1,586 research outputs found
Perfect Anomalous Reflection with a Binary Huygens' Metasurface
In this paper we propose a new metasurface that is able to reflect a known
incoming electromagnetic wave into an arbitrary direction, with perfect power
efficiency. This seemingly simple task, which we hereafter call perfect
anomalous reflection, is actually highly non-trivial due to the differing wave
impedances and complex interference between the incident and reflected waves.
Heretofore, proposed metasurfaces which achieve perfect anomalous reflection
require complicated, deeply subwavelength and/or multilayer element structures
which allow them to couple to and from leaky and/or evanescent waves. In
contrast, we demonstrate that using a Binary Huygens' Metasurface (BHM) --- a
passive and lossless metasurface with only two cells per period --- perfect
anomalous reflection can be achieved over a wide angular and frequency range.
Through simulations and experiments at 24 GHz, we show that a properly designed
BHM can anomalously reflect an incident electromagnetic wave from to , with perfect power efficiency to within
experimental precision
Bipartite Dielectric Huygens' Metasurface for Anomalous Refraction
Huygens' metasurfaces - fundamentally based on Schelkunoff's equivalence
principle, Huygens' metasurfaces consist of a two-dimensional array of Huygens'
sources formed by co-located orthogonal electric and magnetic dipoles. Such
metasurfaces provide electric and magnetic responses to an incoming
electromagnetic (EM) wave, leading to unidirectional scattering and 2
phase coverage. We herein report a near-reflectionless coarsely discretized
dielectric Huygens' metasurface that performs anomalous refraction, offering a
low-loss platform for wave manipulation at high frequencies as compared to
their lossy metallic analogue. The coarse discretization dramatically
simplifies the design, resulting in a metasurface that is highly efficient,
cost-effective, and robust. In this paper, the proposed metasurface comprises
two meta-atoms per period and is hence named the bipartite dielectric Huygens'
metasurface. Through full-wave simulations at 28 GHz, we show that the proposed
metasurface can reroute an incident EM wave from to
with very high efficiency: 87% of the scattered power
is anomalously transmitted to . Based on our observations, a coarsely
discretized dielectric Huygens' metasurface platform can be efficacious to
design meta-devices with multifaceted functionalities in different frequency
regimes.Comment: 28 pages, 14 figure
A spatially shifted beam approach to subwavelength focusing
Although negative-refractive-index metamaterials have successfully achieved
subwavelength focusing, image resolution is limited by the presence of losses.
In this Letter, a metal transmission screen with subwavelength spaced slots is
proposed that focuses the near-field beyond the diffraction limit and
furthermore, is easily scaled from microwave frequencies to the optical regime.
An analytical model based on the superposition of shifted beam patterns is
developed that agrees very well with full-wave simulations and is corroborated
by experimental results at microwave frequencies.Comment: 5 pages, 7 figures. Content updated following reviewer comments to
match final published pape
Directional Dipole Dice Enabled by Anisotropic Chirality
Directional radiation and scattering play an essential role in light
manipulation for various applications in integrated nanophotonics, antenna and
metasurface designs, quantum optics, etc. The most elemental system with this
property is the class of directional dipoles, including the circular dipole,
Huygens dipole, and Janus dipole. A unified realization of all three dipole
types and a mechanism to freely switch among them are previously unreported,
yet highly desirable for developing compact and multifunctional directional
sources. Here, we theoretically and experimentally demonstrate that the synergy
of chirality and anisotropy can give rise to all three directional dipoles in
one structure at the same frequency under linearly polarized plane wave
excitations. This mechanism enables a simple helix particle to serve as a
directional dipole dice (DDD), achieving selective manipulation of optical
directionality via different "faces" of the particle. We employ three "faces"
of the DDD to realize face-multiplexed routing of guided waves in three
orthogonal directions with the directionality determined by spin, power flow,
and reactive power, respectively. This construction of the complete
directionality space can enable the unprecedented high-dimensional control of
both near-field and far-field directionality with broad applications in
photonic integrated circuits, quantum information processing, and
subwavelength-resolution imaging.Comment: 17 pages, 16 figure
Fronto-cerebellar connectivity mediating cognitive processing speed
