Oral Oltulu

Comparative QSTR Study Using Semi-Empirical and First Principle Methods Based Descriptors for Acute Toxicity of Diverse Organic Compounds to the Fathead Minnow

Several quantum-mechanics-based descriptors were derived for a diverse set of 48 organic compounds using AM1, PM3, HF/6-31+G, and DFT-B3LYP/6-31+G (d) level of the theory. LC50 values of acute toxicity of the compounds were correlated to the fathead minnow and predicted using calculated descriptors by employing Comprehensive Descriptors for Structural and Statistical Analysis (CODESSA) program. The heuristic method, implemented in the CODESSA program for selecting the ‘best’ regression model, was applied to a pre-selection of the most-representative descriptors by sequentially eliminating descriptors that did not satisfy a certain level of statistical criterion. First model, statistically, the most significant one has been drawn up with the help of DFT calculations in which the squared correlation coefficient R2 is 0.85, and the squared cross-validation correlation coefficient RCV2 is 0.79. Second model, which has been drawn up with the help of HF calculations, has its statistical quality very close to the DFT-based one and in this model value of R2 is 0.84 and that of RCV2 is 0.78. Third and fourth models have been drawn up with the help of AM1 and PM3 calculations, respectively. The values of R2 and RCV2 in the third case are correspondingly 0.79 and 0.66, whereas in the fourth case they are 0.78 and 0.65 respectively. Results of this study clearly demonstrate that for the calculations of descriptors in modeling of acute toxicity of organic compounds to the fathead minnow, first principal methods are much more useful than semi-empirical methods.

Visible spectroscopy of 5CB/8CB liquid crystals

Electro-optical properties of nematic liquid crystals (LCs) have attracted a great deal of research interest and have resulted in a number of practical applications in many areas. In the present study, wavelength dependence of electro-optical properties of two different types of nematic LCs and their binary mixtures are investigated. LCs used in this study are 5CB and 8CB and their mixtures in different proportions. The optical transmittance of the structures has been studied by means of visible spectroscopy by measuring the transmitted light intensity as a function of the wavelength under various driving AC electric field values. Experiments were carried out at the wavelength interval 380–780 nm at a constant temperature of 25 °C in order to see the effect of the applied field alone.

Topological insulator based locally resonant phononic crystals: Wave propagation and acoustic band gaps

ABSTRACT In the present work the acoustic band structure of a two-dimensional phononic crystal (PC) containing an organic ferroelectric (PVDF- polyvinylidene fluoride) and topological insulator (Bi2Te3) were investigated by the plane-wave-expansion (PWE) method. Two-dimensional PC with square lattices composed of Bi2Te3 cylindrical rods embedded in the PVDF matrix are studied to find the existence of stop bands for the waves of certain energy. Phononic band diagram ω = ω(k) for a 2D PC along the Г-X-M-Г path in the square Brillouin zone show four stop bands in the frequency range 0.01–8.0 kHz.

SbSI Based Photonic Crystal Superlattices: Band Structure and Optics

In this work, we present an investigation of the optical properties and band structure calculations for the photonic crystal structures (PCs) based on one-dimensional (1D)-photonic crystal. Here we use 1D SbSI based layers in air background. We have theoretically calculated the photonic band structure and optical properties of SbSI based PC superlattices. In our simulation, we employed the finite-difference time domain (FDTD) technique and the plane wave expansion method (PWE), which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives.

Dynamic Nonlinear Optical Processes in Some Oxygen-Octahedra Ferroelectrics: First Principle Calculations

The nonlinear optical properties and electro-optic effects of some oxygen-octahedra ferroelectrics are studied by the density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. We present calculations of the frequency- dependent complex dielectric function and the second harmonic generation response coefficient over a large frequency range in tetragonal and rhombohedral phases. The electronic linear electro-optic susceptibility is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. The results for are in agreement with the experiment below the band gap and those for are compared with the experimental data where available.

AVBVICVII ferroelectrics as novel materials for phononic crystals

ABSTRACT In the present work the acoustic band structure of a two-dimensional (2D) phononic crystal (PC) containing a semiconducting ferroelectric - AVBVICVII (A = Sb, Bi; B = S, Se, Te; C = I, Br, and Cl) was investigated theoretically and numerically by the plane-wave-expansion (PWE) method. Two-dimensional PC with square lattices composed of semiconducting ferroelectric cylindrical rods embedded in the organic/inorganic matrix is studied to find the existence of stop bands for the waves of certain energy. This phononic bandgap - forbidden frequency range - allows sound to be controlled in many useful ways in structures that can act as sonic filters, waveguides or resonant cavities. Phononic band diagram ω = ω(k) for a 2D PC was plotted versus the wavevector k along the Г-X-M-Г path in the square Brillouin zone (BZ). The band diagram shows four stop bands in the wide frequency range. The unusual properties of matrix and ferroelectric properties of AVBVICVII give us ability to control the wave propagation through the PC in over a wide frequency range. We study the 2D composites by solving the basic acoustic wave equation and use Bloch wave analysis to identify the band gaps.

Phononic band gap and wave propagation on polyvinylidene fluoride-based acoustic metamaterials

Abstract In the present work, the acoustic band structure of a two-dimensional phononic crystal (PC) containing an organic ferroelectric (PVDF-polyvinylidene fluoride) and topological insulator (SnTe) was investigated by the plane-wave-expansion (PWE) method. Two-dimensional PC with square lattices composed of SnTe cylindrical rods embedded in the PVDF matrix is studied to find the allowed and stop bands for the waves of certain energy. Phononic band diagram ω = ω(k) for a 2D PC, in which non-dimensional frequencies ωa/2πc (c-velocity of wave) were plotted vs. the wavevector k along the Г–X–M–Г path in the square Brillouin zone shows five stop bands in the frequency range between 10 and 110 kHz. The ferroelectric properties of PVDF and the unusual properties of SnTe as a topological material give us the ability to control the wave propagation through the PC over a wide frequency range of 103–106 Hz. SnTe is a discrete component that allows conducting electricity on its surface but shows insulator properties through its bulk volume. Tin telluride is considered as an acoustic topological insulator as the extension of topological insulators into the field of “topological phononics”.

Multiple Image Radiography With Diffraction Enhanced Imaging For Breast Specimen

Biological samples are of great interest for many imaging techniques. The samples usually contain small structures and weak absorption properties. The combinations of weak signals with overlying structures make feature recognition difficult in many cases. In the x‐ray regime, a relatively new imaging technique Diffraction Enhanced Imaging (DEI) has superior tissue contrast over conventional radiography and is proven to be very sensitive method. Multiple images taken by DEI are called Multiple Image Radiography (MIR). The purpose of this study is to validate the potential application of the method and to show that MIR‐DEI method may give more information about the sample.