38 research outputs found
Functional complex plasmonics : understanding and realizing chiral and active plasmonic systems
The present thesis concerns itself with the theoretical study and experimental realization of complex plasmonic systems for highly integrated nanophotonic devices and enhanced chiroptical spectroscopy. In particular, the two broad topics of active metasurfaces and chiral plasmonic systems are investigated to this end.
In this context, the chalcogenide phase change material GeSbTe is utilized to demonstrate, for the first time, metasurface based beam steering and varifocal lensing devices.
The versatility of this approach to lending active functionality to plasmonic systems is further evidenced through our realization of a chiral plasmonic system that both exhibits a wavelength tunable and handedness switchable chiroptical response.
Furthermore, in order to enable a systematic study of plasmon- enhanced chiroptical spectroscopy, we rst establish and analyze canonical chiral plasmonic building blocks, in particular, the loop wire and chiral dimer structure. The results from this undertaking lead to fundamental insights for understanding complex chiral plas- monic systems.
Finally, we implement chiral media in the commercial electromagnetic full- field solver Comsol Multiphysics to carry out rigorous numerical studies of the macroscopic electrodynamic processes involved in plasmon-enhanced circular dichroism spectroscopy revealing both substantial enhancement due to near-field effects as well as upper boundaries to the magnitude of such enhancements
Formation of chiral fields in a symmetric environment
Chiral fields, i. e., electromagnetic fields with nonvanishing optical chirality, can occur next to symmetric nanostructures without geometrical chirality illuminated with linearly polarized light at normal incidence. A simple dipole model is utilized to explain this behavior theoretically. Illuminated with circularly polarized light, the chiral near-fields are still dominated by the distributions found for the linear polarization but show additional features due to the optical chirality of the incident light. Rotating the angle of linear polarization introduces more subtle changes to the distribution of optical chirality. Using our findings, we propose a novel scheme to obtain chiroptical far-field response using linearly polarized light, which could be utilized for applications such as optical enantiomer sensing
Causal State Estimation and Heisenberg Uncertainty Principle
The observables of a noisy quantum system can be estimated by appropriately
filtering the records of their continuous measurement. Such filtering is
relevant for state estimation and measurement-based quantum feedback control.
It is therefore imperative that the observables estimated through a causal
filter satisfy the Heisenberg uncertainty principle. In the Markovian setting,
prior work implicitly guarantees this requirement. We show that any causal
estimate of linear observables of a linear, but not necessarily Markovian,
system will satisfy the uncertainty principle. In particular, this is true
irrespective of any feedback control of the system and of where in the feedback
loop -- inside or outside -- the measurement record is accessed. Indeed, causal
estimators using the in-loop measurement record can be as precise as those
using the out-of-loop record. These results clarify the role of causal
estimators to a large class of quantum systems, restores the equanimity of
in-loop and out-of-loop measurements in their estimation and control, and
simplifies future experiments on measurement-based quantum feedback control
Polariton Nanophotonics using Phase Change Materials
Polaritons formed by the coupling of light and material excitations such as
plasmons, phonons, or excitons enable light-matter interactions at the
nanoscale beyond what is currently possible with conventional optics. Recently,
significant interest has been attracted by polaritons in van der Waals
materials, which could lead to applications in sensing, integrated photonic
circuits and detectors. However, novel techniques are required to control the
propagation of polaritons at the nanoscale and to implement the first practical
devices. Here we report the experimental realization of polariton refractive
and meta-optics in the mid-infrared by exploiting the properties of low-loss
phonon polaritons in isotopically pure hexagonal boron nitride (hBN), which
allow it to interact with the surrounding dielectric environment comprising the
low-loss phase change material, GeSbTe (GST). We demonstrate
waveguides which confine polaritons in a 1D geometry, and refractive optical
elements such as lenses and prisms for phonon polaritons in hBN, which we
characterize using scanning near field optical microscopy. Furthermore, we
demonstrate metalenses, which allow for polariton wavefront engineering and
sub-wavelength focusing. Our method, due to its sub-diffraction and planar
nature, will enable the realization of programmable miniaturized integrated
optoelectronic devices, and will lay the foundation for on-demand biosensors.Comment: 15 pages, 4 figures, typos corrected in v
Interactions between curcumin and human salt-induced kinase 3 elucidated from computational tools and experimental methods
