@article{43018,
  author       = {{Alhaddad, Samer and Förstner, Jens and Grynko, Yevgen}},
  issn         = {{0022-4073}},
  journal      = {{Journal of Quantitative Spectroscopy and Radiative Transfer}},
  keywords     = {{tet_topic_scattering}},
  publisher    = {{Elsevier BV}},
  title        = {{{Numerical study of light backscattering from layers of absorbing irregular particles larger than the wavelength}}},
  doi          = {{10.1016/j.jqsrt.2023.108557}},
  volume       = {{302}},
  year         = {{2023}},
}

@article{31574,
  abstract     = {{We model negative polarization, which is observed for planetary regoliths at backscattering, solving a full wave problem of light scattering with a numerically exact Discontinuous Galerkin Time Domain (DGTD) method. Pieces of layers with the bulk packing density of particles close to 0.5 are used. The model particles are highly absorbing and have irregular shapes and sizes larger than the wavelength of light. This represents a realistic analog of low-albedo planetary regoliths. Our simulations confirm coherent backscattering mechanism of the origin of negative polarization. We show that angular profiles of polarization are stabilized if the number of particles in a layer piece becomes larger than ten. This allows application of our approach to the negative polarization modeling for planetary regoliths.}},
  author       = {{Grynko, Yevgen and Shkuratov, Yuriy and Alhaddad, Samer and Förstner, Jens}},
  issn         = {{0019-1035}},
  journal      = {{Icarus}},
  keywords     = {{tet_topic_scattering}},
  pages        = {{115099}},
  publisher    = {{Elsevier BV}},
  title        = {{{Negative polarization of light at backscattering from a numerical analog of planetary regoliths}}},
  doi          = {{10.1016/j.icarus.2022.115099}},
  volume       = {{384}},
  year         = {{2022}},
}

@inbook{33466,
  abstract     = {{We review our results of numerical simulations of light scattering from different systems of densely packed irregular particles. We consider spherical clusters, thick layers and monolayers with realistic topologies and dimensions much larger than the wavelength of light. The maximum bulk packing density of clusters is 0.5. A numerically exact solution of the electromagnetic problem is obtained using the Discontinuous Galerkin Time Domain method and with application of high- performance computing. We show that high packing density causes light localization in such structures which makes an impact on the opposition phenomena: backscattering intensity surge and negative linear polarization feature. Diffuse multiple scattering is significantly reduced in the case of non-absorbing particles and near-field interaction results in a percolation-like light transport determined by the topology of the medium. With this the negative polarization feature caused by single scattering gets enhanced if compared to lower density samples. We also confirm coherent double scattering mechanism of negative polarization for light scattered from dense absorbing slabs. In this case convergent result for the scattering angle polarization dependency at backscattering can be obtained for a layer of just a few tens of particles if they are larger than the wavelength.}},
  author       = {{Grynko, Yevgen and Shkuratov, Yuriy and Alhaddad, Samer and Förstner, Jens}},
  booktitle    = {{Springer Series in Light Scattering - Volume 8: Light Polarization and Multiple Scattering in Turbid Media}},
  editor       = {{Kokhanovsky, Alexander}},
  isbn         = {{9783031102974}},
  issn         = {{2509-2790}},
  keywords     = {{tet_topic_scattering}},
  publisher    = {{Springer International Publishing}},
  title        = {{{Light Scattering by Large Densely Packed Clusters of Particles}}},
  doi          = {{10.1007/978-3-031-10298-1_4}},
  volume       = {{8}},
  year         = {{2022}},
}

@article{29075,
  abstract     = {{We study a double-scattering coherent mechanism of negative polarization (NP) near opposition that is observed for powder-like surfaces. The problem is solved numerically for absorbing structures with irregular constituents, cubes, spheres, and ellipsoids larger than the wavelength of incident light. Our simulations show that double scattering between two random irregular particles shows weak NP. Adding one more particle significantly increases the relative contribution of double scattering which enhances NP. Simulations with regular shapes and controlled geometric parameters show that the interference mechanism is sensitive to the geometry of the scattering system and can also result in no polarization or even strong enhancement of positive polarization at backscattering.}},
  author       = {{Alhaddad, Samer and Grynko, Yevgen and Farheen, Henna and Förstner, Jens}},
  issn         = {{0146-9592}},
  journal      = {{Optics Letters}},
  keywords     = {{tet_topic_scattering}},
  number       = {{1}},
  pages        = {{58}},
  title        = {{{Numerical analysis of the coherent mechanism producing negative polarization at backscattering from systems of absorbing particles}}},
  doi          = {{10.1364/ol.444953}},
  volume       = {{47}},
  year         = {{2022}},
}

