4,182 research outputs found
Topological Dirac states beyond orbitals for silicene on SiC(0001) surface
The discovery of intriguing properties related to the Dirac states in
graphene has spurred huge interest in exploring its two-dimensional group-IV
counterparts, such as silicene, germanene, and stanene. However, these
materials have to be obtained via synthesizing on substrates with strong
interfacial interactions, which usually destroy their intrinsic
()-orbital Dirac states. Here we report a theoretical study on the
existence of Dirac states arising from the orbitals instead of
orbitals in silicene on 4H-SiC(0001), which survive in spite of the strong
interfacial interactions. We also show that the exchange field together with
the spin-orbital coupling give rise to a detectable band gap of 1.3 meV. Berry
curvature calculations demonstrate the nontrivial topological nature of such
Dirac states with a Chern number , presenting the potential of realizing
quantum anomalous Hall effect for silicene on SiC(0001). Finally, we construct
a minimal effective model to capture the low-energy physics of this system.
This finding is expected to be also applicable to germanene and stanene, and
imply great application potentials in nanoelectronics.Comment: 6 Figures , Accepted by Nano Letter
The Impact of Social Media Use on Online Collective Action During China’s COVID-19 Pandemic Mitigation: A Social Identity Model of Collective Action (SIMCA) Perspective
The role of social media in fostering collective action in China is under constant debate,
and the mechanism underlying the effects of social media use on collective action has not
garnered sufficient scholarly attention. This study aims to investigate the (in)direct effects
of attention to social media—administered by the governmental (gov) and
nongovernmental sectors (nongov), respectively—for information about COVID-19
mitigation in China on intention to participate in online collective action (IPOCA). Findings
from a survey suggest that attention to both social media (gov) and social media (nongov)
directly predicted IPOCA. The indirect effect of attention to social media (gov) on IPOCA
was significantly mediated by social identification. This study evidences the impact of
social media on collective action in China and theoretically underpins its mechanisms
through the social identity model of collective action
Hamiltonian formalism in Friedmann cosmology and its quantization
We propose a Hamiltonian formalism for a generalized
Friedmann-Roberson-Walker cosmology model in the presence of both a variable
equation of state (EOS) parameter and a variable cosmological constant
, where is the scale factor. This Hamiltonian system containing
1 degree of freedom and without constraint, gives Friedmann equations as the
equation of motion, which describes a mechanical system with a variable mass
object moving in a potential field. After an appropriate transformation of the
scale factor, this system can be further simplified to an object with constant
mass moving in an effective potential field. In this framework, the
cold dark matter model as the current standard model of cosmology corresponds
to a harmonic oscillator. We further generalize this formalism to take into
account the bulk viscosity and other cases. The Hamiltonian can be quantized
straightforwardly, but this is different from the approach of the
Wheeler-DeWitt equation in quantum cosmology.Comment: 7 pages, no figure; v2: matches the version accepted by PR
Fast Differentially Private Matrix Factorization
Differentially private collaborative filtering is a challenging task, both in
terms of accuracy and speed. We present a simple algorithm that is provably
differentially private, while offering good performance, using a novel
connection of differential privacy to Bayesian posterior sampling via
Stochastic Gradient Langevin Dynamics. Due to its simplicity the algorithm
lends itself to efficient implementation. By careful systems design and by
exploiting the power law behavior of the data to maximize CPU cache bandwidth
we are able to generate 1024 dimensional models at a rate of 8.5 million
recommendations per second on a single PC
- …