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- 저자 : Saif, L. J. (검색결과 103 건)
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Analysis and structural design of various turbine blades under variable conditions: A review
Saif, Mohd,Mullick, Parth,Imam, Ashhad Techno-Press 2019 Advances in materials research Vol.8 No.1
This paper presents a review study for energy-efficient gas turbines (GTs) with cycles which contributes significantly towards sustainable usage. Nonetheless, these progressive engines, operative at turbine inlet temperatures as high as $1600^{\circ}C$, require the employment of highly creep resistant materials for use in hotter section components of gas turbines like combustion chamber and blades. However, the gas turbine obtain its driving power by utilizing the energy of treated gases and air which is at piercing temperature and pushing by expanding through the several rings of steady and vibratory blades. Since the turbine blades works at very high temperature and pressure, high stress concentration are observed on the blades. With the increasing demand of service, to provide adequate efficiency and power within the optimized level, turbine blades are to be made of those materials which can withstand high thermal and working load condition for longer cycle time. This paper depicts the recent developments in the field of implementing the best suited materials for the GTs, selection of proper Thermal Barrier Coating (TBC), fracture analysis and experiments on failed or used turbine blades and several other designing and operating factors which are effecting the blade life and efficiency. It is revealed that Nickel based Superalloys were promising, Cast Iron with Zirconium and Pt-Al coatings are used as best TBC material, material defects are the foremost and prominent reason for blade failure.
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Saif Ahmad,Adam Kindelin,Maaz Ahmed,Md Nasrul Hoda,Kanchan Bhatia,Andrew F. Ducruet 한국뇌신경과학회 2019 Experimental Neurobiology Vol.28 No.2
The complement cascade is a central component of innate immunity which plays a critical role in brain inflammation. Complement C3a receptor (C3aR) is a key mediator of post-ischemic cerebral injury, and pharmacological antagonism of the C3a receptor is neuroprotective in stroke. Cerebral ischemia injures brain endothelial cells, causing blood brain barrier (BBB) disruption which further exacerbates ischemic neuronal injury. In this study, we used an in vitro model of ischemia (oxygen glucose deprivation; OGD) to investigate the protective effect of a C3aR antagonist (C3aRA, SB290157) on brain endothelial cells (bEnd.3). Following 24 hours of reperfusion, OGD-induced cell death was assessed by TUNEL and Caspase-3 staining. Western blot and immunocytochemistry were utilized to demonstrate that OGD upregulates inflammatory, oxidative stress and antioxidant markers (ICAM-1, Cox-2, Nox- 2 and MnSOD) in endothelial cells and that C3aRA treatment significantly attenuate these markers. We also found that C3aRA administration restored the expression level of the tight junction protein occludin in endothelial cells following OGD. Interestingly, OGD/reperfusion injury increased the phosphorylation of ERK1/2 and C3aR inhibition significantly reduced the activation of ERK suggesting that endothelial C3aR may act via ERK signaling. Furthermore, exogenous C3a administration stimulates these same inflammatory mechanisms both with and without OGD, and C3aRA suppresses these C3a-mediated responses, supporting an antagonist role for C3aRA. Based on these results, we conclude that C3aRA administration attenuates inflammation, oxidative stress, ERK activation, and protects brain endothelial cells following experimental brain ischemia.
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Saif Haider Kayani,Jae‑Gil Jung,Min‑Seok Kim,Kwangjun Euh 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.7
We investigate the effect of cooling rate on the precipitation behavior during cooling from solution treatment temperatureand post-aging of a high-strength Al–7.65Zn–2.59Mg–1.95Cu–0.11Zr–0.04Ti extruded alloy. Solution treatment at 450 °Ccaused the partial dissolution and disintegration of η phase, along with a partial recrystallization of Al grains. The formationof fine L12-type Al3Zr/Al3(Zr,Ti) (~ 20 nm) and relatively large Ti-rich dispersoids (~ 100 nm) took place during extrusionand/or solution treatment processes. The slow cooling from solution treatment temperature (0.3 °C/min) caused theprecipitation of η phases on coarse Al3(Zr,Ti) particles (formed during solidification), Ti-rich dispersoids (formed duringextrusion/solution treatment), grain boundaries, and grain interiors, thereby resulting in negligible aging responses duringpost-aging at room and elevated temperatures. During fast cooling at 850 °C/min, however, the η phases did not precipitateand thus the Al matrix remained supersaturated, leading to significant aging responses by the formation of GP zones andmetastable η″/η′ precipitates.
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Saif L. Altai,Sarah L. Orton,Zhen Chen 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.83 No.4
Constitutive modeling that could reasonably predict and effectively evaluate the post-peak structural behavior while eliminating the mesh-dependency in numerical simulation remains to be developed for general engineering applications. Based on the previous work, a simple one-dimensional modeling procedure is proposed to predict and evaluate the post-peak response, as characterized by the evolution of localized strain field, of a steel member to monotonically uniaxial tension. The proposed model extends the classic one-dimensional softening with localization model as introduced by (Schreyer and Chen 1986) to account for the localization length, and bifurcation and rupture points. The new findings of this research are as follows. Two types of strain-softening functions (bilinear and nonlinear) are proposed for comparison. The new failure criterion corresponding to the constitutive modeling is formulated based on the engineering strain inside the localization zone at rupture. Furthermore, a new mathematical expression is developed, based on the strain rate inside and outside the localization zone, to describe the displacement field at which bifurcation occurs. The model solutions are compared with the experimental data on four lowcarbon cylindrical steel bars of different lengths. For engineering applications, the model solutions are also compared to the experimental data of a cylindrical steel bar system (three steel bars arranged in series). It is shown that the bilinear and nonlinear softening models can predict the energy dissipation in the post-peak regime with an average difference of only 4%.
