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- 저자 : M. R. Ahmad (검색결과 62 건)
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Abdelwahed R. Sayed,Hany M Abd El-lateef,Ahmad Desoky M. Mohamad 한국고분자학회 2018 Macromolecular Research Vol.26 No.10
In this paper polyhydrazide incorporated with thiadiazole moiety (S5) was prepared and its chemical configuration was confirmed by spectroscopic methods (FTIR, 1H NMR, and 13C NMR). The inhibitive action of S5 polymer and its monomer 2,5-dihydrazinyl-1,3,4-thiadiazole (M1) on the C-steel corrosion in pickling acids solution was investigated by weight loss, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements. PDP method exhibited that the investigated polymer is mixed-type corrosion inhibitor in both acids (HCl and H2SO4). The data revealed that S5 compound is a good inhibitor for Csteel in studied acids, and protection efficiency (P%) follows this sequence: H2SO4<HCl. Also, it was found that, the P% of the S5 polymer is higher than that obtained for its monomer (M1). Adsorption of the titled polymer obeyed the isotherm of Langmuir and involves both chemical and physical adsorptions. Scanning electron microscopy (SEM) investigations established the protective layer formation from the studied polymer on the metal substrate and shield it from direct Cl- and/ or SO4 2- attack.
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Shrestha, B.K.,Ahmad, R.,Mousa, H.M.,Kim, I.G.,Kim, J.I.,Neupane, M.P.,Park, C.H.,Kim, C.S. Academic Press 2016 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.482 No.-
A highly electroactive bio-nanohybrid film of polypyrrole (PPy)-Nafion (Nf)-functionalized multi-walled carbon nanotubes (fMWCNTs) nanocomposite was prepared on the glassy carbon electrode (GCE) by a facile one-step electrochemical polymerization technique followed by chitosan-glucose oxidase (CH-GOx) immobilization on its surface to achieve a high-performance glucose biosensor. The as-fabricated nanohybrid composite provides high surface area for GOx immobilization and thus enhances the enzyme-loading efficiency. The structural characterization revealed that the PPy-Nf-fMWCNTs nanocomposite films were uniformly formed on GCE and after GOx immobilization, the surface porosities of the film were decreased due to enzyme encapsulation inside the bio-nanohybrid composite materials. The electrochemical behavior of the fabricated biosensor was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry measurements. The results indicated an excellent catalytic property of bio-nanohybrid film for glucose detection with improved sensitivity of 2860.3μAmM<SUP>-1</SUP>cm<SUP>-2</SUP>, the linear range up to 4.7mM (R<SUP>2</SUP>=0.9992), and a low detection limit of 5μM under a signal/noise (S/N) ratio of 3. Furthermore, the resulting biosensor presented reliable selectivity, better long-term stability, good repeatability, reproducibility, and acceptable measurement of glucose concentration in real serum samples. Thus, this fabricated biosensor provides an efficient and highly sensitive platform for glucose sensing and can open up new avenues for clinical applications.
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Lead Sorption by Carbon Nanofibers Grown on Powdered Activated Carbon - Kinetics and Equilibrium
Abdullah Al Mamun,Yehya M. Ahmed,Ma'an Fahmi R. AlKhatib,Ahmad Tariq Jameel,Mohammed Abdul Hakeem Abdul Rahman AlSaadi 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.2
Carbon nanofibers (CNFs) were synthesized by using a safe and less hazardous method, compared to using floating catalysts in chemical vapor deposition (CVD) process. This process used C2H2 as carbon source and oil palm kernel shell-based powdered activated carbon (PAC) as cheap solid substrate. Use of nickel (Ni2+) impregnated PAC as fixed substrate for the synthesis of CNF is one of the novelties of the research work accomplished by the authors. The PAC–CNFs porous nanocomposite product was used for the sorption of lead ions (Pb2+) from synthetic aqueous solution. Kinetics of Pb2+ adsorption and isotherms were investigated by varying initial concentration of lead and contact time. PAC–CNFs were found to remove Pb2+ better at acidic pH of about 5.5. Langmuir and Freundlich isotherms were applied to the sorption equilibrium data to find the best fitted model. Langmuir isotherm model with R2=0.965 fitted the adsorption data better than the Freundlich isotherm. The kinetic processes of Pb2+ adsorption on CNFs were investigated by applying different kinetic models, namely zero-order, pseudo-first-order and pseudo-second-order. The pseudo-second-order rate equation exhibited the best results with R=0.999, qe=74.79 (mg/g) and K2=0.029 (min·g/mg). The novel nanocomposite product seemed to have the potential to remove Pb2+ ions from aqueous solution.
