Implementation of Thermite Reactions in the Production of Advanced Intermetallic-Matrix Composites: The Case of Nb2O5/Al Thermite Mixture

Arman Ahmadi‑Binahri,Mandana Adeli,M. Reza Aboutalebi,Sergey Krasikov 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.6

In this study, the application of thermite reactions in Nb2O5–Al system in the fabrication of novel NbAl3/Al2O3 compositeswas investigated. Combining the thermite reactions with self-propagating high-temperature synthesis (SHS) techniquein compressed powder mixtures of Nb2O5+ Al resulted in layer-by-layer progress of the exothermic reaction, controlledformation of the desired products and their coexistence in each reacted layer. Characterization of the products using X-raydiffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) techniques showedthat all samples were composed of a metallic matrix including NbAl3as the main compound, along with Al2O3as ceramicreinforcing phase. Differential thermal analysis (DTA) analysis was used to study the mechanism of reaction using bothstoichiometric and over-stoichiometric amounts of aluminum. The effect of such parameters as stoichiometry and greendensity of the samples on the combustion temperature, formed phases, microstructure, and hardness of the obtained compositeswas investigated using samples with stoichiometric as well 20 wt% and 40 wt% excess aluminum, and samples withgreen densities of 75%, 85%, and 95% of theoretical maximum density (TMD). The presence of excess aluminum resultedin prolonged reaction times, lower combustion temperatures, and lower mean values of hardness. While the variations ingreen density had no remarkable effect on the microstructural features of products within the density range under study, themost intensive reactions, highest combustion temperature, and highest mean value of hardness were encountered in sampleswith green density of 85%TMD.

ON SYMMETRIC DUALITY IN NONDIFFERENTIABLE MATHEMATICAL PROGRAMMING WITH F-CONVEXITY

AHMAD, I.,HUSAIN, Z. 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.19 No.1

Usual symmetric duality results are proved for Wolfe and Mond-Weir type nondifferentiable nonlinear symmetric dual programs under F-convexity F-concavity and F-pseudoconvexity F-pseudoconcavity assumptions. These duality results are then used to formulate Wolfe and Mond-Weir type nondifferentiable minimax mixed integer dual programs and symmetric duality theorems are established. Moreover, nondifferentiable fractional symmetric dual programs are studied by using the above programs.

SUFFICIENCY AND DUALITY IN MINMAX FRACTIONAL SUBSET PROGRAMMING INVOLVING GENERALIZED TYPE-I FUNCTIONS

Ahmad, I.,Sharma, Sarita Korean Society of Computational and Applied Mathem 2008 Journal of applied mathematics & informatics Vol.26 No.5

A discrete minmax fractional subset programming problem is considered. Various parametric and parameter-free global sufficient optimality conditions and duality results are discussed under generalized ($F,{\alpha},{\rho},{\theta}$)-V-type-I n-set functions.

MULTIOBJECTIVE FRACTIONAL SYMMETRIC DUALITY INVOLVING CONES

Ahmad, I.,Sharma, Sarita Korean Society of Computational and Applied Mathem 2008 Journal of applied mathematics & informatics Vol.26 No.1

A pair of multiobjective fractional symmetric dual programs is formulated over arbitrary cones. Weak, strong and converse duality theorems are proved under pseudoinvexity assumptions. A self duality theorem is also discussed.

Numerical study on flow field in inlet plenum of a pebble-bed modular reactor

Ahmad, I.,Kim, K.Y.,Lee, W.J.,Park, G.C. North-Holland Pub. Co 2007 Nuclear engineering and design Vol.237 No.6

Flow distribution and pressure drop analysis in the inlet plenum of a pebble-bed modular reactor (PBMR) have been performed numerically. Three-dimensional Navier-Stokes equations have been solved in conjunction with the k-@? model as a turbulence closure. Non-uniformity in the flow distribution is assessed for the reference case, and parametric studies have been performed for rising channels diameter, Reynolds number, angle between the rising channels, angle between the inlet ports, and aspect ratio of the plenum cross-section. Also, two different shapes of the inlet plenum, namely, rectangular and oval shapes, have been analyzed. The relative flow mal-distribution parameter variation shows that the flow distribution in rising channels for the reference case is strongly non-uniform. As the rising channels diameter is decreased, the flow uniformity as well as the pressure drop is found to increase. The flow distribution in the rising channels is independent of Reynolds number. Increase in the angle between the inlet ports and aspect ratio is found to increase the uniformity in flow distribution.

SYMMETRIC DUALITY FOR FRACTIONAL VARIATIONAL PROBLEMS WITH CONE CONSTRAINTS

Ahmad, I.,Yaqub, Mohd.,Ahmed, A. 한국전산응용수학회 2007 Journal of applied mathematics & informatics Vol.23 No.1

A pair of symmetric fractional variational programming problems is formulated over cones. Weak, strong, converse and self duality theorems are discussed under pseudoinvexity. Static symmetric dual fractional programs are included as special case and corresponding symmetric duality results are merely stated.

