2,397 research outputs found
Full Hydrodynamic Model of Nonlinear Electromagnetic Response in Metallic Metamaterials
Applications of metallic metamaterials have generated significant interest in
recent years. Electromagnetic behavior of metamaterials in the optical range is
usually characterized by a local-linear response. In this article, we develop a
finite-difference time-domain (FDTD) solution of the hydrodynamic model that
describes a free electron gas in metals. Extending beyond the local-linear
response, the hydrodynamic model enables numerical investigation of nonlocal
and nonlinear interactions between electromagnetic waves and metallic
metamaterials. By explicitly imposing the current continuity constraint, the
proposed model is solved in a self-consistent manner. Charge, energy and
angular momentum conservation laws of high-order harmonic generation have been
demonstrated for the first time by the Maxwell-hydrodynamic FDTD model. The
model yields nonlinear optical responses for complex metallic metamaterials
irradiated by a variety of waveforms. Consequently, the multiphysics model
opens up unique opportunities for characterizing and designing nonlinear
nanodevices.Comment: 11 pages, 14 figure
An efficient marching-on-in-degree solution of transient multiscale EM scattering problems
A marching-on-in-degree (MOD)-based time-domain domain decomposition method is proposed to efficiently analyze the transient electromagnetic scattering from electrically large multiscale targets. The algorithm starts with an octree that divides the whole scattering target into several subdomains. Then using the equivalence principle algorithm, each subdomain is enclosed by an equivalence sphere (ES), where both the RWG and BoR spatial basis functions are employed to expand the unknown currents. The interactions of the near-field subdomains are directly calculated by the method of moments, while the far-field interactions can be converted into the interactions of corresponding ESs. This scheme implicitly satisfies the current continuity condition, and the convergence can be accelerated as well. By harnessing the rotational symmetry of the ESs, the computational resources are reduced significantly compared with the traditional MOD method. Several numerical examples are presented to demonstrate the accuracy and efficiency of the proposed algorithm. © 2016 IEEE.postprin
Thermal effects on lattice strain in hcp Fe under pressure
We compute the c/a lattice strain versus temperature for nonmagnetic hcp iron
at high pressures using both first-principles linear response quasiharmonic
calculations based on the full potential linear-muffin-tin-orbital (LMTO)
method and the particle-in-cell (PIC) model for the vibrational partition
function using a tight-binding total-energy method. The tight-binding model
shows excellent agreement with the all-electron LMTO method. When hcp structure
is stable, the calculated geometric mean frequency and Helmholtz free energy of
hcp Fe from PIC and linear response lattice dynamics agree very well, as does
the axial ratio as a function of temperature and pressure. On-site
anharmonicity proves to be small up to the melting temperature, and PIC gives a
good estimate of its sign and magnitude. At low pressures, hcp Fe becomes
dynamically unstable at large c/a ratios, and the PIC model might fail where
the structure approaches lattice instability. The PIC approximation describes
well the vibrational behavior away from the instability, and thus is a
reasonable approach to compute high temperature properties of materials. Our
results show significant differences from earlier PIC studies, which gave much
larger axial ratio increases with increasing temperature, or reported large
differences between PIC and lattice dynamics results.Comment: 9 figure
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Economic policy uncertainty and mergers and acquisitions: Evidence from China
Patterns of brain asymmetry associated with polygenic risks for autism and schizophrenia implicate language and executive functions but not brain masculinization
Autism spectrum disorder (ASD) and schizophrenia have been conceived as partly opposing disorders in terms of systemizing versus empathizing cognitive styles, with resemblances to male versus female average sex differences. Left-right asymmetry of the brain is an important aspect of its organization that shows average differences between the sexes, and can be altered in both ASD and schizophrenia. Here we mapped multivariate associations of polygenic risk scores for ASD and schizophrenia with asymmetries of regional cerebral cortical surface area, thickness and subcortical volume measures in 32,256 participants from the UK Biobank. Polygenic risks for the two disorders were positively correlated (r=0.08, p=7.13×10-50), and both were higher in females compared to males, consistent with biased participation against higher-risk males. Each polygenic risk score was associated with multivariate brain asymmetry after adjusting for sex, ASD r=0.03, p=2.17×10-9, schizophrenia r=0.04, p=2.61×10-11, but the multivariate patterns were mostly distinct for the two polygenic risks, and neither resembled average sex differences. Annotation based on meta-analyzed functional imaging data showed that both polygenic risks were associated with asymmetries of regions important for language and executive functions, consistent with behavioural associations that arose in phenome-wide association analysis. Overall, the results indicate that distinct patterns of subtly altered brain asymmetry may be functionally relevant manifestations of polygenic risks for ASD and schizophrenia, but do not support brain masculinization or feminization in their etiologies
Exciton delocalization incorporated drift-diffusion model for bulk-heterojunction organic solar cells
published_or_final_versio
Mixing of spin and orbital angular momenta via second-harmonic generation in plasmonic and dielectric chiral nanostructures
We present a theoretical study of the characteristics of the nonlinear
spin-orbital angular momentum coupling induced by second-harmonic generation in
plasmonic and dielectric nanostructures made of centrosymmetric materials. In
particular, the connection between the phase singularities and polarization
helicities in the longitudinal components of the fundamental and
second-harmonic optical fields and the scatterer symmetry properties are
discussed. By in-depth comparison between the interaction of structured optical
beams with plasmonic and dielectric nanostructures, we have found that
all-dielectric and plasmonic nanostructures that exhibit magnetic and electric
resonances have comparable second-harmonic conversion efficiency. In addition,
mechanisms for second-harmonic enhancement for single and chiral clusters of
scatterers are unveiled and the relationships between the content of optical
angular momentum of the incident optical beams and the enhancement of nonlinear
light scattering is discussed. In particular, we formulate a general angular
momenta conservation law for the nonlinear spin-orbital angular momentum
interaction, which includes the quasi-angular-momentum of chiral structures
with different-order rotational symmetry. As a key conclusion of our study
relevant to nanophotonics, we argue that all-dielectric nanostructures provide
a more suitable platform to investigate experimentally the nonlinear
interaction between spin and orbital angular momenta, as compared to plasmonic
ones, chiefly due to their narrower resonance peaks, lower intrinsic losses,
and higher sustainable optical power
Dispersion Characteristics Analysis of One Dimensional Multiple Periodic Structures and Their Applications to Antennas
published_or_final_versio
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