@inproceedings{34136,
  author       = {{Grynko, Yevgen and Shkuratov, Yuriy and Alhaddad, Samer and Förstner, Jens}},
  keywords     = {{tet_topic_scattering}},
  location     = {{Granada, Spain}},
  publisher    = {{Copernicus GmbH}},
  title        = {{{Light backscattering from numerical analog of planetary regoliths}}},
  doi          = {{10.5194/epsc2022-151}},
  year         = {{2022}},
}

@inbook{21587,
  abstract     = {{Solving partial differential equations on unstructured grids is a cornerstone of engineering and scientific computing. Nowadays, heterogeneous parallel platforms with CPUs, GPUs, and FPGAs enable energy-efficient and computationally demanding simulations. We developed the HighPerMeshes C++-embedded Domain-Specific Language (DSL) for bridging the abstraction gap between the mathematical and algorithmic formulation of mesh-based algorithms for PDE problems on the one hand and an increasing number of heterogeneous platforms with their different parallel programming and runtime models on the other hand. Thus, the HighPerMeshes DSL aims at higher productivity in the code development process for multiple target platforms. We introduce the concepts as well as the basic structure of the HighPerMeshes DSL, and demonstrate its usage with three examples, a Poisson and monodomain problem, respectively, solved by the continuous finite element method, and the discontinuous Galerkin method for Maxwell’s equation. The mapping of the abstract algorithmic description onto parallel hardware, including distributed memory compute clusters, is presented. Finally, the achievable performance and scalability are demonstrated for a typical example problem on a multi-core CPU cluster.}},
  author       = {{Alhaddad, Samer and Förstner, Jens and Groth, Stefan and Grünewald, Daniel and Grynko, Yevgen and Hannig, Frank and Kenter, Tobias and Pfreundt, Franz-Josef and Plessl, Christian and Schotte, Merlind and Steinke, Thomas and Teich, Jürgen and Weiser, Martin and Wende, Florian}},
  booktitle    = {{Euro-Par 2020: Parallel Processing Workshops}},
  isbn         = {{9783030715922}},
  issn         = {{0302-9743}},
  keywords     = {{tet_topic_hpc}},
  title        = {{{HighPerMeshes – A Domain-Specific Language for Numerical Algorithms on Unstructured Grids}}},
  doi          = {{10.1007/978-3-030-71593-9_15}},
  year         = {{2021}},
}

@article{24788,
  author       = {{Alhaddad, Samer and Förstner, Jens and Groth, Stefan and Grünewald, Daniel and Grynko, Yevgen and Hannig, Frank and Kenter, Tobias and Pfreundt, Franz‐Josef and Plessl, Christian and Schotte, Merlind and Steinke, Thomas and Teich, Jürgen and Weiser, Martin and Wende, Florian}},
  issn         = {{1532-0626}},
  journal      = {{Concurrency and Computation: Practice and Experience}},
  keywords     = {{tet_topic_hpc}},
  pages        = {{e6616}},
  title        = {{{The HighPerMeshes framework for numerical algorithms on unstructured grids}}},
  doi          = {{10.1002/cpe.6616}},
  year         = {{2021}},
}

@inproceedings{3588,
  abstract     = {{In scientific computing, unstructured meshes are a crucial foundation for the simulation of real-world physical phenomena. Compared to regular grids, they allow resembling the computational domain with a much higher accuracy, which in turn leads to more efficient computations.<br />There exists a wealth of supporting libraries and frameworks that aid programmers with the implementation of applications working on such grids, each built on top of existing parallelization technologies. However, many approaches require the programmer to introduce a different programming paradigm into their application or provide different variants of the code. SYCL is a new programming standard providing a remedy to this dilemma by building on standard C ++17 with its so-called single-source approach: Programmers write standard C ++ code and expose parallelism using C++17 keywords. The application is<br />then transformed into a concrete implementation by the SYCL implementation. By encapsulating the OpenCL ecosystem, different SYCL implementations enable not only the programming of CPUs but also of heterogeneous platforms such as GPUs or other devices. For the first time, this paper showcases a SYCL-<br />based solver for the nodal Discontinuous Galerkin method for Maxwell’s equations on unstructured meshes. We compare our solution to a previous C-based implementation with respect to programmability and performance on heterogeneous platforms.<br}},
  author       = {{Afzal, Ayesha and Schmitt, Christian and Alhaddad, Samer and Grynko, Yevgen and Teich, Jürgen and Förstner, Jens and Hannig, Frank}},
  booktitle    = {{Proceedings of the 29th Annual IEEE International Conference on Application-specific Systems, Architectures and Processors (ASAP)}},
  isbn         = {{978-1-5386-7479-6}},
  keywords     = {{tet_topic_hpc}},
  pages        = {{49--56}},
  title        = {{{Solving Maxwell's Equations with Modern C++ and SYCL: A Case Study}}},
  doi          = {{10.1109/ASAP.2018.8445127}},
  year         = {{2018}},
}

