9 research outputs found
Combining ultrahigh index with exceptional nonlinearity in resonant transition metal dichalcogenide nanodisks
Second-order nonlinearity in solids gives rise to a plethora of unique
physical phenomena ranging from piezoelectricity and optical rectification to
optical parametric amplification, spontaneous parametric down-conversion, and
the generation of entangled photon pairs. Monolayer transition metal
dichalcogenides (TMDs), such as MoS, exhibit one of the highest known
second-order nonlinear coefficients. However, the monolayer nature of these
materials prevents the fabrication of resonant objects exclusively from the
material itself, necessitating the use of external structures to achieve
optical enhancement of nonlinear processes. Here, we exploit the 3R phase of a
molybdenum disulfide multilayer for resonant nonlinear nanophotonics. The lack
of inversion symmetry, even in the bulk of the material, provides a combination
of a massive second-order susceptibility, an extremely high and anisotropic
refractive index in the near-infrared region (~4.5), and low absorption
losses, making 3R-MoS highly attractive for nonlinear nanophotonics. We
demonstrate this by fabricating 3R-MoS nanodisks of various radii, which
support resonant anapole states, and observing substantial ( 100-fold)
enhancement of second-harmonic generation in a single resonant nanodisk
compared to an unpatterned flake of the same thickness. The enhancement is
maximized at the spectral overlap between the anapole state of the disk and the
material resonance of the second-order susceptibility. Our approach unveils a
powerful tool for enhancing the entire spectrum of optical second-order
nonlinear processes in nanostructured van der Waals materials, thereby paving
the way for nonlinear and quantum high-index TMD-nanophotonics
Computational Design of Alloy Nanostructures for Optical Sensing of Hydrogen
Pd nanoalloys show great potential as hysteresis-free, reliable hydrogen sensors. Here, a multiscale modeling approach is employed to determine optimal conditions for optical hydrogen sensing using the Pd-Au-H system. Changes in hydrogen pressure translate to changes in hydrogen content and eventually the optical spectrum. At the single particle level, the shift of the plasmon peak position with hydrogen concentration (i.e., the "optical" sensitivity) is approximately constant at 180 nm/c(H) for nanodisk diameters of greater than or similar to 100 nm. For smaller particles, the optical sensitivity is negative and increases with decreasing diameter, due to the emergence of a second peak originating from coupling between a localized surface plasmon and interband transitions. In addition to tracking peak position, the onset of extinction as well as extinction at fixed wavelengths is considered. We carefully compare the simulation results with experimental data and assess the potential sources for discrepancies. Invariably, the results suggest that there is an upper bound for the optical sensitivity that cannot be overcome by engineering composition and/or geometry. While the alloy composition has a limited impact on optical sensitivity, it can strongly affect H uptake and consequently the "thermodynamic" sensitivity and the detection limit. Here, it is shown how the latter can be improved by compositional engineering and even substantially enhanced via the formation of an ordered phase that can be synthesized at higher hydrogen partial pressures
The emergence of coordinative dialogue – pragmatic context in multi-agent communication
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The emergence of coordinative dialogue – pragmatic context in multi-agent communication
We introduce a model of emergent communication between agents involved in signalling games inspired by early caregiver--child interactions. In the model, the child agent has to communicate its dynamically changing needs to the caregiver agent, which is able to address them. We demonstrate that the dialogical strategy performs better than one-directional communication. When the child's signalling frequency is limited, a particular structure of signals and actions emerges that separates the child's needs into urgent and quiet. The meaning of emerging communication is better understood in pragmatic terms than in terms of mapping. Our model underscores the relationship between the dynamics of the environment and the dynamics of communication as one of the factors driving the language structure
Multipole analysis of substrate-supported dielectric nanoresonator metasurfaces via the T
Computational Design of Alloy Nanostructures for Optical Sensing of Hydrogen
Pd nanoalloys show great potential as hysteresis-free, reliable hydrogen
sensors. Here, a multi-scale modeling approach is employed to determine optimal
conditions for optical hydrogen sensing using the Pd-Au-H system. Changes in
hydrogen pressure translate to changes in hydrogen content and eventually the
optical spectrum. At the single particle level, the shift of the plasmon peak
position with hydrogen concentration (i.e., the "optical" sensitivity) is
approximately constant at 180 nm/c_H for nanodisk diameters >~ 100 nm. For
smaller particles, the optical sensitivity is negative and increases with
decreasing diameter, due to the emergence of a second peak originating from
coupling between a localized surface plasmon and interband transitions. In
addition to tracking peak position, the onset of extinction as well as
extinction at fixed wavelengths is considered. We carefully compare the
simulation results with experimental data and assess the potential sources for
discrepancies. Invariably, the results suggest that there is an upper bound for
the optical sensitivity that cannot be overcome by engineering composition
and/or geometry. While the alloy composition has a limited impact on optical
sensitivity, it can strongly affect H uptake and consequently the
"thermodynamic" sensitivity and the detection limit. Here, it is shown how the
latter can be improved by compositional engineering and even substantially
enhanced via the formation of an ordered phase that can be synthesized at
higher hydrogen partial pressures.Comment: 14 pages, 8 figure
A selective chemical probe for exploring the role of CDK8 and CDK19 in human disease
There is unmet need for chemical tools to explore the role of the Mediator complex in human pathologies ranging from cancer to cardiovascular disease. Here we determine that CCT251545, a small-molecule inhibitor of the WNT pathway discovered through cell-based screening, is a potent and selective chemical probe for the human Mediator complex–associated protein kinases CDK8 and CDK19 with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates a type 1 binding mode involving insertion of the CDK8 C terminus into the ligand binding site. In contrast to type II inhibitors of CDK8 and CDK19, CCT251545 displays potent cell-based activity. We show that CCT251545 and close analogs alter WNT pathway–regulated gene expression and other on-target effects of modulating CDK8 and CDK19, including expression of genes regulated by STAT1. Consistent with this, we find that phosphorylation of STAT1SER727 is a biomarker of CDK8 kinase activity in vitro and in vivo. Finally, we demonstrate in vivo activity of CCT251545 in WNT-dependent tumors