12,764 research outputs found
Width-tuned magnetic order oscillation on zigzag edges of honeycomb nanoribbons
Quantum confinement and interference often generate exotic properties in
nanostructures. One recent highlight is the experimental indication of a
magnetic phase transition in zigzag-edged graphene nanoribbons at the critical
ribbon width of about 7 nm [G. Z. Magda et al., Nature \textbf{514}, 608
(2014)]. Here we show theoretically that with further increase in the ribbon
width, the magnetic correlation of the two edges can exhibit an intriguing
oscillatory behavior between antiferromagnetic and ferromagnetic, driven by
acquiring the positive coherence between the two edges to lower the free
energy. The oscillation effect is readily tunable in applied magnetic fields.
These novel properties suggest new experimental manifestation of the edge
magnetic orders in graphene nanoribbons, and enhance the hopes of graphene-like
spintronic nanodevices functioning at room temperature.Comment: 22 pages, 9 figure
One-loop correction to the enhanced curvature perturbation with local-type non-Gaussianity for the formation of primordial black holes
As one of the promising candidates of cold dark matter (DM), primordial black
holes (PBHs) were formed due to the collapse of over-densed regions generated
by the enhanced curvature perturbations during the radiation-dominated era. The
enhanced curvature perturbations are expected to be non-Gaussian in some
relevant inflation models and hence the higher-order loop corrections to the
curvature power spectrum might be non-negligible as well as altering the
abundance of PBHs. In this paper, we calculate the one-loop correction to the
curvature power spectrum with local-type non-Gaussianities characterizing by
and standing for the quadratic and cubic
non-Gaussian parameters, respectively. Requiring that the one-loop correction
be subdominant, we find a perturbativity condition, namely
, where is a constant
coefficient which can be explicitly calculated in the given model and
denotes the variance of Gaussian part of enhanced curvature perturbation, and
such a perturbativity condition can provide a stringent constraint on the
relevant inflation models for the formation of PBHs.Comment: 6 pages, 5 figure
Full analysis of the scalar-induced gravitational waves for the curvature perturbation with local-type non-Gaussianities
Primordial black holes (PBHs) are supposed to form through the gravitational
collapse of regions with large density fluctuations. The formation of PBHs
inevitably leads to the emission of scalar-induced gravitational wave (SIGW)
signals, offering a unique opportunity to test the hypothesis of PBHs as a
constituent of dark matter (DM). Previous studies have calculated the energy
spectrum of SIGWs in local-type non-Gaussian models, primarily considering the
contributions from the -order or the -order
while neglecting connected diagrams. In this study, we extend the previous work
by (i) considering the full contribution of non-Gaussian diagrams up to the
-order; (ii) deriving the generic scaling of the SIGW energy
spectrum in the infrared region. We derive semi-analytical results applicable
to arbitrary primordial power spectra and numerically evaluate the energy
spectrum of SIGWs for a log-normal power spectrum.Comment: 21 pages, 2 figure
Population Genetic Structure of Monimopetalum chinense (Celastraceae), an Endangered Endemic Species of Eastern China
• Background and Aims Monimopetalum chinense (Celastraceae) standing for the monotypic genus is endemic to eastern China. Its conservation status is vulnerable as most populations are small and isolated. Monimopetalum chinense is capable of reproducing both sexually and asexually. The aim of this study was to understand the genetic structure of M. chinense and to suggest conservation strategies. • Methods One hundred and ninety individuals from ten populations sampled from the entire distribution area of M. chinense were investigated by using inter-simple sequence repeats (ISSR). • Key Results A total of 110 different ISSR bands were generated using ten primers. Low levels of genetic variation were revealed both at the species level (Isp = 0·183) and at the population level (Ipop = 0·083). High clonal diversity (D = 0·997) was found, and strong genetic differentiation among populations was detected (49·06 %). • Conclusions Small population size, possible inbreeding, limited gene flow due to short distances of seed dispersal, fragmentation of the once continuous range and subsequent genetic drift, may have contributed to shaping the population genetic structure of the specie
More on volume dependence of spectral weight function
Spectral weight functions are easily obtained from two-point correlation
functions and they might be used to distinguish single-particle from
multi-particle states in a finite-volume lattice calculation, a problem crucial
for many lattice QCD simulations. In previous studies, it is shown that the
spectral weight function for a broad resonance shares the typical volume
dependence of a two-particle scattering state i.e. proportional to in a
large cubic box of size while the narrow resonance case requires further
investigation. In this paper, a generalized formula is found for the spectral
weight function which incorporates both narrow and broad resonance cases.
Within L\"uscher's formalism, it is shown that the volume dependence of the
spectral weight function exhibits a single-particle behavior for a extremely
narrow resonance and a two-particle behavior for a broad resonance. The
corresponding formulas for both and channels are derived. The
potential application of these formulas in the extraction of resonance
parameters are also discussed
Data-driven design of fault diagnosis for three-phase PWM rectifier using random forests technique with transient synthetic features
A three-phase pulse-width modulation (PWM) rectifier can usually maintain
operation when open-circuit faults occur in insulated-gate bipolar transistors
(IGBTs), which will lead the system to be unstable and unsafe. Aiming at this
problem, based on random forests with transient synthetic features, a
data-driven online fault diagnosis method is proposed to locate the
open-circuit faults of IGBTs timely and effectively in this study. Firstly, by
analysing the open-circuit fault features of IGBTs in the three-phase PWM
rectifier, it is found that the occurrence of the fault features is related to
the fault location and time, and the fault features do not always appear
immediately with the occurrence of the fault. Secondly, different data-driven
fault diagnosis methods are compared and evaluated, the performance of random
forests algorithm is better than that of support vector machine or artificial
neural networks. Meanwhile, the accuracy of fault diagnosis classifier trained
by transient synthetic features is higher than that trained by original
features. Also, the random forests fault diagnosis classifier trained by
multiplicative features is the best with fault diagnosis accuracy can reach
98.32%. Finally, the online fault diagnosis experiments are carried out and the
results demonstrate the effectiveness of the proposed method, which can
accurately locate the open-circuit faults in IGBTs while ensuring system
safety.Comment: IET Power Electronic
Radiative transitions in charmonium from twisted mass lattice QCD
We present a study for charmonium radiative transitions:
, and
using twisted mass lattice QCD gauge
configurations. The single-quark vector form factors for and
are also determined. The simulation is performed at a lattice
spacing of fm and the lattice size is . After
extrapolation of lattice data at nonzero to 0, we compare our results
with previous quenched lattice results and the available experimental values.Comment: typeset with revtex, 15 pages, 11 figures, 4 table
- …