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Predictive model for the shear strength of concrete beams reinforced with longitudinal FRP bars
Saif Alzabeebee,Moahmmed K. Dhahir,Suraparb Keawsawasvong 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.84 No.2
Corrosion of steel reinforcement is considered as the main cause of concrete structures deterioration, especially those under humid environmental conditions. Hence, fiber reinforced polymer (FRP) bars are being increasingly used as a replacement for conventional steel owing to their non-corrodible characteristics. However, predicting the shear strength of beams reinforced with FRP bars still challenging due to the lack of robust shear theory. Thus, this paper aims to develop an explicit data driven based model to predict the shear strength of FRP reinforced beams using multi-objective evolutionary polynomial regression analysis (MOGA-EPR) as data driven models learn the behavior from the input data without the need to employee a theory that aid the derivation, and thus they have an enhanced accuracy. This study also evaluates the accuracy of predictive models of shear strength of FRP reinforced concrete beams employed by different design codes by calculating and comparing the values of the mean absolute error (MAE), root mean square error (RMSE), mean (μ), standard deviation of the mean (σ), coefficient of determination (R2), and percentage of prediction within error range of ±20% (a20-index). Experimental database has been developed and employed in the model learning, validation, and accuracy examination. The statistical analysis illustrated the robustness of the developed model with MAE, RMSE, μ, σ, R2, and a20-index of 14.6, 20.8, 1.05, 0.27, 0.85, and 0.61, respectively for training data and 10.4, 14.1, 0.98, 0.25, 0.94, and 0.60, respectively for validation data. Furthermore, the developed model achieved much better predictions than the standard predictive models as it scored lower MAE, RMSE, and σ, and higher R2 and a20-index. The new model can be used in future with confidence in optimized designs as its accuracy is higher than standard predictive models.
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Impact of Sulphur and Nitrogen Application on Seed and Xanthotoxin Yield in Ammi mejus L.
Saif Ahmad,Arshad Jamal,Inayat Saleem Fazili,Tanweer Alam,Mather Ali Khan,Kamaluddin,Mohd. Iqbal,Malik Zainul Abdin 韓國作物學會 2007 한국작물학회지 Vol.52 No.2
Field experiments were conducted to determine the physiological and biochemical basis of the interactive effect of sulphur (S) and nitrogen (N) application on seed and xanthotoxin yield of Ammi majus L. Six treatments were tested (T1 = control-without manure and fertilizers, T2 = manure @ 9 kg plot-1-10~;t~;ha-1,~;T3=A0N50K25P25,~;T4=S40N50K25P25,~;T5=S40N100K25P25~;T6=S20+20N50+50K25P25) ). Nitrate reductase (NR) activity and ATP-sulphurylase activity in the leaves were measured at various phonological stages, as the two enzymes catalyze rate-limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these two enzymes were strongly correlated with seed and xanthotoxin yield. The highest nitrate reductase activity, ATP-sulphurylase activity and xanthotoxin yield were achieved with the treatment T4 . Any variation from this treatment decreased the activity of these enzymes, resulting in a reduction of the seed and xanthotoxin yield in Ammi majus L. The higher seed and xanthotoxin yield achieved in Ammi majus L. at treatment T4 could be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are Influenced by S and N assimilation.
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Impact of sulphur and nitrogen application on seed and xanthotoxin yield in Ammi majus L.
Saif Ahmad,Arshad Jamal,Inayat Saleem Fazili,Tanweer Alam,Mather Ali Khan,Kamaluddin,Mohd. Iqbal,Malik Zainul Abdin 한국작물학회 2007 한국작물학회지 Vol.52 No.2
Field experiments were conducted to determine the physiological and biochemical basis of the interactive effect of sulphur (S) and nitrogen (N) application on seed and xanthotoxin yield of Ammi majus L. Six treatments were tested (T1=control-without manure and fertilizers, T2=manure @ 9 kg plot-1-10 t ha-1, T3=S0N50 K25P25, T4=S40N50K25P25, T5=S40N100K25P25, T6=S20+20N50+50 K25P25). Nitrate reductase (NR) activity and ATP-sulphurylase activity in the leaves were measured at various phenological stages, as the two enzymes catalyze rate-limiting steps of the assimilatory pathways of nitrate and sulphate, respectively. The activities of these two enzymes were strongly correlated with seed and xanthotoxin yield. The highest nitrate reductase activity, ATP-sulphurylase activity and xanthotoxin yield were achieved with the treatment T4. Any variation from this treatment decreased the activity of these enzymes, resulting in a reduction of the seed and xanthotoxin yield in Ammi majus L. The higher seed and xanthotoxin yield achieved in Ammi majus L. at treatment T4 could be due to optimization of leaf soluble protein and photosynthetic rate, as these parameters are influenced by S and N assimilation.
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