Showing 8 results for Aging
Sayed Mahmoud Sakhaei, A.mahlooji Far, Hassan Ghassemian,
Volume 2, Issue 2 (4-2006)
Abstract
Contrast resolution and detail resolution are two important parameters in
ultrasound imaging. This paper presents a new method to enhance these parameters,
simultaneously. A parallel auxiliary beamformer has been employed whose weightings are
such that an estimation of the leaked signal through the main beamformer is obtained. Then
the output of main beamformer is modified according to the estimated leaked signal. The
efficiency of our adaptive method is demonstrated by applying it over an experimental data
set and provided an enhancement of about 22 percent in lateral resolution and 15-20 dB in
contrast resolution. This method also has the advantages of simplicity and possibility of real
time implementation.
S. M. Zabihi, H. Ghanei-Yakhdan, N. Mehrshad,
Volume 16, Issue 4 (12-2020)
Abstract
In order to enhance the accuracy of the motion vector (MV) estimation and also reduce the error propagation issue during the estimation, in this paper, a new adaptive error concealment (EC) approach is proposed based on the information extracted from the video scene. In this regard, the motion information of the video scene around the degraded MB is first analyzed to estimate the motion type of the degraded MB. If the neighboring MBs possess uniform motion, the degraded MB imitates the behavior of neighboring MBs by choosing the MV of the collocated MB. Otherwise, the lost MV is estimated through the second proposed EC technique (i.e., IOBMA). In the IOBMA, unlike the conventional boundary matching criterion-based EC techniques, not only each boundary distortion is evaluated regarding both the luminance and the chrominance components of the boundary pixels, but also the total boundary distortion corresponding to each candidate MV is calculated as the weighted average of the available boundary distortions. Compared with the state-of-the-art EC techniques, the simulation results indicate the superiority of the proposed EC approach in terms of both the objective and subjective quality assessments.
Y. McHaouar, A. Abouloifa, I. Lachkar, H. Katir, F. Giri, A. El Aroudi, A. Elallali, C. Taghzaoui,
Volume 18, Issue 1 (3-2022)
Abstract
In this paper, the problem of controlling PWM single-phase AC/DC converters is addressed. The control objectives are twofold: (i) regulating the output voltage to a selected reference value, and (ii) ensuring a unitary power factor by forcing the grid current to be in phase with the grid voltage. To achieve these objectives, the singular perturbation technique is used to prove that the power factor correction can be done in the open-loop system with respect to certain conditions that are not likely to take place in reality. It is also applied to fulfill the control objectives in the closed-loop through a cascade nonlinear controller based on the three-time scale singular perturbation theory. Additionally, this study develops a rigorous and complete formal stability analysis, based on multi-time-scale singular perturbation and averaging theory, to examine the performance of the proposed controller. The theoretical results have been validated by numerical simulation in MATLAB/Simulink/SimPowerSystems environment.
Hassan Alizadeh Shyrayeh, Iraj Ahmadi, Mohammad Mirzaie, Masoud Ahmadi Gorji,
Volume 18, Issue 4 (12-2022)
Abstract
The progressive application of non-linear loads in distribution systems (DS) increases current harmonics flow in DS's apparatuses, especially distribution transformers (DTs). Since DTs' operating temperature rises due to the harmonics flow, their loading should be reduced such that the hot spot temperature (HST) is preserved under its permissible value. This means that DTs' available capacity is influenced by load harmonic content. In this paper, a novel formulation for DTs' failure rate in the presence of harmonics is presented as a function of load harmonic contents. Using the suggested equivalent failure rate, DTs' available capacity in harmonic polluted DS is mathematically formulated. Additionally, the presence of the harmonic increases the HST, leading to DTs' aging acceleration. Therefore, the impact of harmonic components on DTs' aging is arithmetically modeled. To evaluate the efficacy of the suggested reliability model, it is applied to three distinct DTs having respectively industrial, commercial, and residential loads. The obtained results indicate that the available capacity of DTs with the same rated capacity would be different regarding to their load harmonic contents. On the other hand, it is comprehended from the achieved results that the aging acceleration factor (Faa) of the DTs increases owing to their load harmonic contents.
