at a frequency of 35-40 kHz with a poloidal wavelength of 10.2 cm in the ion diamagnetic drift direction, providing continuous heat and particle exhaust, thus preventing the transient heat deposition on plasma facing components and impurity accumulation in the confined plasma. It is truly remarkable that Li injection appears to promote the growth of the ECM, owing to the increase in Li concentration and hence collisionality at the edge, as predicted by GYRO simulations. This new steady-state ELM-free H-mode regime, enabled by real-time Li injection, may open a new avenue for next-step fusion development.
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