The Elaboration of Effective Coatings for Photonic Crystal Chips in Optical Biosensors

Here, we propose and study several types of quartz surface coatings designed for the high-performance sorption of biomolecules and their subsequent detection by a photonic crystal surface mode (PC SM) biosensor. The deposition and sorption of biomolecules are revealed by analyzing changes in the propagation parameters of optical modes on the surface of a photonic crystal (PC). The method makes it possible to measure molecular and cellular affinity interactions in real time by independently recording the values of the angle of total internal reflection and the angle of excitation of the surface wave on the surface of the PC. A series of dextrans with various anchor groups (aldehyde, carboxy, epoxy) suitable for binding with bioligands have been studied. We have carried out comparative experiments with dextrans with other molecular weights. The results confirmed that dextran with a Mw of 500 kDa and anchor epoxy groups have a promising potential as a matrix for the detection of proteins in optical biosensors. The proposed approach would make it possible to enhance the sensitivity of the PC SM biosensor and also permit studying the binding process of low molecular weight molecules in real time.

Reorganization of the topological surface mode of topological insulating α-Sn

α-Sn is a topologically nontrivial semimetal in its natural structure. Upon compressively strained in plane, it transforms into a topological insulator. But, up to now, a clear and systematic understanding of the topological surface mode of topological insulating α-Sn is still lacking. In the present work, first-principle simulations are employed to investigate the electronic structure evolution of Ge1-xSnx alloys aiming at understanding the band reordering, topological phase transition and topological surface mode of α-Sn in detail. Progressing from Ge to Sn with increasing Sn content in Ge1-xSnx, the conduction band inverts with the first valence band and then with the second valence band sequentially, rather than inverting with the latter directly. Correspondingly, a topologically nontrivial surface mode arises in the first inverted band gap. Meanwhile, a fragile Dirac cone appears in the second inverted band gap as a result of the reorganization of the topological surface mode caused by the first valence band. The reorganization of the topological surface mode in α-Sn is very similar to the HgTe case. The findings of the present work are helpful for understanding and utilizing of the topological surface mode of α-Sn.

The impact of the Helmholtz-Kohlrausch effect on the appearance of near-white paper colours

This paper investigates the impact of the Helmholtz-Kohlrausch effect on near-white substrate colours. As the luminance of the test colour (or its simulated reflectance in a softproof setup) approaches that of the adapting white point the viewing mode changes from 'surface mode' to 'aperture mode', and the appearance of the test colour becomes self-luminous. However, some substrates with optical brighteners fall close to this threshold between viewing modes, since the OBAs not only increase the perceived reflectance but also increase the H-K effect, where it is very prominent in bluish colours. For graphic arts content shown on a display system, this essentially breaks the soft-proofing paradigm. The practical application of this work relates to cross-media colour reproduction, where the lightness appearance of some substrates is not adequately described by their colorimetric values, and this may impact on choice of proofing strategies.

Modal analysis of a viscous fluid falling over a compliantwall

We study the modal instability of a three-dimensional Newtonian viscous fluid falling over a compliant wall under the framework of coupled evolution equations for normal velocity and normal vorticity, respectively. The Chebyshev spectral collocation numerical technique is applied in exploring unstable modes for the three-dimensional disturbances. The unstable zones pertaining to surface mode, wall mode and shear mode reduce as long as the spanwise wavenumber amplifies and corroborates the stabilizing influence of spanwise wavenumber. However, the onset of instability for the wall mode decays as long as the capillary number amplifies and ensures the destabilizing influence of the capillary number. Furthermore, the critical Reynolds number corresponding to surface mode found in the long-wave zone shifts towards the finite wavelength zone with increasing spanwise wavenumber and confirms the extinction of long-wave instability. But the inertialess instability created due to the wall mode disappears with increasing spanwise wavenumber. Moreover, the shear mode emerges in the high Reynolds number zone and is stabilized in the presence of spanwise wavenumber. In addition, the analytical derivation of Squire’s theorem is provided in appendix B for the flow over a compliant wall.

Geographical Variability of the Deformation Radius of the First Surface Mode

In areas with rough bathymetry, the vertical structure of ocean eddies can be decomposed into “surface modes,” which are surface intensified, and exhibit a velocity of nearly zero at the bottom. Furthermore, ocean surface modes are ubiquitous. Atlases of the first surface mode (SM1) deformation radius were computed on a global 0.25°×0.25° grid using WOA2013 and the data from Generalized Digital Environment Model (GDEM). Monthly and seasonal changes were also analyzed. The annual average SM1 deformation radius was approximately 1.5 times larger than the Rossby radius of deformation; the main difference occurred in areas with rough bathymetry, including continental margins and mid-ocean ridges. The seasonal and monthly average SM1 deformation radius shows an evident annual cycle.

Influence of NaCl on the Structure and Dynamics of Phospholipid Layers

We present a structural and dynamical analysis of the influence of NaCl on multilayer stacks of phospholipids on a solid surface. To this end, multilayer stacks of phospholipids (L-α-phosphatidylcholine, abbreviated as SoyPC) are investigated with neutron reflectometry, grazing-incidence small-angle neutron scattering (GISANS) and grazing-incidence neutron-spin echo spectroscopy (GINSES). We show both that the NaCl influence on the structure is predominantly on water-head group interface and also, that the change in dynamics is restricted to an associated change in the inter-plane viscosity. Using this knowledge, it is possible to model the dynamical behavior of a phospholipid membrane in response to a salt concentration of the solvent using only a single parameter, namely the in-plane viscosity. The excellent agreement with our previously published model also strongly supports the existence of a thermally excited surface mode in phospholipid membranes for close-to-physiological conditions.

Sensing of Surface and Bulk Refractive Index Using Magnetophotonic Crystal with Hybrid Magneto-Optical Response

We propose an all-dielectric magneto-photonic crystal with a hybrid magneto-optical response that allows for the simultaneous measurements of the surface and bulk refractive index of the analyzed substance. The approach is based on two different spectral features of the magneto-optical response corresponding to the resonances in p- and s-polarizations of the incident light. Angular spectra of p-polarized light have a step-like behavior near the total internal reflection angle which position is sensitive to the bulk refractive index. S-polarized light excites the TE-polarized optical Tamm surface mode localized in a submicron region near the photonic crystal surface and is sensitive to the refractive index of the near-surface analyte. We propose to measure a hybrid magneto-optical intensity modulation of p-polarized light obtained by switching the magnetic field between the transverse and polar configurations. The transversal component of the external magnetic field is responsible for the magneto-optical resonance near total internal reflection conditions, and the polar component reveals the resonance of the Tamm surface mode. Therefore, both surface- and bulk-associated features are present in the magneto-optical spectra of the p-polarized light.