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.

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.

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.

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.

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.

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.

Heavy baryonic _Λb→Λ^η(′) decays

Ahmady, M.R.,Kim, C.S.,Oh, Sechul,Yu, Chaehyun Elsevier 2004 Physics letters: B Vol.598 No.3

<P><B>Abstract</B></P><P>We calculate the branching ratios of the hadronic <SUB>Λb</SUB> decays to <I>η</I> and <SUP>η′</SUP> in the factorization approximation where the form factors are estimated via QCD sum rules and the pole model. Our results indicate that, contrary to B→K<SUP>η(′)</SUP> decays, the branching ratios for <SUB>Λb</SUB>→Λη and <SUB>Λb</SUB>→Λ<SUP>η′</SUP> are more or less the same in the hadronic <SUB>Λb</SUB> transitions. We find that the anomaly contribution is crucial in <SUB>Λb</SUB>→Λ<SUP>η(′)</SUP> decays. We obtain the branching ratio of <SUB>Λb</SUB>→Λ<SUP>η(′)</SUP> to be 11.47(11.33)×<SUP>10−6</SUP> in QCD sum rules, and 2.95(3.24)×<SUP>10−6</SUP> in the pole model. We also consider the contribution of the charm content in the <SUP>η′</SUP> production in <SUB>Λb</SUB>→Λ transition.</P>

Fruit and vegetable discards preserved with sodium metabisulfite as a high-moisture ingredient in total mixed ration for ruminants: effect on in vitro ruminal fermentation and in vivo metabolism

Ahmadi, Farhad,Lee, Won Hee,Oh, Young-Kyoon,Park, Keunkyu,Kwak, Wan Sup Asian Australasian Association of Animal Productio 2020 Animal Bioscience Vol.33 No.3

Objective: Our recent series of laboratory- and large-scale experiments confirmed that under aerobic and anaerobic conditions, sodium metabisulfite (SMB) was effective in preserving nutrients and antioxidant capacity of highly perishable fruit and vegetable discards (FVD). Hence, the purpose of this study was to examine how partial inclusion of SMB-treated FVD in total mixed ration (TMR) influences in vitro ruminal fermentation, whole-tract digestibility, nitrogen metabolism, blood metabolites, and voluntary feed intake of sheep. Methods: The FVD were mixed thoroughly with 6 g SMB/kg wet biomass and kept outdoors under aerobic conditions for 7 days. Four TMRs including four levels of SMB-treated FVD (as-fed basis) at 0%, 10%, 20%, and 30% (equaling to 0%, 1.9%, 3.8%, and 5.7% on dry matter basis, respectively), were prepared as replacement for corn grain. The ruminal fermentation metabolites were studied using an in vitro gas production test. Four mature male Corriedale sheep were assigned at random to the 4 diets for two separate sub-experiments; i) digestibility trial with four 21-d periods, and ii) voluntary feed intake trial with four 28-d periods. Results: Inclusion of SMB-treated FVD in the TMR tended to quadratically increase partitioning factor. No effect was seen on total-tract digestibility of organic matter, ether extract, crude protein, and acid detergent fiber, except for neutral detergent fiber digestibility that tended to linearly increase with increasing SMB-treated FVD in the TMR. The progressive increase of FVD preserved with SMB in the diet had no effect on nitrogen metabolism. Treatment had no effect on serum antioxidant capacity and blood metabolites assayed. Voluntary feed intake was not impaired by inclusion of SMB-treated FVD in the TMR. Conclusion: It appears that FVD preserved with SMB can be safely incorporated into TMR as replacement of corn grain without impairment of nutrient metabolism and feed intake.

ON THE κ-REGULAR SEQUENCES AND THE GENERALIZATION OF F-MODULES

Ahmadi-Amoli, Khadijeh,Sanaei, Navid Korean Mathematical Society 2012 대한수학회지 Vol.49 No.5

For a given ideal I of a Noetherian ring R and an arbitrary integer ${\kappa}{\geq}-1$, we apply the concept of ${\kappa}$-regular sequences and the notion of ${\kappa}$-depth to give some results on modules called ${\kappa}$-Cohen Macaulay modules, which in local case, is exactly the ${\kappa}$-modules (as a generalization of f-modules). Meanwhile, we give an expression of local cohomology with respect to any ${\kappa}$-regular sequence in I, in a particular case. We prove that the dimension of homology modules of the Koszul complex with respect to any ${\kappa}$-regular sequence is at most ${\kappa}$. Therefore homology modules of the Koszul complex with respect to any filter regular sequence has finite length.