49 research outputs found
Metallic and All-Dielectric Metasurfaces Sustaining Displacement-Mediated Bound States in the Continuum
Bound states in the continuum (BICs) are localized electromagnetic modes
within the continuous spectrum of radiating waves. Due to their infinite
lifetimes without radiation losses, BICs are driving research directions in
lasing, non-linear optical processes, and sensing. However, conventional
methods for converting BICs into leaky resonances, or quasi-BICs, with
high-quality factors typically rely on breaking the in-plane inversion symmetry
of the metasurface and often result in resonances that are strongly dependent
on the angle of the incident light, making them unsuitable for many practical
applications. Here, we numerically analyze and experimentally demonstrate an
emerging class of BIC-driven metasurfaces, where the coupling to the far field
is controlled by the displacement of individual resonators. In particular, we
investigate both all-dielectric and metallic as well as positive and inverse
displacement-mediated metasurfaces sustaining angular-robust quasi-BICs in the
mid-infrared spectral region. We explore their behavior with changes in the
incidence angle of illumination and experimentally show their superior
performance compared to two conventional alternatives: silicon-based tilted
ellipses and cylindrical nanoholes in gold. We anticipate our findings to open
exciting perspectives for bio-sensing, conformal optical devices, and photonic
devices using focused light.Comment: 27 pages, 7 figures, 1 tabl
3D-printed SAXS chamber for controlled in situ dialysis and optical characterization
3D printing changes the scope of how samples can be mounted for small-angle X-ray scattering (SAXS). In this paper a 3D-printed X-ray chamber, which allows for in situ exchange of buffer and in situ optical transmission spectroscopy, is presented. The chamber is made of cyclic olefin copolymers (COC), including COC X-ray windows providing ultra-low SAXS background. The design integrates a membrane insert for in situ dialysis of the 100 ml sample volume against a reservoir, which enables measurements of the same sample under multiple conditions using an in-house X-ray setup equipped with a 17.4 keV molybdenum source. The design's capabilities are demonstrated by measuring reversible structural changes in lipid and polymer systems as a function of salt concentration and pH. In the same chambers optical light transmission spectroscopy was carried out measuring the optical turbidity of the mesophases and local pH values using pH-responsive dyes. Microfluidic exchange and optical spectroscopy combined with in situ X-ray scattering enables vast applications for the study of responsive materials
Permittivity-asymmetric quasi-bound states in the continuum
Broken symmetries lie at the heart of nontrivial physical phenomena. Breaking
the in-plane geometrical symmetry of optical systems allows to access a set of
electromagnetic states termed symmetry-protected quasi-bound states in the
continuum (qBICs). Here we demonstrate, theoretically, numerically and
experimentally, that such optical states can also be accessed in metasurfaces
by breaking the in-plane symmetry in the permittivity of the comprising
materials, showing a remarkable equivalence to their geometrically-asymmetric
counterparts. However, while the physical size of atoms imposes a limit on the
lowest achievable geometrical asymmetry, weak permittivity modulations due to
carrier doping and electro-optical Pockels and Kerr effects, usually considered
insignificant, open up the possibility of infinitesimal permittivity
asymmetries for on-demand, and dynamically tuneable optical resonances of
extremely high quality factors. We probe the excitation of
permittivity-asymmetric qBICs (-qBICs) using a prototype
Si/TiO metasurface, in which the asymmetry in the unit cell is provided
by the refractive index contrast of the dissimilar materials, surpassing any
unwanted asymmetries from nanofabrication defects or angular deviations of
light from normal incidence. -qBICs can also be excited in 1D
gratings, where quality-factor enhancement and tailored interference phenomena
via the interplay of geometrical and permittivity asymmetries are numerically
demonstrated. The emergence of -qBICs in systems with broken
symmetries in their permittivity may enable to test time-energy uncertainties
in quantum mechanics, and lead to a whole new class of low-footprint optical
and optoelectronic devices, from arbitrarily narrow filters and topological
sources, biosensing and ultrastrong light-matter interaction platforms, to
tuneable optical switches.Comment: Manuscript and Supplementary Information, 27 pages, 4 Figures
manuscript + 4 Supplementary Figure
A mean-field kinetic lattice gas model of electrochemical cells
We develop Electrochemical Mean-Field Kinetic Equations (EMFKE) to simulate
electrochemical cells. We start from a microscopic lattice-gas model with
charged particles, and build mean-field kinetic equations following the lines
of earlier work for neutral particles. We include the Poisson equation to
account for the influence of the electric field on ion migration, and
oxido-reduction processes on the electrode surfaces to allow for growth and