@inproceedings{4579,
  abstract     = {{Semi-guided waves confined in dielectric slab waveguides are being considered for oblique angles of propagation. If the waves encounter a linear discontinuity of (mostly) arbitrary shape and extension, a variant of Snell's law applies, separately for each pair of incoming and outgoing modes. Depending on the effective indices involved, and on the angle of incidence, power transfer to specific outgoing waves can be allowed or forbidden. In particular, critical angles of incidence can be identified, beyond which any power transfer to non-guided waves is forbidden, i.e. all radiative losses are suppressed. In that case the input power is carried away from the discontinuity exclusively by reflected semi-guided waves in the input slab, or by semi-guided waves that are transmitted into other outgoing slab waveguides. Vectorial equations on a 2-D cross sectional domain apply. These are formally identical to the equations that govern the eigenmodes of 3-D channel waveguides. Here, however, these need to be solved not as an eigenvalue problem, but as an inhomogeneous problem with a right-hand-side that is given by the incoming semi-guided wave, and subject to transparent boundary conditions. The equations resemble a standard 2-D Helmholtz problem, with an effective permittivity in place of the actual relative permittivity. Depending on the properties of the incoming wave, including the angle of incidence, this effective permittivity can become locally negative, causing the suppression of propagating outgoing waves. A series of high-contrast example configurations are discussed, where these effects lead to - in some respects - quite surprising transmission characteristics.}},
  author       = {{Hammer, Manfred and Ebers, Lena and Hildebrandt, Andre and Alhaddad, Samer and Förstner, Jens}},
  booktitle    = {{2018 IEEE 17th International Conference on Mathematical Methods in Electromagnetic Theory (MMET)}},
  isbn         = {{9781538654385}},
  keywords     = {{tet_topic_waveguides}},
  publisher    = {{IEEE}},
  title        = {{{Oblique Semi-Guided Waves: 2-D Integrated Photonics with Negative Effective Permittivity}}},
  doi          = {{10.1109/mmet.2018.8460455}},
  year         = {{2018}},
}

@inproceedings{1588,
  abstract     = {{The exploration of FPGAs as accelerators for scientific simulations has so far mostly been focused on small kernels of methods working on regular data structures, for example in the form of stencil computations for finite difference methods. In computational sciences, often more advanced methods are employed that promise better stability, convergence, locality and scaling. Unstructured meshes are shown to be more effective and more accurate, compared to regular grids, in representing computation domains of various shapes. Using unstructured meshes, the discontinuous Galerkin method preserves the ability to perform explicit local update operations for simulations in the time domain. In this work, we investigate FPGAs as target platform for an implementation of the nodal discontinuous Galerkin method to find time-domain solutions of Maxwell's equations in an unstructured mesh. When maximizing data reuse and fitting constant coefficients into suitably partitioned on-chip memory, high computational intensity allows us to implement and feed wide data paths with hundreds of floating point operators. By decoupling off-chip memory accesses from the computations, high memory bandwidth can be sustained, even for the irregular access pattern required by parts of the application. Using the Intel/Altera OpenCL SDK for FPGAs, we present different implementation variants for different polynomial orders of the method. In different phases of the algorithm, either computational or bandwidth limits of the Arria 10 platform are almost reached, thus outperforming a highly multithreaded CPU implementation by around 2x.}},
  author       = {{Kenter, Tobias and Mahale, Gopinath and Alhaddad, Samer and Grynko, Yevgen and Schmitt, Christian and Afzal, Ayesha and Hannig, Frank and Förstner, Jens and Plessl, Christian}},
  booktitle    = {{Proc. Int. Symp. on Field-Programmable Custom Computing Machines (FCCM)}},
  keywords     = {{tet_topic_hpc}},
  publisher    = {{IEEE}},
  title        = {{{OpenCL-based FPGA Design to Accelerate the Nodal Discontinuous Galerkin Method for Unstructured Meshes}}},
  doi          = {{10.1109/FCCM.2018.00037}},
  year         = {{2018}},
}

@inproceedings{3543,
  author       = {{Hildebrandt, Andre and Alhaddad, Samer and Hammer, Manfred and Förstner, Jens}},
  booktitle    = {{Integrated Optics: Devices, Materials, and Technologies XX}},
  editor       = {{Broquin, Jean-Emmanuel and Nunzi Conti, Gualtiero}},
  keywords     = {{tet_topic_waveguide}},
  publisher    = {{SPIE}},
  title        = {{{Oblique incidence of semi-guided waves on step-like folds in planar dielectric slabs: Lossless vertical interconnects in 3D integrated photonic circuits}}},
  doi          = {{10.1117/12.2214460}},
  year         = {{2016}},
}