Modeling of transient and steady-state dark current in amorphous silicon p–i–n photodiodes

S.A. Mahmood,M.Z. Kabir 한국물리학회 2009 Current Applied Physics Vol.9 No.6

A theoretical model for describing the bias-dependent transient and steady-state behavior of dark current in hydrogenated amorphous silicon (a-Si:H) p–i–n photodiode has been developed. An analytical expression for the bias-dependent steady-state thermal generation current is derived by solving the continuity equations for both electrons and holes. The model for describing transient dark current in a-Si:H p–i–n photodiode is developed by considering the depletion of electrons from the i-layer and carrier injection through p–i interface. For photodiodes that have very good junction properties, the high initial dark current decreases with time monotonously and reaches a plateau. However, in case of poor junctions, the injection current can be the dominating mechanism for transient leakage current at relatively high biases, the dark current decays initially and then rises to a steady-state value. The proposed physics-based dark current model is compared with published experimental results on several photodiodes. The comparison of the model with the experimental data allows an estimate of active dopant concentration in the p-layer and the defect density in the midgap of i-layer. A theoretical model for describing the bias-dependent transient and steady-state behavior of dark current in hydrogenated amorphous silicon (a-Si:H) p–i–n photodiode has been developed. An analytical expression for the bias-dependent steady-state thermal generation current is derived by solving the continuity equations for both electrons and holes. The model for describing transient dark current in a-Si:H p–i–n photodiode is developed by considering the depletion of electrons from the i-layer and carrier injection through p–i interface. For photodiodes that have very good junction properties, the high initial dark current decreases with time monotonously and reaches a plateau. However, in case of poor junctions, the injection current can be the dominating mechanism for transient leakage current at relatively high biases, the dark current decays initially and then rises to a steady-state value. The proposed physics-based dark current model is compared with published experimental results on several photodiodes. The comparison of the model with the experimental data allows an estimate of active dopant concentration in the p-layer and the defect density in the midgap of i-layer.

Down-Regulation of CYP1A1 Expression in Breast Cancer

Hafeez, S.,Ahmed, A.,Rashid, Asif Z.,Kayani, Mahmood Akhtar Asian Pacific Journal of Cancer Prevention 2012 Asian Pacific journal of cancer prevention Vol.13 No.5

Breast cancer is a major cause of death in women worldwide. Mammary tissue expressing xenobiotic metabolizing enzymes metabolically activate or detoxify potential genotoxic breast carcinogens. Deregulation of these xenobiotic metabolizing enzymes is considered to be a major contributory factor to breast cancer. The present study is focused on the expression of the xenobiotic metabolizing gene, CYP1A1, in breast cancer and its possible relationships with different risk factors. Twenty five tumors and twenty five control breast tissue samples were collected from patients undergoing planned surgery or biopsy from different hospitals. Semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and western-blotting were used to investigate the expression of CYP1A1 in breast cancer control and disease samples. mRNA expression of CYP1A1 was down-regulated in 40% of breast tumor samples. Down-regulation was also observed at the protein level. Significnat relations were noted with marital status and tumour grade but not histopathological type. In conclusion, CYP1A1 protein expression was markedly reduced in tumor breast tissues samples as compared to paired control tissue samples.

Pathogenesis and Bone Resorption in Acquired Cholesteatoma: Current Knowledge and Future Prospectives

Mahmood A. Hamed,Seiichi Nakata,Ramadan H. Sayed,Hiromi Ueda,Badawy S. Badawy,Yoichi Nishimura,Takuro Kojima,Noboru Iwata,Ahmed R. Ahmed,Khalid Dahy,Naoki Kondo,Kenji Suzuki 대한이비인후과학회 2016 Clinical and Experimental Otorhinolaryngology Vol.9 No.4

Cholesteatoma is a cystic non tumorous lesion of the temporal bone that has the ability to destroy nearby structures by its power to cause bone resorption and as a result, fatal complications prevail. We aimed to conduct a comprehensive review for pathogenesis of acquired cholesteatoma, bone resorption mechanisms, and offer a future vision of this serious disease. We have reviewed different theories for pathogenesis of acquired cholesteatoma including the most relevant and updated ones with special emphasis on the mechanisms of bone resorption through Medline/PubMed research using the keywords ‘aetiopathogenesis, bone resorption, acquired cholesteatoma, temporal bone, and cytokines.’ In order to strengthen our study, we searched the reference lists of identified reviews. Cholesteatoma is a subject of debate among otolaryngologists since it was prescribed firstly. Over many decades, several theories were postulated for aetiopathogenesis of cholesteatoma with a tendency to follow more than one theory to explain the proper nature of that disease. Until now, the mechanism of bone resorption has yet to be more clarified. In the last century, a leap has occurred in the field of biomolecular cholesteatoma research which improved our knowledge about its pathophysiology and bone destructive mechanism. However, surgery is still the only available treatment. We conclude that discovery of new therapeutic choices for cholesteatoma other than surgery by the use of anti-growth, anti-proliferative, apoptotic agents as well as medications that antagonize osteoclastogenesis should be the main concern in the future clinical and experimental research work. Also, searching for predictors of the aggressiveness of cholesteatoma can affect the timing of intervention and prevent occurrence of complications.

