arXiv subjects

Zheng Yan

Publications and source records attributed to Zheng Yan.

170 records · Page 10Linked to original sources

arXiv2017

Resolving ECRH deposition broadening due to edge turbulence in DIII-D by 3D full-wave simulations

Edge plasma density fluctuations are shown to have a significant effect on the electron cyclotron resonance heating (ECRH) beam in the DIII-D tokamak. Experimental measurements of the ECRH deposition profile have been taken in three operating scenarios: L-mode, H-mode and negative triangularity. Each scenario corresponds to distinct turbulence characteristics in the edge region through which the beam must propagate. The measured ECRH deposition profile is significantly broadened by comparison to the profile predicted by the ray tracing code TORAY-GA and has been shown to scale with the severity of edge turbulence. Conventional ray tracing does not include the effects of turbulence and therefore a 3D full-wave cold plasma finite difference time domain code EMIT-3D is presented and used for the simulations. The turbulence is generated through the Hermes model in the BOUT++ framework which takes as input the measured time averaged electron density, temperature and magnetic field profiles for the specific shot in question. The simulated turbulence is constrained to match the experimentally measured (by use of the BES and DBS systems) correlation length and normalised fluctuation levels. The predictions of the beam broadening from the simulations are found to agree very well with the experimentally-observed broadening in all cases: L-mode, H-mode and negative triangularity. Due to the large gradients within the H-mode edge, the resolution uncertainty and error in the measurement from Thomson scattering and BES diagnostics result in a spread in the simulated turbulence amplitude. In light of this a parameter scan through the range in experimental diagnostic measurement uncertainty has been conducted to explore the impact on beam broadening predictions.

physics.plasm-ph↗

arXiv2017

On conditional fault tolerance of hierarchical cubic networks

This paper considers the conditional fault tolerance, $h$-super connectivity $κ^{h}$ and $h$-super edge-connectivity $λ^{h}$ of the hierarchical cubic network $HCN_n$, an attractive alternative network to the hypercube, and shows $κ^h(HCN_n)=λ^h(HCN_n)=2^h(n+1-h)$ for any $h$ with $0\leq h\leq n-1$. The results imply that at least $2^h(n+1-h)$ vertices or edges have to be removed from $HCN_n$ to make it disconnected with no vertices of degree less than $h$, and generalize some known results.

math.CO↗

arXiv2016

On fault tolerance of (n,k)-star networks

Fault tolerance of an $(n,k)$-star network is measured by its $h$-super connectivity $κ_s^{(h)}$ or $h$-super edge-connectivity $λ_s^{(h)}$. Li {\it et al.} [Appl. Math. Comput. 248 (2014), 525-530; Math. Sci. Lett. 1 (2012), 133-138] determined $κ_s^{(h)}$ and $λ_s^{(h)}$ for $0\leq h\leq n-k$. This paper determines $κ_s^{(h)}=λ_s^{(h)}=\frac{(h+1)!(n-h-1)}{(n-k)!}$ for $n-k\leq h \leq n-2$.

math.CO↗

arXiv2016

Optimal Scheduling of Electric Vehicles Charging in low-Voltage Distribution Systems

Uncoordinated charging of large-scale electric vehicles (EVs) will have a negative impact on the secure and economic operation of the power system, especially at the distribution level. Given that the charging load of EVs can be controlled to some extent, research on the optimal charging control of EVs has been extensively carried out. In this paper, two possible smart charging scenarios in China are studied: centralized optimal charging operated by an aggregator and decentralized optimal charging managed by individual users. Under the assumption that the aggregators and individual users only concern the economic benefits, new load peaks will arise under time of use (TOU) pricing which is extensively employed in China. To solve this problem, a simple incentive mechanism is proposed for centralized optimal charging while a rolling-update pricing scheme is devised for decentralized optimal charging. The original optimal charging models are modified to account for the developed schemes. Simulated tests corroborate the efficacy of optimal scheduling for charging EVs in various scenarios.

eess.SY↗

arXiv2015

Embedded connectivity of recursive networks

Let $G_n$ be an $n$-dimensional recursive network. The $h$-embedded connectivity $ζ_h(G_n)$ (resp. edge-connectivity $η_h(G_n)$) of $G_n$ is the minimum number of vertices (resp. edges) whose removal results in disconnected and each vertex is contained in an $h$-dimensional subnetwork $G_h$. This paper determines $ζ_h$ and $η_h$ for the hypercube $Q_n$ and the star graph $S_n$, and $η_3$ for the bubble-sort network $B_n$.

math.CO↗

arXiv2014

Cyber Behavior of Microblog Users: Onlies Versus Others

Much research has been conducted to investigate personality and daily behavior of these only children ('Onlies') due to the Chinese one-child-per-family policy, and report the singleton generation to be more selfish. As Microblog becomes increasingly popular recently in China, we studied cyber behavior of Onlies and children with siblings ('Others') on Sina Microblog ('Weibo'), a leading Microblog service provider in China. Participants were 1792 Weibo users. Their recorded data on Weibo were downloaded to assess their cyber behaviors. The general results show that (1) Onlies have a smaller social circle; (2)Onlies are more significantly active on social platform.

cs.CY↗

arXiv2012

Global Gyrokinetic Simulation of Tokamak Edge Pedestal Instabilities

Global electromagnetic gyrokinetic simulations show the existence of near threshold conditions for both a high-$n$ kinetic ballooning mode (KBM) and an intermediate-$n$ kinetic version of peeling-ballooning mode (KPBM) in the edge pedestal of two DIII-D H-mode discharges. When the magnetic shear is reduced in a narrow region of steep pressure gradient, the KPBM is significantly stabilized, while the KBM is weakly destabilized and hence becomes the most-unstable mode. Collisions decrease the KBM's critical $β$ and increase the growth rate.

physics.plasm-ph↗

arXiv2012

Terahertz and Infrared Spectroscopy of Gated Large-Area Graphene

We have fabricated a centimeter-size single-layer graphene device, with a gate electrode, which can modulate the transmission of terahertz and infrared waves. Using time-domain terahertz spectroscopy and Fourier-transform infrared spectroscopy in a wide frequency range (10-10000 cm^{-1}), we measured the dynamic conductivity change induced by electrical gating and thermal annealing. Both methods were able to effectively tune the Fermi energy, E_F, which in turn modified the Drude-like intraband absorption in the terahertz as well as the '2E_F onset' for interband absorption in the mid-infrared. These results not only provide fundamental insight into the electromagnetic response of Dirac fermions in graphene but also demonstrate the key functionalities of large-area graphene devices that are desired for components in terahertz and infrared optoelectronics.

cond-mat.mes-hall↗