Dmitry Chikrin

Bio: Dmitry Chikrin is an academic researcher. The author has contributed to research in topics: Dipole antenna & Brightness. The author has an hindex of 1, co-authored 1 publications receiving 8 citations.

Miniaturization of a Koch-Type Fractal Antenna for Wi-Fi Applications

Abstract: Koch-type wire dipole antennas are considered herein. In the case of a first-order prefractal, such antennas differ from a Koch-type dipole by the position of the central vertex of the dipole arm. Earlier, we investigated the dependence of the base frequency for different antenna scales for an arm in the form of a first-order prefractal. In this paper, dipoles for second-order prefractals are considered. The dependence of the base frequency and the reflection coefficient on the dipole wire length and scale is analyzed. It is shown that it is possible to distinguish a family of antennas operating at a given (identical) base frequency. The same length of a Koch-type curve can be obtained with different coordinates of the central vertex. This allows for obtaining numerous antennas with various scales and geometries of the arm. An algorithm for obtaining small antennas for Wi-Fi applications is proposed. Two antennas were obtained: an antenna with the smallest linear dimensions and a minimum antenna for a given reflection coefficient.

Elimination of Defects in Mammograms Caused by a Malfunction of the Device Matrix

Abstract: Today, the processing and analysis of mammograms is quite an important field of medical image processing. Small defects in images can lead to false conclusions. This is especially true when the distortion occurs due to minor malfunctions in the equipment. In the present work, an algorithm for eliminating a defect is proposed, which includes a change in intensity on a mammogram and deteriorations in the contrast of individual areas. The algorithm consists of three stages. The first is the defect identification stage. The second involves improvement and equalization of the contrasts of different parts of the image outside the defect. The third involves restoration of the defect area via a combination of interpolation and an artificial neural network. The mammogram obtained as a result of applying the algorithm shows significantly better image quality and does not contain distortions caused by changes in brightness of the pixels. The resulting images are evaluated using Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE) and Naturalness Image Quality Evaluator (NIQE) metrics. In total, 98 radiomics features are extracted from the original and obtained images, and conclusions are drawn about the minimum changes in features between the original image and the image obtained by the proposed algorithm.

Relationship Between Base Frequency of the Koch-Type Wire Dipole and Various Dimensions

Abstract: A dipole wire antenna of the Koch type is considered. The antenna consists of a wire dipole with symmetrical arms with respect to the feed point with the geometry similar to the Koch prefractal. The curves forming the arms differ from the classical Koch fractal only by the position of the central vertex. The work’s goal is to establish the dependence of the base frequency on the dimension of the curve forming the antenna arm. Various dimensions as characteristics of the curve are considered. The dimensions are Minkowski dimension, information dimension, correlation dimension and Higuchi fractal dimension. The algorithm to calculate the Higuchi dimension for our curves is adapted. Also, algorithms for calculating the other dimensions are described. Relationships between the base frequency of the Koch-type wire dipole and the dimensions are explored. The correlation analysis for the first three Koch-type prefractals is carried out. The values of all correlation coefficients between the base frequency and the considered dimensions are given in the tables. It is concluded that for the second and third iterations, the best correlation is a correlation between the base frequency and the Higuchi dimension. The optimal one-parameter regression models for the base frequency in the case of the second and third iterations are constructed. The obtained regression model for the second iteration approximates the frequency values with an error of 1.17%. The model for the third iteration approximates the frequency values with an error of 1.46%.

Enhancement Technique Based on the Breast Density Level for Mammogram for Computer-Aided Diagnosis

Abstract: Mass detection in mammograms has a limited approach to the presence of a mass in overlapping denser fibroglandular breast regions. In addition, various breast density levels could decrease the learning system’s ability to extract sufficient feature descriptors and may result in lower accuracy performance. Therefore, this study is proposing a textural-based image enhancement technique named Spatial-based Breast Density Enhancement for Mass Detection (SbBDEM) to boost textural features of the overlapped mass region based on the breast density level. This approach determines the optimal exposure threshold of the images’ lower contrast limit and optimizes the parameters by selecting the best intensity factor guided by the best Blind/Reference-less Image Spatial Quality Evaluator (BRISQUE) scores separately for both dense and non-dense breast classes prior to training. Meanwhile, a modified You Only Look Once v3 (YOLOv3) architecture is employed for mass detection by specifically assigning an extra number of higher-valued anchor boxes to the shallower detection head using the enhanced image. The experimental results show that the use of SbBDEM prior to training mass detection promotes superior performance with an increase in mean Average Precision (mAP) of 17.24% improvement over the non-enhanced trained image for mass detection, mass segmentation of 94.41% accuracy, and 96% accuracy for benign and malignant mass classification. Enhancing the mammogram images based on breast density is proven to increase the overall system’s performance and can aid in an improved clinical diagnosis process.

An Optimal Multiband Compact Modified Crinkle Fractal Antenna for Wireless Applications

Abstract: An optimal multiband compact modified crinkle fractal antenna is proposed in this report which is designed on FR-4 substrate having dimension of $14\ \mathbf{mm} \times 12.5\ \mathbf{mm} \times 1 \mathbf{mm}$ , dielectric constant 4.4, and loss tangent of 0.02. Proposed fractal antenna is optimized using dragonfly optimization (DO) and resonates at 1.3584 GHz, 1.9925GHz, 2.5714 GHz, 4.3910 GHz, 5.1629 GHz, 5.6591 GHz, 6.2932 GHz, 7.6165 GHz, 8.3609 GHz, 9.2431 GHz, and 10.4010GHz. Proposed antenna is characterized on the basis of various performance parameters like return loss, VSWR, radiation pattern, gain and bandwidth.

On $$(\phi ,\psi )$$ ( ϕ , ψ ) -Inframonogenic Functions in Clifford Analysis

Abstract: Solutions of the sandwich equation $${^\phi \!\underline{\partial }}[f]{^\psi \!\underline{\partial }}=0$$ , where $${^\phi \!\underline{\partial }}$$ stands for the Dirac operator with respect to a structural set $$\phi $$ , are referred to as $$(\phi ,\psi )$$ -inframonogenic functions and capture the standard inframonogenic ones as special case. We derive a new integral representation formula for such functions as well as for multidimensional Ahlfors–Beurling transforms closely connected to the use of two different orthogonal basis in $${{\mathbb {R}}}^m$$ . Moreover, we also establish sufficient conditions for the solvability of a jump problem for the system $${^\phi \!\underline{\partial }}[f]{^\psi \!\underline{\partial }}=0$$ in domains with fractal boundary.