arXiv subjects

S. Danilov

Publications and source records attributed to S. Danilov.

6 recordsLinked to original sources

arXiv2023

Simulating sea-ice deformation in viscous-plastic sea-ice models with CD-grids

Linear Kinematic Features (LKFs) are found everywhere in the Arctic sea-ice cover. They are strongly localized deformations often associated with the formation of leads and pressure ridges. Viscous-plastic sea-ice models start to produce LKFs at high spatial grid resolution, typically with a grid spacing below 5 km. A recent study showed that the placement of the variables on the grid plays an important role for the number of simulated LKFs. The study found that a nonconforming finite element discretization with a CD-grid placement (CD1) resolves more LKFs per degree of freedom compared to more common A,B and C-grids. A new CD-grid formulation (CD2) has just been proposed based on a conforming subgrid discretization. To analyze the resolution properties of the new CD2 approach we evaluate runs from different models (e.g FESOM, MPAS) on a benchmark problem using quadrilateral, hexagonal and triangular meshes. We found that the CD1 setup simulates more deformation structure than the CD2 approximation. This highlights the importance of the type of spatial discretization for the simulation of LKFs. Due to the higher number of degrees of freedom both CD-grids resolve more LKFs than traditional A,B and C-grids at fixed mesh level. This is an appealing feature as high spatial mesh resolution is needed in viscous-plastic sea-ice models to simulate LKFs.

math.NA↗

arXiv2022

Current-induced enhancement of photo-response in graphene THz radiation detectors

Thermoelectric readout in a graphene THz radiation detector requires a p-n junction across the graphene channel. Even without an intentional p-n junction, two latent junctions can exist in the vicinity of the electrodes/antennas through the proximity to metal. In a symmetrical structure, these junctions are connected back-to-back and therefore counterbalance each other with regard to rectification of the ac signal. Because of the Peltier effect, a small dc current results in additional heating in one- and cooling in another p-n junction, thereby breaking the symmetry. The p-n junctions then no longer cancel, resulting in a greatly enhanced rectified signal. This allows to simplify the design and effectively control the sensitivity of the THz-radiation detectors.

cond-mat.mes-hall↗

arXiv2021

Carbon nanotubes for polarization sensitive terahertz plasmonic interferometry

We report on helicity sensitive photovoltaic terahertz radiation response of a carbon nanotube made in a conguration of a field effect transistor. We find that the magnitude of the rectified voltage is different for clockwise and anticlockwise circularly polarized radiation. We demonstrate that this effect is a fingerprint of the plasma waves interference in the transistor channel. We also find that that the presence of the helicity- and phase-sensitive interference part of the photovoltaic response is a universal phenomenon which is obtained in the systems of different dimensionality with different single particle spectrum. Its magnitude is characteristic of the plasma wave decay length. This opens up a wide avenue for applications in the area of plasmonic interferometry.

cond-mat.mtrl-sci↗

arXiv2021

On discretizing sea-ice dynamics on triangular meshes using vertex, cell or edge velocities

Discretization of the equations of Viscous Plastic and Elastic Viscous Plastic (EVP) sea ice dynamics on triangular meshes can be done by placing discrete velocities at vertices, cells or edges. Since there are more cells and edges than vertices, the cell- and edge-based discretizations simulate more linear kinematic features at the same mesh than the vertex discretization. However, the discretization based on cell and edge velocities suffer from kernels in the strain rate or stress divergence operators and need either special strain rate computations as proposed here for cell velocities, or stabilization as proposed earlier for edge velocities. An elementary Fourier analysis clarifies how kernels are removed, and also shows that cell and edge velocity placement leads to spurious branches of stress divergence operator with large negative eigenvalues. Although spurious branches correspond to fast decay and are not expected to distort sea ice dynamics, they demand either smaller internal time steps or higher stability parameters in explicit EVP-like methods.

math.NA↗

arXiv2021

Simulating linear kinematic features in viscous-plastic sea ice models on quadrilateral and triangular grids

Linear Kinematic Features (LKFs) are found everywhere in the Arctic sea ice cover. They are strongly localized deformations often associated with the formation of leads and pressure ridges. Viscous-plastic sea ice models start to generate LKFs at high spatial grid resolution, typically with a grid spacing below 5 km. Besides grid spacing, other aspects of a numerical implementation, such as discretization details, may affect the number and definition of simulated LKFs. To explore these effects, the solutions of sea ice models with different grid spacings, mesh types, and numerical discretization techniques are compared in an idealized configuration, which could also serve as a benchmark problem in the future. The A, B, and C-grid discretizations of sea ice dynamics on quadrilateral meshes leads to a similar number of LKFs as the A-grid approximation on triangular meshes (with the same number of vertices). The discretization on an Arakawa CD-grid on both structured quadrilateral and triangular meshes resolves the same number of LKFs as conventional Arakawa A-grid, B-grid, and C-grid approaches, but on two times coarser meshes. This is due to the fact that the CD-grid approach has a higher number of degrees of freedom to discretize the velocity field. Due to its enhanced resolving properties, the CD-grid discretization is an attractive alternative to conventional discretizations.

math.NA↗

arXiv2020

Helicity sensitive plasmonic teraherts interferometer

Plasmonic interferometry is a rapidly growing area of research with a huge potential for applications in terahertz frequency range. In this Letter, we explore a plasmonic interferometer based on graphene Field Effect Transistor connected to specially designed antennas. As a key result, we observe helicity- and phase-sensitive conversion of circularly-polarized radiation into dc photovoltage caused by the plasmon-interference mechanism: two plasma waves, excited at the source and drain part of the transistor interfere inside the channel. The helicity sensitive phase shift between these waves is achieved by using an asymmetric antenna configuration. The dc signal changes sign with inversion of the helicity. Suggested plasmonic interferometer is capable for measuring of phase difference between two arbitrary phase-shifted optical signals. The observed effect opens a wide avenue for phase-sensisitve probing of plasma wave excitations in two-dimensional materials.

cond-mat.mes-hall↗