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- 저자 : Ahmed, Ahsan (검색결과 5,457 건)
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Sohail AHMED1,Waqas WAKIL,David MANTLE,Richard M. WILKINS,권용정 한국곤충학회 2008 Entomological Research Vol.38 No.3
To investigate the high activity of intracellular proteases in insecticide resistant strains of Musca domestica L., purification by anion-exchange chromatography and gel filtration of one of the enzymes, alanyl aminopeptidase (Ala AP), in three strains of Musca domestica was carried out. The fractions collected by gel filtration of soluble homogenates of the three strains (571ab, 17bb and Cooper) showed a single peak of Ala AP activity. Partially purified Ala AP of the three strains showed high activity at pH 7.5. The presence or absence of Ca2+ in the assay medium did not produce any difference in activity of Ala AP in the 571ab and Cooper strains, but there was a significant difference in the 17bb strain. The activity of Ala AP in all three strains was essentially unaltered in the presence of inhibitors of serine (PMSF), cysteine (E-64) proteases and carboxypeptidases (pepstatin). Ala AP hydrolyzed alanine amino methylcoumarin (Ala-AMC) maximally, followed by phenyl alanine amino methylcoumarin (Phe-AMC), leucyl amino methylcoumarin (Leu-AMC) and ornithine amino methylcoumarin (Orn-AMC). Ala AP from the three strains showed differential activity towards various substrates. The comparison of alanyl aminopeptidase’'s activity from different sources is discussed.
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Static analysis of multilayer nonlocal strain gradient nanobeam reinforced by carbon nanotubes
Ahmed Amine Daikh,Ahmed Drai,Mohamed Sid Ahmed Houari,Mohamed A. Eltaher 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.36 No.6
This article presents a comprehensive static analysis of simply supported cross-ply carbon nanotubes reinforced composite (CNTRC) laminated nanobeams under various loading profiles. The nonlocal strain gradient constitutive relation is exploited to present the size-dependence of nano-scale. New higher shear deformation beam theory with hyperbolic function is proposed to satisfy the zero-shear effect at boundaries and parabolic variation through the thickness. Carbon nanotubes (CNTs), as the reinforced elements, are distributed through the beam thickness with different distribution functions, which are, uniform distribution (UD-CNTRC), V- distribution (FG-V CNTRC), O- distribution (FG-O CNTRC) and X- distribution (FG-X CNTRC). The equilibrium equations are derived, and Fourier series function are used to solve the obtained differential equation and get the response of nanobeam under uniform, linear or sinusoidal mechanical loadings. Numerical results are obtained to present influences of CNTs reinforcement patterns, composite laminate structure, nonlocal parameter, length scale parameter, geometric parameters on center deflection ad stresses of CNTRC laminated nanobeams. The proposed model is effective in analysis and design of composite structure ranging from macro-scale to nano-scale.
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Ahmed Elserougi,Ahmed Massoud,Shehab Ahmed 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.1
Conventionally, in order to reduce the ac components of the dc-link capacitors of the two-level Half-Bridge Voltage Source Inverter (HB-VSI), high dc-link capacitances are required. This necessitates the employment of short-lifetime and bulky electrolytic capacitors. In this paper, an analysis for the performance of low dc-link capacitances-based HB-VSI is presented to elucidate its ability to generate an enhanced fundamental output voltage magnitude without increasing the voltage rating of the involved switches. This feature is constrained by the load displacement factor. The introduced enhancement is due to the ac components of the capacitors’ voltages. The presented approach can be employed for multi-phase systems through using multi single-phase HB-VSI(s). Mathematical analysis of the proposed approach is presented in this paper. To ensure a successful operation of the proposed approach, a closed loop current controller is examined. An expression for the critical dc-link capacitance, which is the lowest dc-link capacitance that can be employed for unipolar capacitors’ voltages, is derived. Finally, simulation and experimental results are presented to validate the proposed claims.
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( Ahmed Ahmed ),( Ayan Banerjea ) 대한내과학회 2014 대한내과학회 추계학술발표논문집 Vol.2014 No.1
Background: Early diagnosis of anastomotic leakage after colorectal surgery and adequate treatment is crucial to reduce both morbidity and mortality. Computed tomography(CT) scanning is the diagnostic investigation of preference, but its role is questionable in the early postoperative days. The accuracy of CT scanning in the early postoperative period within the fi rst few days after surgery may even be lower when compared to a CT scan more than a week after surgery. Methods: 185 patients underwent 1 or more bowel anastomosis during the period of 6 months. A prospective data sheet was updated regularly with post op morbidity and mortality. The type of anastomosis, timing of postoperative CT scan, diagnosis of leakage and accuracy of the CT scan in detecting it were all recorded. Results: 54 patients (29%) had CT scans post operatively, of whom 48 happened during the same admission with a mean time of 5±3 days postoperatively.A total of 9 patients had their fi rst CT scan onday 3 or earlier postoperatively with one leak detected on that. The mean time for diagnosing a leak was 14±8 days. Conclusions: Timely and correct diagnosis and treatment of anastomotic leakage after bowel surgery remains to be a major challenge.Clinical decision remains of utmost importance in the individual patient and should therefore not depend on one specifi c clinical or additional diagnostic factor.
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A Buck-Boost Converter-Based Bipolar Pulse Generator
Ahmed A. Elserougi,Ahmed M. Massoud,Shehab Ahmed 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.6
This paper presents a buck-boost converter-based bipolar pulse generator, which is able to generate bipolar exponential pulses across a resistive load. The concept of the proposed approach depends on operating the involved buck-boost converters in discontinuous current conduction mode with high-voltage gain and enhanced efficiency. A full design of the pulse generator and its passive components is presented to ensure generating the pulses with the desired specifications (rise time, pulse width, and pulse magnitude) for a given load resistance and input dc voltage. In case of moderate pulsed output voltages (i.e. few of kV), one module of the presented bipolar generator can be employed. While in case of high-voltage pulsed output, multi-module version can be employed, where each module is fed from an isolated dc source and their outputs are connected in series. Simulation models for the proposed approach are built to elucidate their performance in case of one-module as well as multi-module based generator. Finally, a scaled-down prototype for one-module of buck-boost converter-based bipolar pulse generator is implemented to validate the proposed concept.
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Control of Open-Loop PWM Delta-Connected Motor-Drive Systems under One Phase Failure Condition
Ahmed Sayed-Ahmed,Nabeel A. O. Demerdash 전력전자학회 2011 JOURNAL OF POWER ELECTRONICS Vol.11 No.6
A new fault-tolerant control topology for open-loop motor-drive systems with Delta-connected stator windings is introduced in this paper. This new control topology enables the operation of a three-phase induction machine as a two-phase machine fed by a three-phase inverter upon a failure in one of the motor phases. This topology utilizes the “open-Delta” configuration to independently control the current in each of the two remaining healthy phases. This new control technique leads to the alleviation of any torque pulsations resulting from the consequences of the asymmetrical conditions associated with this class of faults.
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