E. Y. Burkin, F. A. Gubarev, V. V. Sviridov, D. V. Shiyanov,
Volume 19, Issue 3 (9-2023)
Abstract
A two-channel pulsed power supply for an imaging system with brightness amplification and independent synchronous laser illumination is designed. The power supply generates synchronized high-voltage pulses with a frequency of 16–24 kHz, an average electrical power of up to 1.2 kW, and an adjustable amplitude of up to 6.2 kV to pump copper bromide gas discharge tubes with independent control of the temperature parameters of the active medium. To generate pumping pulses for laser media, we used a two-channel thyratron circuit with a common source of stabilized voltage provided by a step-down pulse stabilizer and a bridge inverter-based circuit for the pulsed charge of storage capacitors. The voltage equalization on the storage capacitors is carried out by means of magnetic coupling of the charging inductances wound on a common core. Adjustable delay lines based on variable inductances provide synchronous operation of two brightness amplifiers with a synchronization accuracy of lasing pulses of ±1 ns. The power supply demonstrated stable operation with two gas discharge tubes having different characteristics, including those with different types of electrodes. It has been integrated into a laboratory facility for the study of high-energy materials combustion.
Seyyedeh Ensiyeh Hashemi, Hamid Behnam,
Volume 21, Issue 3 (8-2025)
Abstract
Increasing the frame rate of ultrasound imaging while keeping image quality is important for following fast movements, especially the heart. There are different modalities for B-mode image recording, including line-by-line scanning with linear, phased, convex array, synthetic aperture imaging (STA), plane waves (PWI), then the combination of plane waves (CPWI), and so on. Researchers have tried to increase the frame rate in each case using different methods. Three approaches for this aim are data acquisition, post-processing, and beamforming. This article reviews these approaches and their solutions for compensating image quality reduction. Ultrafast ultrasound imaging, which provides exceptional temporal resolution (high frame rate), is promising in diagnosing heart diseases due to its ability to capture rapid heart movements. It can record images faster than conventional imaging, usually exceeding 1000 frames per second. This can be achieved through plane wave imaging (PWI). However, high frame rate data acquisition can lead to a decrease in image quality. Transmitting at different angles and then combining plane wave imaging is a popular method to enhance PWI quality but reduces the frame rate by the number of angles. As a result, researchers have aimed to increase the temporal resolution while compensating for the loss of quality.
Sowmya M, Sumi M, Harikrishnan A I,
Volume 22, Issue 2 (3-2026)
Abstract
This article presents the design and optimization of a Minkowski fractal slot-integrated antipodal Vivaldi antenna (MFS-AVA) for brain stroke detection. The antenna is proposed on a 65 × 65 × 1.6 mm³ FR-4 substrate and integrates a tapered slot radiator with a microstrip feed. Key parameters are optimized through parametric analysis. The exponential curve of the radiator arms and edge conductor is fine-tuned for improved bandwidth and impedance matching, while Minkowski fractal slots enhance the reflection coefficient, gain, and directivity. Simulated using CST Studio Suite 2016, the antenna attains an extensive bandwidth spanning from 1.23 GHz to 12 GHz, a maximum gain of 9 dBi, and a radiation efficiency of 87%. The radiation pattern exhibits a directional beam with minimal side lobes, making it suitable for focused microwave imaging. Compared to a conventional design, the MFS-AVA shows improved S11, VSWR, and surface current performance. Its effectiveness is validated using a four-layered tissue-mimicking cylindrical human head model, confirming adequate field penetration and compliance with safety standards. These results demonstrate the proposed antenna’s suitability for UWB microwave imaging in brain stroke detection.
Elahe Parham, Mohamad Feshki, Alireza Fallahi, Hamid Soltanian-Zadeh,
Volume 22, Issue 3 (9-2026)
Abstract
The discovery of relationships between brain connectivity and human intelligence is of great interest. In this study, we identify structural connections correlated with human intelligence and investigate the predictability of intelligence from brain structural connectivity. The study uses data from 137 healthy subjects from the Human Connectome Project (HCP, 1200 Subjects Release). Structural connectivity was estimated using tractography derived from diffusion tensor imaging (DTI) data. A connectivity matrix was constructed using the mean fractional anisotropy (FA) of white-matter pathways between 116 regions defined by the AAL atlas. Global graph measures and correlation analysis were applied to identify connections relevant to predicting fluid intelligence (Gf) and crystallized intelligence (Gc). For prediction, three regression models of linear regression, support vector regression (SVR), and multi-layer perceptron (MLP) were employed. Most connections associated with Gf or Gc were located in the right hemisphere. Connections originating from prefrontal, right temporal, limbic, and right occipital regions were related to Gf, whereas connections originating from prefrontal, temporal, and left parietal regions were related to Gc. Among the models, SVR showed superior performance, achieving R² values of 0.45 and 0.52 for Gf and Gc, respectively. No significant relationships were observed between global graph measures and Gf or Gc scores. These findings demonstrate that DTI-based structural connectivity can be used to predict both fluid and crystallized intelligence, with fine-grained regional definitions enabling more specific connectivity patterns than in previous studies.