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M. S. Salwa,M. N. Nur Asshifa,A. A. Amirul,Ahmad R. M. Yahya 한국생물공학회 2009 Biotechnology and Bioprocess Engineering Vol.14 No.6
A locally-isolated=Pseudomonas aeruginosa USM AR2 possessing the ability to produce glycolipid-type biosurfactant (rhamnolipid) was used in this research to explore fermentation technology for rhamnolipid production. Rhamnolipid concentration in 2.5 L fed-batch fermentation was improved from 0.173 to 8.06 g/L by manipulating the feeding strategy and cultivation protocol. The culture was fed with petroleum diesel and complex medium. The highest rhamnolipid concentration was achieved when the culture was initially fed with both petroleum diesel and complex medium, followed by feeding of petroleum diesel only at the end of the stationary phase. Severe foaming problem was resolved by modifying and integrating a foam recycler to the bioreactor. This successfully extended the cultivation period and increased the yield of final rhamnolipid. No antifoam agent was added as this modified bioreactor allowed cultivation to proceed even under foam generation. The viscosity measurement, surface tension activity test, and drop-collapse test were performed as an indirect measure of rhamnolipid presence A locally-isolated=Pseudomonas aeruginosa USM AR2 possessing the ability to produce glycolipid-type biosurfactant (rhamnolipid) was used in this research to explore fermentation technology for rhamnolipid production. Rhamnolipid concentration in 2.5 L fed-batch fermentation was improved from 0.173 to 8.06 g/L by manipulating the feeding strategy and cultivation protocol. The culture was fed with petroleum diesel and complex medium. The highest rhamnolipid concentration was achieved when the culture was initially fed with both petroleum diesel and complex medium, followed by feeding of petroleum diesel only at the end of the stationary phase. Severe foaming problem was resolved by modifying and integrating a foam recycler to the bioreactor. This successfully extended the cultivation period and increased the yield of final rhamnolipid. No antifoam agent was added as this modified bioreactor allowed cultivation to proceed even under foam generation. The viscosity measurement, surface tension activity test, and drop-collapse test were performed as an indirect measure of rhamnolipid presence
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Preparation of highly efficient Al-doped ZnO photocatalyst by combustion synthesis
M. Ahmad,E. Ahmed,Yuewei Zhang,N.R. Khalid,Jianfeng Xu,M. Ullah,Zhanglian Hong 한국물리학회 2013 Current Applied Physics Vol.13 No.4
Novel Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5e6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 ℃ for 3 h. The obtained nanopowders were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) combined with EDX, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UVevis spectroscopy and photoluminescence spectroscopy. The XRD patterns of AZO nanopowders were assigned to wurtzite structure of ZnO with the smallest crystallite size about 11 nm consistent with the results from TEM. The doping of Al in ZnO crystal structure successfully suppressed the growth of ZnO nanoparticles confirmed by XRD patterns. The absorption spectra analysis showed that the optical band gap energy (Eg) for the AZO nanopowders were in the range of 3.12-3.21 eV and decreased with increasing of Al dopant. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange under visible light (λ≥ 420 nm) and sunlight irradiation. The results showed that the AZO photocatalyst doped with 4.0 mol% Al exhibited five times enhanced photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity could be attributed to extended visible light absorption, inhibition of the electronehole pair’s recombination and enhanced adsorptivity of MO dye molecule on the surface of AZO nanopowders.
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Ahmad, R. T. M.,Hong, Seung-Ho,Shen, Tian-Zi,Song, Jang-Kun The Optical Society 2015 Optics express Vol.23 No.4
<P>In order to use graphene oxide (GO) dispersions for electro-optical applications, both a high GO concentration and a high electrical sensitivity are essential; however, these have not been achieved to date. Here, we report that by optimizing the mean size of GO particles to approximately 0.5 μm, one can obtain a high GO concentration of up to 2 wt% and high electrical sensitivity simultaneously. By reducing the mean GO-particle size, the interparticle interaction and the rotational viscosity can be significantly reduced, and a high-concentration isotropic phase can be obtained. As a result, the maximum birefringence increases and the dynamic response becomes faster. However, further decrease of the mean size below 0.1 μm causes a decrease in the anisotropy of electrical polarizability, resulting in the reduction of the electrical sensitivity of GO dispersions.</P>
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Effect of perforation patterns on the fundamental natural frequency of microsatellite structure
Ahmad M. Baiomy,M. Kassab,B.M. El-Sehily,R.M. El-Kady Techno-Press 2023 Advances in aircraft and spacecraft science Vol.10 No.3
There is a burgeoning demand for minimizing the mass of satellites because of its direct impact on reducing launch-to-orbit cost. This must be done without compromising the structure's efficiency. The present paper introduces a relatively low-cost and easily implementable approach for optimizing structural mass to a maximum natural frequency. The natural frequencies of the satellite are of utmost pertinence to the application requirements, as the sensitive electronic instrumentation and onboard computers should not be affected by the vibrations of the satellite structure. This methodology is applied to a realistic model of Al-Azhar University micro-satellite in partnership with the Egyptian Space Agency. The procedure used in structural design can be summarized in two steps. The first step is to select the most favorable primary structural configuration among several different candidate variants. The nominated variant is selected as the one scoring maximum relative dynamic stiffness. The second step is to use perforation patterns reduce the overall mass of structural elements in the selected variant without changing the weight. The results of the presented procedure demonstrate that the mass reduction percentage was found to be 39% when compared to the unperforated configuration that had the same plate thickness. The findings of this study challenge the commonly accepted notion that isogrid perforations are the most effective means of achieving the goal of reducing mass while maintaining stiffness. Rather, the study highlights the potential benefits of exploring a wider range of perforation unit cells during the design process. The study revealed that rectangular perforation patterns had the lowest efficiency in terms of modal stiffness, while triangular patterns resulted in the highest efficiency. These results suggest that there may be significant gains to be made by considering a broader range of perforation shapes and configurations in the design of lightweight structures.
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Experimental analysis of electromagnetic vibration damping of a cantilever beam
M. R. Siddiqui,I. Ahmad,M. Khan,S.M. Ahmad 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10
Vibration attenuation is necessary in many electro-mechanical systems. In this paper electromagnetic damping is applied on a flexible cantilever beam (FCB) made of ferromagnetic material. The lateral vibration is controlled by employing two electromagnetic poles mounted in the same axis as that of a vibrating cantilever beam. A power amplifier is developed to provide desired current to the electromagnet. Comparison of damping achieved at different electromagnetic forces is presented. The study employs a new method of applying a constant DC power to one of the electromagnets while other is connected to a variable current source. Experimental results are presented that show the effectiveness of the presented approach.
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