Processing speed is an important construct in understanding cognition. This study was aimed to control task specificity for understanding the neural mechanisms underlying cognitive processing speed. Forty young adult subjects performed attention tasks of two modalities (auditory and visual) and two levels of task rules (compatible and incompatible). Block-design fMRI captured BOLD signals during the tasks. Thirteen regions of interest were defined with reference to publicly available activation maps for processing speed tasks. Cognitive speed was derived from task reaction times, which yielded six sets of connectivity measures. Mixed-effect LASSO regression revealed six significant paths suggestive of a cerebello-frontal network predicting the cognitive speed. Among them, three are long range (two fronto-cerebellar, one cerebello-frontal), and three are short range (fronto-frontal, cerebello-cerebellar, and cerebello-thalamic). The long-range connections are likely to relate to cognitive control, and the short-range connections relate to rule-based stimulus-response processes. The revealed neural network suggests that automaticity, acting on the task rules and interplaying with effortful top-down attentional control, accounts for cognitive speed
Relationship of dietary nitrate intake from vegetables with cardiovascular disease mortality: a prospective study in a cohort of older Australians
Purpose Short-term trials indicate inorganic nitrate and nitrate-rich vegetables may have vascular health benefits. However, few observational studies have explored the relationship between nitrate intake and long-term cardiovascular disease (CVD) outcomes. The primary aim of this study was to investigate the association of nitrate intake from vegetables with CVD mortality in a sample of older Australians. Methods A subgroup of participants without diabetes or major CVD at baseline (1992–1994) were included from the Blue Mountains Eye Study, a population-based cohort study of men and women aged ≥ 49 years. Diets were evaluated using a validated food frequency questionnaire at baseline, 5 years and 10 years of follow-up. Vegetable nitrate intake was estimated using a comprehensive vegetable nitrate database. Cox proportional hazard regression was used to explore the association between vegetable nitrate intake and CVD mortality. Results During 14 years of follow-up, 188/2229 (8.4%) participants died from CVD. In multivariable-adjusted analysis, participants in quartile 2 [69.5–99.6 mg/day; HR 0.53 (95% CI 0.35, 0.82)], quartile 3 [99.7–137.8 mg/day; HR 0.51 (95% CI 0.32, 0.80)], and quartile 4 [\u3e 137.8 mg/day; HR 0.63 (95% CI 0.41, 0.95)] of vegetable nitrate intake had lower hazards for CVD mortality compared to participants in quartile 1 (\u3c 69.5 mg/day). Conclusions In older Australian men and women, vegetable nitrate intake was inversely associated with CVD mortality, independent of lifestyle and cardiovascular risk factors. These findings confirm a recent report that intake of vegetable nitrate lowers the risk of CVD mortality in older women and extend these findings to older men
A High-Spin Ground-State Donor-Acceptor Conjugated Polymer
Interest in high-spin organic materials is driven by opportunities to enable far-reaching fundamental science and develop technologies that integrate light element spin, magnetic, and quantum functionalities. Although extensively studied, the intrinsic instability of these materials complicates synthesis and precludes an understanding of how fundamental properties associated with the nature of the chemical bond and electron pairing in organic materials systems manifest in practical applications. Here, we demonstrate a conjugated polymer semiconductor, based on alternating cyclopentadithiophene and thiadiazoloquinoxaline units, that is a ground-state triplet in its neutral form. Electron paramagnetic resonance and magnetic susceptibility measurements are consistent with a high-to-low spin energy gap of 9.30 × 10−3 kcal mol−1. The strongly correlated electronic structure, very narrow bandgap, intramolecular ferromagnetic coupling, high electrical conductivity, solution processability, and robust stability open access to a broad variety of technologically relevant applications once thought of as beyond the current scope of organic semiconductors
Macrophage development and activation involve coordinated intron retention in key inflammatory regulators
Monocytes and macrophages are essential components of the innate immune system. Herein, we
report that intron retention (IR) plays an important role in the development and function of these
cells. Using Illumina mRNA sequencing, Nanopore
direct cDNA sequencing and proteomics analysis,
we identify IR events that affect the expression of
key genes/proteins involved in macrophage development and function. We demonstrate that decreased
IR in nuclear-detained mRNA is coupled with increased expression of genes encoding regulators of
macrophage transcription, phagocytosis and inflammatory signalling, including ID2, IRF7, ENG and LAT.
We further show that this dynamic IR program persists during the polarisation of resting macrophages
into activated macrophages. In the presence of proinflammatory stimuli, intron-retaining CXCL2 and NFKBIZ transcripts are rapidly spliced, enabling timely
expression of these key inflammatory regulators by
macrophages. Our study provides novel insights into
the molecular factors controlling vital regulators of
the innate immune response
- …