Evaluation of the Collapse Potential Magnitude of Untreated and Treated Collapsible Gypseous Soil – A New Procedure

Ahmed S. A. Al-Gharbawi,Mohammed Y. Fattaha,Mahmood R. Mahmood 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.6

Many researches have been conducted to study the collapse potential of collapsible soils using collapse tests; single-oedometer tests, and double-oedometer tests. The radical rearranging of particles in response to a significant volume loss from wetting under loading is the definition of collapse. The main goal of this study is to create a method for recognition of gypseous soil that is susceptible to collapse. The suggested procedure depends on using a sample larger than that used in conventional collapse tests and the saturation of sample is done by flowing water from the bottom to the top of the sample. The new idea for the modified collapse test was made because of the limitations of conventional tests including the small size of sample that may not give a suitable collapse. In addition, the saturation process of the sample may not saturate all the particles. Also, the behavior of collapsible gypseous soil was investigated on soil improved with different Magnesium Oxide percentages (0, 5, 10, and 15%) and carbonated Magnesium Oxide with variable carbonation times (0, 1, 3, and 24 hours). The soil was prepared at two relative densities of 35 and 75 percent relative density. The collapse potential was investigated using a modified Rowe cell with soil moisture content sensors. The results illustrated that the size of the sample affects the collapsibility, the collapse potential increased from 15.8% to 22.3% and the collapse severity is changed from (severe trouble) to (very severe trouble) for the natural untreated gypseous soil using the conversional tests and modified test, respectively. The collapse potential increased by about 40% for the soil treated with different percentages of “Magnesium Oxide”. For the modified test, the collapse potential decreased by about 93% when using 10 percent of Magnesium Oxide then the sample was carbonated for 3 hours as compared with untreated soil.

Optimal depth estimation by combining focus measures using genetic programming

Mahmood, M.T.,Majid, A.,Choi, T.S. North-Holland [etc ; Elsevier Science Ltd 2011 Information sciences Vol.181 No.7

Three-dimensional (3D) shape reconstruction is a fundamental problem in machine vision applications. Shape From Focus (SFF) is one of the passive optical methods for 3D shape recovery that uses degree of focus as a cue to estimate 3D shape. In this approach, usually a single focus measure operator is applied to measure the focus quality of each pixel in the image sequence. However, the applicability of a single focus measure is limited to estimate accurately the depth map for diverse type of real objects. To address this problem, we develop Optimal Composite Depth (OCD) function through genetic programming (GP) for accurate depth estimation. The OCD function is constructed by optimally combining the primary information extracted using one/or more focus measures. The genetically developed composite function is then used to compute the optimal depth map of objects. The performance of the developed nonlinear function is investigated using both the synthetic and the real world image sequences. Experimental results demonstrate that the proposed estimator is more useful in computing accurate depth maps as compared to the existing SFF methods. Moreover, it is found that the heterogeneous function is more effective than homogeneous function.

Improvement of the superconducting properties of an infiltrated YBCO bulk superconductor by a BaCeO₃ addition

Mahmood, A.,Park, S.D.,Jun, B.H.,Youn, J.S.,Han, Y.H.,Sung, T.H.,Kim, C.J. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15

Single grain YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-x</SUB> (Y123) bulk superconductors with Y<SUB>2</SUB>BaCuO<SUB>5</SUB> (Y211) and various amounts of BaCeO<SUB>3</SUB> (5-45wt.% by an increment of 10wt.%) were fabricated by a seeded infiltration process. The addition of BaCeO<SUB>3</SUB> was found to be effective for a modification of the microstructure and an improvement of the superconducting properties. The refinement effect for Y211 particles within an entire superconducting YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-x</SUB> (Y123) matrix was achieved by BaCeO<SUB>3</SUB> additions. The critical current density (J<SUB>c</SUB>) values were increased as the BaCeO<SUB>3</SUB> contents were increased (maximum J<SUB>c</SUB> at 35wt.% BaCeO<SUB>3</SUB> addition). The J<SUB>c</SUB> improvement by BaCeO<SUB>3</SUB> additions might be due to the microstructure modifications associated with the finely distributed Y211 and BaCeO<SUB>3</SUB> particles. With the addition of BaCeO<SUB>3</SUB> the onset T<SUB>c</SUB> values decreased slightly, indicating highly limited Ce substitution for Y site. It can be concluded that the BaCeO<SUB>3</SUB> addition has a beneficial effect on the morphology, the size and the distribution of the Y211 inclusions and the microstructure regarding pinning improvement.