Natural products are widely used for treating mitochondrial dysfunction-related diseases and cancers. Curcumin, a well-known natural product, can be potentially used to treat cancer. Human salt-induced kinase 3 (SIK3) is one of the target proteins for curcumin. However, the interactions between curcumin and human SIK3 have not yet been investigated in detail. In this study, we studied the binding models for the interactions between curcumin and human SIK3 using computational tools such as homology modeling, molecular docking, molecular dynamics simulations, and binding free energy calculations. The open activity loop conformation of SIK3 with the ketoenol form of curcumin was the optimal binding model. The I72, V80, A93, Y144, A145, and L195 residues played a key role for curcumin binding with human SIK3. The interactions between curcumin and human SIK3 were also investigated using the kinase assay. Moreover, curcumin exhibited an IC50 (half-maximal inhibitory concentration) value of 131 nM, and it showed significant antiproliferative activities of 9.62 ± 0.33 µM and 72.37 ± 0.37 µM against the MCF-7 and MDA-MB-23 cell lines, respectively. This study provides detailed information on the binding of curcumin with human SIK3 and may facilitate the design of novel salt-inducible kinases inhibitors
bFGF promotes adipocyte differentiation in human mesenchymal stem cells derived from embryonic stem cells
Highly efficient energy-conserving moment method for the multi-dimensional Vlasov-Maxwell system
We present an energy-conserving numerical scheme to solve the Vlasov-Maxwell
(VM) system based on the regularized moment method proposed in [Z. Cai, Y. Fan,
and R. Li. CPAM, 2014]. The globally hyperbolic moment system is deduced for
the multi-dimensional VM system under the framework of the Hermite expansions,
where the expansion center and the scaling factor are set as the macroscopic
velocity and local temperature, respectively. Thus, the effect of the Lorentz
force term could be reduced into several ODEs about the macroscopic velocity
and the moment coefficients of higher order, which could significantly reduce
the computational cost of the whole system. An energy-conserving numerical
scheme is proposed to solve the moment equations and the Maxwell equations,
where only a linear equation system needs to be solved. Several numerical
examples such as the two-stream instability, Weibel instability, and the
two-dimensional Orszag Tang vortex problem are studied to validate the
efficiency and excellent energy-preserving property of the numerical scheme
Bulk β-Te to few layered β-tellurenes: indirect to direct band-Gap transitions showing semiconducting property
Herein we report a prediction of a highly kinetic stable layered structure of tellurium (namely, bulk beta-Te), which is similar to these layered bulk materials such as graphite, black phosphorus, and gray arsenic. Bulk beta-Te turns out to be a semiconductor that has a band gap of 0.325 eV (HSE06: 0.605 eV), based on first-principles calculations. Moreover, the single-layer form of the bulk beta-Te, called beta-tellurene, is predicted to have a high stability. When the bulk beta-Te is thinned to one atomic layer, an indirect semiconductor of band gap is changed to 1.265 eV (HSE06: 1.932 eV) with a very high kinetic stability. Interestingly, an increase of the number of the beta-tellurene layers from one to three is accompanied by a shift from an indirect to direct band gap. Furthermore, the effective carrier masses, the optical properties and phonon modes of few-layer beta-tellurenes are characterized. Few-layer beta-tellurenes strongly absorb the ultraviolet and blue-violet visible lights. The dramatic changes in the electronic structure and excellent photo absorptivities are expected to pave the way for high speed ultrathin transistors, as well as optoelectronic devices working in the UV or blue-green visible regions. © Copyright 2017 IOP Publishing Terms & conditions Disclaime
Image Fusion for Travel Time Tomography Inversion
The travel time tomography technology had achieved wide application, the hinge of tomography was inversion algorithm, the ray path tracing technology had a great impact on the inversion results. In order to improve the SNR of inversion image, comprehensive utilization of inversion results with different ray tracing can be used. We presented an imaging fusion method based on improved Wilkinson iteration method. Firstly, the shortest path method and the linear travel time interpolation were used for forward calculation; then combined the improved Wilkinson iteration method with super relaxation precondition method to reduce the condition number of matrix and accelerate iterative speed, the precise integration method was used to solve the inverse matrix more precisely in tomography inversion process; finally, use wavelet transform for image fusion, obtain the final image. Therefore, the ill-conditioned linear equations were changed into iterative normal system through two times of treatment and using images with different forward algorithms for image fusion, it reduced the influence effect of measurement error on imaging. Simulation results showed that, this method can eliminate the artifacts in images effectively, it had extensive practical significance