The Effects of Hearing Aid Digital Noise Reduction and Directionality on Acceptable Noise Level

Roghayeh Ahmadi,Hamid Jalilvand,Mohammad Ebrahim Mahdavi,Fatemeh Ahmadi,Ali Reza Akbarzade Baghban 대한이비인후과학회 2018 Clinical and Experimental Otorhinolaryngology Vol.11 No.4

Objectives. Two main digital signal processing technologies inside the modern hearing aid to provide the best conditions for hearing aid users are directionality (DIR) and digital noise reduction (DNR) algorithms. There are various possible settings for these algorithms. The present study evaluates the effects of various DIR and DNR conditions (both separately and in combination) on listening comfort among hearing aid users. Methods. In 18 participants who received hearing aid fitting services from the Rehabilitation School of Shahid Beheshti University of Medical Sciences regularly, we applied acceptable noise level (ANL) as our subjective measure of listening comfort. We evaluated both of these under six different hearing aid conditions: omnidirectional-baseline, omnidirectional-broadband DNR, omnidirectional-multichannel DNR, directional, directional-broadband DNR, and directional-multichannel DNR. Results. The ANL results ranged from −3 dB to 14 dB in all conditions. The results show, among all conditions, both the omnidirectional-baseline condition and the omnidirectional-broadband DNR condition are the worst conditions for listening in noise. The DIR always reduces the amount of noise that patients received during testing. The DNR algorithm does not improve listening in noise significantly when compared with the DIR algorithms. Although both DNR and DIR algorithms yielded a lower ANL, the DIR algorithm was more effective than the DNR. Conclusion. The DIR and DNR technologies provide listening comfort in the presence of noise. Thus, user benefit depends on how the digital signal processing settings inside the hearing aid are adjusted.

Estimation of Hazard Function and its Associated Factors in Gastric Cancer Patients using Wavelet and Kernel Smoothing Methods

Ahmadi, Azadeh,Roudbari, Masoud,Gohari, Mahmood Reza,Hosseini, Bistoon Asian Pacific Journal of Cancer Prevention 2012 Asian Pacific journal of cancer prevention Vol.13 No.11

Background and Objectives: Increase of mortality rates of gastric cancer in Iran and the world in recent years reveal necessity of studies on this disease. Here, hazard function for gastric cancer patients was estimated using Wavelet and Kernel methods and some related factors were assessed. Materials and Methods: Ninety-five gastric cancer patients in Fayazbakhsh Hospital between 1996 and 2003 were studied. The effects of age of patients, gender, stage of disease and treatment method on patient's lifetime were assessed. For data analyses, survival analyses using Wavelet method and Log-rank test in R software were used. Results: Nearly 25.3% of patients were female. Fourteen percent had surgery treatment and the rest had treatment without surgery. Three fourths died and the rest were censored. Almost 9.5% of patients were in early stages of the disease, 53.7% in locally advance stage and 36.8% in metastatic stage. Hazard function estimation with the wavelet method showed significant difference for stages of disease (P<0.001) and did not reveal any significant difference for age, gender and treatment method. Conclusion: Only stage of disease had effects on hazard and most patients were diagnosed in late stages of disease, which is possibly one of the most reasons for high hazard rate and low survival. Therefore, it seems to be necessary a public education about symptoms of disease by media and regular tests and screening for early diagnosis.

Evaluation of prooxidant-antioxidant balance in in vitro fertilization-conceived mice

Ahmadi, Hamid,Fathi, Fardin,Moeini, Ashraf,Amidi, Fardin,Sobhani, Aligholi The Korean Society for Reproductive Medicine 2018 Clinical and Experimental Reproductive Medicine Vol.45 No.2

Objective: Concerns about the safety of assisted reproductive technology (ART) have been raised, as some studies have shown elevated incidence rates of childhood cancer, asthma, allergies, and other diseases in ART-conceived babies. Findings regarding the health of ART-conceived babies are controversial. The present study was conducted to evaluate the prooxidant-antioxidant balance (PAB) in in vitro fertilization (IVF)-conceived mice in comparison to naturally conceived offspring. Methods: Mice (6-8 weeks) were divided into two groups (IVF-conceived and naturally conceived) matched by sex, age, weight, and litter size. A 1-mL blood sample was taken and the sera were separated. The oxidant-antioxidant balance was evaluated using a fast and reliable PAB assay. The results were expressed as $mean{\pm}standard$ deviation. Results: The mean PAB values (HK units) in the IVF-conceived and naturally conceived groups were $59.70{\pm}22.30$ and $54.70{\pm}18.22$, respectively (p= 0.82). Conclusion: Since free radicals contribute to several pathological conditions and antioxidants play an important protective role against oxidative stress, evaluating the oxidant-antioxidant balance is very important. Although the results of this study showed that the quality of the defense mechanism against free radicals was not significantly different between the IVF-conceived and naturally conceived mice, other parameters of metabolic dysfunction need to be measured.

Laboratory evaluation of roller compacted concrete containing RAP

Ahmadi, Amin,Gogheri, Mohammad K.,Adresi, Mostafa,Amoosoltani, Ershad Techno-Press 2020 Advances in concrete construction Vol.10 No.6

This paper investigates mechanical properties of roller compacted concrete (RCC) involving reclaimed asphalt pavement (RAP). In this way, a set of 276 cylindrical RCC specimens were prepared with different RAP sizes (i.e., fine, coarse & total) at various ratios (i.e., 10%, 20%, and 40%). Results reveal that incorporation of RAP decreases unconfined compressive strength (UCS), modulus of elasticity (E), and indirect tensile (IDT) strength of RCC. For each RAP size, a regression model was used to maximize RAP content while satisfying the UCS lower limit (27.6 Mpa) mentioned by ACI as a minimum requirement for RCC used in pavement construction. Moreover, UCS of RAP incorporated mixes, dissimilar to that of control mixes, was found to be sensitive and insensitive to the testing temperature and curing time after 7 days, respectively. The results also demonstrate that the higher amounts of RAP, the more flexibility in RCC is. This issue was also proved by the results of modulus of elasticity test. In addition, the toughness index (TI) shows that increase in RAP content leads to up to 43% increase in energy absorbance capacity of RCC.