A Nonlinear Transform Based Three-Dimensional Shape Recovery from Image Focus

Khan, A.,Mahmood, M.T.,Choi, T.-S. WORLD SCIENTIFIC PUBLISHING CO PTE LTD 2010 International journal of pattern recognition and a Vol.24 No.5

Simultaneous Effects of Slip and Wall Stretching/Shrinking on Radiative Flow of Magneto Nanofluid Through Porous Medium

A. Zeeshan,H. F. Ismael,M. A. Yousif,T. Mahmood,S. U. Rahman Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

Effects of the uniform magnetic field on aqueous magneto-Nanofluid confined in a porous domain with wall stretching/shrinking non-linearly is analyzed via this communication. The problem is modeled using continuity, momentum and energy equation along with linear thermal radiation. The effects of physical quantities are observed for Cu, Al₂O₃, TiO₂ and Ag particles in water. The coupled boundary layer PDE’s are reduced into the system of ODEs by utilizing similarity transformation and solved using shooting and Runga-Kutta fourth order technique. Stability of the obtained results are also analyzed. The results are displayed through graphs. It is observed that the momentum boundary layer is thicker when silver particles are introduced in water. Whereas, temperature profile has the minimum value for silver nanoparticles and maximum for Titanium dioxide. Also, in case of shrinking sheet dual solutions are obtained along with smallest Eigen values.

Cytokeratin 13, Cytokeratin 17, and Ki-67 Expression in Human Acquired Cholesteatoma and Their Correlation With Its Destructive Capacity

Mahmood A. Hamed,Seiichi Nakata,Kazuya Shiogama,Kenji Suzuki,Ramadan H. Sayed,Yoichi Nishimura,Noboru Iwata,Kouhei Sakurai,Badawy S. Badawy,Ken-ichi Inada,Hayato Tsuge,Yutaka Tsutsumi 대한이비인후과학회 2017 Clinical and Experimental Otorhinolaryngology Vol.10 No.3

Objectives. Cholesteatoma is a nonneoplastic destructive lesion of the temporal bone with debated pathogenesis and bone resorptive mechanism. Both molecular and cellular events chiefly master its activity. Continued research is necessary to clarify factors related to its aggressiveness. We aimed to investigate the expression of Ki-67, cytokeratin 13 (CK13) and cytokeratin 17 (CK17) in acquired nonrecurrent human cholesteatoma and correlate them with its bone destructive capacity. Methods. A prospective quantitative immunohistochemical study was carried out using fresh acquired cholesteatoma tissues (n=19), collected during cholesteatoma surgery. Deep meatal skin tissues from the same patients were used as control (n=8). Cholesteatoma patients were divided into 2 groups and compared (invasive and noninvasive) according to a grading score for bone resorption based upon clinical, radiologic and intraoperative findings. To our knowledge, the role of CK17 in cholesteatoma aggressiveness was first investigated in this paper. Results. Both Ki-67 and CK17 were significantly overexpressed in cholesteatoma than control tissues (P<0.001 for both Ki-67 and CK17). In addition, Ki-67 and CK17 were significantly higher in the invasive group than noninvasive group of cholesteatoma (P=0.029, P=0.033, respectively). Furthermore, Ki-67 and CK17 showed a moderate positive correlation with bone erosion scores (r=0.547, P=0.015 and r=0.588, P=0.008, respectively). In terms of CK13, no significant difference was found between cholesteatoma and skin (P=0.766). Conclusion. Both Ki-67 and CK17 were overexpressed in cholesteatoma tissue and positively correlated with bone resorption activity. The concept that Ki-67 can be a predictor for aggressiveness of cholesteatoma was supported. In addition, this is the first study demonstrating CK17 as a favoring marker in the aggressiveness of acquired cholesteatoma.

Miniaturized Traveling-Wave Thermoacoustic Refrigerator Driven by Loudspeaker: Numerical Design

Oday S. Mahmood,Abdul Mun’em A. Karim,Samir Gh. Yahya,Itimad D. J. Azzawi 대한설비공학회 2020 International Journal of Air-Conditioning and Refr Vol.28 No.4

Ordinary refrigeration systems such as vapor-compression refrigerators are the commonly used devices in industry, mostly for their high efficiencies. However, they make a significant contribution to the depletion of Ozone and global warming due to their operational refrigerants. Hence, thermoacoustic refrigeration can be a great alternative candidate which uses inert gases such as air, helium and nitrogen as the primary refrigerant. Thermoacoustic refrigerators convert the acoustic power (sound waves) into a thermal effect (cooling power). Thermoacoustics can be counted as a new technology that has a strong potential toward the development of the thermal applications. This study aims to design and fabricate miniaturized traveling wave thermoacoustic refrigerator which can be driven by an ordinary loudspeaker. The optimized numerical design of the refrigerator shows an overall efficiency (cooling power over input electricity) of nearly 66% at a temperature difference of 25 K (between cold and ambient heat exchangers). The maximum estimated cooling power is 65 W at coefficient of performance (COP) of 2.65.