Size dependent electronic properties of silicon quantum dots - an analysis with hybrid, screened hybrid and local density functional theory

We use an efficient projection scheme for the Fock operator to analyze the size dependence of silicon quantum dots (QDs) electronic properties. We compare the behavior of hybrid, screened hybrid and local density functionals as a function of the dot size up to $\sim$800 silicon atoms and volume of up to $\sim$20nm$^3$. This allows comparing the calculations of hybrid and screened hybrid functionals to experimental results over a wide range of QD sizes. We demonstrate the size dependent behavior of the band gap, density of states, ionization potential and HOMO level shift after ionization. Those results are compared to experiment and to other theoretical approaches, such as tight-binding, empirical pseudopotentials, TDDFT and GW

Metamaterials for Enhanced Polarization Conversion in Plasmonic Excitation

Surface plasmons efficient excitation is typically expected to be strongly constrained to transverse magnetic (TM) polarized incidence, as demonstrated so far, due to its intrinsic TM polarization. We report a designer plasmonic metamaterial that is engineered in a deep subwavelength scale in visible optical frequencies to overcome this fundamental limitation, and allows transverse electric (TE) polarized incidence to be strongly coupled to surface plasmons. The experimental verification, which is consistent with the analytical and numerical models, demonstrates this enhanced TE-to-plasmon coupling with efficiency close to 100%, which is far from what is possible through naturally available materials. This discovery will help to efficiently utilize the energy fallen into TE polarization and drastically increase overall excitation efficiency of future plasmonic devices

ALGORITHM OF GLOBAL EXTREMUM SEARCH AREA DEFINITION FOR SEVERAL VARIABLES FUNCTION

Abstract: The article is devoted to the problem of global extremum search for several variables function. Amodified algorithm is developed for the search of global extremum function, based on evolutionary calculations and differing by the approach of an area development to create an initial population of agents. They developed the algorithm for the function extremum search area definition, which ultimately performs the decomposition of the research area into subsets. It is suggested to take into account the knowledge of an expert, an agent and the available group agents. Based on the available knowledge, the region is divided into three subsets with different priorities. At that, the possibility of the function extremum drift is taken into account and a separate procedure of a search area definition is implemented, taking into account the retrospective information on the drift of parameters.Keywords: multicriteria optimization, multiextremal function, global extremum, extremum drift, solutionsearch area, decision support system

Rapidly convergent representations for 2D and 3D Green's functions for a linear periodic array of dipole sources

Hybrid spectral-spatial representations are introduced to rapidly calculate periodic scalar and dyadic Green's functions of the Helmholtz equation for 2D and 3D configurations with a 1D (linear) periodicity. The presented schemes work seamlessly for any observation location near the array and for any practical array periodicities, including electrically small and large periodicities. The representations are based on the expansion of the periodic Green's functions in terms of the continuous spectral integrals over the transverse (to the array) spectral parameters. To achieve high convergence and numerical efficiency, the introduced integral representations are cast in a hybrid form in terms of (i) a small number of contributions due to sources located around the unit cell of interest, (ii) a small number of symmetric combinations of the Floquet modes, and (iii) an integral evaluated along the steepest descent path (SDP). The SDP integral is regularized by extracting the singular behavior near the saddle point of the integrand and integrating the extracted components in closed form. Efficient quadrature rules are established to evaluate this integral using a small number of quadrature nodes with arbitrary small error for a wide range of structure parameters. Strengths of the introduced approach are demonstrated via extensive numerical examples.Comment: 28 pages, 8 figures, accepted for publication in IEEE Transactions on Antennas and Propagatio

Influence of manufacturing shrinkage and microstructural features on the strength properties of carbon fibers/PEEK composite material

This research discusses the micromechanical modelling for thermoplastic composite material. Elastoplastic and damage model for PEEK matrix composite with the dependency of properties to stress state is presented. Plasticity initiation conditions and failure criterion are analyzed. The influence of manufacturing residual stresses is considered. All typical engineering experiments for neat PEEK under different stress state are good predicted by the model. Numerical experiment for macro-properties estimation based on micromechanical model is conducted and the results are compared with the test data