dissolution. We confirm the viability of our approach by simulating (i) the
electrochemical equilibrium at flat electrodes, which displays the correct
charged double-layer, (ii) the growth kinetics of one-dimensional
electrochemical cells during growth and dissolution, and (iii) electrochemical
dendrites in two dimensions.Comment: 14 pages twocolumn, 17 figure
Different paths to the modern state in Europe: the interaction between domestic political economy and interstate competition
Theoretical work on state formation and capacity has focused mostly on early modern Europe and on the experience of western European states during this period. While a number of European states monopolized domestic tax collection and achieved gains in state capacity during the early modern era, for others revenues stagnated or even declined, and these variations motivated alternative hypotheses for determinants of fiscal and state capacity. In this study we test the basic hypotheses in the existing literature making use of the large date set we have compiled for all of the leading states across the continent. We find strong empirical support for two prevailing threads in the literature, arguing respectively that interstate wars and changes in economic structure towards an urbanized economy had positive fiscal impact. Regarding the main point of contention in the theoretical literature, whether it was representative or authoritarian political regimes that facilitated the gains in fiscal capacity, we do not find conclusive evidence that one performed better than the other. Instead, the empirical evidence we have gathered lends supports to the hypothesis that when under pressure of war, the fiscal performance of representative regimes was better in the more urbanized-commercial economies and the fiscal performance of authoritarian regimes was better in rural-agrarian economie
The ‘Tribal Politics’ of Field Research: A Reflection on Power and Partiality in 21st-Century Warzones
Different Paths to the Modern State in Europe: The Interaction between Domestic Political Economy and Interstate Competition
Impact of primary kidney disease on the effects of empagliflozin in patients with chronic kidney disease: secondary analyses of the EMPA-KIDNEY trial
Background: The EMPA KIDNEY trial showed that empagliflozin reduced the risk of the primary composite outcome of kidney disease progression or cardiovascular death in patients with chronic kidney disease mainly through slowing progression. We aimed to assess how effects of empagliflozin might differ by primary kidney disease across its broad population. Methods: EMPA-KIDNEY, a randomised, controlled, phase 3 trial, was conducted at 241 centres in eight countries (Canada, China, Germany, Italy, Japan, Malaysia, the UK, and the USA). Patients were eligible if their estimated glomerular filtration rate (eGFR) was 20 to less than 45 mL/min per 1·73 m2, or 45 to less than 90 mL/min per 1·73 m2 with a urinary albumin-to-creatinine ratio (uACR) of 200 mg/g or higher at screening. They were randomly assigned (1:1) to 10 mg oral empagliflozin once daily or matching placebo. Effects on kidney disease progression (defined as a sustained ≥40% eGFR decline from randomisation, end-stage kidney disease, a sustained eGFR below 10 mL/min per 1·73 m2, or death from kidney failure) were assessed using prespecified Cox models, and eGFR slope analyses used shared parameter models. Subgroup comparisons were performed by including relevant interaction terms in models. EMPA-KIDNEY is registered with ClinicalTrials.gov, NCT03594110. Findings: Between May 15, 2019, and April 16, 2021, 6609 participants were randomly assigned and followed up for a median of 2·0 years (IQR 1·5–2·4). Prespecified subgroupings by primary kidney disease included 2057 (31·1%) participants with diabetic kidney disease, 1669 (25·3%) with glomerular disease, 1445 (21·9%) with hypertensive or renovascular disease, and 1438 (21·8%) with other or unknown causes. Kidney disease progression occurred in 384 (11·6%) of 3304 patients in the empagliflozin group and 504 (15·2%) of 3305 patients in the placebo group (hazard ratio 0·71 [95% CI 0·62–0·81]), with no evidence that the relative effect size varied significantly by primary kidney disease (pheterogeneity=0·62). The between-group difference in chronic eGFR slopes (ie, from 2 months to final follow-up) was 1·37 mL/min per 1·73 m2 per year (95% CI 1·16–1·59), representing a 50% (42–58) reduction in the rate of chronic eGFR decline. This relative effect of empagliflozin on chronic eGFR slope was similar in analyses by different primary kidney diseases, including in explorations by type of glomerular disease and diabetes (p values for heterogeneity all >0·1). Interpretation: In a broad range of patients with chronic kidney disease at risk of progression, including a wide range of non-diabetic causes of chronic kidney disease, empagliflozin reduced risk of kidney disease progression. Relative effect sizes were broadly similar irrespective of the cause of primary kidney disease, suggesting that SGLT2 inhibitors should be part of a standard of care to minimise risk of kidney failure in chronic kidney disease. Funding: Boehringer Ingelheim, Eli Lilly, and UK Medical Research Council